Plant Journal

Correction.

Publication Date: 2008 May 12 PMID: 18477066
Authors:
Journal: Plant J

post to: CiteULike

Correction.

Publication Date: 2008 May 12 PMID: 18477065
Authors:
Journal: Plant J

post to: CiteULike

Opium poppy and Madagascar periwinkle: model non-model systems to investigate alkaloid biosynthesis in plants.

Publication Date: 2008 May PMID: 18476877
Authors: Facchini, P. J. - De Luca, V.
Journal: Plant J

Alkaloids represent a large and diverse group of compounds that are related by the occurrence of a nitrogen atom within a heterocyclic backbone. Unlike other types of secondary metabolites, the various structural categories of alkaloids are unrelated in terms of biosynthesis and evolution. Although the biology of each group is unique, common patterns have become apparent. Opium poppy (Papaver somniferum), which produces several benzylisoquinoline alkaloids, and Madagascar periwinkle (Catharanthus roseus), which accumulates an array of monoterpenoid indole alkaloids, have emerged as the premier organisms used to study plant alkaloid metabolism. The status of these species as model systems results from decades of research on the chemistry, enzymology and molecular biology responsible for the biosynthesis of valuable pharmaceutical alkaloids. Opium poppy remains the only commercial source for morphine, codeine and semi-synthetic analgesics, such as oxycodone, derived from thebaine. Catharanthus roseus is the only source for the anti-cancer drugs vinblastine and vincristine. Impressive collections of cDNAs encoding biosynthetic enzymes and regulatory proteins involved in the formation of benzylisoquinoline and monoterpenoid indole alkaloids are now available, and the rate of gene discovery has accelerated with the application of genomics. Such tools have allowed the establishment of models that describe the complex cell biology of alkaloid metabolism in these important medicinal plants. A suite of biotechnological resources, including genetic transformation protocols, has allowed the application of metabolic engineering to modify the alkaloid content of these and related species. An overview of recent progress on benzylisoquinoline and monoterpenoid indole alkaloid biosynthesis in opium poppy and C. roseus is presented.

post to: CiteULike

Nature's assembly line: biosynthesis of simple phenylpropanoids and polyketides.

Publication Date: 2008 May PMID: 18476876
Authors: Yu, O. - Jez, J. M.
Journal: Plant J

Plants produce large amounts of phenylpropanoids, both in terms of molecular diversity and absolute quantity of these compounds. The phenylpropanoids, and the related plant polyketides, have multiple biological functions. They serve to attract pollinators, support secondary cell-wall growth, provide protection against various plant diseases, and interact with beneficial soil microbes. Their basic chemical properties also make them useful in the biofuel and biomaterial industries. Phenylpropanoid metabolism begins with the amino acid phenylalanine, which feeds into various biosynthetic pathways that generate a wide range of structurally related polyphenolic compounds. This review focuses on four sub-groups of these polyphenolic compounds - polyketides, stilbenes, isoflavones and catechins. We discuss the biosynthesis of these molecules, their physiological role in plants, and their striking pharmacological and physiological effects on humans. This review also highlights metabolic engineering efforts aimed at increasing or decreasing the amounts of each class of compound in various model plants and crops.

post to: CiteULike

Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids.

Publication Date: 2008 May PMID: 18476875
Authors: Tanaka, Y. - Sasaki, N. - Ohmiya, A.
Journal: Plant J

Plant compounds that are perceived by humans to have color are generally referred to as 'pigments'. Their varied structures and colors have long fascinated chemists and biologists, who have examined their chemical and physical properties, their mode of synthesis, and their physiological and ecological roles. Plant pigments also have a long history of use by humans. The major classes of plant pigments, with the exception of the chlorophylls, are reviewed here. Anthocyanins, a class of flavonoids derived ultimately from phenylalanine, are water-soluble, synthesized in the cytosol, and localized in vacuoles. They provide a wide range of colors ranging from orange/red to violet/blue. In addition to various modifications to their structures, their specific color also depends on co-pigments, metal ions and pH. They are widely distributed in the plant kingdom. The lipid-soluble, yellow-to-red carotenoids, a subclass of terpenoids, are also distributed ubiquitously in plants. They are synthesized in chloroplasts and are essential to the integrity of the photosynthetic apparatus. Betalains, also conferring yellow-to-red colors, are nitrogen-containing water-soluble compounds derived from tyrosine that are found only in a limited number of plant lineages. In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood. All three classes of pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal. They also protect plants from damage caused by UV and visible light.

post to: CiteULike

Biosynthesis of plant-derived flavor compounds.

Publication Date: 2008 May PMID: 18476874
Authors: Schwab, W. - Davidovich-Rikanati, R. - Lewinsohn, E.
Journal: Plant J

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artificial flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.

post to: CiteULike

Harnessing plant trichome biochemistry for the production of useful compounds.

Publication Date: 2008 May PMID: 18476873
Authors: Schilmiller, A. L. - Last, R. L. - Pichersky, E.
Journal: Plant J

Plant trichomes come in a variety of shapes, sizes and cellular composition. Some types, commonly called glandular trichomes, produce large amounts of specialized (secondary) metabolites of diverse classes. Trichomes are implicated in a variety of adaptive processes, including defense against herbivores and micro-organisms as well as in ion homeostasis. Because trichomes protrude from the epidermis and can often be easily separated from it and harvested, the mRNAs, proteins and small molecules that they contain are unusually accessible to analysis. This property makes them excellent experimental systems for identification of the enzymes and pathways responsible for the synthesis of the specialized metabolites found in these structures and sometimes elsewhere in the plant. We review the literature on the biochemistry of trichomes and consider the attributes that might make them highly useful targets for plant metabolic engineering.

post to: CiteULike

Production of renewable polymers from crop plants.

Publication Date: 2008 May PMID: 18476872
Authors: van Beilen, J. B. - Poirier, Y.
Journal: Plant J

Plants produce a range of biopolymers for purposes such as maintenance of structural integrity, carbon storage, and defense against pathogens and desiccation. Several of these natural polymers are used by humans as food and materials, and increasingly as an energy carrier. In this review, we focus on plant biopolymers that are used as materials in bulk applications, such as plastics and elastomers, in the context of depleting resources and climate change, and consider technical and scientific bottlenecks in the production of novel or improved materials in transgenic or alternative crop plants. The biopolymers discussed are natural rubber and several polymers that are not naturally produced in plants, such as polyhydroxyalkanoates, fibrous proteins and poly-amino acids. In addition, monomers or precursors for the chemical synthesis of biopolymers, such as 4-hydroxybenzoate, itaconic acid, fructose and sorbitol, are discussed briefly.

post to: CiteULike

Plant surface lipid biosynthetic pathways and their utility for metabolic engineering of waxes and hydrocarbon biofuels.

Publication Date: 2008 May PMID: 18476871
Authors: Jetter, R. - Kunst, L.
Journal: Plant J

Due to their unique physical properties, waxes are high-value materials that are used in a variety of industrial applications. They are generated by chemical synthesis, extracted from fossil sources, or harvested from a small number of plant and animal species. As a result, the diversity of chemical structures in commercial waxes is low and so are their yields. These limitations can be overcome by engineering of wax biosynthetic pathways in the seeds of high-yielding oil crops to produce designer waxes for specific industrial end uses. In this review, we first summarize the current knowledge regarding the genes and enzymes generating the chemical diversity of cuticular waxes that accumulate at the surfaces of primary plant organs. We then consider the potential of cuticle biosynthetic genes for biotechnological wax production, focusing on selected examples of wax ester chain lengths and isomers. Finally, we discuss the genes/enzymes of cuticular alkane biosynthesis and their potential in future metabolic engineering of plants for the production of renewable hydrocarbon fuels.

post to: CiteULike

Terpenoid biomaterials.

Publication Date: 2008 May PMID: 18476870
Authors: Bohlmann, J. - Keeling, C. I.
Journal: Plant J

Terpenoids (isoprenoids) encompass more than 40 000 structures and form the largest class of all known plant metabolites. Some terpenoids have well-characterized physiological functions that are common to most plant species. In addition, many of the structurally diverse plant terpenoids may function in taxonomically more discrete, specialized interactions with other organisms. Historically, specialized terpenoids, together with alkaloids and many of the phenolics, have been referred to as secondary metabolites. More recently, these compounds have become widely recognized, conceptually and/or empirically, for their essential ecological functions in plant biology. Owing to their diverse biological activities and their diverse physical and chemical properties, terpenoid plant chemicals have been exploited by humans as traditional biomaterials in the form of complex mixtures or in the form of more or less pure compounds since ancient times. Plant terpenoids are widely used as industrially relevant chemicals, including many pharmaceuticals, flavours, fragrances, pesticides and disinfectants, and as large-volume feedstocks for chemical industries. Recently, there has been a renaissance of awareness of plant terpenoids as a valuable biological resource for societies that will have to become less reliant on petrochemicals. Harnessing the powers of plant and microbial systems for production of economically valuable plant terpenoids requires interdisciplinary and often expensive research into their chemistry, biosynthesis and genomics, as well as metabolic and biochemical engineering. This paper provides an overview of the formation of hemi-, mono-, sesqui- and diterpenoids in plants, and highlights some well-established examples for these classes of terpenoids in the context of biomaterials and biofuels.

post to: CiteULike

High-value oils from plants.

Publication Date: 2008 May PMID: 18476869
Authors: Dyer, J. M. - Stymne, S. - Green, A. G. - Carlsson, A. S.
Journal: Plant J

The seed oils of domesticated oilseed crops are major agricultural commodities that are used primarily for nutritional applications, but in recent years there has been increasing use of these oils for production of biofuels and chemical feedstocks. This is being driven in part by the rapidly rising costs of petroleum, increased concern about the environmental impact of using fossil oil, and the need to develop renewable domestic sources of fuel and industrial raw materials. There is also a need to develop sustainable sources of nutritionally important fatty acids such as those that are typically derived from fish oil. Plant oils can provide renewable sources of high-value fatty acids for both the chemical and health-related industries. The value and application of an oil are determined largely by its fatty acid composition, and while most vegetable oils contain just five basic fatty acid structures, there is a rich diversity of fatty acids present in nature, many of which have potential usage in industry. In this review, we describe several areas where plant oils can have a significant impact on the emerging bioeconomy and the types of fatty acids that are required in these various applications. We also outline the current understanding of the underlying biochemical and molecular mechanisms of seed oil production, and the challenges and potential in translating this knowledge into the rational design and engineering of crop plants to produce high-value oils in plant seeds.

post to: CiteULike

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances.

Publication Date: 2008 May PMID: 18476868
Authors: Hu, Q. - Sommerfeld, M. - Jarvis, E. - Ghirardi, M. - Posewitz, M. - Seibert, M. - Darzins, A.
Journal: Plant J

Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.

post to: CiteULike

Deciphering gene regulatory networks that control seed development and maturation in Arabidopsis.

Publication Date: 2008 May PMID: 18476867
Authors: Santos-Mendoza, M. - Dubreucq, B. - Baud, S. - Parcy, F. - Caboche, M. - Lepiniec, L.
Journal: Plant J

Seeds represent the main source of nutrients for animals and humans, and knowledge of their biology provides tools for improving agricultural practices and managing genetic resources. There is also tremendous interest in using seeds as a sustainable alternative to fossil reserves for green chemistry. Seeds accumulate large amounts of storage compounds such as carbohydrates, proteins and oils. It would be useful for agro-industrial purposes to produce seeds that accumulate these storage compounds more specifically and at higher levels. The main metabolic pathways necessary for oil, starch or protein accumulation are well characterized. However, the overall regulation of partitioning between the various pathways remains unclear. Such knowledge could provide new molecular tools for improving the qualities of crop seeds (Focks and Benning, 1998, Plant Physiol. 118, 91). Studies to improve understanding of the genetic controls of seed development and metabolism therefore remain a key area of research. In the model plant Arabidopsis, genetic analyses have demonstrated that LEAFY COTYLEDON genes, namely LEC1, LEC2 and FUSCA3 (FUS3), are key transcriptional regulators of seed maturation, together with ABSCISIC ACID INSENSITIVE 3 (ABI3). Interestingly, LEC2, FUS3 and ABI3 are related proteins that all contain a 'B3' DNA-binding domain. In recent years, genetic and molecular studies have shed new light on the intricate regulatory network involving these regulators and their interactions with other factors such as LEC1, PICKLE, ABI5 or WRI1, as well as with sugar and hormonal signaling. Here, we summarize the most recent advances in our understanding of this complex regulatory network and its role in the control of seed maturation.

post to: CiteULike

Plant triacylglycerols as feedstocks for the production of biofuels.

Publication Date: 2008 May PMID: 18476866
Authors: Durrett, T. P. - Benning, C. - Ohlrogge, J.
Journal: Plant J

Triacylglycerols produced by plants are one of the most energy-rich and abundant forms of reduced carbon available from nature. Given their chemical similarities, plant oils represent a logical substitute for conventional diesel, a non-renewable energy source. However, as plant oils are too viscous for use in modern diesel engines, they are converted to fatty acid esters. The resulting fuel is commonly referred to as biodiesel, and offers many advantages over conventional diesel. Chief among these is that biodiesel is derived from renewable sources. In addition, the production and subsequent consumption of biodiesel results in less greenhouse gas emission compared to conventional diesel. However, the widespread adoption of biodiesel faces a number of challenges. The biggest of these is a limited supply of biodiesel feedstocks. Thus, plant oil production needs to be greatly increased for biodiesel to replace a major proportion of the current and future fuel needs of the world. An increased understanding of how plants synthesize fatty acids and triacylglycerols will ultimately allow the development of novel energy crops. For example, knowledge of the regulation of oil synthesis has suggested ways to produce triacylglycerols in abundant non-seed tissues. Additionally, biodiesel has poor cold-temperature performance and low oxidative stability. Improving the fuel characteristics of biodiesel can be achieved by altering the fatty acid composition. In this regard, the generation of transgenic soybean lines with high oleic acid content represents one way in which plant biotechnology has already contributed to the improvement of biodiesel.

post to: CiteULike

Microbial conversion of sugars from plant biomass to lactic acid or ethanol.

Publication Date: 2008 May PMID: 18476865
Authors: Doran-Peterson, J. - Cook, D. M. - Brandon, S. K.
Journal: Plant J

Concerns for our environment and unease with our dependence on foreign oil have renewed interest in converting plant biomass into fuels and 'green' chemicals. The volume of plant matter available makes lignocellulose conversion desirable, although no single isolated organism has been shown to depolymerize lignocellulose and efficiently metabolize the resulting sugars into a specific product. This work reviews selected chemicals and fuels that can be produced from microbial fermentation of plant-derived cell-wall sugars and directed engineering for improvement of microbial biocatalysts. Lactic acid and ethanol production are highlighted, with a focus on engineered Escherichia coli.

post to: CiteULike

Improvement of biomass through lignin modification.

Publication Date: 2008 May PMID: 18476864
Authors: Li, X. - Weng, J. K. - Chapple, C.
Journal: Plant J

Lignin, a major component of the cell wall of vascular plants, has long been recognized for its negative impact on forage quality, paper manufacturing, and, more recently, cellulosic biofuel production. Over the last two decades, genetic and biochemical analyses of brown midrib mutants of maize, sorghum and related grasses have advanced our understanding of the relationship between lignification and forage digestibility. This work has also inspired genetic engineering efforts aimed at generating crops with altered lignin, with the expectation that these strategies would enhance forage digestibility and/or pulping efficiency. The knowledge gained from these bioengineering efforts has greatly improved our understanding of the optimal lignin characteristics required for various applications of lignocellulosic materials while also contributing to our understanding of the lignin biosynthetic pathway. The recent upswing of interest in cellulosic biofuel production has become the new focus of lignin engineering. Populus trichocarpa and Brachypodium distachyon are emerging as model systems for energy crops. Lignin research on these systems, as well as on a variety of proposed energy crop species, is expected to shed new light on lignin biosynthesis and its regulation in energy crops, and lead to rational genetic engineering approaches to modify lignin for improved biofuel production.

post to: CiteULike

Cell-wall carbohydrates and their modification as a resource for biofuels.

Publication Date: 2008 May PMID: 18476863
Authors: Pauly, M. - Keegstra, K.
Journal: Plant J

Plant cell walls represent the most abundant renewable resource on this planet. Despite their great abundance, only 2% of this resource is currently used by humans. Hence, research into the feasibility of using plant cell walls in the production of cost-effective biofuels is desirable. The main bottleneck for using wall materials is the recalcitrance of walls to efficient degradation into fermentable sugars. Manipulation of the wall polysaccharide biosynthetic machinery or addition of wall structure-altering agents should make it possible to tailor wall composition and architecture to enhance sugar yields upon wall digestion for biofuel fermentation. Study of the biosynthetic machinery and its regulation is still in its infancy and represents a major scientific and technical research challenge. Of course, any change in wall structure to accommodate cost-efficient biofuel production may have detrimental effects on plant growth and development due to the diverse roles of walls in the life of a plant. However, the diversity and abundance of wall structures present in the plant kingdom gives hope that this challenge can be met.

post to: CiteULike

Prospects for increasing starch and sucrose yields for bioethanol production.

Publication Date: 2008 May PMID: 18476862
Authors: Smith, A. M.
Journal: Plant J

In the short term, the production of bioethanol as a liquid transport fuel is almost entirely dependent on starch and sugars from existing food crops. The sustainability of this industry would be enhanced by increases in the yield of starch/sugar per hectare without further inputs into the crops concerned. Efforts to achieve increased yields of starch over the last three decades, in particular via manipulation of the enzyme ADPglucose pyrophosphorylase, have met with limited success. Other approaches have included manipulation of carbon partitioning within storage organs in favour of starch synthesis, and attempts to manipulate source-sink relationships. Some of the most promising results so far have come from manipulations that increase the availability of ATP for starch synthesis. Future options for achieving increased starch contents could include manipulation of starch degradation in organs in which starch turnover is occurring, and introduction of starch synthesis into the cytosol. Sucrose accumulation is much less well understood than starch synthesis, but recent results from research on sugar cane suggest that total sugar content can be greatly increased by conversion of sucrose into a non-metabolizable isomer. A better understanding of carbohydrate storage and turnover in relation to carbon assimilation and plant growth is required, both for improvement of starch and sugar crops and for attempts to increase biomass production in second-generation biofuel crops.

post to: CiteULike

Platform biochemicals for a biorenewable chemical industry.

Publication Date: 2008 May PMID: 18476861
Authors: Nikolau, B. J. - Perera, M. A. - Brachova, L. - Shanks, B.
Journal: Plant J

The chemical industry is currently reliant on a historically inexpensive, petroleum-based carbon feedstock that generates a small collection of platform chemicals from which highly efficient chemical conversions lead to the manufacture of a large variety of chemical products. Recently, a number of factors have coalesced to provide the impetus to explore alternative renewable sources of carbon. Here we discuss the potential impact on the chemical industry of shifting from non-renewable carbon sources to renewable carbon sources. This change to the manufacture of chemicals from biological carbon sources will provide an opportunity for the biological research community to contribute fundamental knowledge concerning carbon metabolism and its regulation. We discuss whether fundamental biological research into metabolic processes at a holistic level, made possible by completed genome sequences and integrated with detailed structural understanding of biocatalysts, can change the chemical industry from being dependent on fossil-carbon feedstocks to using biorenewable feedstocks. We illustrate this potential by discussing the prospect of building a platform technology based upon a concept of combinatorial biosynthesis, which would explore the enzymological flexibilities of polyketide biosynthesis.

post to: CiteULike

Harnessing plant biomass for biofuels and biomaterials.

Publication Date: 2008 May PMID: 18476860
Authors: Benning, C. - Pichersky, E.
Journal: Plant J

post to: CiteULike

Genetic and physical interaction suggest that BARREN STALK1 is a target of BARREN INFLORESCENCE2 in maize inflorescence development.

Publication Date: 2008 May 9 PMID: 18466309
Authors: Skirpan, A. - Wu, X. - McSteen, P.
Journal: Plant J

Organogenesis in plants is controlled by polar auxin transport. In maize (Zea mays), barren inflorescence2 (bif2) encodes a co-ortholog of the serine/threonine protein kinase PINOID (PID), which regulates auxin transport in Arabidopsis. In this paper, we report that the basic helix loop helix transcription factor BARREN STALK1 (BA1), is a putative target of BIF2, revealing a previously unknown function of BIF2 in the nucleus. Both bif2 and ba1 are required for axillary meristem initiation during inflorescence and vegetative development in maize. Using a yeast two-hybrid approach, we identified BA1 as an interacting partner with BIF2. We confirmed the interaction by in vitro GST-pull down assays and demonstrated that BIF2 phosphorylates BA1 in vitro. Previously, RNA in situ hybridization showed that bif2 and ba1 are both expressed during axillary meristem initiation. Here, we heterologously expressed BIF2 and BA1 and found that they colocalize in the nucleus. Based on these findings, we propose that in addition to regulating auxin transport at the cell periphery, BIF2 also functions in the nucleus by interacting with BA1 to promote axillary meristem initiation. Double mutant analysis is consistent with these results showing that bif2 and ba1 have overlapping as well as unique roles in inflorescence development.

post to: CiteULike

A novel homodimeric geranyl diphosphate synthase from the orchid Phalaenopsis bellina lacking a DD(X)2-4D motif.

Publication Date: 2008 May 9 PMID: 18466308
Authors: Hsiao, Y. Y. - Jeng, M. F. - Tsai, W. C. - Chuang, Y. C. - Li, C. Y. - Wu, T. S. - Kuoh, C. S. - Chen, W. H. - Chen, H. H.
Journal: Plant J

Geranyl diphosphate (GDP) is the precursor of monoterpenes, the major floral scent compounds in Phalaenopsis bellina. The cDNA of P. bellina GDP synthase (PbGDPS) was cloned, and its sequence corresponds to the second Asp-rich motif (SARM) but no any aspartate-rich (Asp-rich). The recombinant PbGDPS enzyme possessed a dual prenyltransferase activity, producing both GDP and farnesyl diphosphate (FDP), and a yeast two-hybrid assay and gel filtration revealed that PbGDPS was able to form a homodimer. Spatial and temporal expression analyses showed that the expression of PbGDPS was flower specific and maximal PbGDPS expression was concomitant with maximal emission of monoterpenes on day 5 post-anthesis. Homology modelling of PbGDPS indicated that the Glu-rich motif might provide a binding site for Mg2+ and catalyze the formation of prenyl products in a similar way to SARM. Replacement of the key Glu residues with alanine totally abolished enzyme activity, whereas their mutation to Asp resulted in a mutant with two thirds of the activity of the wild-type protein. Phylogenetic analysis indicated that plant GDPS proteins formed four clades: members of both GDPS-a and GDPS-b clades contain Asp-rich motifs, and function as homodimers. In contrast, proteins in the GDPS-c and GDPS-d clades do not contain Asp-rich motifs, but while members of the GDPS-c clade function as heterodimers, PbGDPS, which is more closely related to the GDPS-c clade proteins than to GDPS-a and GDPS-b proteins, and is currently the sole member of the GDPS-d clade, functions as homodimer.

post to: CiteULike

A new whole-mount DNA quantification method and the analysis of nuclear DNA content in the stem cell niche of Arabidopsis roots.

Publication Date: 2008 May 9 PMID: 18466307
Authors: Willemse, J. - Kulikova, O. - de Jong, H. - Bisseling, T.
Journal: Plant J

A semi-automated method to quantify fluorescence intensity of objects in intact organs and tissues, composed of several cell layers has been designed. The method has been developed on whole mount Propidium Iodide stained Arabidopsis thaliana (Arabidopsis) root tips, in which DNA content of individual nuclei could be quantified. A diameter of less than 150 mum makes this organ most appropriate for whole mount imaging. Further advantages are the lack of chlorophyll and transparent cell walls with only little background fluorescence. The method has great advantage over flow cytometry as positional information of nuclei is maintained and nuclei with aberrant DNA content can be re-assessed individually, which facilitates efficient distinction between technical artefact and aberrant DNA content. Our averaging 3D method calculates the average of the summed fluorescence intensities of all sections of a nucleus and interpolates the missing sections, thereby allowing correction of detection problems. Further this method has the advantage of detecting objects in tissues covering multiple cell layers. The results of our method in Arabidopsis root tips showed that the Quiescent Centre cells, which rarely divide, are diploid and are arrested in G1 or G0. Most stem cells, with the exception of those of the vascular tissue, are diploid cells and their rather low division rate is caused by an elongated G1 phase. In contrast the majority of the vascular stem cells are tetraploid.

post to: CiteULike

A role for SENSITIVE TO FREEZING2 in protecting chloroplasts against freeze induced damage in Arabidopsis.

Publication Date: 2008 May 9 PMID: 18466306
Authors: Fourrier, N. - Bedard, J. - Lopez-Juez, E. - Barbrook, A. - Bowyer, J. - Jarvis, P. - Warren, G. - Thorlby, G.
Journal: Plant J

The SENSITIVE TO FREEZING2 (SFR2) gene has an important role in freezing tolerance in Arabidopsis thaliana. We show that homologous genes are present, and expressed, in a wide range of terrestrial plants including species not able to tolerate freezing. Expression constructs derived from the cDNAs of a number of different plant species, including examples not tolerant to freezing, are able to complement the freezing sensitivity of the Arabidopsis sfr2 mutant. In Arabidopsis the SFR2 protein is localised to the chloroplast outer envelope membrane, as revealed by the analysis of transgenic plants expressing SFR2 fusions to GFP by confocal microscopy and by the immunological analysis of isolated chloroplasts treated with thermolysin protease. Moreover, the chloroplasts of the sfr2 mutant show clear evidence of rapid damage after a freezing episode suggesting a role for SFR2 in the protection of the chloroplast.

post to: CiteULike

A simple and rapid technique for detecting protein phosphorylation using one-dimensional isoelectric focusing gels and immunoblot analysis.

Publication Date: 2008 May 9 PMID: 18466305
Authors: Anderson, J. C. - Peck, S. C.
Journal: Plant J

We report a technique for detecting protein phosphorylation that involves isoelectric focusing in a vertical mini-gel format followed by immunoblot detection of the target protein. This method uses standard protein gel equipment, allows sensitive detection of protein phosphorylation when phosphospecific antibodies are not available, and provides a stoichiometric measure of phosphorylation. We demonstrate the application of this method for observing phosphorylation of an Arabidopsis thaliana protein in response to biotic stress.

post to: CiteULike

Arabidopsis ethylene signaling involves feedback regulation via the elaborate control of EBF2 expression by EIN3.

Publication Date: 2008 May 9 PMID: 18466304
Authors: Konishi, M. - Yanagisawa, S.
Journal: Plant J

EIN3 is a key transcription factor in the signaling pathway of the plant hormone, ethylene, in Arabidopsis. Ethylene signaling suppresses the 26S proteasome-mediated proteolysis of EIN3, the accumulation of which induces ethylene-responsive gene expression. The proteolysis of EIN3 has been suggested to be mediated by the E3 ubiquitin ligase SCF(EBF1/2) that contains either of the two closely related F-box proteins, EBF1 or EBF2. Here, we demonstrate a feedback regulation in ethylene signaling that results from the direct upregulation of the EBF2 gene by EIN3. Although EBF1 and EBF2 show comparable activities as repressors of EIN3-dependent transcription, our analysis of transgenic Arabidopsis plants has revealed that the EBF2 promoter but not the EBF1 promoter is activated by ethylene. Furthermore, the results of protoplast transient assays in vivo and electrophoretic mobility shift assays in vitro have revealed that EIN3 can bind and activate the EBF2 promoter, indicating that EIN3 modulates EBF2 gene expression in planta. An ebf2 mutant transformed with the EBF2 gene under the control of a mutant promoter in which the EIN3-binding site was disrupted still showed an ethylene hyper-responsive phenotype, indicating the physiological relevance of EIN3-mediated activation of the EBF2 gene in the downregulation of ethylene signaling. We show an additional finding that a sequence downstream of the EBF2 coding region is also involved in modulations of both the EBF2 expression level and sensitivity to ethylene. These results thus indicate that the fine-tuning of ethylene signaling involves the intricate regulations of the EBF2 expression in Arabidopsis.

post to: CiteULike

SOC1 translocated to nucleus by interaction with AGL24 directly regulates LEAFY.

Publication Date: 2008 May 9 PMID: 18466303
Authors: Lee, J. - Oh, M. - Park, H. - Lee, I.
Journal: Plant J

SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) is one of the flowering pathway integrators, and regulates the expression of LEAFY (LFY), which links floral induction and floral development. However, the mechanism by which SOC1, a MADS box protein, regulates LFY has been elusive. Here, we show that SOC1 directly binds to the distal and proximal region of LFY promoter where critical cis-elements are located. Intragenic suppressor mutant analysis shows that the missense mutation in the MADS box of SOC1 causes the loss of binding to LFY promoter as well as the suppression of the flowering promotion function. The full length SOC1 protein locates in the cytoplasm if expressed alone in protoplast transient expression assay, but relocates to the nucleus if expressed with AGAMOUS-LIKE 24 (AGL24), another flowering pathway integrator and a MADS box protein. The domain analysis shows that the co-localization of SOC1 and AGL24 is mediated by the MADS and the intervening region of SOC1. Finally, we show that LFY is expressed only in the tissues where SOC1 and AGL24 expressions overlap. Thus, we propose that the heterodimerization of SOC1 and AGL24 is a key mechanism in activating LFY expression.

post to: CiteULike

D'orenone Blocks Polarized Tip-Growth of Root Hairs by Interfering with the PIN2-Mediated Auxin Transport Network in the Root Apex.

Publication Date: 2008 May 9 PMID: 18466302
Authors: Schlicht, M. - Samajova, O. - Schachtschabel, D. - Mancuso, S. - Menzel, D. - Boland, W. - Baluska, F.
Journal: Plant J

The C(18)-ketone ((5E,7E)-6-methyl-8-(2,6,6-trimethylcyclohex-1-enyl)octa-5,7-dien-2-one) (D'orenone) has been postulated to be an early cleavage product of beta-carotene en route to trisporic acids; these act as morphogenetic factors during the sexual reproduction of zygomycetes. Here we report that D'orenone blocks the highly polarized tip growth of root hairs at causing tip-growth to stop completely within a few minutes. Importantly, external auxin restores these effects of D'orenone on root hairs. Further analysis revealed that D'orenone lowers auxin concentration in trichoblasts via PIN2-mediated auxin efflux below critical levels essential for root hair growth. D'orenone increases specifically PIN2 protein abundance without affecting PIN2 transcripts, and that the PIN2 expression domain enlarges and shifts basipetally, resulting in more active auxin transport. Final evidence for PIN2 acting as the specific target of D'orenone is the observation that this compound does not interfere with the root hair growth in roots of null mutant lines.

post to: CiteULike

The calmodulin-binding protein kinase 3 is part of heat shock signal transduction in Arabidopsis thaliana.

Publication Date: 2008 May 9 PMID: 18466301
Authors: Liu, H. T. - Gao, F. - Li, G. L. - Han, J. L. - Liu, D. L. - Sun, D. Y. - Zhou, R. G.
Journal: Plant J

Based on our previous findings, we have proposed a pathway for the participation of Ca(2+)-calmodulin (CaM) in heat shock (HS) signal transduction. The specific mechanism by which CaM regulates activation of heat shock transcription factors (HSF) is not known. The CaM-binding protein kinases (CBK) are the most poorly understood of the CaM target proteins in plants. Herein using a yeast two-hybrid assay, we found that AtCBK3 interacts with AtHSFA1a. Fluorescence resonance energy transfer was used to confirm interaction between AtCBK3-YFP and AtHSFA1a-CFP. Furthermore, we demonstrated that purified recombinant AtCBK3 could phosphorylate recombinant AtHSFA1a in vitro. We also describe results from both the down-regulation of AtCBK3 expression, and ectopic overexpression, in Arabidopsis thaliana. The T-DNA insertion AtCBK3 knockout lines had impaired basal thermotolerance, which could be complemented by transformation of plants with the native gene. Overexpression of AtCBK3 resulted in plants with increased basal thermotolerance. Results from real-time quantitative PCR and protein gel blot analyses suggest that AtCBK3 regulates transcription of heat shock protein (HSP) genes and synthesis of HSPs. The binding activity of HSF to heat shock element (HSE), mRNA level of HSP genes and synthesis of HSPs were up-regulated in AtCBK3-overexpressing lines after HS, but down-regulated in AtCBK3 null lines. These results indicate that AtCBK3 controls the binding activity of HSF to HSE by phosphorylation of AtHSFA1a, and is an important component of the HS signal transduction pathway.

post to: CiteULike

The glutathione-deficient mutant pad2-1 accumulates lower amounts of glucosinolates and is more susceptible to the insect herbivore Spodoptera littoralis.

Publication Date: 2008 May 8 PMID: 18466300
Authors: Schlaeppi, K. - Bodenhausen, N. - Buchala, A. - Mauch, F. - Reymond, P.
Journal: Plant J

Plants often respond to pathogen or insect attack by inducing the synthesis of toxic compounds such as phytoalexins and glucosinolates (GS). The Arabidopsis mutant pad2-1 has reduced levels of the phytoalexin camalexin and is known for its increased susceptibility to fungal and bacterial pathogens. We found that pad2-1 is also more susceptible to the generalist insect Spodoptera littoralis but not to the specialist Pieris brassicae. The PAD2 gene encodes a gamma-glutamylcysteine synthetase involved in glutathione (GSH) synthesis and consequently the pad2-1 mutant contains about 20% of the GSH found in wild-type plants. Lower GSH levels of pad2-1 were correlated with a reduced accumulation of the two major indole and aliphatic GS of Arabidopsis, indolyl-3-methyl-GS and 4-methylsulfinylbutyl-GS, in response to insect feeding. This effect was specific to GSH, it was not complemented by a treatment of pad2-1 with the strong reducing agent dithiothreitol and was not observed with the ascorbate-deficient mutant vtc1-1. In contrast to the jasmonate-insensitive mutant coi1-1, the expression of insect regulated- and GS-biosynthesis genes was not affected in pad2-1. Our data suggest a crucial role for GSH in GS-biosynthesis and insect resistance.

post to: CiteULike

Tocopherol metabolism, oxidation and recycling under high light stress in Arabidopsis.

Publication Date: 2008 Apr 30 PMID: 18452591
Authors: Kobayashi, N. - Dellapenna, D.
Journal: Plant J

Tocopherols are synthesized and accumulated by all plants and many cyanobacteria. The quenching and scavenging of reactive oxygen species and lipid peroxyradicals by tocopherols can result in the formation of various tocopherol oxidation compounds. A targeted GC/MS profiling method was developed to quantify all tocopherols and pathway intermediates and twenty-three potential alpha- and gamma-tocopherol oxidation products. This method was used to study the response of wild type Arabidopsis (Col) and the tocopherol biosynthetic mutants, vte1, vte2 and vte4 during 12 h low and high light treatments (LL and HL, 90 and 1,500 mumol photon m(-2) s(-1), respectively) and a subsequent 12 h dark recovery period. All tocopherols and pathway intermediates exhibited HL dependent increases except DMPBQ in vte1 and beta-tocopherol in Col. Profiling of potential tocopherol oxidation products during HL treatment only detected alpha-tocopherolquinol (alpha-TQH(2)) in Col and gamma-tocopherolquinol (gamma-TQH(2)) in vte4, both of which accumulated to similar levels and with similar kinetics the two genotypes. However, during dark recovery alpha- TQH(2) in Col decreased several times faster than gamma-TQH(2) in vte4, suggesting the presence of biochemical processes with higher specificity for alpha-TQH(2). (14)C-labeled alpha-tocopherolquinone (alpha-TQ) applied to isolated Col chloroplasts could be converted to (14)C-alpha-tocopherol demonstrating the existence of a plastid based system for recycling oxidized alpha-tocopherol. The accumulation of (14)C- trimethylphytylbenzoquinone (TMPBQ) by isolated vte1 plastids treated with (14)C-labeled alpha-TQ is consistent with the tocopherolquinone recycling pathway employing a yet to be identified plastid-localized dehydratase that converts TQ to TMPBQ.

post to: CiteULike

Wounding of Arabidopsis leaves causes a powerful but transient protection against Botrytis infection.

Publication Date: 2008 Apr 30 PMID: 18452590
Authors: Chassot, C. - Buchala, A. - Schoonbeek, H. J. - Metraux, J. P. - Lamotte, O.
Journal: Plant J

Physical injury inflicted to living tissue makes it vulnerable to invasion by pathogens. Wounding of Arabidopsis thaliana leaves, however, does not follow this concept and leads to immunity to Botrytis cinerea, the causal agent of grey mould. In wounded leaves, hyphal growth was strongly inhibited compared to unwounded controls. Wound-induced resistance was not associated with salicylic acid (SA)-, jasmonic acid (JA)- or ethylene (ET)-dependent defence responses. The phytoalexin camalexin was found to be involved in this defence response since camalexin-deficient mutants were not protected after wounding and the B. cinerea strains used here were sensitive to this compound. Wounding alone did not induce camalexin but primed its accumulation after inoculation with B. cinerea, further supporting the role of camalexin in wound-induced resistance. In parallel to increased camalexin production, genes involved in the biosynthesis of camalexin were induced faster in wounded and infected plants in comparison with unwounded and infected plants. Glutathione was also found to be required for the resistance, as mutants deficient in gamma-glutamylcysteine synthetase showed susceptibility to B. cinerea after wounding, indicating that wild-type basal levels of glutathione are required for the wound-induced resistance. Furthermore, expression of the gene encoding glutathione-S-transferase 1 was primed by wounding in leaves inoculated with B. cinerea. In addition, the priming of MAP-kinase activity was observed after inoculation of wounded leaves with B. cinerea compared to unwounded inoculated controls. Our results demonstrate how abiotic stress can induce immunity to virulent strains of B. cinerea, a process that involves camalexin and glutathione.

post to: CiteULike

The Arabidopsis sweetie mutant is affected in carbohydrate metabolism and defective in the control of growth, development and senescence.

Publication Date: 2008 Apr 30 PMID: 18452589
Authors: Veyres, N. - Danon, A. - Aono, M. - Galliot, S. - Karibasappa, Y. B. - Diet, A. - Grandmottet, F. - Tamaoki, M. - Lesur, D. - Pilard, S. - Boitel-Conti, M. - Sangwan-Norreel, B. S. - Sangwan, R. S.
Journal: Plant J

Sugars modulate many vital metabolic and developmental processes in plants from seed germination to flowering, senescence and protection against diverse abiotic and biotic stresses. However, the exact mechanisms involved in morphogenesis, developmental signalling and stress tolerance remain largely unknown. Here we report the characterization of a novel Arabidopsis thaliana mutant, sweetie, with drastically altered morphogenesis, and a strongly modified carbohydrate metabolism leading to elevated levels of trehalose, trehalose 6-phosphate and starch. We additionally show that the disruption of SWEETIE causes significant growth and developmental alterations such as severe dwarfism, lancet-shaped leaves, early senescence and flower sterility. Genes implicated in sugar metabolism, senescence, ethylene biosynthesis and abiotic stress were found to be up-regulated in sweetie. Our physiological, biochemical, genetic and molecular data indicate that the mutation in sweetie was nuclear, single and recessive. The effects of metabolizable sugars and osmolytes on sweetie morphogenesis were distinct; in light sweetie was hypersensitive to sucrose and glucose during vegetative growth and a partial phenotypic reversion took place in the presence of high sorbitol concentrations. However, SWEETIE encodes a protein that is unrelated to any known enzyme involved in sugar metabolism. We suggest that SWEETIE plays an important regulatory function which influences multiple metabolic, hormonal and stress-related pathways, leading to altered gene expression and pronounced changes in the accumulation of sugar, starch, and ethylene.

post to: CiteULike

Silencing of NtMPK4 impairs CO(2)-induced stomatal closure, activation of anion channels and cytosolic Ca(2+)-signals in Nicotiana tabacum guard cells.

Publication Date: 2008 Apr 30 PMID: 18452588
Authors: Marten, H. - Hyun, T. - Gomi, K. - Seo, S. - Hedrich, R. - Roelfsema, M. R.
Journal: Plant J

Light-induced stomatal opening in C3- and C4-plants is mediated by two signalling pathways. One pathway is specific for blue light and involves phototropins, while the second pathway depends on Photosynthetic Active Radiation (PAR). Here, the role of NtMPK4 on light-induced stomatal opening was studied, since silencing of this MAP kinase stimulates stomatal opening. Stomata of NtMPK4-silenced plants do not close in elevated atmospheric CO(2) and show a reduced response to PAR. However, stomatal closure can still be induced by ABA. Measurements with multi-barrelled intracellular micro electrodes showed that CO(2) activates plasma membrane anion channels in wild type Nicotiana tabacum guard cells, but not in NtMPK4-silenced cells. Anion channels also were activated after switching off PAR in wild type guard cells. In approximately half of these cells, the activation of anion channels was accompanied by a rise of the cytosolic free Ca(2+) concentration. The activity of anion channels was higher in cells displaying a parallel rise in cytosolic Ca(2+), than in those with steady Ca(2+) levels. Both the darkness-induced anion channel activation and Ca(2+)-signals were repressed in NtMPK4-silenced guard cells. These data show that CO(2) and darkness can activate anion channels in a Ca(2+)-independent manner, but the anion channel activity is enhanced by parallel rises of the cytosolic Ca(2+) concentration. NtMPK4 plays an essential role in CO(2)- and darkness-induced activation of guard cell anion channels, through Ca(2+)-independent as well as Ca(2+)-dependent signalling pathways.

post to: CiteULike

AtCYP38 ensures early biogenesis, correct assembly and sustenance of photosystem II.

Publication Date: 2008 Apr 24 PMID: 18445132
Authors: Sirpio, S. - Khrouchtchova, A. - Allahverdiyeva, Y. - Hansson, M. - Fristedt, R. - Vener, A. V. - Scheller, H. V. - Jensen, P. E. - Haldrup, A. - Aro, E. M.
Journal: Plant J

AtCYP38 is a thylakoid lumen protein comprising the immunophilin domain and the phosphatase inhibitor module. Here we show the association of AtCYP38 with photosystem (PS)II monomer complex and address its functional role using AtCYP38 deficient mutants. The dynamic greening process of etiolated leaves failed in the absence of AtCYP38, due to specific problems in biogenesis of PSII complexes. Also the development of leaves under short day condition was severely disturbed. Detailed biophysical and biochemical analysis of mature AtCYP38 deficient plants from favourable growth conditions (long photoperiod) revealed (i) intrinsic malfunction of PSII, which (ii) occurred on the donor side of PSII and (iii) was dependent on growth light intensity. AtCYP38 mutant plants also showed decreased accumulation of PSII, which was shown not to originate from impaired D1 synthesis or assembly of PSII monomers, dimers and supercomplexes as such but rather from the incorrect fine-tuning of the oxygen evolving side of PSII. This, in turn, rendered PSII centers extremely susceptible to photoinhibition. AtCYP38-deficiency also drastically decreased the in vivo phosphorylation of PSII core proteins, probably related to the absence of AtCYP38 phosphatase inhibitor domain. It is proposed that during PSII assembly the AtCYP38 protein guides the proper folding of D1 (and CP43) into PSII thereby making the correct assembly of the water-splitting Mn(4)-Ca cluster feasible even upon high turnover of PSII.

post to: CiteULike

VASCULAR-RELATED NAC-DOMAIN7 is involved in differentiation of all types of xylem vessels in Arabidopsis roots and shoots.

Publication Date: 2008 Apr 24 PMID: 18445131
Authors: Yamaguchi, M. - Kubo, M. - Fukuda, H. - Demura, T.
Journal: Plant J

The Arabidopsis thaliana NAC domain transcription factor, VASCULAR-RELATED NAC-DOMAIN7 (VND7), plays a pivotal role in regulating root protoxylem vessel differentiation. In order to understand the mechanisms underscoring VND7 function in vessel differentiation in more detail, we conducted extensive molecular analyses in yeast (Saccharomyces cerevisiae), Arabidopsis, and Nicotiana tabacum L. cv. Bright Yellow 2 (tobacco BY-2) cells. The transcriptional activation activity of VND7 was confirmed in yeast and Arabidopsis, and the C-terminal region was shown to be required for VND7 transcriptional activation. Expression of the C-terminus-truncated VND7 protein under the control of the native VND7 promoter resulted in inhibition of normal development of metaxylem vessels in roots and vessels in aerial organs, as well as protoxylem vessels in roots. The expression pattern of VND7 overlapped that of VND2 to VND5 in most of the differentiating vessels. Furthermore, a yeast two-hybrid assay revealed the ability of VND7 to form homodimers and heterodimers with other VND proteins via their N-termini, which includes the NAC domain. The heterologous expression of VND7 in tobacco BY-2 cells demonstrated that VND7 stability could be regulated by proteasome-mediated degradation. Together these data suggested that VND7 regulates the differentiation of all types of vessels in roots and shoots, possibly in cooperation with VND2 to VND5 and other regulatory proteins.

post to: CiteULike

Isoprene emission is not temperature-dependent during and after severe drought-stress: a physiological and biochemical analysis.

Publication Date: 2008 Apr 25 PMID: 18445130
Authors: Fortunati, A. - Barta, C. - Brilli, F. - Centritto, M. - Zimmer, I. - Schnitzler, J. P. - Loreto, F.
Journal: Plant J

Black poplar (Populus nigra L.) plants grown at 25 and 35 degrees C were subjected to a drought stress to assess the combined impact of two consequences of global change, rising temperature and drought, on isoprene biosynthesis and emission. At both temperatures, photosynthesis was inhibited by moderate drought, but isoprene emission only decreased when drought was prolonged. Isoprene synthase (ISPS) mRNA transcript level, protein concentration and activity changed in concert with isoprene emission during drought stress. However, ISPS activity decreased before isoprene emission during drought development, indicating a tighter control of the emission at transcriptional or post-transcriptional level under moderate drought stress, and under both temperatures. A residual isoprene emission was measured when photosynthesis was totally inhibited after a 35 days of drought. This photosynthesis-independent emission of isoprene was likely dependent on a cytosolic carbon supply as all ISPS properties were drastically inhibited. Isoprene emission was associated with dark respiration during the entire drought stress period, and at both temperatures,, indicating that the two processes are sustained by, but do not compete for the same carbon source. Isoprene emission was directly related with phosphoenolpyruvate carboxylase activity in plants grown at 25 degrees C and inversely related in plants grown at 35 degrees C, suggesting a strong temperature control on the regulation of the pyruvate flowing from cytosol to plastidic isoprenoid biosynthetic pathway under drought stress and recovery. In re-watered plants, the temperature control on isoprene emission was suppressed, despite complete recovery of photosynthesis and ISPS activity similar to levels of plants subjected to mild drought stress. Our results reveal overriding effects of drought on isoprene emission, possibly affecting protein level or substrate supply. These effects may largely offset the predicted impact of rising temperatures on the emission of isoprene in terrestrial ecosystems.

post to: CiteULike

Ethylene-auxin interactions regulate lateral root initiation and emergence in Arabidopsis thaliana.

Publication Date: 2008 Apr 24 PMID: 18435826
Authors: Ivanchenko, M. G. - Muday, G. K. - Dubrovsky, J. G.
Journal: Plant J

Plant root systems display considerable plasticity in response to endogenous and environmental signals. Auxin stimulates pericycle cells within elongating primary roots to enter de novo organogenesis leading to establishment of new lateral root meristems. Cross talk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in root branching are not well characterized. We find that enhanced ethylene synthesis due to application of low concentrations of the ethylene precursor ACC promotes initiation of lateral root primordia. Treatment with higher ACC doses, or the eto1 mutation, strongly inhibits the ability of pericycle cells to initiate new lateral root primordia, but promotes emergence of existing lateral root primordia. These effects are correlated with decreased pericycle cell length and increased lateral root primordia cell width. When auxin is applied simultaneously with ACC, ACC is unable to prevent the auxin stimulation of lateral root formation in the root tissues formed prior to ACC exposure. However, in root tissues formed after transfer to ACC in which elongation is reduced, auxin does not rescue the ethylene inhibition of primordia initiation, but instead increases it several fold. Mutations that block auxin responses, slr1 and arf7 arf19, render initiation of lateral root primordia insensitive to the promoting effect of low ethylene levels, and mutations that inhibit ethylene-stimulated auxin biosynthesis, wei2 and wei7, reduce the inhibitory effect of higher ethylene levels, consistent with ethylene regulating root branching through interactions with auxin.

post to: CiteULike

Suppression mechanism of mitochondrial ORF79 accumulation by Rf1 protein, in BT-type cytoplasmic male sterile rice.

Publication Date: 2008 Apr 24 PMID: 18435825
Authors: Kazama, T. - Nakamura, T. - Watanabe, M. - Sugita, M. - Toriyama, K.
Journal: Plant J

In BT- type CMS of rice (Oryza sativa L.) with Chinsurah Boro II cytoplasm, CMS is caused by an accumulation of cytotoxic peptide, ORF79. The ORF79 protein is expressed from a dicistronic gene, atp6-orf79, that exists in addition to normal atp6 gene in the BT-type mitochondrial genome. The CMS is restored by a PPR (pentatricopeptide-repeat) gene, Rf1, via an RNA processing. However, it has not yet been elucidated how accumulation of ORF79 is reduced by the action of Rf1 protein. Here we report that the amount of the processed orf79 transcripts in the restorer line was reduced to 50% of the unprocessed atp6-orf79 transcripts in the CMS line. Ninety percent of the processed orf79 transcripts, which remained from degradation, were not associated with ribosome for translation. Our data suggests that the processing of atp6-orf79 transcripts diminishes the expression of orf79 by translational reduction and degradation of the processed orf79 transcripts.

post to: CiteULike

Both ATM and ATR promote the efficient and accurate processing of programmed meiotic double-strand breaks.

Publication Date: 2008 Apr 24 PMID: 18435824
Authors: Culligan, K. M. - Britt, A. B.
Journal: Plant J

The ATM and ATR protein kinases play central roles in the cellular response to double-strand breaks (DSBs) by regulating DNA repair, cell-cycle arrest and apoptosis. During meiosis, SPO11-dependent DSBs are generated, initiating recombination between homologous chromosomes. Previous studies in mice and plants have shown that defects in ATM result in the appearance of abnormally fragmented chromosomes. However, the role of ATR in promoting normal meiosis has not been elucidated. Employing null Arabidopsis mutants of ATR and ATM, we demonstrate here that while atr mutants display no obvious defects in any phase of meiotic progression, the combination of defects in atr and atm exacerbates the fragmentation observed in the atm single mutant, prevents complete synapsis of chromosomes, and results in extensive and persistent interactions between nonhomologous DNAs. The observed nonhomologous interactions require the induction of programmed breaks: combination of atm or the atr atm double mutant with a spo11 defect eliminates the ectopic interactions observed in the double mutant as well as significantly reducing the fragmentation seen in atm or atr atm. Our results suggest that ATM is required for efficient processing of SPO11-dependent DSBs during meiosis. They also indicate that ATM and ATR act redundantly to inhibit sustained interactions between nonhomologous chromatids, and that these ectopic interactions require SPO11 activity.

post to: CiteULike

The Medicago truncatula ortholog of Arabidopsis EIN2, sickle, is a negative regulator of symbiotic and pathogenic microbial associations.

Publication Date: 2008 Apr 24 PMID: 18435823
Authors: Varma Penmetsa, R. - Uribe, P. - Anderson, J. - Lichtenzveig, J. - Gish, J. C. - Nam, Y. W. - Engstrom, E. - Xu, K. - Sckisel, G. - Pereira, M. - Baek, J. M. - Lopez-Meyer, M. - Long, S. R. - Harrison, M. J. - Singh, K. B. - Kiss, G. B. - Cook, D. R.
Journal: Plant J

The plant hormone ethylene negatively regulates bacterial infection and nodule formation in legumes in response to symbiotic rhizobia, but the molecular mechanism(s) of ethylene action in symbiosis remain obscure. We have identified and characterized multiple mutant alleles of the MtSkl1 gene which controls both ethylene-sensitivity and nodule numbers. We show that this locus encodes the M. truncatula ortholog of the Arabidopsis ethylene signaling protein EIN2. In addition to the well-characterized role of MtSkl1 in rhizobial symbiosis, we show that MtSkl1 is involved in regulating early phases of the symbiotic interaction with mycorrhizal fungi, and in mediating root responses to cytokinin. MtSkl1 also functions in the defense against Rhizoctonia solani and Phytophthora medicaginis, with the latter interaction likely to involve positive feed back amplification of ethylene biosynthesis. Over expression of the C-terminal domain of MtEIN2 is sufficient to block nodulation responses, consistent with previous reports in Arabidopsis on the activation of ethylene signaling. This same C-terminal region is uniquely conserved throughout EIN2 homologs of angiosperms, consistent with its role as a higher plant specific innovation, essential to EIN2 function.

post to: CiteULike

Molecular and Genomic Basis of Volatile-mediated Indirect Defense against Insects in Rice.

Publication Date: 2008 Apr 22 PMID: 18433439
Authors: Yuan, J. S. - Kollner, T. G. - Wiggins, G. - Grant, J. - Degenhardt, J. - Chen, F.
Journal: Plant J

Rice plants fed on by fall armyworm (Spodoptera frugiperda, FAW) caterpillars emitted a blend of volatiles predominated by terpenoids. These volatiles were highly attractive to females of parasitoid Cotesia marginiventris. Microarray analysis identified 196 rice genes whose expression was significantly up-regulated by FAW feeding, 18 of which encode metabolic enzymes potentially involved in volatile biosynthesis. Significant induction of expression of seven of the 11 terpene synthase (TPS) genes identified through the microarray experiments was validated using real-time RT-PCR. Enzymes encoded by three TPS genes, Os02g02930, Os08g07100 and Os08g04500, were biochemically characterized. Os02g02930 was determined to encode a monoterpene synthase making a single product S-linalool, which is the most abundant volatile emitted from FAW-damaged rice plants. Both Os08g07100 and Os08g04500 were determined to encode sesquiterpene synthases with each producing multiple products. These three enzymes are responsible for production of the majority of the terpenes released from FAW-damaged rice plants. In addition to TPS genes, several key genes in the upstream terpenoid pathways were also found to be up-regulated by FAW feeding. The work presented provides a comprehensive analysis of FAW-induced volatiles and genes for their biosynthesis involved in indirect defense in rice. Evolution of the genetic basis governing volatile terpenoid biosynthesis for indirect defense is discussed.

post to: CiteULike

NRPD1a and NRPD1b are required to maintain post-transcriptional RNA silencing and RNA-directed DNA methylation in Arabidopsis.

Publication Date: 2008 Apr 22 PMID: 18433438
Authors: Eamens, A. - Vaistij, F. E. - Jones, L.
Journal: Plant J

In plants, both transcriptional (TGS) and post-transcriptional gene silencing (PTGS) can be self-reinforcing and this allows for maintenance of silencing once the initiator has been removed or suppressed. For TGS, this can be accomplished by the generation of small interfering RNAs (siRNAs) from methylated DNA templates by RNA Polymerase IV (PolIV), RNA-dependent RNA Polymerase 2 (RDR2), DICER-LIKE 3 (DCL3) and the RNA-directed DNA methylation (RdDM) machinery. Maintenance of PTGS requires RNA-dependent RNA Polymerase 6 (RDR6) and can be associated with DNA methylation and transitive production of secondary siRNAs. In this work, mutants defective for the NRPD1a and NRPD1b alternative largest subunits of PolIV were tested for their ability to undergo RdDM, transitive RNA silencing and maintenance of PTGS. PTGS could be initiated in both nrpd1a and nrpd1b mutants and this was associated with production of secondary siRNAs, however silencing was not maintained. nrpd1a mutants could support RdDM although this was lost upon reversal of silencing as was methylation in rdr6 mutants. We conclude that components of the machinery that maintain TGS are required for maintenance of PTGS and that RDR6 uses distinct templates in the initiation and maintenance phases of RNA silencing.

post to: CiteULike

Wheat FT protein regulates VRN1 transcription through interactions with FDL2.

Publication Date: 2008 Apr 22 PMID: 18433437
Authors: Li, C. - Dubcovsky, J.
Journal: Plant J

A precise regulation of flowering time is central to plant species survival. Therefore, mechanisms have evolved in plants to integrate different environmental cues to optimize flowering time. In this study we show that the wheat gene TaFT, which integrates photoperiod and vernalization signals promoting flowering, interacts with bZIP proteins TaFDL2 and TaFDL6. We also show that TaFDL2 can interact in vitro with five ACGT elements in the promoter of the meristem identity gene VRN1, suggesting that TaFDL2 is a functional homologue of Arabidopsis FD. No direct interactions between the TaFT protein and the VRN1 promoter were detected. Transgenic wheat plants overexpressing TaFT showed parallel increases in VRN1 transcripts, suggesting that TaFT provides transcriptional activation to VRN1, possibly through interactions with the TaFDL2 protein. The same transgenic plants also showed increased transcript levels of TaFT2 (a TaFT paralogue) indicating that TaFT2 acts downstream of TaFT. The fact that TaFT2 interacts with the different bZIP protein TaFDL13, which lacks the ability to interact with the VRN1 promoter, suggests that TaFT and TaFT2 have different gene targets. This observation agrees with the functional divergence observed for the TaFT and TaFT2 orthologous genes in rice. The temperate cereals analyzed so far show VRN1 transcripts in the leaves, a characteristic not observed in Arabidopsis or rice. The high levels of TaFDL2 transcripts observed in wheat leaves provide a simple explanation for this difference. We present a hypothesis to explain the conservation of VRN1 expression in the leaves of temperate cereals.

post to: CiteULike

CUL1 regulates TOC1 protein stability in the Arabidopsis circadian clock.

Publication Date: 2008 Apr 22 PMID: 18433436
Authors: Harmon, F. - Imaizumi, T. - Gray, W. M.
Journal: Plant J

The circadian clock is the endogenous timer that coordinates physiological processes with daily and seasonal environmental changes. In Arabidopsis thaliana, establishment of the circadian period relies on targeted degradation of TIMING OF CAB EXPRESSION 1 (TOC1) by the 26S proteasome. ZEITLUPE (ZTL) is the F-box protein that associates with the SCF (for Skp/Cullin/F-box) E3 ubiquitin ligase that is responsible for marking TOC1 for turnover. CULLIN1 (CUL1) is a core component of SCF complexes and is involved in multiple signaling pathways. To assess the contribution of CUL1-containing SCF complexes to signaling within the plant oscillator, circadian rhythms were examined in the recessive, temperature-sensitive CUL1 allele axr6-3. The activity of CUL1 in this mutant declines progressively with increasing ambient temperature, resulting in more severe defects in CUL1-dependent activities at elevated temperature. Examination of circadian rhythms in axr6-3 revealed circadian phenotypes comparable to those observed in ztl null mutants; namely, a lengthened circadian period, altered expression of core oscillator genes, and limited degradation of TOC1. In addition, treatment of seedlings with exogenous auxin did not alter TOC1 stability. These results demonstrate that CUL1 is required for TOC1 degradation and further suggest that this protein is the functional cullin for the SCF(ZTL) complex.

post to: CiteULike

The eer5 mutation, which affects a novel proteasome related subunit, suggests a prominent role for the COP9 signalosome in resetting the ethylene-signaling pathway in Arabidopsis.

Publication Date: 2008 Apr 17 PMID: 18429939
Authors: Christians, M. J. - Robles, L. M. - Zeller, S. M. - Larsen, P. B.
Journal: Plant J

An Arabidopsis mutant, eer5-1, which has an enhanced ethylene response in etiolated seedlings, including hypersensitivity and extreme exaggeration of response to ethylene, was isolated and characterized. As with other identified eer mutants, the enhanced response phenotype of eer5-1 was correlated with failure to induce appropriately a subset of ethylene regulated genes, suggesting that proper ethylene responsive gene expression is necessary for resetting the ethylene response pathway. eer5-1 represents a mutation that causes an amino acid substitution in a previously uncharacterized gene, which encodes a protein with a PAM (PCI/PINT associated module) domain similar to those found in components of the COP9 signalosome (CSN). Genetic analysis shows that manifestation of the eer5 mutant phenotype is solely dependent on ethylene signaling since an ein2-5;eer5-1 double mutant is indistinguishable from ein2-5 in the presence of saturating ethylene. In contrast, an ein3-1;eer5-1 double mutant displays characteristics of an enhanced ethylene response and suggests that EER5 regulates ethylene signaling independently of EIN3. Analysis of the EER5 protein indicates that it interacts both with the C-terminus of EIN2 and the CSN, suggesting that EER5 serves as a bridge between EIN2 and the modification or degradation of target proteins, including a proposed group of transcriptional repressors, as part of a reset mechanism during or following ethylene signaling.

post to: CiteULike

Interdependence of dimerization and organelle binding in myosin XI.

Publication Date: 2008 Apr 17 PMID: 18429938
Authors: Li, J. F. - Nebenfuhr, A.
Journal: Plant J

Cytoplasmic streaming is a ubiquitous process in plant cells which is thought to be driven by the active movement of myosin XI motor proteins along actin filaments. These myosin motors bind to organelles through their C-terminal globular tail domain, although recent studies also suggested a role of the central coiled-coil region during organelle binding. Here we have investigated the relationship between these two protein domains of MYA1, an Arabidopsis myosin XI, in a series of in vivo experiments which demonstrated that dimerization of the coiled-coil region stabilizes organelle binding of the globular tail. Surprisingly, yeast two-hybrid, bimolecular fluorescence complementation, Forster resonance energy transfer as well as in vitro pull-down experiments all demonstrated that dimerization of the 174-residue-long MYA1 coiled coils by themselves was unstable. Furthermore, only the first of the two major coiled-coil segments in MYA1 contributed significantly to dimer formation. Interestingly, dimerization of myosin tail constructs that included the organelle-binding globular tail was stable, although the globular tails by themselves did not interact. This suggests an interdependent relationship between dimerization and organelle binding in myosin XI where each process synergistically stimulates the other.

post to: CiteULike

Deletion of the chloroplast-localized AtTerC gene product in Arabidopsis thaliana leads to loss of the thylakoid membrane and to seedling lethality.

Publication Date: 2008 Apr 17 PMID: 18429937
Authors: Kwon, K. C. - Cho, M. H.
Journal: Plant J

Early seedling development in plants depends on the biogenesis of chloroplasts from proplastids, accompanied by the formation of thylakoid membranes. An Arabidopsis thaliana gene, AtTerC, whose gene product shares sequence similarity with bacterial tellurite resistance C (TerC), is shown to be involved in a critical step required for the normal organization of prothylakoids and the transition into mature thylakoid stacks. The AtTerC gene encodes an integral membrane protein, which contains eight putative transmembrane helices, localized in the thylakoid of chloroplast, as shown by localization of an AtTerC:GFP fusion product in protoplasts and by immunoblot analysis of subfractions of chloroplasts. T-DNA insertional mutants of AtTerC resulted in a pigment-deficient and seedling-lethal phenotype in normal light conditions. Transmission electron microscopic analysis revealed that mutant etioplasts had normal prolamellar bodies (PLBs), although the prothylakoids had ring-like shapes surrounding the PLBs. In addition, the ultrastructures of mutant chloroplasts lacked thylakoid, did not have grana stacks, and showed numerous globular structures of varying sizes. Also, the accumulation of thylakoid membrane proteins was severely defective in this mutant. These results suggest that the AtTerC protein plays a crucial role in prothylakoid membrane biogenesis and thylakoid formation in early chloroplast development.

post to: CiteULike

A membrane-bound NAC transcription factor NTL8 regulates gibberellic acid-mediated salt signaling in Arabidopsis seed germination.

Publication Date: 2008 May 10 PMID: 18363782
Authors: Kim, S. G. - Lee, A. K. - Yoon, H. K. - Park, C. M.
Journal: Plant J

Gibberellic acid (GA) plays a key role in seed germination through coordinate interactions with other growth hormones and external signals. However, the way in which external signals are incorporated into the GA-signaling pathway is largely unknown. Here, we demonstrate that a membrane-bound NAC transcription factor NTL8 mediates the salt regulation of seed germination via the GA pathway, primarily independently of ABA. NTL8 is induced by high salinity. Its expression is also elevated by a GA biosynthetic inhibitor paclabutrazol (PAC), but is repressed by GA. Notably, high salinity greatly represses the GA3 oxidase 1 (GA3ox1) gene, supporting the hypothesis that salt signals inhibit seed germination by repressing GA biosynthesis. Induction of NTL8 and repression of GA3ox1 by high salinity still occur in the ABA-deficient aba3-1 mutant. Accordingly, the germination of a T-DNA insertional ntl8-1 mutant seed is resistant to high salinity and PAC. Interestingly, NTL8 is significantly induced during cold imbibition, but the induction declines quickly in germinating seeds, like RGL2. NTL8 activity is also regulated by controlled proteolytic release of the membrane-bound NTL8 form. Its release from the membranes is activated by PAC and high salinity. Our data support that NTL8 modulates GA-mediated salt signaling in regulating seed germination. This regulatory scheme may provide an adaptative fitness, which delays seed germination under high salinity conditions.

post to: CiteULike

Two nearly identical terpene synthases catalyze the formation of nerolidol and linalool in snapdragon flowers.

Publication Date: 2008 May 10 PMID: 18363779
Authors: Nagegowda, D. A. - Gutensohn, M. - Wilkerson, C. G. - Dudareva, N.
Journal: Plant J

Terpenoids emitted from snapdragon flowers include three monoterpenes derived from geranyl diphosphate (GPP), myrcene, (E)-beta-ocimene and linalool, and a sesquiterpene, nerolidol, derived from farnesyl diphosphate (FPP). Using a functional genomics approach, we have isolated and biochemically characterized two nearly identical nerolidol/linalool synthases, AmNES/LIS-1 and AmNES/LIS-2, two enzymes responsible for the terpenoid profile of snapdragon scent remaining to be characterized. The AmNES/LIS-2 protein has an additional 30 amino acids in the N-terminus, and shares 95% amino acid sequence identity with AmNES/LIS-1, with only 23 amino acid substitutions distributed across the homologous regions of the proteins. Although these two terpene synthases have very similar catalytic properties, and synthesize linalool and nerolidol as specific products from GPP and FPP, respectively, they are compartmentally segregated. GFP localization studies and analysis of enzyme activities in purified leucoplasts, together with our previous feeding experiments, revealed that AmNES/LIS-1 is localized in cytosol, and is responsible for nerolidol biosynthesis, whereas AmNES/LIS-2 is located in plastids, and accounts for linalool formation. Our results show that subcellular localization of bifunctional enzymes, in addition to the availability of substrate, controls the type of product formed. By directing nearly identical bifunctional enzymes to more than one cellular compartment, plants extend the range of available substrates for enzyme utilization, thus increasing the diversity of the metabolites produced.

post to: CiteULike

Identification of indole glucosinolate breakdown products with antifeedant effects on Myzus persicae (green peach aphid).

Publication Date: 2008 May 8 PMID: 18346197
Authors: Kim, J. H. - Lee, B. W. - Schroeder, F. C. - Jander, G.
Journal: Plant J

The cleavage of glucosinolates by myrosinase to produce toxic breakdown products is a characteristic insect defense of cruciferous plants. Although green peach aphids (Myzus persicae) are able to avoid most contact with myrosinase when feeding from the phloem of Arabidopsis thaliana, indole glucosinolates are nevertheless degraded during passage through the insects. A defensive role for indole glucosinolates is suggested by the observation that atr1D mutant plants, which overproduce indole glucosinolates, are more resistant to M. persicae, whereas cyp79B2 cyp79B3 double mutants, which lack indole glucosinolates, succumb to M. persicae more rapidly. Indole glucosinolate breakdown products, including conjugates formed with ascorbate, glutathione and amino acids, are elevated in the honeydew of M. persicae feeding from atr1D mutant plants, but are absent when the aphids are feeding on cyp79B2 cyp79B3 double mutants. M. persicae feeding from wild-type plants and myrosinase-deficient tgg1 tgg2 double mutants excrete a similar profile of indole glucosinolate-derived metabolites, indicating that the breakdown is independent of these foliar myrosinases. Artificial diet experiments show that the reaction of indole-3-carbinol, a breakdown product of indol-3-ylmethylglucosinolate, with ascorbate, glutathione and cysteine produces diindolylmethylcysteines and other conjugates that have antifeedant effects on M. persicae. Therefore, the post-ingestive breakdown of indole glucosinolates provides a defense against herbivores such as aphids that can avoid glucosinolate activation by plant myrosinases.

post to: CiteULike

The redox switch of gamma-glutamylcysteine ligase via a reversible monomer-dimer transition is a mechanism unique to plants.

Publication Date: 2008 May 8 PMID: 18346196
Authors: Gromes, R. - Hothorn, M. - Lenherr, E. D. - Rybin, V. - Scheffzek, K. - Rausch, T.
Journal: Plant J

In plants, the first committed enzyme for glutathione biosynthesis, gamma-glutamylcysteine ligase (GCL), is under multiple controls. The recent elucidation of GCL structure from Brassica juncea (BjGCL) has revealed the presence of two intramolecular disulfide bridges (CC1, CC2), which both strongly impact on GCL activity in vitro. Here we demonstrate that cysteines of CC1 are confined to plant species from the Rosids clade, and are absent in other plant families. Conversely, cysteines of CC2 involved in the monomer-dimer transition in BjGCL are not only conserved in the plant kingdom, but are also conserved in the evolutionarily related alpha- (and some gamma-) proteobacterial GCLs. Focusing on the role of CC2 for GCL redox regulation, we have extended our analysis to all available plant (31; including moss and algal) and related proteobacterial GCL (46) protein sequences. Amino acids contributing to the homodimer interface in BjGCL are highly conserved among plant GCLs, but are not conserved in related proteobacterial GCLs. To probe the significance of this distinction, recombinant GCLs from Nicotiana tabacum (NtGCL), Agrobacterium tumefaciens (AtuGCL, alpha-proteobacteria) and Xanthomonas campestris (XcaGCL, gamma-proteobacteria) were analyzed for their redox response. As expected, NtGCL forms a homodimer under oxidizing conditions, and is activated more than threefold. Conversely, proteobacterial GCLs remain monomeric under oxidizing and reducing conditions, and their activities are not inhibited by DTT, despite the presence of CC2. We conclude that although plant GCLs are evolutionarily related to proteobacterial GCLs, redox regulation of their GCLs via CC2-dependent dimerization has been acquired later in evolution, possibly as a consequence of compartmentation in the redox-modulated plastid environment.

post to: CiteULike

Lindernia brevidens: a novel desiccation-tolerant vascular plant, endemic to ancient tropical rainforests.

Publication Date: 2008 Apr 23 PMID: 18346195
Authors: Phillips, J. R. - Fischer, E. - Baron, M. - van den Dries, N. - Facchinelli, F. - Kutzer, M. - Rahmanzadeh, R. - Remus, D. - Bartels, D.
Journal: Plant J

A particular adaptation to survival under limited water availability has been realized in the desiccation-tolerant resurrection plants, which tend to grow in a habitat with seasonal rainfall and long dry periods. One of the best-studied examples is Craterostigma plantagineum. Here we report an unexpected finding: Lindernia brevidens, a close relative of C. plantagineum, exhibits desiccation tolerance, even though it is endemic to the montane rainforests of Tanzania and Kenya, where it never experiences seasonal dry periods. L. brevidens has been found exclusively in two fragments of the ancient Eastern Arc Mountains, which were protected from the devastating Pleistocene droughts by the stable Indian Ocean temperature. Analysis of the microhabitat reveals that L. brevidens is found in the same habitat as hygrophilous plant species, which further indicates that the plant never dries out completely. The objective of this investigation was to address whether C. plantagineum and L. brevidens have desiccation-related pathways in common, or whether L. brevidens has acquired novel pathways. A third, closely related, desiccation-sensitive species, Lindernia subracemosa, has been included for comparison. Mechanisms that confer cellular protection during extreme water loss are well conserved between C. plantagineum and L. brevidens, including the interconversion of 2-octulose to sucrose within the two desiccation-tolerant species. Furthermore, transcriptional control regions of desiccation-related genes belonging to the late embryogenesis abundant (LEA) protein family are also highly conserved. We propose that L. brevidens is a neoendemic species that has retained desiccation tolerance through genome stability, despite tolerance being superfluous to environmental conditions.

post to: CiteULike

Heteromeric K(+) channels in plants.

Publication Date: 2008 May 8 PMID: 18346194
Authors: Lebaudy, A. - Hosy, E. - Simonneau, T. - Sentenac, H. - Thibaud, J. B. - Dreyer, I.
Journal: Plant J

Voltage-gated potassium channels of plants are multimeric proteins built of four alpha-subunits. In the model plant Arabidopsis thaliana, nine genes coding for K(+) channel alpha-subunits have been identified. When co-expressed in heterologous expression systems, most of them display the ability to form heteromeric K(+) channels. Till now it was not clear whether plants use this potential of heteromerization to increase the functional diversity of potassium channels. Here, we designed an experimental approach employing different transgenic plant lines that allowed us to prove the existence of heteromeric K(+) channels in plants. The chosen strategy might also be useful for investigating the activity and function of other multimeric channel proteins like, for instance, cyclic-nucleotide gated channels, tandem-pore K(+) channels and glutamate receptor channels.

post to: CiteULike

Generation of a 3D indexed Petunia insertion database for reverse genetics.

Publication Date: 2008 May 8 PMID: 18346192
Authors: Vandenbussche, M. - Janssen, A. - Zethof, J. - van Orsouw, N. - Peters, J. - van Eijk, M. J. - Rijpkema, A. S. - Schneiders, H. - Santhanam, P. - de Been, M. - van Tunen, A. - Gerats, T.
Journal: Plant J

BLAST searchable databases containing insertion flanking sequences have revolutionized reverse genetics in plant research. The development of such databases has so far been limited to a small number of model species and normally requires extensive labour input. Here we describe a highly efficient and widely applicable method that we adapted to identify unique transposon-flanking genomic sequences in Petunia. The procedure is based on a multi-dimensional pooling strategy for the collection of DNA samples; up to thousands of different templates are amplified from each of the DNA pools separately, and knowledge of their source is safeguarded by the use of pool-specific (sample) identification tags in one of the amplification primers. All products are combined into a single sample that is subsequently used as a template for unidirectional pyrosequencing. Computational analysis of the clustered sequence output allows automatic assignment of sequences to individual DNA sources. We have amplified and analysed transposon-flanking sequences from a Petunia transposon insertion library of 1000 individuals. Using 30 DNA isolations, 70 PCR reactions and two GS20 sequencing runs, we were able to allocate around 10 000 transposon flanking sequences to specific plants in the library. These sequences have been organized in a database that can be BLAST-searched for insertions into genes of interest. As a proof of concept, we have performed an in silico screen for insertions into members of the NAM/NAC transcription factor family. All in silico-predicted transposon insertions into members of this family could be confirmed in planta.

post to: CiteULike

Identification of major lysine residues of S(3)-RNase of Petunia inflata involved in ubiquitin-26S proteasome-mediated degradation in vitro.

Publication Date: 2008 May 9 PMID: 18346191
Authors: Hua, Z. - Kao, T. H.
Journal: Plant J

S-RNase-based self-incompatibility has been identified in three flowering plant families, including the Solanaceae, and this self/non-self recognition mechanism between pollen and pistil is controlled by two polymorphic genes at the S-locus, S-RNase and S-locus F-box (SLF). S-RNase is produced in the pistil and taken up by pollen tubes in a non-S-haplotype-specific manner. How an allelic product of SLF interacts with self and non-self S-RNases to result in growth inhibition of self pollen tubes is not completely understood. One model predicts that SLF targets non-self S-RNases for ubiquitin/26S proteasome-mediated degradation, thereby only allowing self S-RNase to exert cytotoxic activity inside a pollen tube. To test this model, we studied whether any of the 20 lysine residues in S(3)-RNase of Petunia inflata might be targets for ubiquitination. We identified six lysines near the C-terminus for which mutation to arginine significantly reduced ubiquitination and degradation of the mutant S(3)-RNase, GST:S(3)-RNase (K141-164R) in pollen tube extracts. We further showed that GST:S(3)-RNase (K141-164R) and GST:S(3)-RNase had similar RNase activity, suggesting that their degradation was probably not caused by an ER-associated protein degradation pathway that removes mis-folded proteins. Finally, we showed that PiSBP1 (P. inflata S-RNase binding protein 1), a potential RING-HC subunit of the PiSLF (P. inflata SLF)-containing E3-like complex, could target S-RNase for ubiquitination in vitro. All these results suggest that ubiquitin/26S proteasome-dependent degradation of S-RNase may be an integral part of the S-RNase-based self-incompatibility mechanism.

post to: CiteULike

Interplay of miR164, CUP-SHAPED COTYLEDON genes and LATERAL SUPPRESSOR controls axillary meristem formation in Arabidopsis thaliana.

Publication Date: 2008 May 10 PMID: 18346190
Authors: Raman, S. - Greb, T. - Peaucelle, A. - Blein, T. - Laufs, P. - Theres, K.
Journal: Plant J

Aerial architecture in higher plants is established post-embryonically by the inception of new meristems in the axils of leaves. These axillary meristems develop into side shoots or flowers. In Arabidopsis, the NAC domain transcription factors CUP SHAPED COTYLEDON1 (CUC1), CUC2 and CUC3 function redundantly in initiating the shoot apical meristem and establishing organ boundaries. Transcripts of CUC1 and CUC2 are targeted for degradation by miR164. In this study, we show that cuc3-2 mutants are impaired in axillary meristem initiation. Overexpression of miR164 in the cuc3-2 mutant caused an almost complete block of axillary meristem formation. Conversely, mir164 mutants and plants harbouring miR164-resistant alleles of CUC1 or CUC2 developed accessory buds in leaf axils. Collectively, these experiments reveal that, in addition to CUC3, redundant functions of CUC1 and CUC2 as well as miR164 regulation are required for the establishment of axillary meristems. Studies on LAS transcript accumulation in mir164 triple mutants and cuc3-2 plants overexpressing miR164 suggest that regulation of axillary meristem formation by miR164 is mediated through CUC1 and CUC2, which in turn regulate LAS.

post to: CiteULike

AGL23, a type I MADS-box gene that controls female gametophyte and embryo development in Arabidopsis.

Publication Date: 2008 Apr 23 PMID: 18346189
Authors: Colombo, M. - Masiero, S. - Vanzulli, S. - Lardelli, P. - Kater, M. M. - Colombo, L.
Journal: Plant J

MADS-box transcription factors are key regulators of plant developmental processes. While the function of MIKC (type II) MADS-box genes has been intensively studied, only limited data are available for the other more recently identified classes of MADS-box genes, despite these latter comprising more than 60% of the Arabidopsis MADS-box gene family. Here we describe the function of AGL23, an Arabidopsis type I MADS-box gene belonging to the Malpha subfamily. We show that AGL23 plays an important role during development of the female gametophyte and embryo. The agl23-1 mutant forms a functional megaspore. However, at this stage female gametophyte development is arrested and the megaspore persists during subsequent phases of ovule development. Despite the incomplete penetrance of the female gametophyte defect, plants homozygous for the agl23-1 mutation were never identified. Analysis of developing seeds showed that embryos homozygous for the agl23-1 allele are albino and unable to give rise to viable plants. Electron microscopy analysis revealed that this phenotype is due to the absence of chloroplasts, strongly suggesting that AGL23 is involved in controlling the biogenesis of organelles during embryo development.

post to: CiteULike

AtMSH5 partners AtMSH4 in the class I meiotic crossover pathway in Arabidopsis thaliana, but is not required for synapsis.

Publication Date: 2008 May 10 PMID: 18318687
Authors: Higgins, J. D. - Vignard, J. - Mercier, R. - Pugh, A. G. - Franklin, F. C. - Jones, G. H.
Journal: Plant J

MSH5, a meiosis-specific member of the MutS-homologue family of genes, is required for normal levels of recombination in budding yeast, mouse and Caenorhabditis elegans. In this paper we report the identification and characterization of the Arabidopsis homologue of MSH5 (AtMSH5). Transcripts of AtMSH5 are specific to reproductive tissues, and immunofluorescence studies indicate that expression of the protein is abundant during prophase I of meiosis. In a T-DNA tagged insertional mutant (Atmsh5-1), recombination is reduced to about 13% of wild-type levels. The residual chiasmata are randomly distributed between cells and chromosomes. These data provide further evidence for at least two pathways of meiotic recombination in Arabidopsis and indicate that AtMSH5 protein is required for the formation of class I interference-sensitive crossovers. Localization of AtMSH5 to meiotic chromosomes occurs at leptotene and is dependent on DNA double-strand break formation and strand exchange. Localization of AtMSH5 to the chromatin at mid-prophase I is dependent on expression of AtMSH4. At late zygotene/early pachytene a proportion of AtMSH5 foci co-localize with AtMLH1 which marks crossover-designated sites. Chromosome synapsis appears to proceed normally, without significant delay, in Atmsh5-1 but the pachytene stage is extended by several hours, indicative of the operation of a surveillance system that monitors the progression of prophase I.

post to: CiteULike

Changing transcriptional initiation sites and alternative 5'- and 3'-splice site selection of the first intron deploys Arabidopsis PROTEIN ISOASPARTYL METHYLTRANSFERASE2 variants to different subcellular compartments.

Publication Date: 2008 May 1 PMID: 18318686
Authors: Dinkins, R. D. - Majee, S. M. - Nayak, N. R. - Martin, D. - Xu, Q. - Belcastro, M. P. - Houtz, R. L. - Beach, C. M. - Downie, A. B.
Journal: Plant J

Arabidopsis thaliana (L.) Heynh. possesses two PROTEIN-L-ISOASPARTATE METHYLTRANSFERASE (PIMT) genes encoding enzymes (EC 2.1.1.77) capable of converting uncoded l-isoaspartyl residues, arising spontaneously at l-asparaginyl and l-aspartyl sites in proteins, to l-aspartate. PIMT2 produces at least eight transcripts by using four transcriptional initiation sites (TIS; resulting in three different initiating methionines) and both 5'- and 3'-alternative splice site selection of the first intron. The transcripts produce mature proteins capable of converting l-isoaspartate to l-aspartate in small peptide substrates. PIMT:GFP fusion proteins generated a detectable signal in the nucleus. However, whether the protein was also detectable in the cytoplasm, endo-membrane system, chloroplasts, and/or mitochondria, depended on the transcript from which it was produced. On-blot-methylation of proteins, prior to the completion of germination, indicated that cruciferin subunits contain isoaspartate. The implications of using transcriptional mechanisms to expand a single gene's repertoire to protein variants capable of entry into the cell's various compartments are discussed in light of PIMT's presumed role in repairing the proteome.

post to: CiteULike

Mitochondrial respiratory pathways modulate nitrate sensing and nitrogen-dependent regulation of plant architecture in Nicotiana sylvestris.

Publication Date: 2008 Apr 23 PMID: 18318685
Authors: Pellny, T. K. - Van Aken, O. - Dutilleul, C. - Wolff, T. - Groten, K. - Bor, M. - De Paepe, R. - Reyss, A. - Van Breusegem, F. - Noctor, G. - Foyer, C. H.
Journal: Plant J

Mitochondrial electron transport pathways exert effects on carbon-nitrogen (C/N) relationships. To examine whether mitochondria-N interactions also influence plant growth and development, we explored the responses of roots and shoots to external N supply in wild-type (WT) Nicotiana sylvestris and the cytoplasmic male sterile II (CMSII) mutant, which has a N-rich phenotype. Root architecture in N. sylvestris seedlings showed classic responses to nitrate and sucrose availability. In contrast, CMSII showed an altered 'nitrate-sensing' phenotype with decreased sensitivity to C and N metabolites. The WT growth phenotype was restored in CMSII seedling roots by high nitrate plus sugars and in shoots by gibberellic acid (GA). Genome-wide cDNA-amplified fragment length polymorphism (AFLP) analysis of leaves from mature plants revealed that only a small subset of transcripts was altered in CMSII. Tissue abscisic acid content was similar in CMSII and WT roots and shoots, and growth responses to zeatin were comparable. However, the abundance of key transcripts associated with GA synthesis was modified both by the availability of N and by the CMSII mutation. The CMSII mutant maintained a much higher shoot/root ratio at low N than WT, whereas no difference was observed at high N. Shoot/root ratios were strikingly correlated with root amines/nitrate ratios, values of <1 being characteristic of high N status. We propose a model in which the amine/nitrate ratio interacts with GA signalling and respiratory pathways to regulate the partitioning of biomass between shoots and roots.

post to: CiteULike