Trends in plant science

Plant LysM proteins: modules mediating symbiosis and immunity.

Publication Date: 2012 May 10 PMID: 22578284
Authors: Gust, A. A. - Willmann, R. - Desaki, Y. - Grabherr, H. M. - Nurnberger, T.
Journal: Trends Plant Sci

Microbial glycans, such as bacterial peptidoglycans, fungal chitin or rhizobacterial Nod factors (NFs), are important signatures for plant immune activation or for the establishment of beneficial symbioses. Plant lysin motif (LysM) domain proteins serve as modules mediating recognition of these different N-acetylglucosamine (GlcNAc)-containing ligands, suggesting that this class of proteins evolved from an ancient sensor for GlcNAc. During early plant evolution, these glycans probably served as immunogenic patterns activating LysM protein receptor-mediated plant immunity and stopping microbial infection. The biochemical potential of plant LysM proteins for sensing microbial GlcNAc-containing glycans has probably since favored the evolution of receptors facilitating microbial infection and symbiosis.

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Epigenetic neofunctionalisation and regulatory gene evolution in grasses.

Publication Date: 2012 May 8 PMID: 22575341
Authors: Dickinson, H. - Costa, L. - Gutierrez-Marcos, J.
Journal: Trends Plant Sci

During plant evolution, genome duplication and subsequent selection acting on new gene pairs has frequently resulted in partition of gene functions, or acquisition of new functions. This 'sub- and neofunctionalisation' (subF and neoF) is held to have driven the expansion of key gene classes. One such gene class in maize (Zea mays) includes a pair of Polycomb group (PcG) protein genes that, unlike their single Arabidopsis (Arabidopsis thaliana) counterpart, are both parentally imprinted with only the maternal alleles being expressed in the seed endosperm. Surprisingly, this imprinting is regulated by different mechanisms in the two genes, resulting in different phasing of parent-specific expression. In this opinion article we propose that recruitment of different imprinting systems constitutes 'epigenetic neoF', and has enhanced maternal control over seed development, with a potential impact on the evolution of the large and persistent endosperms of cereal grains.

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The rhizosphere microbiome and plant health.

Publication Date: 2012 May 5 PMID: 22564542
Authors: Berendsen, R. L. - Pieterse, C. M. - Bakker, P. A.
Journal: Trends Plant Sci

The diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant-microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production.

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Plants as alternative hosts for Salmonella.

Publication Date: 2012 May PMID: 22513107
Authors: Schikora, A. - Garcia, A. V. - Hirt, H.
Journal: Trends Plant Sci

Recent findings show that many human pathogenic bacteria can use multiple host organisms. For example, Salmonella Typhimurium can use plants as alternative hosts to humans and other animals. These bacteria are able to adhere to plant surfaces and actively infect the interior of plants. Similarly to the infection of animal cells, S. Typhimurium suppresses plant defense responses by a type III secretion mechanism, indicating that these bacteria possess a dedicated multi-kingdom infection strategy, raising the question of host specificity. In addition, evidence is accumulating that the interaction of Salmonella with plants is an active process with different levels of specificity, because different Salmonella serovars show variations in pathogenicity, and different plant species reveal various levels of resistance towards these bacteria.

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The specificity of herbivore-induced plant volatiles in attracting herbivore enemies.

Publication Date: 2012 May PMID: 22503606
Authors: Clavijo McCormick, A. - Unsicker, S. B. - Gershenzon, J.
Journal: Trends Plant Sci

Plants respond to herbivore attack by emitting complex mixtures of volatile compounds that attract herbivore enemies, both predators and parasitoids. Here, we explore whether these mixtures provide significant value as information cues in herbivore enemy attraction. Our survey indicates that blends of volatiles released from damaged plants are frequently specific depending on the type of herbivore and its age, abundance and feeding guild. The sensory perception of plant volatiles by herbivore enemies is also specific, according to the latest evidence from studies of insect olfaction. Thus, enemies do exploit the detailed information provided by plant volatile mixtures in searching for their prey or hosts, but this varies with the diet breadth of the enemy.

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Synthesizing specificity: multiple approaches to understanding the attack and defense of plants.

Publication Date: 2012 May PMID: 22502773
Authors: Agrawal, A. A. - Heil, M.
Journal: Trends Plant Sci

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Evolution of jasmonate and salicylate signal crosstalk.

Publication Date: 2012 May PMID: 22498450
Authors: Thaler, J. S. - Humphrey, P. T. - Whiteman, N. K.
Journal: Trends Plant Sci

The evolution of land plants approximately 470 million years ago created a new adaptive zone for natural enemies (attackers) of plants. In response to attack, plants evolved highly effective, inducible defense systems. Two plant hormones modulating inducible defenses are salicylic acid (SA) and jasmonic acid (JA). Current thinking is that SA induces resistance against biotrophic pathogens and some phloem feeding insects and JA induces resistance against necrotrophic pathogens, some phloem feeding insects and chewing herbivores. Signaling crosstalk between SA and JA commonly manifests as a reciprocal antagonism and may be adaptive, but this remains speculative. We examine evidence for and against adaptive explanations for antagonistic crosstalk, trace its phylogenetic origins and provide a hypothesis-testing framework for future research on the adaptive significance of SA-JA crosstalk.

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Unifying concepts and mechanisms in the specificity of plant-enemy interactions.

Publication Date: 2012 May PMID: 22465042
Authors: Barrett, L. G. - Heil, M.
Journal: Trends Plant Sci

Host ranges are commonly quantified to classify herbivores and plant pathogens as either generalists or specialists. Here, we summarize patterns and mechanisms in the interactions of plants with these enemies along different axes of specificity. We highlight the many dimensions within which plant enemies can specify and consider the underlying ecological, evolutionary and molecular mechanisms. Host resistance traits and enemy effectors emerge as central players determining host utilization and thus host range. Finally, we review approaches to studying the causes and consequences of variation in the specificity of plant-enemy interactions. Knowledge of the molecular mechanisms that determine host range is required to understand host shifts, and evolutionary transitions among specialist and generalist strategies, and to predict potential host ranges of pathogens and herbivores.

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Specialist versus generalist insect herbivores and plant defense.

Publication Date: 2012 May PMID: 22425020
Authors: Ali, J. G. - Agrawal, A. A.
Journal: Trends Plant Sci

There has been a long-standing hypothesis that specialist and generalist insects interact with plants in distinct ways. Although many tests exist, they typically compare only one species of each, they sometimes confound specialization and feeding guild, and often do not link chemical or transcriptional measures of the plant to actual resistance. In this review, we synthesize current data on whether specialists and generalists actually differ, with special attention to comparisons of their differential elicitation of plant responses. Although we find few consistencies in plant induction by specialists versus generalists, feeding guilds are predictive of differential plant responses. We outline a novel set of predictions based on current coevolutionary hypotheses and make methodological suggestions for improved comparisons of specialists and generalists.

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Association mapping of plant resistance to insects.

Publication Date: 2012 May PMID: 22322003
Authors: Kloth, K. J. - Thoen, M. P. - Bouwmeester, H. J. - Jongsma, M. A. - Dicke, M.
Journal: Trends Plant Sci

Association mapping is rapidly becoming an important method to explore the genetic architecture of complex traits in plants and offers unique opportunities for studying resistance to insect herbivores. Recent studies indicate that there is a trade-off between resistance against generalist and specialist insects. Most studies, however, use a targeted approach that will easily miss important components of insect resistance. Genome-wide association mapping provides a comprehensive approach to explore the whole array of plant defense mechanisms in the context of the generalist-specialist paradigm. As association mapping involves the screening of large numbers of plant lines, specific and accurate high-throughput phenotyping (HTP) methods are needed. Here, we discuss the prospects of association mapping for insect resistance and HTP requirements.

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Community specificity: life and afterlife effects of genes.

Publication Date: 2012 May PMID: 22322002
Authors: Whitham, T. G. - Gehring, C. A. - Lamit, L. J. - Wojtowicz, T. - Evans, L. M. - Keith, A. R. - Smith, D. S.
Journal: Trends Plant Sci

Community-level genetic specificity results when individual genotypes or populations of the same species support different communities. Our review of the literature shows that genetic specificity exhibits both life and afterlife effects; it is a widespread phenomenon occurring in diverse taxonomic groups, aquatic to terrestrial ecosystems, and species-poor to species-rich systems. Such specificity affects species interactions, evolution, ecosystem processes and leads to community feedbacks on the performance of the individuals expressing the traits. Thus, genetic specificity by communities appears to be fundamentally important, suggesting that specificity is a major driver of the biodiversity and stability of the world's ecosystems.

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Role of phytohormones in insect-specific plant reactions.

Publication Date: 2012 May PMID: 22305233
Authors: Erb, M. - Meldau, S. - Howe, G. A.
Journal: Trends Plant Sci

The capacity to perceive and respond is integral to biological immune systems, but to what extent can plants specifically recognize and respond to insects? Recent findings suggest that plants possess surveillance systems that are able to detect general patterns of cellular damage as well as highly specific herbivore-associated cues. The jasmonate (JA) pathway has emerged as the major signaling cassette that integrates information perceived at the plant-insect interface into broad-spectrum defense responses. Specificity can be achieved via JA-independent processes and spatio-temporal changes of JA-modulating hormones, including ethylene (ET), salicylic acid (SA), abscisic acid (ABA), auxin, cytokinins (CK), brassinosteroids (BR) and gibberellins (GB). The identification of receptors and ligands and an integrative view of hormone-mediated response systems are crucial to understand specificity in plant immunity to herbivores.

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