Current Opinion in Plant Biology

Phytochrome: structural basis for its functions.

Publication Date: 2010 Aug 27 PMID: 20801708
Authors: Nagatani, A.
Journal: Curr Opin Plant Biol

Phytochrome mediates various physiological as well as developmental responses to light stimuli in plants. Phytochrome is a soluble chromoprotein consisting of the N-terminal photosensory and C-terminal dimerization moieties. Close homologues of plant phytochromes are widely found in prokaryotes. Recently, the crystal structures of the core photosensory module of bacterial phytochromes are resolved. Intriguingly, three sub-domains (PAS, GAF and PHY) in the module are connected by unusual structures named 'light-sensing knot' and 'tongue', which are in tight contact with the chromophore. These findings enable us to review previous data on the structure-function relationships in phytochrome. Consequently, functional importance of these peculiar structures is further highlighted. Thus, the three-dimensional structure provides a framework for understanding how phytochrome processes the light signals.

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The V-ATPase: small cargo, large effects.

Publication Date: 2010 Aug 26 PMID: 20801076
Authors: Schumacher, K. - Krebs, M.
Journal: Curr Opin Plant Biol

About 30 years ago seminal reports of anion-sensitive proton-pumping activity associated with microsomal membranes initiated research on the plant vacuolar-type H(+)-ATPase (V-ATPase, VHA). Since, it has been firmly established that these complex molecular machines are essential for what can be defined as cellular logistics. In a eukaryotic cell, the flow of goods between compartments is achieved either by protein-mediated membrane transport or via vesicular trafficking. Over the past years, it has become increasingly clear that V-ATPases do not only energize secondary active transport but are also important regulators of membrane trafficking.

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Plant hormone signaling lightens up: integrators of light and hormones.

Publication Date: 2010 Aug 23 PMID: 20739215
Authors: Lau, O. S. - Deng, X. W.
Journal: Curr Opin Plant Biol

Light is an important environmental signal that regulates diverse growth and developmental processes in plants. In these light-regulated processes, multiple hormonal pathways are often modulated by light to mediate the developmental changes. Conversely, hormone levels in plants also serve as endogenous cues in influencing light responsiveness. Although interactions between light and hormone signaling pathways have long been observed, recent studies have advanced our understanding by identifying signaling integrators that connect the pathways. These integrators, namely PHYTOCHROME-INTERACTING FACTOR 3 (PIF3), PIF4, PIF3-LIKE 5 (PIL5)/PIF1 and LONG HYPOCOTYL 5 (HY5), are key light signaling components and they link light signals to the signaling of phytohormones, such as gibberellin (GA), abscisic acid (ABA), auxin and cytokinin, in regulating seedling photomorphogenesis and seed germination. This review focuses on these integrators in illustrating how light and hormone interact.

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Plant stem cell niches: from signalling to execution.

Publication Date: 2010 Aug 23 PMID: 20739214
Authors: Sablowski, R.
Journal: Curr Opin Plant Biol

The shoot and root meristems contain small populations of stem cells that constantly renew themselves while providing precursor cells to build all other plant tissues and organs. Cell renewal, growth and differentiation in the meristems are co-ordinated by networks of transcription factors and intercellular signals. The past two years have revealed how auxin and cytokinin signals are integrated with each other and with regulatory genes in the shoot and root meristems. Small RNAs have also emerged as novel intercellular signals. Downstream of meristem regulatory genes, links have been made to cell division control and chromatin function. Protection of genome integrity, partly through programmed cell death after DNA damage, has recently been revealed as a specialised function in plant stem cells.

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