The bare necessities of plant K+ channel regulation

Potassium (K+) channels serve a wide range of functions in plants from mineral nutrition and osmotic balance to turgor generation for cell expansion and guard cell aperture control. Plant K+ channels are members of the superfamily of voltage-dependent K+ channels, or Kv channels, that include the Shaker channels first identified in fruit flies (Drosophila melanogaster). Kv channels have been studied in depth over the past half-century and are the best-known of the voltage-dependent channels in plants. Like the Kv channels of animals, the plant Kv channels are regulated over timescales of milliseconds by conformational mechanisms that are commonly referred to as gating. Many aspects of gating are now well established, but these channels still hold some secrets, especially when it comes to the control of gating. How this control is achieved is especially important, as it holds substantial prospects for solutions to plant breeding with improved growth and water use efficiencies. Resolution of the structure for the KAT1 K+ channel, the first channel from plants to be crystallized, shows that many previous assumptions about how the channels function need now to be revisited. Here, I strip the plant Kv channels bare to understand how they work, how they are gated by voltage and, in some cases, by K+ itself, and how the gating of these channels can be regulated by the binding with other protein partners. Each of these features of plant Kv channels has important implications for plant physiology

Regulation of shaker potassium channels by protein complexes.

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Molecular mechanisms involved in plant adaptation to low K+ availability.

International audiencePotassium is a major inorganic constituent of the living cell and the most abundant cation in the cytosol. It plays a role in various functions at the cell level, such as electrical neutralization of anionic charges, protein synthesis, long- and short-term control of membrane polarization, and regulation of the osmotic potential. Through the latter function, K(+) is involved at the whole-plant level in osmotically driven functions such as cell movements, regulation of stomatal aperture, or phloem transport. Thus, plant growth and development require that large amounts of K(+) are taken up from the soil and translocated to the various organs. In most ecosystems, however, soil K(+) availability is low and fluctuating, so plants have developed strategies to take up K(+) more efficiently and preserve vital functions and growth when K(+) availability is becoming limited. These strategies include increased capacity for high-affinity K(+) uptake from the soil, K(+) redistribution between the cytosolic and vacuolar pools, ensuring cytosolic homeostasis, and modification of root system development and architecture. Our knowledge about the mechanisms and signalling cascades involved in these different adaptive responses has been rapidly growing during the last decade, revealing a highly complex network of interacting processes. This review is focused on the different physiological responses induced by K(+) deprivation, their underlying molecular events, and the present knowledge and hypotheses regarding the mechanisms responsible for K(+) sensing and signalling

Regulation of Shaker potassium channels by protein complexes

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Characterization of natural Zn tolerance variation in A. thaliana

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Characterization of natural Zn tolerance variation in A. thaliana

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Natural variation at the FRD3 MATE transporter locus reveals cross-talk between Fe homeostasis and Zn tolerance in Arabidopsis thaliana

Zinc (Zn) is essential for the optimal growth of plants but is toxic if present in excess, so Zn homeostasis needs to be finely tuned. Understanding Zn homeostasis mechanisms in plants will help in the development of innovative approaches for the phytoremediation of Zn-contaminated sites. In this study, Zn tolerance quantitative trait loci (QTL) were identified by analyzing differences in the Bay-0 and Shahdara accessions of Arabidopsis thaliana. Fine-scale mapping showed that a variant of the Fe homeostasis-related FERRIC REDUCTASE DEFECTIVE3 (FRD3) gene, which encodes a multidrug and toxin efflux (MATE) transporter, is responsible for reduced Zn tolerance in A. thaliana. Allelic variation in FRD3 revealed which amino acids are necessary for FRD3 function. In addition, the results of allele-specific expression assays in F1 individuals provide evidence for the existence of at least one putative metal-responsive cis-regulatory element. Our results suggest that FRD3 works as a multimer and is involved in loading Zn into xylem. Cross-homeostasis between Fe and Zn therefore appears to be important for Zn tolerance in A. thaliana with FRD3 acting as an essential regulator

Mécanisme moléculaire d’action de l’acide abscissique en réponse à la sécheresse chez les végétaux

La consommation d’eau douce dans les pays les plus développés est aux alentours de 200 à 700 litres par habitant et par jour, dont environ 70 % seraient destinés aux besoins agricoles. Contrairement à d’autres ressources naturelles (comme les différentes formes d’énergie), l’eau n’a pas de produit de substitution. Au cours des dernières années, un énorme chemin a été parcouru concernant notre compréhension de la perception de l’acide abscissique (ABA), une phytohormone qui régule la majorité des réponses adaptatives au déficit hydrique. Face à des conditions environnementales toujours plus contraignantes, notre état de connaissance actuel sur la signalisation de l’ABA est-il suffisant pour assurer le maintien de la productivité des plantes de grande culture tout en consommant moins d’eau ? Cette question suscite des réflexions autant scientifiques que politiques. Bien que l’ABA soit historiquement considéré comme une phytohormone depuis 1960, elle a été redécouverte dans les années 1980 chez de nombreux organismes (éponges de mer, certains parasites, hydres, etc.), dont l’Homme. De manière étonnante, l’ABA présente des propriétés anti-inflammatoires et antivirales. De plus, les gènes homologues codant les récepteurs et les principaux intermédiaires de la signalisation sont conservés, ce qui suggère que les connaissances issues des études utilisant la plante comme modèle seraient applicables à d’autres organismes. La teneur en ABA pourrait atteindre un niveau 10 à 30 fois supérieur à la normale chez des plantes soumises à un stress hydrique; l’ABA agit alors comme un déclencheur de diverses voies d’adaptation permettant à la plante de mieux résister au stress hydrique. Un modèle expérimental qui se prête particulièrement bien à l’étude de la complexité de l’action de l’ABA est la fermeture des stomates, une réponse physiologique mise en place par les végétaux supérieurs pour limiter la perte d’eau par transpiration. Les stomates sont de petits pores à la surface des feuilles. Chaque pore est entouré par une paire de cellules oblongues et légèrement courbées (en forme de rein), appelées cellules de garde, dont les mouvements contrôlent son degré d’ouverture. L’essor de la recherche sur les rôles physiologiques joués par l’ABA au cours du développement de la plante (notamment sur l’abscission des fruits et la dormance des bourgeons) a débuté dans les années 1960, et a abouti en 2009 à l’identification d’une famille de récepteurs cytosoliques de l’hormone. Cette découverte a été suivie très rapidement par la reconstitution de plusieurs cascades de transduction signalétiques ABA-dépendantes in vitro. De nombreuses études ont été réalisées sur les structures cristallines des protéines appartenant au complexe cœur de la signalisation par l’ABA (un récepteur, une phosphatase et une kinase), prises individuellement ou en combinaison, en complexe ou non avec l’ABA. Ces études laissent entrevoir la possibilité de concevoir des agonistes et antagonistes de l’hormone afin de permettre aux végétaux de mieux s’adapter au stress hydrique. Cette revue retracera le progrès extraordinaire qui a permis d’éclairer la façon dont l’ABA agit sur les transports à travers la membrane plasmique, aboutissant à la fermeture des stomates pour limiter la transpiration

Commandeering Channel Voltage Sensors for Secretion, Cell Turgor, and Volume Control

Control of cell volume and osmolarity is central to cellular homeostasis in all eukaryotes. It lies at the heart of the century-old problem of how plants regulate turgor, mineral and water transport. Plants use strongly electrogenic H+-ATPases, and the substantial membrane voltages they foster, to drive solute accumulation and generate turgor pressure for cell expansion. Vesicle traffic adds membrane surface and contributes to wall remodelling as the cell grows. Although a balance between vesicle traffic and ion transport is essential for cell turgor and volume control, the mechanisms coordinating these processes have remained obscure. Recent discoveries have now uncovered interactions between conserved subsets of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins that drive the final steps in secretory vesicle traffic and ion channels that mediate in inorganic solute uptake. These findings establish the core of molecular links, previously unanticipated, that coordinate cellular homeostasis and cell expansion

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SIGLEBibliothek Weltwirtschaft Kiel C 150063 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman