Régulation fine des H+-ATPases de la membrane plasmique des cellules de garde : Rôle dans le contrôle des échanges gazeux – Energizer

Drought is one of the greatest limitations to crop expansion outside the present-day agricultural areas. It will become increasingly important in regions of the globe where, in the past, the problem was negligible, due to the recognized changes in global climate. Today there is a concern with improving cultural practices and crop genotypes for drought-prone areas; therefore, understanding the mechanisms behind drought resistance and the efficient use of water by the plants is fundamental for the achievement of those goals. In plants, the majority of all water loss occurs through pores on the leaf surface, which are called stomata. The size of the stomatal pores in a leaf is variable and controls the rate of diffusion of water vapour out of the plant. In addition to controlling water loss, stomata allow CO2 to diffuse into the leaf for photosynthesis. Thereby, stomata permanently control the trade-off between carbon uptake and water loss. Regulation of stomatal movements by guard cells in response to environmental stimuli and stress conditions is a primary factor in determining water use efficiency and productivity of crop plants. Guard cells also provide an ideal system to elucidate early events in higher plant signal transduction. Up today, several key guard cell ion channels have been proposed to function as important signal transducers and mediators of stomatal movements. During stomatal opening under favourable conditions, activation of a plasma-membrane-localized proton pump, H+-ATPase, establishes a negative membrane voltage that drives the uptake of K+. For stomatal closure, anion channels that depolarize the membrane are activated, setting conditions for long-term K+ and anion efflux. The question of whether deactivation of the proton pump is needed for stomatal closure, or whether the activation of anion channels is sufficient to sustain the membrane depolarization necessary to drive K+ efflux, remains largely unsolved. Recently, we have demonstrated that the down-regulation of guard-cell H+-ATPase activity is therefore an essential factor of ABA-induced stomatal closure. As several different H+-ATPases with a broad functional overlap are assumed to be expressed in guard cells, the objective of the present project is to enlighten the functions of these proteins in the guard cell signalling networks controlling stomatal movements. This submitted project will be performed using a multidisciplinary approach involving physiology, electrophysiology, molecular biology, biochemistry and molecular genetics in order to gain insight into the roles and the mechanisms of regulation of the plasma membrane H+-ATPases in guard cell at biochemical and physiological levels. The long term goal of this research is to characterize the chain of events of the signaling cascade which integrates physiological stimuli, such as abscisic acid, intracellular coupling proteins, second messengers, and ion channels to produce stomatal closing and to improve models of early signal transduction elements and signalling cascade in plants. More generally, this study could provide valuable information to understand the mechanisms that fine-tune membrane transporters and therefore the basis of ion homeostasis in plants.