Résumé
Submission 178Drought is a major environmental factor affecting crop productivity whose impact is predicted to increase with climate changes. In land plants, stomata are crucial to regulate water transpiration and CO2 uptake. The stomatal pore is delimited by two guard cells and its aperture is modulated according to environmental cues like CO2 concentration, hormones and water status. The mechanisms influencing stomata aperture rely on ion fluxes across the cellular membranes of guard cells. Concerted ion fluxes across the plasma membrane and the vacuolar membrane lead to the swelling and shrinking of guard cells. Hence, transport system residing in both membranes need to cooperate. The ALMT ion channels play important roles in guard cells responses in both the plasma and the vacuolar membranes. Two ALMTs, ALMT4 and ALMT12, localized in the vacuolar membrane and in the plasma membrane, respectively, mediate ionic fluxes during stomatal closure. To understand the interplay between ALMT4 and ALMT12 channels in guard cells, we generated double knock-out (KO) lines by crossing almt4 and almt12 single KO lines. These lines were then examined with different approaches. The stomatal conductance and the net photosynthesis rate was assessed on almt4, almt12 and almt4 almt12 mutant leaves upon ABA application and increased CO2 concentration. Upon ABA treatment, our data show that ALMT12 function dominate the induction of stomata closure. Differently, we found that in response to increased CO2 concentration, ALMT4 and ALMT12 channels work in synergy to induce stomatal closure. Our data highlight the importance of the interplay between the plasma and vacuolar membrane ion channels in stomata response to their environment.