Signaling mechanisms in abscisic acid-mediated stomatal closure.

The plant hormone abscisic acid (ABA) plays a central role in the regulation of stomatal movements under water-deficit conditions. The identification of ABA receptors and the ABA signaling core consisting of PYR/PYL/RCAR ABA receptors, PP2C protein phosphatases and SnRK2 protein kinases has led to studies that have greatly advanced the knowledge of the molecular mechanisms mediating ABA-induced stomatal closure in the past decade. This review focuses on recent progress at illuminating the regulatory mechanisms of ABA signal transduction, and the physiological importance of basal ABA signaling in stomatal regulation by CO2 and, as hypothesized here, vapor pressure deficit. Furthermore, advances at understanding the interactions of ABA and other stomatal signaling pathways are reviewed here. We also review recent studies investigating the utilization of ABA signaling mechanisms for manipulation of stomatal conductance and enhancement of drought tolerance and water use efficiency of plants.