Direct Modulation of the Guard Cell Outward-Rectifying Potassium Channel (GORK) by Abscisic Acid

Abscisic acid (ABA) induces turgor loss and hence stomatal closure by promoting rapid net K+ efflux from guard cells (GCs) through outward-rectifying K+ (K+out) channels (Schroeder et al., 1987; Blatt, 1990). The mechanisms of ABA signaling in GCs are detailed elsewhere (see Munemasa et al., 2015; Weiner et al., 2010; Pandey et al., 2007). Briefly, ABA binds to the PYR/PYL/RCARs, a family of soluble steroidogenic acute regulatory-related lipid transfer (START) proteins, and, in turn, inactivates the downstream PP2C (type 2C protein phosphatase), leading to the activation of SnRK2.6 (SNF1 [sucrose non-fermenting-1-related protein kinase]/OST1 [open stomata 1]) protein kinases.