RIC7 plays a negative role in ABA-induced stomatal closure by inhibiting HO production.

When plants encounter environmental stresses, phytohormone abscisic acid (ABA) accumulates quickly and efficiently reduces water loss by inducing stomatal closure. Reactive oxygen species (ROS) is an important regulator in ABA-induced stomatal closure, and ROS generation is modulated by multiple components in guard-cell ABA signaling. ROP interactive CRIB-containing protein 7 (RIC7) has been found to negatively regulate ABA-induced stomatal closure. However, the molecular details of the RIC7 function in this process are unclear. Here, by using two overexpressing mutants, we confirmed the negative role of RIC7 in ABA-induced stomatal closure and found that guard cells of overexpressing mutants generated less HO than the wild type with ABA treatment, which were consistent with the reduced expression levels of ROS generation related NADPH oxidase genes and , and cytosolic polyamine oxidase genes and in the overexpressing mutants. Furthermore, external applied HO failed to rescue the defects of stomatal closure in overexpressing mutants. These results suggest that RIC7 affects HO generation in guard cells, and the function of HO is dependent on RIC7 in ABA-induced stomatal closure, indicative of interdependency between RIC7 and HO in ABA guard-cell signaling.