Oryza sativa H⁺-ATPase (OSA) is Involved in the Regulation of Dumbbell-Shaped Guard Cells of Rice

The stomatal apparatus consists of a pair of guard cells and regulates gas exchange between the leaf and atmosphere. In guard cells, blue light (BL) activates H⁺-ATPase in the plasma membrane through the phosphorylation of its penultimate threonine, mediating stomatal opening. Although this regulation is thought to be widely adopted among kidney-shaped guard cells in dicots, the molecular basis underlying that of dumbbell-shaped guard cells in monocots remains unclear. Here, we show that H⁺-ATPases are involved in the regulation of dumbbell-shaped guard cells. Stomatal opening of rice was promoted by the H⁺-ATPase activator fusicoccin and by BL, and the latter was suppressed by the H⁺-ATPase inhibitor vanadate. Using H⁺-ATPase antibodies, we showed the presence of phosphoregulation of the penultimate threonine in Oryza sativa H⁺-ATPases (OSAs) and localization of OSAs in the plasma membrane of guard cells. Interestingly, we identified one H⁺-ATPase isoform, OSA7, that is preferentially expressed among the OSA genes in guard cells, and found that loss of function of OSA7 resulted in partial insensitivity to BL. We conclude that H⁺-ATPase is involved in BL-induced stomatal opening of dumbbell-shaped guard cells in monocotyledon species.