Os ASR 5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H 2 O 2 signalling in rice

Summary Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid , stress and ripening ( ASR ) genes from upland rice variety, IRAT 109 ( Oryza sativa L. ssp. japonica ), and demonstrated that overexpression of Os ASR 5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of Os ASR 5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H 2 O 2 , a second messenger for the induction of stomatal closure in response to ABA , was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss‐of‐function mutant, osasr5 , showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that Os ASR 5 functioned as chaperone‐like protein and interacted with stress‐related HSP 40 and 2 OG ‐Fe ( II ) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that Os ASR 5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone‐like protein that possibly prevents drought stress‐related proteins from inactivation.