Rice Stomatal Closure Requires Guard Cell Plasma Membrane ATP-Binding Cassette Transporter RCN1/OsABCG5

Water stress is one of the major environmental stresses that affect agricultural production worldwide. Water loss from plants occurs primarily through stomatal pores. Here, we report that an Oryza sativa half-size ATP-binding cassette （ABC） subfamily G protein, RCN 1/OsABCG5, is involved in stomatal closure mediated by phytohormone abscisic acid （ABA） accumulation in guard cells. We found that the GFP-RCN1/ OsABCG5-fusion protein was localized at the plasma membrane in guard cells. The percentage of guard cell pairs containing both ABA and GFP-RCN1/OsABCG5 increased after exogenous ABA treatment, whereas they were co-localized in guard cell pairs regardless of whether exogenous ABA was applied. ABA application resulted in a smaller increase in the percentage of guard cell pairs containing ABA in rcnl mutant （A684P） and RCN1-RNAi than in wild-type plants. Furthermore, polyethylene glycol （drought stress）-inducible ABA accumulation in guard cells did not occur in rcnl mutants. Stomata closure mediated by exogenous ABA application was strongly reduced in rcnl mutants. Finally, rcnl mutant plants had more rapid water loss from detached leaves than the wild-type plants. These results indicate that in response to drought stress, RCN1/OsABCG5 is involved in accumulation of ABA in guard cells, which is indispensable for stomatal closure.