A rice calmodulin-like protein OsCML27 participates in drought tolerance by fine-tuning OsRbohB-mediated ROS signaling

Respiratory burst oxidase homolog (RBOH)–based ROS production was widely verified playing vital roles in plant stress responses; however, its inhibitory mechanism remains largely unknown. Here, we demonstrate that a calmodulin-like (CML) protein OsCML27 functions as a flexible brake of OsRbohB-mediated ROS production to regulate rice drought tolerance via an OsMRLK63-OsCML27-OsRbohB module. OsCML27 negatively regulates drought tolerance of rice where the overexpression lines showed a faster water loss rate and a lower survival rate under drought, while the oscml27 mutants exhibited a slower dehydration rate and a slightly lower survival rate as compared to wild type. OsCML27 can interact with and be phosphorylated by a receptor-like kinase OsMRLK63 primarily at Ser ¹¹ , and the phosphorylation level could be increased by drought. The phosphorylation by OsMRLK63 enhances OsCML27 stability, and OsCML27 inhibits ROS production by interacting with OsRbohB in the Ca ²⁺ -dependent manner. All these results reveal that OsCML27 integrates phosphorylation and Ca ²⁺ signals to regulate drought tolerance of rice by fine-tuning OsRbohB-mediated ROS signaling.