RST31 controls salt tolerance in rice (Oryza sativa) by regulating the cytokinin pathway

Salt stress affects the growth of rice, which reduces grain yield. However, the mechanism of the rice response to salt stress is not fully understood. The rice salt tolerance 31 (rst31) mutant exhibits longer shoots and greater dry weight than wild type (WT) plants under salt stress conditions. Through map-based cloning and genetic complementation methods, we determined that RST31 encodes a half-size ABCG transporter protein, ABCG18. We showed that mutation of RST31 reduces DNA damage under salt stress, with less accumulation of reactive oxygen species (ROS). The deficiency of RST31 suppressed the root-to-shoot transport of cytokinin, which resulted in a decrease in cytokinin content in the shoot and an increase in cytokinin content in the root. ROS accumulated abundantly in WT and rst31 mutant plants after exogenous treatment with trans-zeatin, reducing rst31 tolerance of salt stress. Collectively, our results suggest that high cytokinin level in shoots leads to an increase in ROS content and severe DNA damage under salt stress, which lead to sensitivity to salt stress. These findings enhance our understanding of plant responses to salt stress through cytokinin pathways.