Overexpression of a C3HC4‐type E3‐ubiquitin ligase contributes to salinity tolerance by modulating Na+ homeostasis in rice

Abstract Soil salinity has a negative effect on crop yield. Therefore, plants have evolved many strategies to overcome decreases in yield under saline conditions. Among these, E3‐ubiquitin ligase regulates salt tolerance. We characterized Oryza sativa Really Interesting New Gene (RING) Finger C3HC4‐type E3 ligase (OsRFPHC‐4), which plays a positive role in improving salt tolerance. The expression of OsRFPHC‐4 was downregulated by high NaCl concentrations and induced by abscisic acid (ABA) treatment. GFP‐fused OsRFPHC‐4 was localized to the plasma membrane of rice protoplasts. OsRFPHC‐4 encodes a cellular protein with a C3HC4‐RING domain with E3 ligase activity. However, its variant OsRFPHC‐4 C161A does not possess this activity. OsRFPHC‐4 ‐overexpressing plants showed enhanced salt tolerance due to low accumulation of Na + in both roots and leaves, low Na + transport in the xylem sap, high accumulation of proline and soluble sugars, high activity of reactive oxygen species (ROS) scavenging enzymes, and differential regulation of Na + /K + transporter expression compared to wild‐type (WT) and osrfphc‐4 plants. In addition, OsRFPHC‐4 ‐overexpressing plants showed higher ABA sensitivity under exogenous ABA treatment than WT and osrfphc‐4 plants. Overall, these results suggest that OsRFPHC‐4 contributes to the improvement of salt tolerance and Na + /K + homeostasis via the regulation of changes in Na + /K + transporters.