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

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.