Rice H2-Type RING E3 Ligase Gene, OsSIRH2-3, Positively Regulates Salt Tolerance by Maintaining Na⁺/K⁺ Homeostasis

High soil salinity possesses a major challenge for plant growth and productivity. Plants have evolved various mechanisms to withstand the adverse effects of salt stress, including E3 ubiquitin ligases that label salt-responsive proteins for degradation. Here, we characterized the mechanisms RING E3 ubiquitin ligase OsSIRH2-3 (Oryza sativa Salt Induced RING H2-type-3 E3 ligase) used to facilitate salt tolerance in rice. OsSIRH2-3 expression was upregulated under high NaCl concentrations and upon abscisic acid (ABA) treatment. OsSIRH2-3 was primarily found in the nucleus of rice protoplasts. The OsSIRH2-3 protein contains an H2-type-RING domain that confers E3 ligase activity. OsSIRH2-3 overexpression was also found to be associated with enhanced salt tolerance in transgenic plants, decreased Na⁺ accumulation in both roots and leaves, decreased Na⁺ transport activity in the xylem sap, increased levels of proline and soluble sugars, elevated activity of reactive oxygen species scavenging enzymes, and altered expression of Na⁺/K⁺ transporters. Furthermore, OsSIRH2-3-overexpressing plants also exhibited high sensitivity to exogenous ABA treatment. Our findings demonstrate that OsSIRH2-3 enhances salt tolerance by regulating Na⁺/K⁺ homeostasis and modulating Na⁺/K⁺ transporter expression. This study illuminates the molecular mechanisms involved in RING E3 ubiquitin ligase-mediated salt tolerance in rice and provides a potential strategy for enhancing crop productivity in saline environments.