GsSnRK1-Dependent Degradation of the E3 Ubiquitin Ligase GsSRF2 Positively Regulates Soybean Resistance to Salt Stress

Protein phosphorylation and ubiquitination play central roles in signal transduction. SnRK1 is a key kinase that mediates plant responses to environmental cues. From a wild soybean cDNA library, we identified GsSRF2, which encodes a RING-domain E3 ligase that interacts with GsSnRK1. GsSRF2 is predominantly expressed in roots and responds dynamically to salt stress. BiFC, pull-down, and co-IP assays this interaction in the cytoplasm and at the plasma membrane. Biochemical analyses revealed that GsSnRK1 phosphorylates GsSRF2 at Thr514. GnSnRK1-mediated phosphorylation enhanced GsSRF2 ubiquitination and promoted its proteasomal degradation. Coexpression assays in soybean hairy roots demonstrated that the GsSnRK1–GsSRF2 module significantly improved salt tolerance, whereas the GsSnRK1–GsSRF2(T514A) and kinase-dead GsSnRK1(K49M)–GsSRF2 modules reduced salt resistance in composite plants. Together, these results indicate that GsSnRK1 positively regulates soybean salt tolerance by modulating GsSRF2 ligase activity and protein stability, providing valuable genetic resources for crop improvement.