The E2 ubiquitin-conjugating enzymes OsUBC11 and OsUBC12 promote rice seed germination by ubiquitinating and destabilizing OsABI3 in the ABA signaling pathway.

The ubiquitin-conjugating enzymes (E2) play critical roles in plant stress responses and development, but their functions in ABA-mediated seed germination in rice remain largely unknown. We identified two homologous E2 enzymes, OsUBC11 and OsUBC12, which are highly expressed in rice seeds and induced by multiple abiotic stresses including salt, osmotic stress, and ABA treatment. We demonstrated that OsUBC11 and OsUBC12 positively regulate rice seed germination, especially under NaCl and ABA treatment, as the double mutants exhibited delayed germination and hypersensitivity to ABA and salt, while overexpression lines showed accelerated germination and reduced sensitivity. OsUBC11 and OsUBC12 negatively regulate the expression of ABA-responsive genes, including OsABI3, OsABI5, OsRAB21, and OsLEA3. Protein interaction assays demonstrated that OsUBC11/12 directly interact with OsABI3, a key transcription factor in ABA signaling. OsUBC11/12 possess ubiquitin-conjugating activity and promote the ubiquitination and subsequent degradation of OsABI3, thereby reducing OsABI3 protein stability. Together, our findings establish that OsUBC11 and OsUBC12 positively regulate seed germination under salt stress by ubiquitinating and destabilizing OsABI3, thus attenuating ABA signaling.