The feedback regulation between DREB2C and E3 ligases DEL1 / DEL2 for balancing the initial growth and ABA signaling in Arabidopsis

Dehydration-Responsive Element Binding Protein 2C (DREB2C) is a vital transcription factor that responds to drought, cold and heat stresses in Arabidopsis. Previous studies have suggested that DREB2C might be involved in abscisic acid (ABA) signaling, but the detailed molecular mechanism remains unclear. In this study, we find that DREB2C positively regulates ABA-mediated seed germination and root elongation. Degradation assays show that the degradation of DREB2C relies on the 26S proteasome pathway and ABA promotes the accumulation of DREB2C. Further analyses confirm that two novel E3 ligases DREB2C-Degrading E3 Ligase 1/2 (DEL1/2) interact with DREB2C and mediate its ubiquitination. Functional analyses demonstrate that DEL1 or DEL2 negatively regulates ABA-mediated seed germination and root elongation, while overexpression of DEL1 or DEL2 in DREB2C-overexpressing lines results in reduced ABA hypersensitivity. Genetic analysis indicates that DEL1 and DEL2 function redundantly in the degradation of DREB2C and act upstream of DREB2C in the ABA signaling pathway. In addition, DREB2C directly binds to the promoters of DEL1 and DEL2 and activates their expression, thereby shutting down the transmission of ABA signals. Collectively, we uncover a novel feedback regulatory loop between DREB2C and DEL1/DEL2 that balances the initial growth stage and ABA responses in Arabidopsis.