Summary Abscisic acid (ABA) HYPERSENSITIVE GERMINATION 1 (AHG1) controls seed dormancy, germination, and early seedling establishment in response to ABA in Arabidopsis thaliana . However, whether and how AHG1 is degraded remain unclear. Here, we identified an unreported REALLY INTERESTING NEW GENE E3 ligase ARABIDOPSIS TÓXICOS EN LEVADURA 17 (ATL17) by RNA‐seq analysis and investigated its functions in ABA responses using multiple biochemical, molecular and genetic methods. ATL17 positively regulates ABA‐mediated suppression of seed germination and postgerminative seedling growth. It interacts with AHG1 and promotes AHG1 degradation by the 26S proteasome in the cytoplasm in response to ABA. AUXIN RESPONSE FACTOR 2 (ARF2), a crucial regulator of auxin signaling, binds to the ATL17 promoter to repress its transcription and functions in ABA responses. ATL17 prominently affects the phosphorylation of class III SUCROSE NONFERMENTING 1‐RELATED KINASE 2.3 and the accumulation of ABA‐INSENSITIVE 5 during ABA‐arrested seed germination and early seedling growth. Our findings reveal ATL17 as a new and essential regulator of AHG1 turnover and uncover a new function of ARF2 in ABA signaling, highlighting the key roles of ATL17‐regulated AHG1 degradation in governing ABA responses and likely mediating the crosstalk among ABA and auxin signaling in A. thaliana .
Wang et al. (Fri,) studied this question.