SUMOylation of AL6 regulates seed dormancy and thermoinhibition in Arabidopsis

DELAY OF GERMINATION1 (DOG1) is a critical regulator of seed dormancy and seed thermoinhibition. However, how DOG1 expression is regulated by post-translational modifications and how seeds transmit the high-temperature signal to DOG1 remain largely unknown. ALFIN1-like 6/7 (AL6/7) was previously found to repress DOG1 expression during seed imbibition. Here, we found that AL6/7 represses seed dormancy partly by downregulating DOG1 expression. AtSIZ1, a SUMO E3 ligase, interacts with AL6 and mediates its SUMOylation mainly at the lysine 181 residue. SIZ1-mediated SUMOylation of AL6 is required for repression of DOG1 transcription and seed dormancy. SUMOylation of AL6 is required for its association with the DOG1 locus and protects it from ubiquitination and subsequent 26S proteasome-mediated protein degradation. High temperatures decrease SUMOylation levels of AL6, resulting in downregulation of AL6 protein levels and an increase in DOG1 transcription, which consequently causes reduced seed germination. Taken together, these results demonstrate that reversible SUMOylation of AL6 fine-tunes DOG1 expression, which is required for precise establishment of seed dormancy and inhibition of seed germination under high-temperature conditions in Arabidopsis thaliana.