QUIRKY controls seed germination via precision degradation of ABI5.

Seed dormancy and germination are dynamically regulated by abscisic acid (ABA), with transcription factor ABA INSENSITIVE 5 (ABI5) serving as a key repressor of germination under stress. Here, we identify QUIRKY (QKY), a MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEIN (MCTP) in Arabidopsis, as a critical regulator of ABA signaling through posttranslational control of ABI5. QKY interacts with ABI5 and facilitates its cytoplasmic degradation via the E3 ubiquitin ligase KEEP ON GOING (KEG), promoting the recruitment of ABI5 into phase-separated condensates. Loss of QKY function enhances ABA hypersensitivity, reducing seed germination rates and impairing seedling establishment. These findings highlight QKY as a scaffold that integrates phase separation and targeted ubiquitination to fine-tune ABA responses, balancing dormancy and germination. Our study expands the understanding of posttranslational ABI5 regulation and reveals MCTPs as central players in coordinating growth-stress trade-offs during early plant development.