UFL1-mediated UFMylation Stabilizes ABI5 to Strengthen ABA-dependent Seed Dormancy in Arabidopsis

UFMylation is a reversible ubiquitin-like modification with an emerging and essential role in mammals, yet its functional mechanisms in plants remain largely unknown. In this study, we systematically characterized the complete UFMylation pathway in Arabidopsis thaliana and demonstrated that its core components-E1 UBA5, E2 UFC1, and E3 UFL1-possessed potent enzymatic activity. UFL1 is an E3 ligase that localizes to both the nucleus and cytoplasm. Expression pattern analyses revealed that UFL1 is strongly upregulated during embryogenesis and progressively accumulates throughout seed maturation. Phenotypic analyses showed that UFL1 overexpression enhances seed dormancy, increases plant sensitivity to abscisic acid (ABA), and significantly delays seed germination and cotyledon greening, identifying UFL1 as a previously unrecognized positive regulator of ABA signaling. Biochemical analyses further demonstrated that UFL1 physically interacts with the bZIP transcription factor ABI5 and mediates its UFMylation, thereby antagonizing ubiquitination and stabilizing ABI5 protein abundance. Genetic evidence further supported that ABI5 acts downstream of UFL1 to regulate seed developmental processes. Collectively, our findings reveal UFMylation as a pivotal regulatory layer in plants and uncover a UFL1-ABI5 signaling module that coordinates seed maturation, dormancy, and germination.