OsABCG22 mediates embryonic abscisic acid export and seed germination in rice

Seed germination is a critical process in the plant life cycle. The translocation of abscisic acid (ABA) across the embryo and endosperm plays a key role in mediating seed germination in plants. While several ABA transporters have been identified, the extracellular transport of embryonic ABA in plants has remained largely uninvestigated. In this study, we characterized OsABCG22 as an embryonic ABA exporter in rice (Oryza sativa). OsABCG22 knockout mutants (Osabcg22) displayed reduced seed germination and hypersensitivity to ABA and upregulated expression of ABA signaling genes, such as OsABI3/5. These mutants also displayed decreased embryonic ABA secretion and increased ABA accumulation compared with wild-type embryos. Additionally, Osabcg22 mutants exhibited reduced cell size and lower cell wall monosaccharide content in embryos. OsABCG22 facilitated ABA export when expressed in yeast, HEK293 cells, and rice embryo tissues. Seeds overexpressing OsABCG22 showed improved seedling vigor. These findings highlight the critical role of OsABCG22-mediated embryonic ABA export in regulating rice seed germination.