OsARF9 integrates auxin-BR-ABA signaling to regulate plant architecture and seed germination in rice

Optimizing rice (Oryza sativa L.) plant architecture and seed germination is critical for improving agronomic performance. Here, we investigated the role of OsARF9, a class B auxin response factor, in regulating these traits. Through analysis of OsARF9 transgenic lines, combined with phenotypic characterization, hormone response assays, and promoter binding studies, we demonstrate that OsARF9 functions as a transcriptional repressor. OsARF9 transgenic lines display clear differences in architecture traits and genotype-dependent responses to auxin, brassinosteroid (BR), and abscisic acid (ABA) treatments. OsARF9 directly binds promoter elements beyond the canonical auxin response element (AuxRE) and represses expression of OsGH3-5 and OsRLA1. Furthermore, it binds the promoters of OsABI3 and OsEm1, reduces their transcription, and thereby modulates ABA-mediated inhibition of seed germination. Collectively, our results establish OsARF9 as an integrative transcriptional repressor that coordinates auxin, BR, and ABA signaling to shape rice architecture and seed germination.