Liquid--Liquid Phase Separation of OsvWA36 Fine-tunes Brassinosteroid Signaling and Leaf Angle in Rice

Rice leaf angle, a major determinant of plant architecture and yield potential, is tightly regulated by brassinosteroid (BR) signaling. Although the core BR pathway is well characterized, how BR responses are precisely controlled in space and time remains unclear. Here, we identify OsvWA36 , a novel regulator required to fine-tune BR signaling. The osvwa36 mutant exhibits typical BR-deficient phenotypes, including decreased leaf angle and reduced BR responsiveness, whereas ubiquitin promoter-driven expression of OsvWA36 confers BR hypersensitivity. We further show that the OsvWA36 protein undergoes intrinsically disordered region (IDR)-driven liquid–liquid phase separation to form dynamic condensates associated with the endoplasmic reticulum. These condensates facilitate a direct interaction between the OsvWA36 protein and the KNOX transcription factor OSH1. Genetic analyses indicate that OsvWA36 is necessary for full activation of the OSH1-regulated transcriptional program, including induction of BR catabolic genes (e.g., CYP734A2/4/6 ). In parallel, OsvWA36 broadly influences the expression of key activators of BR signaling and biosynthesis. Collectively, OsvWA36 integrates both positive and negative regulatory branches of the BR network to optimize leaf angle. These findings reveal a phase separation-based mechanism underlying hormone signaling and suggest that OsvWA36 is a promising target for the engineering of plant architecture.