A Novel Rice Gene, OsEBR1 , Promotes Brassinosteroid Signalling and Is Transcriptionally Repressed by Both OsOFP22 and OsBZR1

Brassinosteroids (BRs) are crucial for plant growth and adaptation. BR signalling is fine-tuned by complex transcriptional networks. Here, we identify a novel rice gene, OsEBR1, which is transcriptionally repressed by both OVATE family protein 22 (OsOFP22) and BRASSINAZOLE RESISTANT1 (OsBZR1). We reveal that OsOFP22 antagonises OsBZR1-mediated repression, explaining the paradoxical upregulation of OsEBR1 in OsOFP22-overexpressing plants. OsEBR1 is a key positive regulator of BR signalling and regulates rice plant architecture and grain morphology. OsEBR1 protein interacts with DWARF AND LOW-TILLERING (DLT) and Oryza sativa homeobox 1 (OSH1), enhancing DLT activity on OsPHI-1 while suppressing OSH1 activation of BR catabolic genes. Evolutionary analysis shows OsEBR1 haplotypes are differentiated between indica and japonica subspecies and correlate with latitude. Our study identifies OsEBR1 as a target of an OVATE family protein in rice and defines an OsOFP22-OsBZR1-OsEBR1 regulatory module that fine-tunes BR signalling output.