BnaA01.BRC1 Negatively Regulates Branch Number and Responds to Gibberellin Signaling in Brassica napus

Plant architecture optimization is central to high-yield crop breeding. The number of branches in Brassica napus (B. napus) determines canopy structure, light use efficiency, and yield. The transcription factor BRANCHED1 (BRC1) integrates multiple signals to negatively regulate branching. This study characterized five BnaBRC1 homologs in B. napus via bioinformatics, expression profiling, and CRISPR/Cas9 editing. All BnaBRC1s contain a conserved TCP domain, and their promoters are enriched with light-responsive and hormone-responsive cis-acting elements. BnaA01.BRC1 is highly expressed in leaves, stem nodes, roots, and siliques, and its transcription is coordinately regulated by low light, sucrose, and exogenous cytokinin, and gibberellin (GA) signals. Functional analysis showed that overexpression of BnaA01.BRC1 suppressed branching, whereas CRISPR/Cas9-mediated knockout of BnaBRC1 substantially increased branch number. In basal axillary buds, high BnaBRC1 expression was accompanied by upregulation of GA-inactivating GIBBERELLIN 2 OXIDASEs and the GA signaling negative regulator SPINDLY, and no direct interaction was detected between BnaA01.BRC1 and DELLA proteins, suggesting indirect regulation of branching via GA homeostasis. Collectively, this study demonstrates the pivotal role of BnaA01.BRC1 in branching regulation and provides a genetic resource and theoretical basis for plant architecture optimization and multi-branch germplasm innovation in B. napus.