BjuBRC1 genes function as conserved negative regulators of tillering in Brassica juncea

• Identification of five BjuBRC1 genes in the Brassica juncea genome encoding conserved TCP-domain transcription factors. • CRISPR/Cas9 knockout of BjuBRC1 genes in a low-tillering variety releases axillary bud suppression, increasing tiller number from 0 to ∼10. Overexpression of BjuBRC1 genes in a high-tillering variety strongly inhibits tillering, confirming their negative regulatory role. • BjuBRC1 genes are specifically highly expressed in suppressed axillary buds, consistent with their function in bud dormancy. • Nuclear localization of BjuBRC1 proteins supports their function as transcriptional regulators. • Provides molecular targets for breeding mustard varieties with optimized tillering architecture for yield improvement. Tillering is a key factor determining the yield of mustard (Brassica juncea), yet its genetic regulation remains unclear. This study identified five BjuBRC1 genes encoding TCP-domain proteins in the mustard genome. Expression analysis showed high transcript levels specifically in suppressed axillary buds of the low-tillering variety ‘GM’. CRISPR/Cas9-mediated multiplex knockout of BjuBRC1 genes in ‘GM’ converted the low-tillering phenotype, increasing tiller number from 0 to approximately 10. Conversely, BjuBRC1 overexpression in the high-tillering variety ‘HJ-3’ strongly inhibited tiller outgrowth, resulting in 0–2 tillers per plant. Subcellular localization confirmed nuclear accumulation of BjuBRC1 proteins. Our results establish the BjuBRC1 gene family as conserved transcriptional repressors of tillering in mustard, providing a molecular target for improvement in this crop.