Genome-Wide Identification of the BPC Gene Family in Brassica juncea and Expression Analysis of Its Regulatory Mechanisms in Response to Light and Salicylic Acid

BASIC PENTACYSTEINE (BPC) transcription factors are plant-specific and play crucial roles in regulating plant development and responses to abiotic stresses. However, the genomic characteristics of the BPC gene family in Brassica juncea and its regulatory mechanisms in response to light and salicylic acid remain poorly understood. In this study, we identified 25 BjuBPC genes in the B. juncea genome using bioinformatic approaches. All BjuBPC proteins were predicted to localize exclusively to the nucleus, with their distribution scattered across 14 chromosomes of B. juncea. Phylogenetic analysis classified these BjuBPC genes into three subfamilies (A, B, and C). The 25 BjuBPC genes showed strong collinearity with BPC orthologs from Arabidopsis thaliana, Brassica rapa, and Brassica nigra, and members of the same subfamily shared highly conserved exon–intron architectures and motif compositions, and a highly conserved canonical GAGA DNA-binding domain. Expression profiling across tissues revealed both tissue-specific and constitutive expression patterns among BjuBPC members. Subsequent expression analyses under four light qualities and exogenous salicylic acid treatment demonstrated that BjuBPC1, BjuBPC9, and BjuBPC24 were specifically responsive to both light and salicylic acid signals, with markedly strong induction by blue light. These findings provide valuable insights for future functional characterization of BjuBPC genes and enhance our understanding of their biological roles in B. juncea.