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 (<i>BPC</i>) transcription factors are plant-specific and play crucial roles in regulating plant development and responses to abiotic stresses. However, the genomic characteristics of the <i>BPC</i> gene family in <i>Brassica juncea</i> and its regulatory mechanisms in response to light and salicylic acid remain poorly understood. In this study, we identified 25 <i>BjuBPC</i> genes in the <i>B. juncea</i> genome using bioinformatic approaches. All BjuBPC proteins were predicted to localize exclusively to the nucleus, with their distribution scattered across 14 chromosomes of <i>B. juncea</i>. Phylogenetic analysis classified these <i>BjuBPC</i> genes into three subfamilies (A, B, and C). The 25 <i>BjuBPC</i> genes showed strong collinearity with <i>BPC</i> orthologs from <i>Arabidopsis thaliana</i>, <i>Brassica rapa</i>, and <i>Brassica nigra</i>, 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 <i>BjuBPC</i> members. Subsequent expression analyses under four light qualities and exogenous salicylic acid treatment demonstrated that <i>BjuBPC1</i>, <i>BjuBPC9</i>, and <i>BjuBPC24</i> 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 <i>BjuBPC</i> genes and enhance our understanding of their biological roles in <i>B. juncea</i>.