Genome-Wide Identification of the OPT Gene Family and Screening of Sb-Responsive Genes in Brassica juncea

Antimony (Sb), a toxic metalloid, inhibits plant growth and threatens human health. Yellow Stripe-Like (YSL) proteins play crucial roles in metal ion transport and cellular homeostasis. While the OPT gene family has been characterized in some species, its genome-wide organization and functional involvement in Sb stress response remain unexplored in <i>Brassica juncea</i>. Here, we identified 47 high-confidence <i>BjOPT</i> genes and combined transcriptomic approaches to elucidate their regulatory roles under Sb stress. Phylogenetic tree, conserved motifs, and gene structure analyses consistently distinguished the BjOPT and BjYSL subfamilies. Comparative and collinearity analyses indicated that <i>OPT</i> genes in <i>Brassica</i> species (including <i>B. rapa</i>, <i>B. nigra</i>, and <i>B. juncea</i>) expanded independently of whole-genome triplication events. Transcriptomic profiling revealed significant enrichment of differentially expressed genes (DEGs) related to key biological processes (oxidative and toxic stress response, metal ion transport, and auxin efflux) and pathways (glutathione metabolism, MAPK signaling, and phytohormone transduction), highlighting their roles in Sb detoxification and tolerance. Notably, three <i>BjYSL3</i> (<i>BjA10.YSL3</i>, <i>BjB02.YSL3</i>, and <i>BjB05.YSL3</i>) genes exhibited strong up-regulation under Sb stress. Heterologous expression in yeast demonstrated that both <i>BjA10.YSL3</i> and <i>BjB02.YSL3</i> enhance Sb tolerance, suggesting their potential role in transporting Sb-nicotianamine (NA) or phytosiderophore (PS) complexes. These findings advance our understanding of Sb tolerance mechanisms and provide a basis for developing metal-resistant crops and phytoremediation strategies.