Fine-Mapping and Functional Characterization of BjMYB113 in Controlling Purple Leaf Coloration in Brassica juncea

The purple leaves of Brassica juncea are abundant in anthocyanins that confer stress tolerance, nutritional benefits, and ornamental value. In this study, we constructed F2 and BC1 segregating populations by crossing the purple leaf inbred line (ZY) with the green leaf inbred line (LY) to investigate the genetic basis of leaf pigmentation. Bulked segregant analysis sequencing (BSA-Seq) and map-based cloning localized the BjZY locus to a 162.08 kb interval on chromosome BB_Chr05. Based on sequence alignment and homology analysis, an R2R3 MYB transcription factor, BjMYB113 (BjuVB05G51160), was identified as a strong candidate gene, with 3 SNPs and 25 bp insert variants in the promoter region. The expression of BjMYB113 in purple leaves was significantly higher than that in green leaves, leading to anthocyanin biosynthesis and accumulation. The transient expression of BjMYB113 in tobacco leaf confirmed that BjMYB113 positively regulates anthocyanin biosynthesis. RNA-seq analysis revealed that BjMYB113 was involved in flavonoid and anthocyanin biosynthesis pathways and regulated the expression of anthocyanin-related genes, such as BjCHS, BjDFR, and BjANS. Yeast one-hybrid assays showed that BjMYB113 activated the expression of BjDFR by directly binding to its promoter. These results provide further understanding of the genetics of purple leaf and potential applications for marker-assisted breeding in B. juncea.