Integration of metabolomic and transcriptomic analyses reveals the mechanism of anthocyanin accumulation in purple leaves of Brassica juncea var. foliosa

Mustard is an important cruciferous vegetable that encompasses numerous varieties and exhibits wide adaptability and high nutritional value. Compared with green leaf mustard, purple leaf mustard has superior antioxidant capacity and industrial value due to its high anthocyanin content. However, the mechanism underlying the accumulation of anthocyanins in purple mustard is unclear. In this study, we quantified the concentrations of pigments in purple leaf mustard (mu_Z) and green leaf mustard (WT) and discovered that the development of purple leaves is attributable to anthocyanin accumulation. The anthocyanin accumulation mechanism was subsequently investigated by integrating transcriptomic and metabolomic analyses and qRT‒PCR. As a result, 81 differentially accumulated metabolites and 13,127 differentially expressed genes were identified, respectively. Metabolites and transcripts from the anthocyanin synthesis, flavone and flavonol biosynthesis, flavonoid biosynthesis, phenylalanine metabolism and phenylpropanoid biosynthesis pathways, which are closely associated with anthocyanin biosynthesis, were significantly enriched in mu_Z. qRT-PCR analysis confirmed that the expression of biosynthetic genes in these pathways was higher in mu_Z than in WT. These results confirm that the development of mu_Z purple leaves is contingent upon the accumulation of metabolites in the anthocyanin synthesis pathway and the expression of associated genes, providing valuable insights into the genetic regulation of anthocyanin metabolism and synthesis in leaf mustard.