Integrated transcriptomic and metabolomic profiles reveal anthocyanin accumulation in Scutellaria baicalensis petal coloration

Scutellaria baicalensis is a flowering plant of the Lamiaceae genus whose petals are mostly purple, with a few being pink and white. To elucidate the kinetics behind S. baicalensis petal coloration, an integrative analysis of target flavonoid metabolic and transcriptome profiles was performed to identify the anthocyanin biosynthesis pathway, which was differently activated in S. baicalensis germplasms with three different petal colors (white, pink and purple). Metabolomic profile data revealed that 18 anthocyanins were significantly different in S. baicalensis petals. Transcriptomic data showed that S. baiANS in anthocyanin biosynthesis was significantly downregulated in white flower petals. Interestingly, the sequence variations were found in the S. baiANS promoter region, where it was likely that a mutation reduced S. baiANS expression in white S. baicalensis flowers. Yeast one-hybrid (Y1H) analysis of S. baiMYB indicated that it was not bound to the S. baiANS promoters of white S. baicalensis flowers. Dual-luciferase assays further confirmed that the S. baiANS promoter decreased promoter activity, which resulted in reduced anthocyanin biosynthesis in white S. baicalensis flowers. The findings of this study elucidate the mechanisms behind the loss-of-color phenotype in white S. baicalensis flowers while providing potential leads for further studies on biological and flower evolution.