Viola × wittrockiana (pansy) is an important ornamental plant, particularly during winter and spring. In previous studies, we found that the tyrosine decarboxylase gene of pansy (VwTYDC) was expressed differently in blotched and non-blotched areas of pansy petals, suggesting that tyrosine may have a role in anthocyanin biosynthesis. In this study, we found that virus-induced gene silencing of VwTYDC caused an accumulation of pink pigmentation in pansy petals. Likewise, exogenous tyrosine treatment (TYRT) induced the formation of black stripes in non-blotched petal areas. Metabolome analysis indicated that the contents of two anthocyanins, cyanidin-3-O-glucoside and cyanidin-3-O-rutinoside, increased significantly in the TYRT areas. RT-qPCR results revealed that the anthocyanin-related genes VwHCT, VwC3′H, VwCHS, and VwUGT were upregulated in the same areas. Transcriptome analysis revealed that four genes involved in the abscisic acid (ABA) biosynthesis pathway (VwNCED, VwABA2, VwAAO3, and VwCYP707A) were significantly upregulated in the same TYRT areas. ABA contents were measured by ESI-HPLC-MS/MS, and ABA content was significantly higher in TYRT areas than in control areas. In addition, when exogenous ABA was spread onto non-blotched petal areas, anthocyanin biosynthesis genes were upregulated just as with tyrosine. Thus, transcriptome and metabolite analyses revealed a possible novel regulatory network for anthocyanin biosynthesis in which tyrosine induces ABA synthesis and ABA then promotes anthocyanin biosynthesis in pansy petals.
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