Tyrosine promotes anthocyanin biosynthesis in pansy (<i>Viola × wittrockiana</i>) by inducing ABA synthesis

Abstract

<italic>Viola × wittrockiana</italic> (pansy) is an important ornamental plant, particularly during winter and spring. In previous studies, we found that the tyrosine decarboxylase gene of pansy (<italic>VwTYDC</italic>) 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 <italic>VwTYDC</italic> 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 <italic>VwHCT</italic>, <italic>VwC3′H</italic>, <italic>VwCHS</italic>, and <italic>VwUGT</italic> were upregulated in the same areas. Transcriptome analysis revealed that four genes involved in the abscisic acid (ABA) biosynthesis pathway (<italic>VwNCED</italic>, <italic>VwABA2</italic>, <italic>VwAAO3</italic>, and <italic>VwCYP707A</italic>) 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.