PpMYB39 Activates PpDFR to Modulate Anthocyanin Biosynthesis during Peach Fruit Maturation

Anthocyanins are a class of water-soluble flavonoids widely present in fruits and vegetables responsible for the red flesh formation of peach fruit. Previously, several genes of the MYB family have been reported as transcriptional regulators of the anthocyanin biosynthetic pathway of structural genes in plants. In this study, through comparative transcriptome analysis of the white and red flesh peach cultivars of Harrow Blood and Asama Hakuto, a predicted transcription factor of the R2R3MYB family, PpMYB39, was identified to be associated with anthocyanin biosynthesis in peach fruit. In red-fleshed peach cultivars, the maximum amount of anthocyanin accumulated 95 days after full bloom (DAFB), at full maturity near ripening. Our results showed that, at this stage, PpMYB39 had the highest expression level among the 13 differentially expressed genes (DEGs) found in both red- and white-fleshed fruits, as well as a high correlation with total anthocyanin content throughout fruit development. Moreover, the expression analysis of the structural genes of the anthocyanin biosynthetic pathway in peach fruit revealed that Prunus persica Dihydroflavonol-4-reductase (PpDFR) was co-expressed and up-regulated with PpMYB39 at 95 DAFB, suggesting its possible role as a transcriptional activator of MYB39. This was further confirmed by a yeast one-hybrid assay and a dual luciferase reporter assay. Our results will be helpful in the breeding of peach cultivars and the identification and significance of color in peaches and related fruit species, in addition to providing an understanding of color formation in peach fruit for future research.