Multiple R2R3-MYB Transcription Factors Involved in the Regulation of Anthocyanin Accumulation in Peach Flower

Abstract

Anthocyanin accumulation is responsible for flower coloration in peach. Here, we report the identification and functional characterization of eight flavonoid-related R2R3-MYB transcription factors, designated <i>PpMYB10.2, PpMYB9, PpMYBPA1, Peace, PpMYB17, PpMYB18, PpMYB19</i>, and <i>PpMYB20</i>, respectively, in peach flower transcriptome. <i>PpMYB10.2</i> and <i>PpMYB9</i> are able to activate transcription of anthocyanin biosynthetic genes, whilst <i>PpMYBPA1</i> and <i>Peace</i> have a strong activation on the promoters of proanthocyanin (PA) biosynthetic genes. <i>PpMYB17-20</i> show a strong repressive effect on transcription of flavonoid pathway genes such as <i>dihydroflavonol 4-reductase</i>. These results indicate that anthocyanin accumulation in peach flower is coordinately regulated by a set of R2R3-MYB genes. In addition, <i>PpMYB9</i> and <i>PpMYB10.2</i> are closely related but separated into two groups, designated MYB9 and MYB10, respectively. <i>PpMYB9</i> shows a strong activation on the <i>PpUGT78A2</i> promoter, but with no effect on the promoter of <i>PpUGT78B</i> (commonly called <i>PpUFGT</i> in previous studies). In contrast, <i>PpMYB10.2</i> is able to activate the <i>PpUFGT</i> promoter, but not for the <i>PpUGT78A2</i> promoter. Unlike the <i>MYB10</i> gene that is universally present in plants, the <i>MYB9</i> gene is lost in most dicot species. Therefore, the <i>PpMYB9</i> gene represents a novel group of anthocyanin-related MYB activators, which may have diverged in function from the <i>MYB10</i> genes. Our study will aid in understanding the complex mechanism regulating floral pigmentation in peach and functional divergence of the R2R3-MYB gene family in plants.