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 PpMYB10.2, PpMYB9, PpMYBPA1, Peace, PpMYB17, PpMYB18, PpMYB19, and PpMYB20, respectively, in peach flower transcriptome. PpMYB10.2 and PpMYB9 are able to activate transcription of anthocyanin biosynthetic genes, whilst PpMYBPA1 and Peace have a strong activation on the promoters of proanthocyanin (PA) biosynthetic genes. PpMYB17-20 show a strong repressive effect on transcription of flavonoid pathway genes such as dihydroflavonol 4-reductase. These results indicate that anthocyanin accumulation in peach flower is coordinately regulated by a set of R2R3-MYB genes. In addition, PpMYB9 and PpMYB10.2 are closely related but separated into two groups, designated MYB9 and MYB10, respectively. PpMYB9 shows a strong activation on the PpUGT78A2 promoter, but with no effect on the promoter of PpUGT78B (commonly called PpUFGT in previous studies). In contrast, PpMYB10.2 is able to activate the PpUFGT promoter, but not for the PpUGT78A2 promoter. Unlike the MYB10 gene that is universally present in plants, the MYB9 gene is lost in most dicot species. Therefore, the PpMYB9 gene represents a novel group of anthocyanin-related MYB activators, which may have diverged in function from the MYB10 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.
Highlights
Flower coloration is one of the most important traits in ornamental plants
Our study reveals a set of R2R3-MYBs involved in the regulation of anthocyanin accumulation in peach flower, which will be helpful for manipulating anthocyanin coloration in peach programs in the future
No pigmentation was observed for the infiltration of proPpUGT78A2::PpUGT78A2 alone (Figure 6C). These results indicated that heterologous expression of PpMYB9 and PpbHLH3 was able to induce anthocyanin accumulation via activating transcription of PpUGT78A2
Summary
Flower coloration is one of the most important traits in ornamental plants. Pigmentation in flowers is due to accumulation of various classes of pigments, such as anthocyanins, chlorophylls, carotenoids, and betalains (Tanaka et al, 2008). Anthocyanins are glycosylated forms of anthocyanidins catalyzed by glycosyltransferase in species-specific manner, with the sugar moiety predominantly attached at the 3-position on the C-ring or the 5-position on the A-ring (Caputi et al, 2012). More than 550 anthocyanins have been identified in nature, there are only six major types of anthocyanidins: pelargonidin, cyanidin, peonidin, delphinidin, petunidin, and malvidin (Kong et al, 2003). Glycosylation of anthocyanidins has a slight reddening effect (Tanaka et al, 2008). Understanding mechanism regulating anthocyanin biosynthesis is crucial for genetic manipulation of flower coloration in ornamental plants
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