| Summary: | Anthocyanins are important pigments in peach fruit and are beneficial to human health. Sugars are both energy-storing and signaling molecules and their roles in inducing anthocyanin biosynthesis have received a great deal of research attention. However, the mechanism by which sugars induce anthocyanin biosynthesis in peach fruit is unknown. In order to understand this induction mechanism, comprehensive transcriptome and metabolome were performed in fruit flesh treated with four different sugars for 12 and 24 h, respectively. Here, we found that cyanidin-3-<i>O</i>-(6-<i>O</i>-p-coumaroyl) glucosides accumulated in fruit flesh treated with glucose, sucrose, sorbitol, and fructose in vitro. Two key structural genes of the anthocyanin biosynthesis pathway, namely, <i>PpDFR</i> and <i>PpUFGT</i>, were upregulated in the flesh of sugar-treated peach fruit. By contrast, the two main transcription factors (TFs) <i>PpMYB10.1</i> and <i>PpBL</i> regulating anthocyanin biosynthetic genes in peach fruit were not upregulated accordingly. Interestingly, two MYB family genes (<i>PpMYB6</i> and <i>PpMYB44-like)</i> and three bHLH family genes (<i>PpbHLH35</i>, <i>PpbHLH51</i>, and <i>PpbHLH36-like)</i> were upregulated. A dual luciferase assay revealed that PpMYB6 strongly activated the <i>PpUFGT</i> promoter when it was co-infiltrated with PpbHLH35, PpbHLH51, and PpbHLH36-like. When <i>PpMYB44-like</i> was co-infiltrated with <i>PpbHLH35</i>, it also potently activated the PpUFGT promoter. The results of this study help clarify the molecular mechanisms by which glucose, sucrose, sorbitol, and fructose regulate anthocyanin accumulation in peach fruit.
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