Impact of cluster thinning on transcriptional regulation of anthocyanin biosynthesis-related genes in ‘Summer Black’ grapes

• Effects of cluster thinning on berry anthocyanin concentration and biosynthesis were investigated.
• Expression level of most anthocyanin biosynthesis-related genes was up-regulated.
• Berry weight and titratable acidity showed no differences.
• Total soluble solid and anthocyanin content in berry skin significantly increased.

Cluster thinning is an agronomic practice that strongly affects anthocyanin biosynthesis in the skin of grape berries. However, the impact of cluster thinning on anthocyanin biosynthesis has not been fully elucidated at the molecular level. Here, we investigated its effects on the berry quality, the biosynthesis of anthocyanins, and the expression levels of related genes from the onset of véraison to harvest in ‘Summer Black’ grapes. It was observed that the total soluble solid and anthocyanin content in berry skin significantly increased under cluster thinning, whereas the berry weight and titratable acidity showed no differences from the beginning of véraison to harvest. The expression level of most anthocyanin biosynthesis-related genes was significantly up-regulated by cluster thinning from the beginning of véraison and was higher at its end compared to the control. Up-regulation of flavonoid 3′,5′-hydroxylase (F3′5′H) and O-methyltransferase (OMT) expression, and down-regulation of flavonoid 3′-hydroxylase (F3′H) expression were observed, which might be the cause of shift in the anthocyanin profile. These findings provide insights into the molecular basis of the relationship between cluster thinning and anthocyanin biosynthesis in the grape berry skin.