An AcMYB10-AcF3GT1/GST1 module restricts anthocyanin synthesis in the fruit flesh of kiwifruit

AcMYB10 promotes anthocyanin accumulation in kiwifruit flesh. Among these genes, the downstream AcF3GT1 and AcGST1 are the key genes that restrict anthocyanin synthesis. The specific accumulation of anthocyanin in organs and tissues is a phenomenon seen in various fruit species, which can drive consumer preferences and product novelty. Certain cultivated kiwifruit develop red flesh, typically localized to the inner pericarp. To elucidate the mechanisms underlying this specific accumulation, we identified and analyzed the genes encoding the enzymes of the anthocyanin biosynthesis pathway, focusing on specificity to the inner pericarp. Our findings revealed that six anthocyanin-related genes and transcription factors, which included the anthocyanin-related AcMYB10, were highly expressed in the inner pericarp. Dual-luciferase assays showed that AcMYB10 can regulate the promoters of these genes-AcCHI1, AcF3H2, AcF3'H3, AcANS4, AcF3GT1, and AcGST1-to activate their expression. Over-expression of AcMYB10 in kiwifruit callus promotes anthocyanin accumulation while significantly inducing the expression of these six anthocyanin-biosynthesis-related genes. However, RNA-seq results indicated that AcCHI1, AcF3H2, AcF3'H3, and AcANS4 had elevated basal expression both in green fruit outer pericarp and non-transgenic callus. In contrast, in non-pigmented tissues, expression of AcF3GT1 and AcGST1 remained extremely low. It, therefore, appears that expression levels of AcF3GT1 and AcGST1 are critical in limiting anthocyanin accumulation within kiwifruit tissues. Our study elucidates how the AcMYB10-AcF3GT1/AcGST1 module regulates tissue-specific anthocyanin accumulation in kiwifruit.