Anthocyanin degradation and the underlying molecular mechanism in a red-fleshed grape variety

Red wine grape color and quality decrease substantially at the late stages of ripening in warm climates because of anthocyanin degradation; however, the underlying mechanism remains unclear. We analyzed the anthocyanin metabolite and transcriptome profiles of Yan73 grape berries from two vintages using HPLC-ESI-MS/MS and RNA-sequencing technologies. The results showed that anthocyanins in Yan73 grape skin and flesh were significantly degraded at the late stages of ripening in both vintages. Moreover, non-methylated anthocyanins were degraded at a higher rate than the methylated anthocyanins. The protocatechuic acid (i.e., possible anthocyanin degradation product) concentration increased significantly in Yan73 skin and flesh at the late stages of ripening. However, the expression of anthocyanin biosynthesis-related structural genes and MYBA1 was upregulated in Yan73 skin and flesh at the late stages of ripening, indicating an increase in the anthocyanin synthesis capacity. Enzyme activity and qRT-PCR assays revealed that peroxidase and polyphenol oxidase activities and the VvPrx31 expression level increased in Yan73 skin and flesh at the late stages of ripening, suggesting they may function in the anthocyanin degradation. The β-glucosidase activity was higher only in Yan73 grape flesh at the late stages of ripening. These findings clarify the pre-harvest anthocyanin degradation in grape berries.