Grafting with rootstocks promotes phenolic compound accumulation in grape berry skin during development based on integrative multi-omics analysis

In viticulture, grafting has been practiced widely and influences grape development as well as berry and wine quality. However, limited knowledge is present about the effects of rootstocks on grape phenolic compounds, which locate primarily in the berry skin and contribute to certain sensory attributes of wine. In this study, scion-rootstock interactions were investigated at green-berry stage and veraison stage when grapevines were hetero-grafted with three commonly used rootstock genotypes (5BB, 101-14MG, and SO4). The physiological investigations showed that hetero-grafts especially for CS/5BB presented higher concentrations of total proanthocyanidins (PAs) and various PA components in the berry skins when compared to the auto-grafted grapevines. Further metabolomics analysis identified 105 differentially accumulated flavonoid compounds, and the majority of them including anthocyanins, PAs and flavonols were significantly increased in the berry skins of hetero-grafted grapevines compared to the auto-grafted control. In addition, transcriptomic analysis using the same samples totally identified several thousand differentially expressed genes between hetero-grafted and auto-grafted vines. The three rootstocks not only increased the transcription levels of stilbene, anthocyanin, PA, and flavonol synthetic genes, but also affected the transcript abundance of a large number of transcription factors. Taken together, our results jointly supported that hetero-grafting could promote phenolic compound accumulation in the grape berry skin during development, which provide new insights for improving the application value of grafting by enhancing the accumulation of the nutritious phenolic components in the grape.