Integrated analysis of metabolites and enzyme activities reveals the plasticity of central carbon metabolism in grape (Vitis vinifera cv. Cabernet Sauvignon) berries under carbon limitation

High temperatures increase the sugar concentration of grape (Vitis vinifera L.) berries, which can negatively affect the composition and quality of wine, and global climate change is expected to exacerbate this problem. Modifying the source-to-sink ratio of grapevines by selective pruning is a potential strategy to mitigate this. To investigate the effects of low source-to-sink ratio (retaining three leaves per cluster) on carbon metabolism of grape (cv. Cabernet Sauvignon) berries, we conducted an analysis of 42 metabolites and 21 enzyme activities at nine berry developmental stages，as well as transcriptomes from berries grown under two leaves per cluster. The results revealed that the metabolic pathways were coordinately regulated to maintain homeostasis under low source-to-sink ratio conditions. Because of a delay between metabolites and enzyme activities, the metabolites were loosely correlated with enzyme activities, and a lower density of connectivity between them appeared in low source-to-sink conditions. Otherwise, transcripts of the carbohydrate and amino acid metabolism pathways were enriched by carbon limitation. In summary, this integrated analysis reveals a coordinated regulation of various metabolic pathways that maintains the balance of carbon metabolism and ensures survival in challenging environments, highlighting the high metabolic plasticity of grape berries.