Global Protein Profiling for Insight into Secondary Metabolite Synthesis in Muscadine Grape

Muscadine grapes (Vitis rotundifolia) which are native to southeastern USA are a rich source of polyphenols. These compounds have been implicated in disease tolerance as well as enological value of muscadine grape. However, little is known about their synthesis and deposition in maturing muscadine berry. To investigate phenolic compound biosynthesis and accumulation we have conducted a detailed proteome profiling study of maturing muscadine berry using iTRAQ labeling followed by LC/MS/MS analysis. The sequence annotation and GO term enrichment analysis by Blast2GO tool permitted analysis of various biological processes and metabolic pathways during berry development and ripening. The data showed that over 60 proteins involved in the synthesis of various secondary metabolites that are related to disease tolerance are differentially expressed during berry development and ripening.  Up-regulation of these proteins enabled synthesis of various secondary metabolites including those associated with disease tolerance and was found to occur mainly during early berry maturation and post-veraison suggesting that their expression is developmentally regulated and varies. The majority of proteins identified were found to be involved in terpenoid, flavonoid and anthocyanins biosynthesis. Further, the defense-related proteins identified were found to belong to PR10, PR-4, MLP and 14-3-3 protein family and were constitutively expressed during berry development indicating their role in enhancing disease tolerance of developing and ripening muscadine berry.  It should be noted that these proteins not only play an important role in disease tolerance but also affect berry composition and its enological value. Supported by the USDA/CBG grant.