Grape berry development is a dynamic process exhibiting a double sigmoid curve separated by a lag phase, characterized by coordinated biosynthesis of primary and secondary metabolites. Anthocyanins are the responsible of berry skin coloration and its regulation has been widely studied. However, few studies have focused on metabolic and genetic characterization using varieties with contrasted color berry skin. Using RNA-seq technology and metabolic analysis, we performed a new comparative characterization of two table grapes, Chimenti Globe (CG) and Red Globe (RG): CG has a bright light red color and RG has a dark purple color. The originality of this model is that CG was generated from a spontaneous event in field from a branch in a vine of RG plant. Thus, the genetic background responsible for the color change is practically the same.
Berry metabolic content analysis showed differences between CG and RG, mainly related to anthocyanin biosynthesis pathway: CG only contained dihydroxylated anthocyanins, and not the trihydroxylated ones. From transcriptomic analysis, we generated a heatmap with 109 genes differentially expressed in CG in comparison to RG. In addition, 11 gene copies of F3’5’-H, a key enzyme for biosynthesis of trihydroxylated anthocyanins, were not induced in CG. From this analysis, we selected a candidate gene, Cytochrome b5, which overexpression in grapevine embryos strongly suggested its participation in the flavonoid pathway, since transgenic embryos exhibited reddish color compared to control.
With these results, we were able to provide new insights in anthocyanins regulation in grapevines responsible for berry skin coloration.