Differential Protein Expression in Berry Skin from Red Grapes with Varying Hybrid Character.

Protein expression from the berry skin of four red grape biotypes with varying hybrid character was compared at a proteome-wide level to identify the metabolic pathways underlying divergent patterns of secondary metabolites. A bottom-up shotgun proteomics approach with label-free quantification and MaxQuant-assisted computational analysis was applied. Red grapes were from (i) purebred (Aglianico .); (ii) (local Sciascinoso .) grafted onto an American rootstock; (iii) interspecific hybrid ( × , Isabel), and (iv) uncharacterized grape genotype with hybrid lineage, producing relatively abundant anthocyanidin 3,5--diglucosides. Proteomics supported the differences between hybrids and purebred grapes, consistently with distinct phenotypic metabolite assets. Methanol -anthraniloyltransferase, which catalyses the synthesis of methyl anthranilate, primarily responsible for the "foxy" odour, was exclusive of the Isabel hybrid grape. Most of the proteins with different expression profiles converged into coordinated biosynthetic networks of primary metabolism, while many possible enzymes of secondary metabolism pathways, including 5-glucosyltransferases expected for hybrid grapes, remained unassigned due to incomplete protein annotation for the genus. Minor differences of protein expression distinguished scion grafted onto American rootstocks from purebred skin grapes, supporting a slight influence of the rootstock on the grape metabolism.