Drawing links from transcriptome to metabolites: the evolution of Muscat aroma in the ripening berry

Owing to the role that aroma plays in the perceived quality of grapes and wines, there is a tremendous interest in understanding how the accumulation of sensory compounds is regulated at the molecular level. To this purpose, we applied an integrative functional genomics approach by simultaneously monitoring the abundance of transcripts and metabolites in ripening berries of Moscato Bianco (Vitis vinifera L.). Gas chromatography-mass spectrometry analysis of thirty-two out of the most important ‘impact’ compounds (monoterpenoids, C13-norisoprenoids, benzenoids and C6-aliphatic compounds) in their free and bound forms was combined with a large-scale transcriptome analysis based on the use of the AROS 1.0 oligonucleotide microarray (14,562 probes) at five developmental stages from pre-véraison to over-ripening. Several exploratory methods were tested for the integration of transcript and metabolite profiles with the final goal to identify genes or groups of genes which are linked with the accumulation of specific metabolites or groups of metabolites. Pair-wise metabolite-to-metabolite and gene-to-metabolite correlations were calculated. Various types of clustering were performed by incorporating both differentially expressed genes and metabolites. Finally, modulated transcripts were checked for their potential co-localization with previously identified QTLs controlling the level of aromatic compounds. This work is expected to provide insight into the regulatory network of grapevine secondary metabolism and is aimed at identifying genes relevant to aroma determination both at the regulatory and catalytic levels