Transcriptome analysis along berry development of 'Syrah' x 'Pinot Noir' offspring extreme for flavonoid content

Anthocyanins and flavonols are natural compounds that accumulate preferentially in grapevine flowers and fruits. They are among the most abundant flavonoids and play a very important role in grape and wine quality. In particular, they confer and stabilize colour and contribute to other organoleptic characteristics of the final product. Their complex profile in terms of concentration and relative abundance varies among cultivars and makes wine typicity. The synthesis of these compounds is mainly regulated at transcriptional level. Flavonoids accumulate at specific stages and in specific tissues during flower and berry development, as a consequence of the timely expression of the genes necessary for their synthesis. Although the general flavonoid pathway has been genetically and biochemically elucidated and the main determinants of colour have been identified, the molecular reasons of the fine variation among grape cultivars are still not completely understood. To shed light on this issue, extreme genotypes of a segregating population derived from the cross Syrah x Pinot Noir were characterized at transcriptional level. The transcriptome analysis along three berry developmental stages of these genotypes has allowed the identification of a large set of transcripts differentially modulated between the two groups. A population derived from ‘Syrah’ x ‘Pinot Noir’ consisting of 170 F1 individuals plus the parental lines was characterized for the content of flavonols and anthocyanins in the skins of mature berries (38E-L; 18°Brix). Based on the biochemical data, two groups of 4 high- and 4 low-flavonol producers each (HFPs and LFPs: F1 16, F1 56, F1 63, F1 223 and F1 64, F1 256, F1 260, PN), three of which having also either very high or very low anthocyanin content (HAPs and LAPs: F1 16, F1 56, F1 63 and F1 256, F1 260, PN), were selected for gene expression analysis. A representative sample of 50 berry skins was collected from each of the eight F1 individuals at three berry developmental stages (hard green berry (33E-L, PV), veraison (35E-L, 50% coloured berries, VER) and maturity (38E-L, 18°Brix, MAT)) during the 2007 season.