The ripening wine grape berry skin transcriptome

Ripening of the grape berry immediately precedes harvesting and is the key phase which determines the composition of wine and table grapes. Although it is apparent that changes in gene expression levels play a role in initiating ripening, it is unknown to what extent gene expression levels differ between cultivars during ripening. We have undertaken a comparison of a selection of wine grape cultivars using a 9200 feature cDNA microarray to gauge the extent to which transcript levels differ between wine grape cultivars in the berry skin during ripening. Clones for microarray slide fabrication were sourced from a cDNA library constructed from mRNA derived from randomly sampled berries. The berries were collected at weekly intervals over four weeks of berry development including véraison. The microarray slides were hybridised with Cy3 and Cy5 labelled cDNA derived from the skin of ripening berries of the cultivars Cabernet Sauvignon, Pinot Noir, Shiraz, Chardonnay, Riesling, Sauvignon Blanc and Semillon. Only a small proportion of the genes within the berry skin showed a three-fold or greater difference in expression level after ripening commenced. Most of the differences appear to arise from environmental signals rather than genome differences.