DIFFERENTIAL EXPRESSION OF GENES IN BERRIES OF CV. 'SANGIOVESE' (VITIS VINIFERA L.) DURING RIPENING FOLLOWING CLUSTER THINNING AT VÉRAISON

Abstract

Cluster thinning is considered a technique, which, through an increase in the source-sink ratio, could lead to improvements in grape berry sugar and anthocyanin concentration. In this research, agronomical, biochemical and molecular approaches were combined to understand the ripening mechanisms leading to a final berry composition in ?Sangiovese? vines submitted to thinning (CT, 50% of total clusters removed at veraison). The yield reduction in CT vines implied a significant increase in leaf area/crop weight ratio, which caused acceleration in berry ripening rate immediately after the treatment and higher values of soluble sugars at harvest compared to control vines (C). Anthocyanin accumulation was strongly and positively affected by the thinning and it increased in parallel with soluble sugar content, reaching higher values than C at harvest. Microarray analyses, carried out with a NimbleGen array assembled on the basis of the 12X Vitis vinifera genome sequence, allowed for discrimination between CT and C at the end of veraison (13.8% of 29,550 genes analyzed were differentially expressed between CT and C at this stage). Genes involved in carbohydrate metabolism and flavonoid accumulation were analyzed in more detail. As a result, the CT transcriptional profile was characterized by an increase in expression of putative sugar storage genes, which usually follow carbohydrate utilization as an energy source. The increase of source/sink ratio positively influenced anthocyanin structural and transcriptional regulatory genes and especially those involved in anthocyanin transport, which were strongly up-regulated in CT compared to C. The results of this research confirm the key role of the source/sink ratio in conditioning sugar metabolism and reveals that carbohydrate availability is a crucial issue in triggering the expression of genes involved in anthocyanin biosynthesis during ripening under field conditions.