Increasing the source/sink ratio in Vitis vinifera (cv Sangiovese) induces extensive transcriptome reprogramming and modifies berry ripening.

Background: Cluster thinning is an agronomic practice in which a proportion of berry clusters areremoved from the vine to increase the source/sink ratio and improve the quality of the remainingberries. Until now no transcriptomic data have been reported describing the mechanisms thatunderlie the agronomic and biochemical effects of thinning.Results: We profiled the transcriptome of Vitis vinifera cv. Sangiovese berries before and afterthinning at veraison using a genome-wide microarray representing all grapevine genes listed in thelatest V1 gene prediction. Thinning increased the source/sink ratio from 0.6 to 1.2 m2 leaf area perkg of berries and boosted the sugar and anthocyanin content at harvest. Extensive transcriptomeremodeling was observed in thinned vines 2 weeks after thinning and at ripening. This included theenhanced modulation of genes that are normally regulated during berry development and theinduction of a large set of genes that are not usually expressed.Conclusion: Cluster thinning has a profound effect on several important cellular processes andmetabolic pathways including carbohydrate metabolism and the synthesis and transport ofsecondary products. The integrated agronomic, biochemical and transcriptomic data revealed thatthe positive impact of cluster thinning on final berry composition reflects a much more complexoutcome than simply enhancing the normal ripening process.