Grapevine fanleaf virus affects grape (Vitis vinifera) berry anthocyanin content via the transcriptional regulation of anthocyanin biosynthetic genes.

Grapevine fanleaf virus (GFLV) causes grapevine fanleaf degeneration, one of the oldest known viral diseases of grapevines. The virus has been found in all winegrowing regions around the world. In the seasons 2011-12 a comparison between field grown GFLV-infected and healthy grapevines was conducted for the cultivars Schioppettino in North-Eastern Italy and Refošk in South-Western Slovenia. Our research showed that GFLV infection caused a drop of the yield due to reduction of both cluster weight and berry weight. Besides the yield, the berry composition was also affected; in detail, anthocyanin concentration increased in both varieties but significantly only in the case of Schioppettino. Upregulation of the F3'5'H gene and downregulation of F3'H gene in the berries of GFLV infected vines compared with the ones of healthy control vines resulted in modified proportions between di- and tri- hydroxylated or methylated derivatives of anthocyanins. The F3H1 gene was identified to be the most strongly regulated gene of the flavonoid biosynthetic pathway by GFLV infection, indicating its important role in increasing anthocyanin concentration in grapes of GFLV infected vines as compared with healthy controls.