Effects of Abscisic Acid Treatment on Berry Coloration and Expression of Flavonoid Biosynthesis Genes in Grape

Abstract

In order to enhance berry coloration of bright-red grape cultivars, the effects of abscisic acid (ABA) treatment on the quantity and composition of anthocyanins as well as the expression of genes re-lated to flavonoid biosynthesis in the berry were examined. Exogenous ABA treatment increased anthocyanin content, especially petunidin-and malvidin-type anthocyanins. Quantitative real-time PCR analysis revealed that ABA treatment around véraison resulted in the upregulation of genes encoding enzymes responsible for both general flavonoid and anthocyanin biosynthesis. On the other hand, the gene expressions of enzymes involved in proanthocyanidin synthesis were drastically decreased at véraison and remained extremely low even with ABA treatment. Thus, in-creases in the total amount and composition ratios of petunidin-and malvidin-type anthocyanins were mainly caused by ABA-induced upregulation of uridine diphosphate glucose flavonoid glu-cosyl transferase, glutathione S-transferase 4, O-methyl transferase and flavonoid 3', 5' hydroxylase expression, resulting in the deep coloration of berry of skin.