A Calcium/Calmodulin–Binding UDP-Glycosyltransferase Is Required for Anthocyanin Biosynthesis in Strawberry Fruit

Strawberry is an economically important horticultural crop.  Strawberry fruit contain high levels of antioxidants such as anthocyanins and flavonoids. These antioxidants are beneficial for human health. However, the accumulation of these phenolic compounds in plant cells depends on biochemical modification, most commonly glycosylation. UDP-glycosyltransferases (UGTs) catalyze the transfer of sugar moieties to a wide range of acceptor molecules, including anthocyanins and flavonoids. UGT-mediated glycosylation can increase solubility and accumulation and regulate bioactivity of these compounds. We have identified a gene encoding a calcium-regulated UGT, FvCUGT1, in the diploid strawberry Fragaria vesca var. Ruegen. Calcium/calmodulin specifically binds to the recombinant FvCUGT1 protein. RT-qPCR analysis indicated that FvCUGT1 is a fruit specific gene in ‘Ruegen’ and also in the commercial octoploid strawberry. Expression of the gene is developmentally regulated; the FvCUGT1 transcript level is low in green fruit, peaks at the white stage, and remains high through to the red stage. The gene expression levels are correlated with the accumulation of anthocynanins in fruits.  Nearly no FvCUGT1 expression is detected in F. vesca var. YW5AF7, which bears yellow fruit and contains only about 4% of pelargonidin 3-O-glucoside as compared to ‘Ruegen’ in ripe fruit. These results indicate that calcium/calmodulin-binding FvCUGT1 is an important regulator of anthocyanin biosynthesis and accumulation in strawberry fruit.