THE CONTROL OF KIWIFRUIT RED FLESH COLOUR

Red-fleshed fruit occur in a few taxa of the genus Actinidia. In such taxa, anthocyanins can accumulate in different parts of the fruit including the skin, the whole pericarp or only the inner pericarp. Differences in the relative amounts of cyanidin- and delphinidin-based anthocyanins account for the different shades of red observed. Red-fleshed fruit of A. chinensis accumulate mainly cyanidin 3-Oxylo-galactoside and cyanidin 3-O-galactoside, which usually are restricted to the inner pericarp of the fruit, creating a characteristic and colourful pattern in mature fruit. In order to understand the process of anthocyanin synthesis in Actinidia fruit, we have studied the expression of the anthocyanin biosynthetic genes identified in our Actinidia EST database. Of the different genes of the pathway, only the expression of one glycosyltransferase (F3GT1), confirmed functionally to be cyanidin 3-O-galactosyltransferase, was strongly correlated with red pigmentation of the fruit. However, inheritance of the gene could not be associated with the segregation of the red phenotype of the fruit, suggesting that other factors are able to regulate the biosynthetic pathway. We show that the F3GT1 gene is regulated by a MYB-bHLH mechanism; allelic variation on these genes is likely to account for the expression of the different phenotype.