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Published:  23 July, 2008

By Jamie Goode

Scientists from Japan have uncovered the molecular basis of what makes some grapes red and others white, identifying the genetic mutation responsible for white-skinned grapes. It is thought that ancestral wild grape species were all dark-skinned and that white grapes arose by mutation, but the precise details were a mystery. Now a research group led by Shozo Kobayashi has discovered the gene mutation that is thought to underlie the emergence of white-grape skin colour. Black- or red-skinned grapes owe their colour to a group of red pigments known as anthocyanins. The synthesis of these pigments is controlled by a set of Myb-related genes. Kobayashi's group has shown that a sequence of DNA known as a retrotransposon, called Gret1, is responsible for turning off the expression of the MybA1 gene and thus switching off pigment production in white grapes. We hypothesise that Gret1 originally inserted upstream of one of the MybA1-coding sequences of a black-skinned ancestor, and that subsequently a white-skinned grape was produced by spontaneous crossing,' says Kobayashi. They also think that this was an ancient mutation, taking place before grapevines were first cultivated. Kobayashi's group has also shown that red pigmentation can be induced in the skins of white grapes by the insertion of a gene. It makes sense', says Professor Andrew Walker of UC Davis's Viticulture department, and backs up observations by breeders, geneticists and viticulturists with some varieties, particularly Pinot Noir and its colour morphs (Pinot Blanc and Pinot Gris).' These results also explain how a black grape, Cabernet Sauvignon, can have both a red grape (Cabernet Franc) and a white grape (Sauvignon Blanc) as its ancestors. This study was published in this week's edition of the leading scientific journal Science.