Rare Double Mutation Led to White Wine

March 1, 2007 — The white grapes used to make wines like chardonnay, riesling and sauvignon blanc evolved because of a lucky genetic coincidence more than 3,000 years ago, Australian scientists have found.

Mandy Walker from CSIRO Plant Industry in Adelaide and her colleagues studied the genetics of Vitis vinifera, the grapevine species used to produce almost all the white and red wine varieties sold today.

In part, they wanted to understand how the white grape varieties of the species first evolved, Walker said. Scientists know white grapes arose as a variant of red grapes at some point in history, but not exactly how.

The new research, published in the latest issue of the Plant Journal, helps answer this question.

Specifically, Walker and her team showed that the color of grape skins is controlled by two genes, VvMYBA1 and VvMYBA2. They found that either gene can regulate the color by switching on production of a molecule called anthocyanin, which turns grape skin red. In white grapes, both the genes are mutated, meaning both ways for producing a red color are switched off.

"This was a lucky coincidence for all the white wine drinkers around the world," Walker said. "Mutations in single genes happen at a fairly low frequency, but the grapes had to have mutations in two genes to turn from red to white and that's just very, very rare."

When Did All This Happen?

Exactly when and where the switch might have happened isn't clear, Walker said.

"It most likely occurred before the time of Tutankhamen," she said.

White wine residue was found in flasks within the ancient Egyptian king's tomb, she explains. The researchers studied more than 55 different strains of white grape and showed that all of them contained both mutations.

"We took grapes from as many different regions of the world as possible, and the changes were all the same," she said.

This evidence suggests that all the white grape varieties have a single genetic ancestor.

"Perhaps someone walked out into a vineyard one day and saw these white grapes and wondered whether they'd make good wine," she said.

For modern winemakers, the new genetic information could prove useful as a tool for breeding new grape varieties with specific color characteristics, Walker said.