Red, White and Grape: From Jumping Genes to Wrapping Leaves
Red or White? Even King Tutankhamun (1332-1322 B.C.) prudently stashed away amphorae of both red and white wines to enjoy in the afterlife. Biochemically, a single class of pigments found in grape skin, the anthocyanins, separates the red from white. White grapes arose from their wild, dark berried ancestors by not one, but two rare and independent genetic events: either one alone would not have given us the white grape. In fact, all ~3000 white cultivars today carry these same gene disruptions, pointing back to a common ancestor that arose millennia ago. The disrupted genes code for transcription factors, aka master regulators of biochemical pathways that can turn other genes on or off.
Science sleuths have peeked back into the gene history of Vitis vinifera to figure this out.
First, the MybA gene duplicated, giving two side-by-side copies, both active in making anthocyanins and red berries. Somewhere along the way, one of them, the MybA2 gene accumulated two mutations (depicted as stars) that rendered the resulting protein non-functional.
Independently, a “jumping gene” or retrotransposon, (green triangle) landed within the adjacent backup gene MybA1, knocking it out as well. The resulting plant, termed heterozygous, still bore red berries, because the unmutated genes on the other chromosome were active. Eventually, two heterozygous plants bred together and some offspring received both chromosomes with two nonfunctional MybA genes.
Voila, white grapes!
If you’ve ever snacked on delicious dolmas, then you know that the goodness of the grape vine goes beyond berries. Legend has it that the gods of Mount Olympus feasted on the tender leaves of the grape wrapped around morsels of rice or meat, alongside ambrosia and nectar! Although stuffed grape leaves are common around the Mediterranean, Greeks claim that dolmades were co-opted by the army of Alexander the Great to parcel out limited rations of meat during the seige of Thebes. Luckily, you only need to lay seige on your local Middle Eastern grocery store to find jarred leaves, preserved in brine. Unfurl them gently and give them a good wash to get started. It doesn’t hurt to have a glass of your favorite vintage, red or white, on hand before embarking on this project!
For the recipe on stuffed rice dolmas, visit my blog at: https://madamescientist.wordpress.com/2016/02/20/red-white-and-grape-from-jumping-genes-to-wrapping-leaves-for-dolma/
REF:White grapes arose through the mutation of two similar and adjacent regulatory genes. Walker et al., 2007 http://www.ncbi.nlm.nih.gov/pubmed/17316172