Last Word: Why We Have White Grape Varieties

I wrote a series of science heavy blogs about Why We Have White Grapes: VvmybA1 Gene Silencing, I wanted to write just one more blogpost about the topic. This really boggled my mind!
The first thing to know is that there is a family of transcription factors called Myb. Transcription factors decode the information contained in the nuclear DNA to produce a single strand of messenger RNA. In grapes, Myb-related genes such as VvmybA1 regulate anthocyanin biosynthesis by controlling expression of the gene for UFGT (UDP glucose-flavonoid 3-o-glucosyl transferase).¹

In fact, there are three alternate forms (alleles) of the VvmybA1 gene.

The VvmybA1a allele contains a retrotransposon, Gret1, upstream of the VvmybA1-coding sequences. Mutations caused by retrotransposon insertions in or near genes can alter gene expression or the structure of the encoded proteins.³ Since no VvmybA1 transcript was detected, the Gret1 insertion in VvmybA1a must block expression of the gene. In addition, the lack of berry color was due to homozygousity of the VvmybA1 containing the Gret1 retrotransposon insertion. In contrast, the alleles VvmybA1b and VvmybA1c were found to be functional.
Cocktail Party Conversation: If you ever find yourself at a cocktail party holding a glass of white wine and needing something to talk about, you might say something like this: "I love white wines. Isn't it cool to know that if it wasn't for a mutation in the gene encoding a transcription factor, we might only have had red wines in this world."
References:
1. Azuma, A., Kobayashi, S., Yakushiji, H., Yamada, M., Mitani, N., and Sato, A., "VvmybA1 genotype determines grape skin color", Vitis 46 (3), 154–155 (2007).
2. Yung-Fen Huang, Sandrine Vialet, Jean-Luc Guiraud, Laurent Torregrosa, Yves Bertrand,Veronique Cheynier, Patrice This and Nancy Terrier, A negative MYB regulator of proanthocyanidin accumulation, identified through expression quantitative locus mapping in the grape berry, New Phytologist, (2014) 201: 795–809 doi: 10.1111/nph.12557.
3. Lijavetzky et al., Molecular genetics of berry colour variation in table grape, 2006, Mol. Genet. Genomics, 2006: 427-435.