Why We Have White Grapes: VvmybA1 Gene Silencing

At the end of my blogpost Genes Involved in Anthocyanin Synthesis, I let the cat out of the bag:
       the Myb gene called VvmybA1 is likely the gene underlying the mapped        locus controlling berry colour in grapes.¹
Now we are really close to answering the question Why Do We Have White Grape Varieties?
In 2004, Kobayashi and his fellow researchers published a brief report in the journal Science that presented the results of experiments that they did. They took two white cultivars, Italia (It) and Muscat of Alexandria (Al) to create two red cultivars, Ruby Okuyama (Ru) and Flame Muscat (Fl) and looked at the genetic transcripts. Here is what they found:

They looked for the presence of the VvmybA1 gene. The results illustrated that the white cultivars in lanes 1-8 showed no expression of VvmybA1, whereas in lanes 9-15, the red cultivars showed expression of VvmybA1.
These experiments showed that the colour phenotype is due to the combined additive effect of the VvMybA gene and its alleles. They showed that a cluster of three MYB-type transcription factor genes, VvMybA1 and VvMybA2 were functionally involved in berry pigmentation. They also identified a third expressed gene, VvMybA3.
Long awaited for answer to why we have white grapes:
Kobayashi et al. discovered the existence of a retrotransposon insertion upstream of the VvmybA1, which they named Gret1 for grape retrotransposon 1, is responsible for the silencing of the first two functional genes creating the white grape!

References:
1. Kobayashi, S., Goto-Yamamoto, N., and Hirochika, H., Retrotransposon-induced mutations in grape skin color. Science, 304, 982 (2004).