Retrotransposon-Induced Mutations in Grape Skin Color

Abstract

The color of grape skins is determined by the accumulation of red plant pigments called anthocyanins. White cultivars of grape are thought to have arisen from dif-ferent red cultivars by independent muta-tions (1), but the molecular bases of these color mutations are unknown. Myb-related genes (such as VlmybA1-1, VlmybA1-2, and VlmybA2) regulate anthocyanin biosynthe-sis in Kyoho, a black-skinned cultivar of Vitis labruscana (2). We show that a retrotransposon-induced mutation in VvmybA1, a homolog of VlmybA1-1, is associated with the loss of pigmentation in white cultivars of V. vinifera. Two red-skinned cultivars of V. vinif-era, Ruby Okuyama (Ru) and Flame Mus-cat (Fl), are derived by bud mutation from the white-skinned cultivars Italia (It) and Muscat of Alexandria (Al), respectively. Using VlmybA1-1 from Kyoho as a probe, we detected two transcripts in white-skinned cultivars and three in the red-skinned sports. Sequencing identified transcripts VvmybA2 (DNA Data Bank of Japan accession no. AB097924) and VvmybA3 (AB097925) in all four cultivars and VvmybA1 (AB097923) in the red cul-tivars (Fig. 1A). In the other cultivars examined, VvmybA1 transcript was also detected only in the colored ones (Fig.1B). VvmybA1 cDNA induced red pigmentation when introduced into the skin tissues of white grapes (3). Genomic clones for VvmybA1 indicated that VvmybA1 is homozygous (VvmybA1a, AB111100) in It, but heterozygous in Ru