A mutant tree with blushed coloring pattern in fruit skin was found and identified as a bud sport of Malus domestica Borkh. cultivar 'Ralls'. This study was aimed at elucidating the genetic basis of this pattern by a comparison of 'Ralls' (striped red) with this bud sport. These two varieties were grown either under normal sunlight (control group) or the fruits were bagged during development (bagged group) and the bags were removed 1 month before harvesting. Anthocyanin content increased during fruit ripening and was higher in the blushed sport than in 'Ralls', by 57% in the control group and by 73% in the bagged group after bag removal. Correspondingly, in both the varieties transcription of six anthocyanin biosynthetic genes was coordinately up-regulated, concomitant with an increase in levels of transcripts of the regulatory gene, MdMYB1, and in general these levels were higher in the blushed sport than in ''Ralls''. However, there were no significant differences between the two varieties in the nucleotide sequences of the genomic region or coding sequence of MdMYB1; nor in the sequences of cDNAs of the other known transcription factors MdbHLH3 and MdbHLH33. Interestingly, DNA methylation in the promoter region of MdMYB1 was inversely correlated with transcript levels of MdMYB1 and was significantly lower in the blushed sport. Thus, we conclude that DNA methylation plays a role in regulating MdMYB1 expression, which in turn regulates anthocyanin biosynthesis and thereby influences the color pattern of the apples.

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