Comparative Analysis of Pigment Biosynthesis Gene Expression Related to Enhanced Skin Color in ‘Mishima’ Apples during Fruit Development

In apple (Malus domestica), red coloration is an attractive trait for consumers. The color of fruit skin is determined by the distribution of carotenoids and anthocyanins in the skin tissue. ‘Fuji’ apples have red stripes over a yellow-green background, and ‘Mishima’, a ‘Fuji’ bud sport variety, has superior coloration compared to its parent. To investigate the genetic mechanism underlying the enhanced pigmentation in ‘Mishima’ fruit skin, we characterized the expression of pigment biosynthesis genes in ‘Fuji’ and ‘Mishima’ apples during fruit development. CIELAB data showed lower L* (relative lightness) and higher a*/b* ratio (relative redness) values in ‘Mishima’ apples, suggesting increased red pigmentation, which correlated with the levels of pigment biosynthesis gene expression. In ‘Mishima’, two carotenoid biosynthesis genes (MdZISO and MdLCY-ε) were upregulated at many stages of fruit development. Furthermore, enhanced red pigmentation was resulted from higher expression levels of three anthocyanin regulatory (MdMYB10, MdWD40, and MdGST) and three structural (MdCHS, MdCHI, and MdF3’H) genes, suggesting their positive interaction. These data further our understanding of the molecular basis of the enhanced skin color of ‘Fuji’ apple varieties. Additional key words: anthocyanin, bud sport, carotenoid, Malus domestica, skin coloration