Expression Profiling of Several Gene Families Involved in Anthocyanin Biosynthesis in Apple (Malus domestica Borkh.) Skin During Fruit Development

Abstract

Anthocyanins are secondary metabolites in higher plants that contribute to the colors of flowers and fruits. MYB, bHLH, and UFGT genes are key genes in fruit anthocyanin synthesis. We identified two MYB1 genes, two bHLH3 genes, three bHLH33 genes, and four UFGT genes in the apple (Malus domestica Borkh.) genome and analyzed the expression of these genes in apple skin at the fruitlet stage and ripening fruit stage, two peaks of anthocyanin accumulation in apple skin. Results showed that the two MYB genes, one bHLH3 gene, one bHLH33 gene, and two UFGT genes were involved in anthocyanin synthesis. MdbHLH3-1 and MdbHLH33-1 transcript levels were correlated with anthocyanin accumulation in the four cultivars during fruit development. However, there was variation in MdMYBs and MdUFGTs expression patterns at different fruit development stages among cultivars. Transcript levels of MdMYB1a and MdUFGT2-1 were higher in the red skin of young fruit, whereas transcript levels of MdMYB1, MdUFGT2-1, and MdUFGT4 were higher in the red skin of ripening fruit. Besides, MdUFGT4 was only expressed in fruit skin of red cultivars, indicating that MdUFGT4 was important for anthocyanin synthesis in red skin cultivars. Furthermore, all these genes transcripts were induced by light. Our results indicated that MdMYB1a, MdMYB1, MdbHLH3-1, MdbHLH33-1, MdUFGT2-1, and MdUFGT4 were involved in apple skin anthocyanin synthesis, but they may function in different roles at different fruit development stages in different cultivars.