Expression and functional analysis of a novel MYB gene, MdMYB110a_JP, responsible for red flesh, not skin color in apple fruit

Abstract

We have succeeded in isolating an MdMYB110a_JP gene responsible for a red-fleshed trait from a fruit of apple cultivar 'JPP35' ('Jonathan'×'Pink Pearl'). The isolated MdMYB110a_JP gene was located on chromosome (ch.) 17, which was different from the location of known MdMYB1/10 gene of ch.9, and 'JPP35' and 'Pink Pearl' did not contain the known R 6 :MdMYB10 allele responsible for the red-skin and red-fleshed trait. The MdMYB110a_JP was expressed strongly and weakly in the cortex and core of 'JPP35' fruit, respectively, at the time of coloring start in flesh, and also weakly in flower buds. Following the MdMYB110a_JP expression, the expression of the genes, MdCHS and MdLDOX, that encode the enzymes of the flavonoid pathway, was induced in flesh of 'JPP35' in accordance with anthocyanin accumulation. In contrast, the MdMYB110a_JP gene was not expressed in any tissues in red-skin and white-fleshed 'Fuji', and in red-skin and red-fleshed 'Maypole'. Instead, MdMYB1-1 allele responsible for red-skin trait was expressed in red-skin of 'Fuji' and 'JPP35', and R 6 :MdMYB10 allele responsible for red-skin and red-flesh trait was expressed in red-core and red-cortex in 'Maypole' as expected. Moreover, 35S:MdMYB110a_JP transgenic apple 'JM2' showed a red-foliage phenotype depending on the MdMYB110a_JP expression level. From the results, it was strongly suggested that the red-fleshed phenotype of 'JPP35' fruit was caused by up-regulation of the genes of anthocyanin pathway induced by the MdMYB110a_JP gene.