An ancient duplication of apple MYB transcription factors is responsible for novel red fruit-flesh phenotypes

Anthocyanin accumulation is coordinated in plants by a number of conserved transcription factors. In apple (Malus x domestica, Borkh.) a R2R3 MYB transcription factor has been shown to control fruit flesh and foliage anthocyanin pigmentation (MYB10), and fruit skin colour (MYB1). However, the pattern of expression and allelic variation at these loci does not explain all anthocyanin-related apple phenotypes. One such example is an open-pollinated seedling of ‘Sangrado’ that has green foliage and develops red flesh in the fruit cortex late in maturity. We used methods that combine plant breeding, molecular biology and genomics to identify duplicated MYB transcription factors that could control this phenotype. We then demonstrated that the red flesh cortex phenotype is associated with enhanced expression of MYB110a, a paralogue of MYB10. Functional characterisation of MYB110a showed that it was able to up-regulate anthocyanin biosynthesis in tobacco. The chromosomal location of MYB110a is consistent with a whole genome duplication event that occurred during evolution of apple within the Maloideae family. Both MYB10 and MYB110a have conserved function in some cultivars but they differ in their expression pattern and response to fruit maturity