Varietal differences in phenolic compounds metabolism of type 2 red-fleshed apples

- Flesh color correlates with the phytochemical content in type 2 red-fleshed apples.
- MdC3H and MdLAR shows a similar expression pattern as MdMYB110a.
- A dCAPS marker for a functional MdMYB110a allele is developed.

Apples are rich source of phenolic compounds exhibiting a strong antioxidant activity. Although type 2 red-fleshed apples highly accumulate health-promoting anthocyanins, accumulation profiles of other phenolic compounds had not been investigated. The objective of this study was to characterize the accumulation profiles of eight phenolic compounds in five type 2 red-fleshed apple varieties with different color intensities in their cortex. Quantification of the phenolic compounds revealed that not only cyanidin-3-galactoside but also chlorogenic acid and epicatechin are the dominant phenolic compounds in type 2 red-fleshed cultivars except for a red flesh lineage showing a white cortex. Bioinformatic analysis further revealed that cultivars with a deep red flesh accumulated caffeic acid and procyanidin B2, but cultivars with a pale-red flesh accumulated catechin and epicatechin. In pale-red flesh cultivars, the correlation between the expression of MdMYB110a gene responsible for the type 2 red flesh phenotype and the two phenylpropanoid pathway genes MdC3H and MdLAR were also observed during the fruit development. Taken together, these results indicate that there is a significant variation in the contents of phenolic compounds between type 2 red-fleshed cultivars and suggest the possibility that biosynthesis of some phenolic compounds other than anthocyanins is also regulated through MdMYB110a. In addition, for selecting type 2 red-fleshed cultivars efficiently, we also reported the development of a dCAPS marker which can detect functional MdMYB110a allele accurately.