The MdAP2-34 modulates flavonoid accumulation in apple (Malus domestica Borkh.) by regulating MdF3′H

Flavonoids are one of the main pigments in horticultural fruit. The AP2/ERF transcription factors play various roles in higher plants, and thus, MdAP2–34 has been reported to regulate carotenoid accumulation in apple. However, it is unclear whether light interferes with the flavonoid accumulation in apple fruit flesh. Here, we found that apple of ‘Benin Shogun’ fruit flesh had higher levels of flavonoids under light treatment than under dark treatment, with an increase of 48% at 15 days after harvest (DAH) and 39% at 30 DAH. The MdAP2–34 transcript levels exhibited a highly positive correlation with the flavonoid content of ‘Benin Shogun’ fruit under dark and light treatments. Furthermore, the structural genes of flavonol biosynthesis, including MdCHS, MdCHI, MdF3′H, and MdFLS, were positively associated with flavonoid contents of fruit and were upregulated in MdAP2–34-OVX apple calli. The MdAP2–34 stimulated flavonoid accumulation via the flavonoid biosynthetic pathway by directly binding to and activating the MdF3′H promoter activity. Our findings demonstrate the use of multiple MdAP2–34-mediated functions in understanding the complex mechanisms of flavonoid synthesis in apple, which may also be useful in apple breeding.