Role of Methyl\nJasmonate on Flavonoid Pathway of UV-B-Irradiated\nApple Fruit

Methyl jasmonate (MeJA) is a growth regulator that is\ninvolved\nin plant defense and development. Studies have demonstrated its role\nin pigmentation, particularly in synergy with UV-B in plant tissues.\nHowever, its role in pigment metabolism remains incompletely understood.\nTo explore the metabolic synergistic effects, we evaluated pigments\nand gene expression in mature green apples. MeJA alone had no effect\non pigment accumulation, while UV-B increased flavonols up to S2 stage\nand anthocyanins up to S3 stage. With UV-B > 2 W m<sup>–2</sup>, MeJA doubled anthocyanin accumulation compared to UV-B alone but\nhad no synergistic effect on flavonols. MeJA selectively upregulated\nstructural genes and transcription factors involved in the late biosynthetic\npathway, transport, and the MYB-bHLH-WD40 complex, inducing anthocyanin\nhyperaccumulation without affecting early flavonoid biosynthetic genes\nor <i>MdFLS</i>, which controls flavonol biosynthesis. These\nresults suggest that MeJA relates to downstream gene expression in\nflavonoid biosynthesis with alternative regulation of the anthocyanin\npathway in UV-B-irradiated apples.