participates in melatonin-induced proanthocyanidin biosynthesis by upregulating expression of and in grape seeds.

This work demonstrated that melatonin increases continuously in seeds, particularly seed coats, during berry ripening. Exogenous melatonin treatments significantly increased the proanthocyanidin (PA) content, partially through ethylene signaling, in seed coats. expression exhibited patterns similar to melatonin accumulation over time, which was largely induced by melatonin treatment in seed coats during berry ripening. Additionally, VvMYB14 bound to the MBS element of the promoter to activate expression. overexpression largely upregulated expression of , and and increased the PA content in grape seed-derived calli. Similar increases in and expression and PA content were found in -overexpressing seeds. It was also observed that overexpression increased ethylene production and thereby induced expression of , which bound to the ERF element of the promoter and activated its expression. Additionally, suppression reduced the overexpression-induced increases in expression of and and PA content. Further experiments revealed that melatonin-induced increases in the expression of , , and and PA accumulation were significantly reduced in -suppressing grape calli and leaves. Collectively, VvMYB14 mediates melatonin-induced PA biosynthesis by directly transactivating expression and indirectly upregulating expression via VvERF104.