The interaction between ethylene and melatonin in the regulation of polyphenol metabolism and the underlying mechanism remain largely unclear. This work demonstrated that ethylene treatment increased melatonin biosynthesis by inducing the VvASMT expression in grape seeds. Ethylene-induced VvERF5 transactivated VvASMT via binding to the ethylene response element in its promoter. VvERF5 overexpression led to an increase in melatonin biosynthesis while its suppression generated the opposite results in grape seeds, calli, and/or Arabidopsis seeds. A melatonin-responsive element (MTRE) was identified, and melatonin-induced VvERF104 was found to bind to the MTRE of the VvMYB14 promoter and activate its expression. VvMYB14 overexpression widely modified the expression of genes in the phenylpropanoid pathway and phenolic compound content in grape seeds. DNA affinity purification sequencing revealed that the MEME-1 motif was the most likely binding sites of VvMYB14. VvPAL, VvC4H, and VvCHS were verified to be the target genes of VvMYB14. Additionally, the overexpression of VvERF5 or VvERF104 increased the expression of VvPAL, VvC4H, and VvCHS, as well as the levels of the corresponding metabolites. Moreover, the roles of VvERF5, VvASMT, and VvERF104 in mediating ethylene-induced changes in the phenylpropanoid pathway were elucidated using their suppressing seeds. Collectively, ethylene increased the VvMYB14 expression via the pathway of ERF5-melatonin-ERF104 and thereby modified the phenylpropanoid pathway.

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