Ethylene Modulates the Phenylpropanoid Pathway by Enhancing VvMYB14 Expression via the ERF5-Melatonin-ERF104 Pathway in Grape Seeds

Ethylene plays a crucial role in regulating polyphenol metabolism, however the underlying mechanism remains largely unknown. This work demonstrated that ethylene release occurred earlier than melatonin during seed ripening. Ethylene treatment increased the VvASMT expression and melatonin content. VvERF5 was elucidated to bind to the ERE element in the VvASMT promoter. VvERF5 overexpression increased ASMT expression and melatonin content while its suppression generated the opposite results in grape seeds, calli and/or Arabidopsis seeds. Using the promoter of VvMYB14, which was strongly induced by melatonin, a melatonin responsive element (MTRE) was identified. VvERF104 was revealed not only to be strongly induced by melatonin but to bind to the MTRE of the VvMYB14. VvERF104 overexpression and suppression largely increased and decreased the MYB14 expression, respectively, in grape seeds, calli and/or Arabidopsis seeds. VvMYB14 overexpression widely modified the expression of genes in phenylpropanoid pathway and phenolic compound content in grape seeds. DAP-seq 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 roles of VvERF5, VvASMT and VvERF104 in mediating ethylene-induced changes in phenylpropanoid pathway were elucidated using their suppressing seeds. Collectively, ethylene increased the VvMYB14 expression via the pathway of ERF5-melatonin-ERF104 and thereby modified phenylpropanoid pathway.