Isolation and characterization of three DREB/ERF-type transcription factors from melon ( Cucumis melo)

A melon 1-aminocyclopropane-1-carboxylate synthase (CMe-ACS2) is a key enzyme in the ethylene biosynthesis pathway in melon, but mechanisms regulating CMe-ACS2 expression remain to be clarified. We characterized three melon AP2/ERF transcription factors (CMe-DREB1, CMe-ERF1 and CMe-ERF2), which were isolated by a yeast one-hybrid screening method using a GCCGAC sequence (DRE/CRT cis-acting element) in the CMe-ACS2 promoter. We demonstrated that CMe-DREB1 strongly bound to the GCCGAC sequence, but CMe-ERF1 and CMe-ERF2 did not. Transient expression analysis showed that only CMe-DREB1 could activate the transcription of the downstream reporter gene through the GCCGAC sequence in melon leaf cells. The expression levels of CMe-ACS2 and CMe-DREB1 in melon leaves were increased by methyl jasmonate (MeJA) treatment. These results suggest that CMe-DREB1 functions as a transcriptional activator of CMe-ACS2 in the presence of jasmonate.