The molecular cloning and functional characterization of MdMYC2, a bHLH transcription factor in apple.

The basic helix-loop-helix (bHLH) Leu zipper transcription factor MYC2 is an important regulator in the Jasmonic acid (JA) signaling pathway. In this study, the apple MdMYC2 gene was isolated and cloned on the basis of its homology with Arabidopsis thaliana MYC2. Quantitative real time PCR (qRT-PCR) analysis demonstrated that MdMYC2 transcripts were induced by Methyl Jasmonate (MeJA) treatment and wounding. The MdMYC2 protein interacted with itself and bound the G-Box motif of the AtJAZ3 gene. MdMYC2 interacted with the MdJAZ2 protein, which is a repressor protein in the JA signaling pathway. Furthermore, we obtained transgenic apple calli that either overexpressed or suppressed the MdMYC2 gene. Expression analysis with qRT-PCR demonstrated that the transcript levels of JA-regulated anthocyanin biosynthetic genes, such as MdDFR, MdUF3GT, MdF3H and MdCHS, were markedly up-regulated in the MdMYC2 overexpressing calli and down-regulated in the suppressing calli compared with the WT control. As a result, the overexpressing calli produced more anthocyanin, and the suppressing calli produced less. Finally, the MdMYC2 gene was ectopically expressed in Arabidopsis. Both phenotypic investigation and expression analysis demonstrated that the MdMYC2 transgenic Arabidopsis lines were more sensitive to MeJA than the WT control. Together, these results indicate that the apple MdMYC2 gene plays a vital role in the JA response.