Identification and characterization of MYC transcription factors in Taxus sp.

Myelocytomatosis (MYC) transcription factors (TFs) are key regulators of the jasmonic acid (JA) signaling pathway. In cell cultures, methyl jasmonate (MeJA) can improve the production of taxol, which is a complex terpenoid compound with an intense antitumor activity. However, the functions of MYC genes in Taxus sp. (yew trees) remain poorly known. Based on Taxus sp. transcriptome changes induced by MeJA, a TcMYC gene was isolated in a previous study. Here, we further characterized the TcMYC TF encoded by that gene and four other yew MYC TFs previously obtained. Three yew MYC TFs had the typical basic helix-loop-helix (bHLH)-MYC_N region, but the other two MYC did not, although all five presented the bHLH domain. TcMYC was localized to the nuclei, and phylogenetic analysis indicated that the yew MYC TFs were closely related to Arabidopsis thaliana MYC1/2 and maize R protein. The yeast one-hybrid assay showed that TcMYC binds the G-box of the promoter of taxane 5α-hydroxylase. Transcript levels of TcMYC revealed that TcMYC was highly expressed in xylem and leaves, and up-regulated by drought and high-salinity stresses. Coronatine (COR) has recently been used as a new elicitor to improve the production of taxol in cell cultures; TcMYC was strongly expressed at 2 and 4 h after COR treatment, but decreased at 12 and 24 h. Overall, the results obtained here provide new insights into the potential regulatory roles of MYC TFs on taxol biosynthesis in yew trees.