Heterologous expression of ZjOMT from Zoysia japonica in Escherichia coli confers aluminum resistance through melatonin production

Melatonin is a molecule that can enhance the resistance of plants to abiotic stress. It can alleviate the damage of heavy metal ions, and other chemical substances, changes in temperature and humidity, oxidative stress in higher plants, and enhance resistance of plants to abiotic stress. The transformation of N-Acetyl-5-hydroxy tryptamin into melatonin requires the involvement of methyltransferase. In this study, a methyltransferase gene ZjOMT has been cloned from Zoysia japonica. The gene was induced by aluminum (Al) stress in the leaves and roots of Zoysia japonica, and was up-regulated by 20.86- and 31.18-folds, respectively. The expression of ZjOMT in Escherichia coli increased the content of melatonin by about 8-fold in the recombinant strain compared with that of the empty vector strain. Al resistance test showed that the resistance of recombinant strain BL21-pET32-ZjOMT to Al was significantly higher than that of the empty vector strain BL21-pET32. The survival rate of the recombinant strain expressing ZjOMT was about 100-fold higher than that of the empty vector strain when treated with 0.35 mM Al. These findings suggest that the heterologous expression of ZjOMT improved the resistance of E. coli to Al by increasing the content of melatonin.