Coexpression of Methyltransferase Gene dmt50 and Methylene Tetrahydrofolate Reductase Gene Increases Arabidopsis thaliana Dicamba Resistance.

Dicamba， a broad-spectrum and highly efficient herbicide， is an excellent target herbicide for the engineering of herbicide-resistant crops. In this study， a new tetrahydrofolate (THF)-dependent dicamba methyltransferase gene， dmt50， was cloned from the dicamba-degrading strain Rhizorhabdus dicambivorans Ndbn-20. Dmt50 catalyzed the methyl transfer from dicamba to THF， generating the herbicidally inactive product 3，6-dichlorosalicylic acid (3，6-DCSA) and 5-methyl-THF. A dmt50 transgenic Arabidopsis thaliana clearly showed dicamba resistance (560 g/ha， the normal field application rate). However， Dmt50 demethylation activity was inhibited by the product 5-methyl-THF. Mthfr66， encoded by the 5，10-methylene-THF reductase gene mthfr66 could relieve the inhibition by removing 5-methyl-THF in vitro. Compared with expression of dmt50 alone， simultaneous expression of dmt50 and mthfr66 further improved the dicamba resistance (1120 g/ha) of transgenic A. thaliana. This study provides new genes for dicamba detoxification and a strategy for the engineering of dicamba-resistant crops.