ABSTRACTSphingomonassp. strain Ndbn-20 degrades and utilizes the herbicide dicamba as its sole carbon and energy source. In the present study, a tetrahydrofolate (THF)-dependent dicamba methyltransferase gene,dmt, was cloned from the strain, and three other genes,metF,dhc, andpurU, which are involved in THF metabolism, were found to be located downstream ofdmt. A transcriptional study revealed that the four genes constituted one transcriptional unit that was constitutively transcribed. Lysates of cells grown with glucose or dicamba exhibited almost the same activities, which further suggested that thedmtgene is constitutively expressed in the strain. Dmt shared 46% and 45% identities with the methyltransferases DesA and LigM fromSphingomonas paucimobilisSYK-6, respectively. The purified Dmt catalyzed the transfer of methyl from dicamba to THF to form the herbicidally inactive metabolite 3,6-dichlorosalicylic acid (DCSA) and 5-methyl-THF. The activity of Dmt was inhibited by 5-methyl-THF but not by DCSA. The introduction of a codon-optimizeddmtgene intoArabidopsis thalianaenhanced resistance against dicamba. In conclusion, this study identified a THF-dependent dicamba methyltransferase, Dmt, with potential applications for the genetic engineering of dicamba-resistant crops.IMPORTANCEDicamba is a very important herbicide that is widely used to control more than 200 types of broadleaf weeds and is a suitable target herbicide for the engineering of herbicide-resistant transgenic crops. A study of the mechanism of dicamba metabolism by soil microorganisms will benefit studies of its dissipation, transformation, and migration in the environment. This study identified a THF-dependent methyltransferase, Dmt, capable of catalyzing dicamba demethylation inSphingomonassp. Ndbn-20, and a preliminary study of its enzymatic characteristics was performed. Introduction of a codon-optimizeddmtgene intoArabidopsis thalianaenhanced resistance against dicamba, suggesting that thedmtgene has potential applications for the genetic engineering of herbicide-resistant crops.
Genetic Engineering of the Biosynthesis of Glycinebetaine Enhances Photosynthesis against High Temperature Stress in Transgenic Tobacco Plants
