Abstract
Dinitrotoluene sulfonates (DNTSes) are highly toxic hazards regulated by the Resource Conservation and Recovery Act (RCRA) in the United States. The trinitrotoluene (TNT) red water formed during the TNT purification process consists mainly of DNTSes. Certain plants, including switchgrass, reed and alfalfa, can detoxify low concentrations of DNTS in TNT red water-contaminated soils. However, the precise mechanism by which these plants detoxify DNTS remains unknown. In order to aid in the development of phytoremediation resources with high DNTS removal rates, we identified and characterized 1-hydroxymethyl-2,4-dinitrobenzene sulfonic acid (HMDNBS) and its glycosylated product HMDNBS O-glucoside as the degradation products of 2,4-DNT-3-SO(3)Na, the major isoform of DNTS in TNT red water-contaminated soils, in switchgrass via LC-MS/MS- and NMR-based metabolite analyses. Transcriptomic analysis revealed that 15 UDP-glycosyltransferase genes were dramatically upregulated in switchgrass plants following 2,4-DNT-3-SO(3)Na treatment. We expressed, purified and assayed the activity of recombinant UGT proteins in vitro and identified PvUGT96C10 as the enzyme responsible for the glycosylation of HMDNBS in switchgrass. Overexpression of PvUGT96C10 in switchgrass significantly alleviated 2,4-DNT-3-SO(3)Na-induced plant growth inhibition. Notably, PvUGT96C10-overexpressing transgenic switchgrass plants removed 83.1% of 2,4-DNT-3-SO(3)Na in liquid medium after 28 days, representing a 3.2-fold higher removal rate than that of control plants. This work clarifies the DNTS detoxification mechanism in plants for the first time, suggesting that PvUGT96C10 is crucial for DNTS degradation. Our results indicate that PvUGT96C10-overexpressing plants may hold great potential for the phytoremediation of TNT red water-contaminated soils.