The Role of Oxophytodienoate Reductases in the Detoxification of the Explosive 2,4,6-Trinitrotoluene by Arabidopsis

Abstract

The explosive 2,4,6-trinitrotoluene (TNT) is a significant environmental pollutant that is both toxic and recalcitrant to degradation. Phytoremediation is being increasingly proposed as a viable alternative to conventional remediation technologies to clean up explosives-contaminated sites. Despite the potential of this technology, relatively little is known about the innate enzymology of TNT detoxification in plants. To further elucidate this, we used microarray analysis to identify Arabidopsis (Arabidopsis thaliana) genes up-regulated by exposure to TNT and found that the expression of oxophytodienoate reductases (OPRs) increased in response to TNT. The OPRs share similarity with the Old Yellow Enzyme family, bacterial members of which have been shown to transform explosives. The three predominantly expressed forms, OPR1, OPR2, and OPR3, were recombinantly expressed and affinity purified. Subsequent biochemical characterization revealed that all three OPRs are able to transform TNT to yield nitro-reduced TNT derivatives, with OPR1 additionally producing the aromatic ring-reduced products hydride and dihydride Meisenheimer complexes. Arabidopsis plants overexpressing OPR1 removed TNT more quickly from liquid culture, produced increased levels of transformation products, and maintained higher fresh weight biomasses than wild-type plants. In contrast, OPR1,2 RNA interference lines removed less TNT, produced fewer transformation products, and had lower biomasses. When grown on solid medium, two of the three OPR1 lines and all of the OPR2-overexpressing lines exhibited significantly enhanced tolerance to TNT. These data suggest that, in concert with other detoxification mechanisms, OPRs play a physiological role in xenobiotic detoxification.

Detoxification without Intoxication: Herbicide Safeners Activate Plant Defense Gene Expression

“…Significantly, treatment of tobacco suspension cultures with B 1 -phytoprostanes protected the cells from subsequent exposure to copper sulfate (Loeffler et al, 2005), analogous to the safener response in protecting cereal crops from herbicide injury (Zhang et al, 2007). In accord with this hypothesis, it has been proposed in the literature that induction of detoxification genes appears to be most strongly stimulated by RES oxylipins (Mueller and Berger, 2009) and that this coordinated detoxification response in Arabidopsis resembles the sequential phase I, II, and III pathway for xenobiotic metabolism in plants (Kreuz et al, 1996;Ekman et al, 2003;Beynon et al, 2009). Collectively, these findings support the hypothesis that safeners may be tapping into a RES oxylipin-mediated signaling pathway, which subsequently induces the expression of proteins involved in a highly conserved detoxification pathway in plants (Table I; Fig.…”

A Wheat Allene Oxide Cyclase Gene Enhances Salinity Tolerance via Jasmonate Signaling

“…OPDA exists as four distinct isomers, namely cis-(+), cis-(-), trans(+), and trans(-); of these, cis-(+)-OPDA is predominant in most plants. OPR enzymes are present in two forms, OPRI and OPRII (Mueller, 1997;Beynon et al, 2009;Schaller and Stintzi, 2009). OPRII reduces cis-(+)-OPDA to form 3-oxo-2-(29-[Z]-pentenyl)cyclopentane-1-octanoic acid, which is finally oxidized to produce JA (Schaller et al, 1998).…”

Arabidopsis Glutathione Transferases U24 and U25 Exhibit a Range of Detoxification Activities with the Environmental Pollutant and Explosive, 2,4,6-Trinitrotoluene

“…First, TNT is transformed by nitroreductases to hydroxylamino dinitrotoluenes (HADNTs), with a varying portion further reduced to amino dinitrotoluenes (ADNTs). In Arabidopsis, oxophytodienoate reductases are known to catalyze these steps (Beynon et al, 2009). Plants engineered to express bacterial nitroreductases, which also perform this transformation step, have increased TNT transformation activity and show dramatically enhanced resistance to TNT (Hannink et al, 2001;Rylott et al, 2011a).…”