Monodehydroascorbate reductase mediates TNT toxicity in plants

Bioremediation from disabled self-destruction Explosives used in mining, construction, or military operations leave behind contaminated soils. Although bioremediation could help, plants do not thrive on these soils. Johnston et al. have now found out why (see the Perspective by Noctor). An enzyme found in plant mitochondria and chloroplasts spins out of control when given the explosive TNT, generating toxic reactive oxygen species and subverting biochemical pathways. With the key enzyme disabled, the plants are better at tolerating and accumulating TNT. These results point the way to future bioremediation and herbicide strategies. Science, this issue p. 1072; see also p. 1052 Reducing levels of an enzyme in plant mitochondria and plastids mitigates their sensitivity to explosive pollution toxicity. [Also see Perspective by Noctor] The explosive 2,4,6-trinitrotoluene (TNT) is a highly toxic and persistent environmental pollutant. Due to the scale of affected areas, one of the most cost-effective and environmentally friendly means of removing explosives pollution could be the use of plants. However, mechanisms of TNT phytotoxicity have been elusive. Here, we reveal that phytotoxicity is caused by reduction of TNT in the mitochondria, forming a nitro radical that reacts with atmospheric oxygen, generating reactive superoxide. The reaction is catalyzed by monodehydroascorbate reductase 6 (MDHAR6), with Arabidopsis deficient in MDHAR6 displaying enhanced TNT tolerance. This discovery will contribute toward the remediation of contaminated sites. Moreover, in an environment of increasing herbicide resistance, with a shortage in new herbicide classes, our findings reveal MDHAR6 as a valuable plant-specific target.