Glutathione <i>S</i>-Transferase Gene <i>GST1</i> Metabolizing Penoxsulam and Conferring Penoxsulam Resistance in <i>Echinochloa phyllopogon</i>

<i>Echinochloa phyllopogon</i>, a malignant weed found in paddy fields, has developed resistance to many acetolactate synthase-inhibiting herbicides. This resistance threatens the effectiveness and sustainability of herbicides. Glutathione <i>S</i>-transferases (GSTs) are important detoxification enzymes responsible for herbicide resistance in plants. Here, we identified and characterized two <i>GST</i> genes (<i>EpGST1</i> and <i>EpGSTU6</i>) that showed higher expression levels in resistant than in susceptible <i>E. phyllopogon</i> populations. Nucleotide sequence alignment showed that <i>EpGST1</i> was identical in both the sensitive and resistant populations without any mutations. The HPLC-MS/MS results showed that the <i>in vitro</i> recombinant GST1 protein had a stronger ability to metabolize the herbicide penoxsulam than the empty vector or <i>Ep</i>GSTU6. Overexpression of <i>EpGST1</i> in <i>Arabidopsis</i> and rice significantly enhanced penoxsulam resistance. Peroxidase, superoxide dismutase, and catalase activities in the resistant population were significantly enhanced after penoxsulam treatment, and the contents of MDA were significantly increased. Similarly, in rice overexpressing <i>EPGST1</i>, the activities of the antioxidant enzymes peroxidase, superoxide dismutase, and catalase were significantly enhanced, and the contents of H₂O₂ were significantly decreased. The results of the subcellular localization study indicated that <i>EpGST1</i> is a nuclear gene. These results suggest that <i>EpGST1</i> plays a significant role in the evolution of penoxsulam resistance by enhancing herbicide metabolism in <i>E. phyllopogon</i>.