Glutathione S-Transferase Gene GST1 Metabolizing Penoxsulam and Conferring Penoxsulam Resistance in Echinochloa phyllopogon

Echinochloa phyllopogon, 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 S-transferases (GSTs) are important detoxification enzymes responsible for herbicide resistance in plants. Here, we identified and characterized two GST genes (EpGST1 and EpGSTU6) that showed higher expression levels in resistant than in susceptible E. phyllopogon populations. Nucleotide sequence alignment showed that EpGST1 was identical in both the sensitive and resistant populations without any mutations. The HPLC-MS/MS results showed that the in vitro recombinant GST1 protein had a stronger ability to metabolize the herbicide penoxsulam than the empty vector or EpGSTU6. Overexpression of EpGST1 in Arabidopsis 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 EPGST1, 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 EpGST1 is a nuclear gene. These results suggest that EpGST1 plays a significant role in the evolution of penoxsulam resistance by enhancing herbicide metabolism in E. phyllopogon.