A natural glutathione S-transferase gene GSTU23 confers metabolic resistance to metamifop in Echinochloa crus-galli

Herbicides are essential for farmers to control weed. However, prolonged use of herbicides has caused the development of herbicide resistance in weeds. Here, the resistant Echinochloa crus-galli (RL5) was obtained by continuous treatment with metamifop for five generations in paddy fields. RL5 plants showed a 13.7-fold higher resistance to metamifop compared to susceptible E. crus-galli (SL5) plants. Pre-treatment with GST inhibitor (NBD-Cl) significantly increased the susceptibility of RL5 plants to metamifop. Faster metamifop metabolism and higher GST activity in RL5 plants than in SL5 plants were also confirmed, highlighting the role of GST in metabolic resistance. RNA-Seq analysis identified EcGSTU23 as a candidate gene, and this gene was up-regulated in RL5 and field-resistant E. crus-galli plants. Furthermore, the EcGSTU23 gene was overexpressed in the transgenic EcGSTU23-Maize, and the EcGSTU23-Maize showed resistance to metamifop. In vitro metabolic studies also revealed that the purified EcGSTU23 displayed catalytic activity in glutathione (GSH) conjugation, and metamifop was rapidly metabolized in the co-incubation system containing EcGSTU23 protein. These results provide direct experimental evidence of EcGSTU23's involvement in the metabolic resistance of E. crus-galli to metamifop. Understanding the resistance mechanism can help in devising effective strategies to combat herbicide resistance and breeding of genetically modified herbicide resistant crops.