Glutathione S ‐transferase genes Pf GSTU6 and Pf GSTL1 involved in mesosulfuron‐methyl resistance in Polypogon fugax

BACKGROUND: Polypogon fugax is a major weed in wheat and winter canola fields in China. Two populations, SD-4 and JS-13, showing resistance to the ALS inhibitor mesosulfuron-methyl, were collected from winter wheat fields. This study aimed to characterize their resistance level and cross-resistance profile, investigate the resistance mechanism and identify its functional genes. RESULTS: Dose-response assays showed that SD-4 and JS-13 have high-level resistance to mesosulfuron-methyl (15.9-and 16.4-fold, respectively) and cross-resistance to the ACCase inhibitors clodinafop-propargyl, fenoxaprop-P-ethyl, quizalofop-p-ethyl, and the PDS inhibitor diflufenican. Sequencing of the ALS gene revealed no known target-site mutations within the eight conserved resistance-associated regions. Pre-treatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion or the glutathione S-transferase (GST) inhibitor NBD-Cl increased herbicide sensitivity in resistant plants. The resistant plants showed higher inducible GST activity. Herbicide residues analysis observed that resistant plants exhibiting increased mesosulfuron-methyl metabolism, and the enhanced metabolism could be reduced by both inhibitors. Integrated transcriptomic and qRT-PCR analysis identified 17 stably upregulated genes, including PfGSTU6 and PfGSTL1. Escherichia coli and rice callus overexpressing PfGSTU6 and PfGSTL1 exhibit significantly enhanced herbicide tolerance to mesosulfuron-methyl, and molecular docking analysis confirmed the strong binding affinity of GST proteins to the target herbicide. CONCLUSIONS: The P450s and GSTs mediated herbicide metabolism confer mesosulfuron-methyl resistance in P. fugax. This study elucidates the resistance mechanism and provides genetic resources for resistance monitoring and crop breeding. In addition, we characterized the cross-resistance profile of the resistant P. fugax population, which provides guidance for developing targeted field weed resistance management strategies. © 2026 Society of Chemical Industry.