TSR and peroxidase genes confer resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl in Alopecurus aequalis

Alopecurus aequalis poses severe threat to global wheat production due to evolving resistance to acetyl-CoA carboxylase (ACCase)- and acetolactate synthase (ALS)-inhibiting herbicides. In this study, the resistance mechanisms of a field-evolved resistant population (R) were systematically investigated using dose-response bioassays, target-site gene sequencing, inhibitor assays, antioxidant enzyme activity measurements, RNA sequencing (RNA-seq), quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), and yeast functional validation.

Dose-response results revealed that the R population exhibited moderate resistance to fenoxaprop-P-ethyl (RI = 9.58) and low-level resistance to mesosulfuron-methyl (RI = 3.07). Cross-resistance testing indicated that the R population was resistant to other ACCase-inhibiting herbicides (haloxyfop-P-methyl, clodinafop-propargyl, clethodim, and pinoxaden) and the ALS-inhibiting herbicide rimsulfuron. Target-site sequence analysis identified two mutations in the R population: Ile-1781-Leu (ACCase) and Pro-197-Ser (ALS1). Pretreatment with the cytochrome P450 and GST inhibitor did not reverse resistance to fenoxaprop-P-ethyl or mesosulfuron-methyl. Compared to the susceptible (S) population, the R population had significantly lower H₂O₂ content and higher activities of peroxidase (POD) and catalase (CAT), indicating an enhanced reactive oxygen species (ROS) scavenging capacity. RNA-seq and qRT-PCR analyses identified three POD-annotated contigs (PODSPC4, POD12-1, POD12-2) that were upregulated in the R population. Yeast heterologous expression validated that AaPOD12-1 and AaPOD12-2 significantly increased yeast resistance to fenoxaprop-P-ethyl and mesosulfuron-methyl.

These results demonstrate that resistance in the R population is co-mediated by target-site mutations and non-target-site resistance involving enhanced ROS scavenging, with AaPOD12-1 and AaPOD12-2 representing the first functionally characterized antioxidant enzyme genes associated with herbicide resistance in A. aequalis. © 2026 Society of Chemical Industry.