Pro-197-his/ser mutation and the metabolic gene DsUGT84A1, synergistically confer resistance to tribenuron-methyl in Descurainia sophia

Descurainia sophia, an invasive weed in wheat fields of China, has developed notable resistance to the acetolactate synthase (ALS)–inhibiting herbicide tribenuron-methyl. In this study, a suspected resistant population (R) of D. sophia was investigated to assess its resistance level and elucidate the underlying mechanisms. Whole-plant bioassays revealed that the R population exhibited a 35.20-fold higher resistance index (RI) to tribenuron-methyl compared with a sensitive (S) population. Treatment with the cytochrome P450 inhibitor malathion partially reversed this resistance, indicating a metabolic component. Target-site resistance (TSR) analysis identified a mutation from proline (Pro) to histidine (His) or serine (Ser) at position 197 of the ALS gene in the R population. Additionally, high-performance liquid chromatography (HPLC) analysis indicated that enhanced tribenuron-methyl metabolism occurred in the R population compared with the S population. Three candidate P450 genes (CYP96A15, CYP81F1, CYP734A1), and one UDP-glycosyltransferase (UGT) gene (UGT84A1) were found to be upregulated in the R population, as verified by RNA sequencing and quantitative reverse transcription PCR (RT-qPCR). Candidate resistance genes were identified and expressed heterologously in Arabidopsis thaliana. Experimental data showed that compared with the green fluorescent protein (GFP) control group, the resistance of three transgenic Arabidopsis lines overexpressing the DsUGT84A1 gene to tribenuron-methyl was significantly increased. When all the plants in the GFP control group died, the fresh weight of these three transgenic lines remained above 20%. The above results fully confirm that the DsUGT84A1 gene demonstrates significant functions pertaining to resistance against tribenuron-methyl. However, the current data suggest that this novel metabolic gene (DsUGT84A1) may not confer cross-resistance among various ALS-inhibiting herbicides. In this respect, the TSR conferred by the Pro197His/Ser mutation may be responsible for cross-resistance. Additionally, antioxidant-related genes were upregulated in A. thaliana overexpressing DsUGT84A1, leading to a reduction in the toxicity level of reactive oxygen species (ROS). Notably, this study identifies and functionally characterizes the UGT gene DsUGT84A1 related to herbicide resistance in broadleaf weeds. This contributes to the understanding of herbicide resistance mechanisms, especially highlighting the role of UGT genes, and enhances the current understanding of resistance evolution in weeds.