Mutations in target gene confers resistance to acetolactate synthase inhibitors in Echinochloa phyllopogon.

Echinochloa phyllopogon is a noxious weed that can harm rice over prolonged periods. Recently, a penoxsulam-resistant variant of E. phyllopogon with a mutation in the acetolactate synthase (ALS) gene was collected in Northeastern China. In the present study, the molecular mechanism underlying herbicide resistance in mutant populations was evaluated. The GR50 and IC50 values of the herbicide-resistant mutant 1-11 were 27.0- and 21.4-fold higher than those of the susceptible population 2-31, respectively. In addition, pre-application of malathion reduced the GR50 value of the resistant population. Additionally, mutant populations developed cross-resistance to other ALS inhibitors. E. phyllopogon ALS sequencing showed a Trp-574-Leu mutation in ALS2 variant 1-11. Molecular docking showed that the Trp-574-Leu substitution reduced the number of hydrogen bonds and altered the interaction between penoxsulam and ALS2. Transgenic Arabidopsis plants harboring the ALS2 mutant gene also showed resistance to penoxsulam and other ALS inhibitors. Overall, our study demonstrated that the Trp-574-Leu mutation and P450-mediated metabolic resistance lead to the cross-resistance of E. phyllopogon to ALS inhibitors.