Molecular characterization and structural insights into the ACCase I1781T mutation conferring pinoxaden resistance in Italian ryegrass (Lolium perenne ssp. multiflorum).

BACKGROUND: The evolution of herbicide resistance in Italian ryegrass (Lolium perenne ssp. multiflorum) poses a significant challenge to wheat production. However, our understanding of resistance status and molecular mechanisms of L. perenne ssp. multiflorum to pinoxaden remains limited. RESULTS: L. perenne ssp. multiflorum populations have evolved diverse degrees of resistance to pinoxaden. A segregating population harboring the ACCase I1781T mutation was subsequently constructed, and it displayed high-level resistance to pinoxaden with a resistance index (RI) of 58.41. This population exhibited cross-resistance to aryloxyphenoxypropionate herbicides and decreased susceptibility to cyclohexanediones, yet remained susceptible to herbicides with distinct modes of action. After genetic segregation, homozygous I1781T ACCase individuals derived from the segregating population exhibited substantially increased pinoxaden resistance, with a RI of 205.40. Molecular dynamics simulations showed stable pinoxaden binding in the wild-type complex, but transient ligand displacement in the I1781T mutant complex, supporting reduced stability of pinoxaden binding within the ACCase herbicide-binding pocket. CONCLUSION: We molecularly characterized the new ACCase I1781T substitution isolated from a pinoxaden-resistant L. perenne ssp. multiflorum population. Herbicide rotation utilizing herbicides with distinct modes of action represents a promising strategy to mitigate the spread of this resistance mutation. © 2026 Society of Chemical Industry.