title: Diversity of acetyl-coenzyme A carboxylase mutations in resistant Lolium populations: evaluation using clethodim.
abstract: The acetyl-coenzyme A carboxylase (ACCase)-inhibiting cyclohexanedione herbicide clethodim is used to control grass weeds infesting dicot crops. In Australia clethodim is widely used to control the weed Lolium rigidum. However, clethodim-resistant Lolium populations have appeared over the last 5 years and now are present in many populations across the western Australian wheat (Triticum aestivum) belt. An aspartate-2078-glycine (Gly) mutation in the plastidic ACCase enzyme has been identified as the only known mutation endowing clethodim resistance. Here, with 14 clethodim-resistant Lolium populations we revealed diversity and complexity in the molecular basis of resistance to ACCase-inhibiting herbicides (clethodim in particular). Several known ACCase mutations (isoleucine-1781-leucine [Leu], tryptophan-2027-cysteine [Cys], isoleucine-2041-asparagine, and aspartate-2078-Gly) and in particular, a new mutation of Cys to arginine at position 2088, were identified in plants surviving the Australian clethodim field rate (60 g ha(-1)). Twelve combination patterns of mutant alleles were revealed in relation to clethodim resistance. Through a molecular, biochemical, and biological approach, we established that the mutation 2078-Gly or 2088-arginine endows sufficient level of resistance to clethodim at the field rate, and in addition, combinations of two mutant 1781-Leu alleles, or two different mutant alleles (i.e. 1781-Leu/2027-Cys, 1781-Leu/2041-asparagine), also confer clethodim resistance. Plants homozygous for the mutant 1781, 2078, or 2088 alleles were found to be clethodim resistant and cross resistant to a number of other ACCase inhibitor herbicides including clodinafop, diclofop, fluazifop, haloxyfop, butroxydim, sethoxydim, tralkoxydim, and pinoxaden. We established that the specific mutation, the homo/heterozygous status of a plant for a specific mutation, and combinations of different resistant alleles plus herbicide rates all are important in contributing to the overall level of herbicide resistance in genetically diverse, cross-pollinated Lolium species.
authors.affiliation: Western Australian Herbicide Resistance Initiative, School of Plant Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
authors.forename: Qin
authors.initials: Q
authors.lastname: Yu
authors.forename: Alberto
authors.initials: A
authors.lastname: Collavo
authors.forename: Ming-Qi
authors.initials: MQ
authors.lastname: Zheng
authors.forename: Mechelle
authors.initials: M
authors.lastname: Owen
authors.forename: Maurizio
authors.initials: M
authors.lastname: Sattin
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Powles
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D003512:Cyclohexanones / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018506:Gene Expression Regulation, Plant; D014644:Genetic Variation; D005838:Genotype; D053209:Herbicide Resistance / Q000235:genetics*; D006540:Herbicides / Q000494:pharmacology*; D008129:Lolium / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*
chemical_list: D003512:Cyclohexanones; D006540:Herbicides; C441919:clethodim; D000103:Acetyl-CoA Carboxylase