title: Copy Number Variation in Acetolactate Synthase Genes of Thifensulfuron-Methyl ResistantAlopecurus aequalis(Shortawn Foxtail) Accessions in Japan.
abstract: Severe infestations ofAlopecurus aequalis(shortawn foxtail), a noxious weed in wheat and barley cropping systems in Japan, can occur even after application of thifensulfuron-methyl, a sulfonylurea (SU) herbicide. In the present study, nine accessions ofA. aequalisgrowing in a single wheat field were tested for sensitivity to thifensulfuron-methyl. Seven of the nine accessions survived application of standard field rates of thifensulfuron-methyl, indicating that severe infestations likely result from herbicide resistance. Acetolactate synthase (ALS) is the target enzyme of SU herbicides. Full-length genes encoding ALS were therefore isolated to determine the mechanism of SU resistance. As a result, differences inALSgene copy numbers among accessions were revealed. Two copies,ALS1andALS2, were conserved in all accessions, while some carried two additional copies,ALS3andALS4. A single-base deletion inALS3andALS4further indicated that they represent pseudogenes. No differences in ploidy level were observed between accessions with two or four copies of theALSgene, suggesting that copy number varies. Resistant plants were found to carry a mutation in either theALS1orALS2gene, with all mutations causing an amino acid substitution at the Pro197 residue, which is known to confer SU resistance. Transcription of eachALSgene copy was confirmed by reverse transcription PCR, supporting involvement of these mutations in SU resistance. The information on the copy number and full-length sequences ofALSgenes inA. aequaliswill aid future analysis of the mechanism of resistance.
authors.affiliation: Graduate School of Agriculture, Kyoto UniversityKyoto, Japan; Crop Production Systems Division, NARO Agricultural Research CenterTsukuba, Japan; Faculty of Life and Environmental Sciences, University of TsukubaTsukuba, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iwakami
authors.affiliation: Graduate School of Agriculture, Kyoto University Kyoto, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Shimono
authors.affiliation: Graduate School of Agriculture, Kyoto University Kyoto, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Manabe
authors.affiliation: Plant Genome Engineering Research Unit, Institute of Agrobiological Sciences, National Agriculture and Food Research Organization Tsukuba, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Endo
authors.affiliation: National Institute for Agro-Environmental Sciences Tsukuba, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Shibaike
authors.affiliation: Crop Production Systems Division, NARO Agricultural Research CenterTsukuba, Japan; Central Region Agricultural Research Center, National Agriculture and Food Research OrganizationTsu, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Uchino
authors.affiliation: Graduate School of Agriculture, Kyoto University Kyoto, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Tominaga
keywords: ALS inhibitor; copy number variation; herbicide resistance; shortawn foxtail; target-site resistance