title: Insect Resistance to Bacillus thuringiensis Toxin Cry2Ab Is Conferred by Mutations in an ABC Transporter Subfamily A Protein.
abstract: The use of conventional chemical insecticides and bacterial toxins to control lepidopteran pests of global agriculture has imposed significant selection pressure leading to the rapid evolution of insecticide resistance. Transgenic crops (e.g., cotton) expressing the Bt Cry toxins are now used world wide to control these pests, including the highly polyphagous and invasive cotton bollworm Helicoverpa armigera. Since 2004, the Cry2Ab toxin has become widely used for controlling H. armigera, often used in combination with Cry1Ac to delay resistance evolution. Isolation of H. armigera and H. punctigera individuals heterozygous for Cry2Ab resistance in 2002 and 2004, respectively, allowed aspects of Cry2Ab resistance (level, fitness costs, genetic dominance, complementation tests) to be characterised in both species. However, the gene identity and genetic changes conferring this resistance were unknown, as was the detailed Cry2Ab mode of action. No cross-resistance to Cry1Ac was observed in mutant lines. Biphasic linkage analysis of a Cry2Ab-resistant H. armigera family followed by exon-primed intron-crossing (EPIC) marker mapping and candidate gene sequencing identified three independent resistance-associated INDEL mutations in an ATP-Binding Cassette (ABC) transporter gene we named HaABCA2. A deletion mutation was also identified in the H. punctigera homolog from the resistant line. All mutations truncate the ABCA2 protein. Isolation of further Cry2Ab resistance alleles in the same gene from field H. armigera populations indicates unequal resistance allele frequencies and the potential for Bt resistance evolution. Identification of the gene involved in resistance as an ABC transporter of the A subfamily adds to the body of evidence on the crucial role this gene family plays in the mode of action of the Bt Cry toxins. The structural differences between the ABCA2, and that of the C subfamily required for Cry1Ac toxicity, indicate differences in the detailed mode-of-action of the two Bt Cry toxins.
authors.affiliation: CSIRO, Black Mountain Laboratories, Canberra, Australian Capital Territory, Australia.
authors.forename: Wee Tek
authors.initials: WT
authors.lastname: Tay
authors.affiliation: CSIRO, Black Mountain Laboratories, Canberra, Australian Capital Territory, Australia.
authors.forename: Rod J
authors.initials: RJ
authors.lastname: Mahon
authors.affiliation: Department of Entomology, Max-Planck Institute for Chemical Ecology, Beutenberg Campus, Jena, Germany.
authors.forename: David G
authors.initials: DG
authors.lastname: Heckel
authors.affiliation: CSIRO, Black Mountain Laboratories, Canberra, Australian Capital Territory, Australia.
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Walsh
authors.affiliation: CSIRO, Australian Cotton Research Institute, Narrabri, New South Wales, Australia.
authors.forename: Sharon
authors.initials: S
authors.lastname: Downes
authors.affiliation: CSIRO, Black Mountain Laboratories, Canberra, Australian Capital Territory, Australia.
authors.forename: William J
authors.initials: WJ
authors.lastname: James
authors.affiliation: Department of Genetics, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Sui-Fai
authors.initials: SF
authors.lastname: Lee
authors.affiliation: Institute for Phytomedicine, Center of Applied Biology, Geisenheim University, Geiesenheim, Germany.
authors.forename: Annette
authors.initials: A
authors.lastname: Reineke
authors.affiliation: Department of Genetics, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Adam K
authors.initials: AK
authors.lastname: Williams
authors.affiliation: CSIRO, Black Mountain Laboratories, Canberra, Australian Capital Territory, Australia.
authors.forename: Karl H J
authors.initials: KH
authors.lastname: Gordon
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics*; D004731:Endotoxins / Q000235:genetics*; D005787:Gene Frequency; D008040:Genetic Linkage; D003368:Gossypium / Q000235:genetics*; D006460:Hemolysin Proteins / Q000235:genetics*; D054643:INDEL Mutation; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000494:pharmacology; D007915:Lepidoptera / Q000187:drug effects / Q000235:genetics* / Q000472:pathogenicity; D030821:Plants, Genetically Modified / Q000235:genetics
chemical_list: D018528:ATP-Binding Cassette Transporters; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis