title: Expressing a moth abcc2 gene in transgenic Drosophila causes susceptibility to Bt Cry1Ac without requiring a cadherin-like protein receptor.
abstract: Bt toxins ingested by insect pests can bind to midgut receptors and cause death, although several steps in this process remain unclear. Multiple Bt toxin receptors have been identified in Lepidoptera, including a cadherin-like protein (CaLP), which is central to several models explaining Bt toxins' mode of action. Mutations in the Plutella xylostella ATP-dependent binding cassette transporter C2 (Px-abcc2), rather than CaLP, are genetically linked with Bt Cry1Ac resistance. Here we expressed Px-abcc2 in Drosophila and performed larval bioassays to determine whether this protein acts as an effective Bt receptor. Cry1Ac had no effect on larvae expressing Px-abcc2 in salivary glands, yet larvae expressing Px-abcc2 in the midgut were highly susceptible to both Cry1Ac protoxin and trypsin activated toxin. Furthermore, the CaLP orthologue has been lost from the Drosophila genome, making this a useful system for investigating the role of CaLP peptides from Manduca sexta (CR12-MPED), which are known to act as Bt synergists in larval feeding assays. Drosophila larvae expressing Px-ABCC2 in the midgut were fed LD50concentrations of Cry1Ac toxin or protoxin, plus purified CR12-MPED cloned from M. sexta or P. xylostella. The M. sexta CR12-MPED protein acted synergistically with Cry1Ac protoxin and activated toxin significantly more effectively than the P. xylostella peptide. This work demonstrates ABCC2 is the major functional Cry1Ac receptor for P. xylostella and the importance of CaLP proteins in Bt mode of action may vary between different lepidopteran species.
authors.affiliation: School of Biological Sciences, University of Adelaide, 5005 Australia.
authors.forename: Tristan
authors.initials: T
authors.lastname: Stevens
authors.affiliation: School of Biological Sciences, University of Adelaide, 5005 Australia.
authors.forename: Sisi
authors.initials: S
authors.lastname: Song
authors.affiliation: School of Biological Sciences, University of Adelaide, 5005 Australia.
authors.forename: John B
authors.initials: JB
authors.lastname: Bruning
authors.affiliation: School of Biological Sciences, University of Adelaide, 5005 Australia.
authors.forename: Amanda
authors.initials: A
authors.lastname: Choo
authors.affiliation: School of Biological Sciences, University of Adelaide, 5005 Australia. Electronic address: simon.baxter@adelaide.edu.au.
authors.forename: Simon W
authors.initials: SW
authors.lastname: Baxter
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001413:Bacillus thuringiensis / Q000737:chemistry; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000633:toxicity*; D015820:Cadherins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D004731:Endotoxins / Q000633:toxicity*; D006460:Hemolysin Proteins / Q000633:toxicity*; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D007814:Larva / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018402:Manduca / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D009036:Moths / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D015820:Cadherins; D004731:Endotoxins; D006460:Hemolysin Proteins; D019476:Insect Proteins; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: Bt toxin; Cry1Ac; Insecticide receptor; Insecticide resistance; Plutella xylostella