title: Dual mode of action of Bt proteins: protoxin efficacy against resistant insects.
abstract: Transgenic crops that produce Bacillus thuringiensis (Bt) proteins for pest control are grown extensively, but insect adaptation can reduce their effectiveness. Established mode of action models assert that Bt proteins Cry1Ab and Cry1Ac are produced as inactive protoxins that require conversion to a smaller activated form to exert toxicity. However, contrary to this widely accepted paradigm, we report evidence from seven resistant strains of three major crop pests showing that Cry1Ab and Cry1Ac protoxins were generally more potent than the corresponding activated toxins. Moreover, resistance was higher to activated toxins than protoxins in eight of nine cases evaluated in this study. These data and previously reported results support a new model in which protoxins and activated toxins kill insects via different pathways. Recognizing that protoxins can be more potent than activated toxins against resistant insects may help to enhance and sustain the efficacy of transgenic Bt crops.
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Tabashnik
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.affiliation: U.S. Department of Agriculture, Agricultural Research Service, U.S. Arid Land Agricultural Research Center, Maricopa, AZ 85138, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Fabrick
authors.affiliation: Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Yidong
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Department of Entomology, College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Meijing
authors.initials: M
authors.lastname: Gao
authors.affiliation: Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA.
authors.forename: Fangneng
authors.initials: F
authors.lastname: Huang
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.|State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100026, China.
authors.forename: Jizhen
authors.initials: J
authors.lastname: Wei
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100026, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Alexander
authors.initials: A
authors.lastname: Yelich
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Gopalan C
authors.initials: GC
authors.lastname: Unnithan
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Bravo
authors.affiliation: Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca 62250, Morelos, Mexico.
authors.forename: Mario
authors.initials: M
authors.lastname: Soberón
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Yves
authors.initials: Y
authors.lastname: Carrière
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ, 85721, USA.
authors.forename: Xianchun
authors.initials: X
authors.lastname: Li
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000737:chemistry* / Q000472:pathogenicity / Q000502:physiology; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D018556:Crops, Agricultural / Q000235:genetics / Q000469:parasitology; D004731:Endotoxins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D015870:Gene Expression; D006460:Hemolysin Proteins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D019476:Insect Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects / Q000502:physiology; D007814:Larva / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D007915:Lepidoptera / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008958:Models, Molecular; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D019076:Transgenes
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D019476:Insect Proteins; D011498:Protein Precursors; C030956:insecticidal crystal protein, Bacillus Thuringiensis