title: Cis-mediated down-regulation of a trypsin gene associated with Bt resistance in cotton bollworm.
abstract: Transgenic plants producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) are useful for pest control, but their efficacy is reduced when pests evolve resistance. Here we examined the mechanism of resistance to Bt toxin Cry1Ac in the laboratory-selected LF5 strain of the cotton bollworm, Helicoverpa armigera. This strain had 110-fold resistance to Cry1Ac protoxin and 39-fold resistance to Cry1Ac activated toxin. Evaluation of five trypsin genes revealed 99% reduced transcription of one trypsin gene (HaTryR) was associated with resistance. Silencing of this gene with RNA interference in susceptible larvae increased their survival on diets containing Cry1Ac. Bioassays of progeny from crosses revealed that resistance to Cry1Ac was genetically linked with HaTryR. We identified mutations in the promoter region of HaTryR in the resistant strain. In transfected insect cell lines, transcription was lower when driven by the resistant promoter compared with the susceptible promoter, implicating cis-mediated down-regulation of HaTryR transcription as a mechanism of resistance. The results suggest that H. armigera can adapt to Bt toxin Cry1Ac by decreased expression of trypsin. Because trypsin activation of protoxin is a critical step in toxicity, transgenic plants with activated toxins rather than protoxins might increase the durability of Bt crops.
authors.affiliation: The State Key Laboratory for Biology of Plant Disease and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, West Yuanmingyuan Road, Beijing, 100193, China.
authors.forename: Chenxi
authors.initials: C
authors.lastname: Liu
authors.affiliation: The State Key Laboratory for Biology of Plant Disease and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, West Yuanmingyuan Road, Beijing, 100193, China.
authors.forename: Yutao
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Xianchun
authors.initials: X
authors.lastname: Li
authors.affiliation: USDA Agricultural Research Service Center for Grain and Animal Health Research, 1515 College Avenue, Manhattan, KS 66502, USA.
authors.forename: Brenda
authors.initials: B
authors.lastname: Oppert
authors.affiliation: Department of Entomology, University of Arizona, Tucson, AZ 85721, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Tabashnik
authors.affiliation: The State Key Laboratory for Biology of Plant Disease and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, West Yuanmingyuan Road, Beijing, 100193, China.
authors.forename: Kongming
authors.initials: K
authors.lastname: Wu
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D001681:Biological Assay / Q000379:methods; D018556:Crops, Agricultural / Q000382:microbiology; D015536:Down-Regulation / Q000235:genetics*; D004731:Endotoxins / Q000235:genetics; D006460:Hemolysin Proteins / Q000235:genetics*; D007305:Insecticide Resistance / Q000235:genetics*; D007306:Insecticides / Q000378:metabolism; D007814:Larva / Q000382:microbiology; D007915:Lepidoptera / Q000382:microbiology; D009036:Moths / Q000382:microbiology*; D030821:Plants, Genetically Modified / Q000382:microbiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014357:Trypsin / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; D014357:Trypsin