title: Activation of Bt Protoxin Cry1Ac in Resistant and Susceptible Cotton Bollworm.
abstract: Crystalline (Cry) proteins from Bacillus thuringiensis (Bt) are used extensively for insect control in sprays and transgenic plants, but their efficacy is reduced by evolution of resistance in pests. Here we evaluated reduced activation of Cry1Ac protoxin as a potential mechanism of resistance in the invasive pest Helicoverpa armigera. Based on the concentration killing 50% of larvae (LC50) for a laboratory-selected resistant strain (LF120) divided by the LC50 for its susceptible parent strain (LF), the resistance ratio was 1600 for Cry1Ac protoxin and 1200 for trypsin-activated Cry1Ac toxin. The high level of resistance to activated toxin as well as to protoxin indicates reduced activation of protoxin is not a major mechanism of resistance to Cry1Ac in LF120. For both insect strains, treatment with either the trypsin inhibitor N-a-tosyl-L-lysine chloromethyl ketone (TLCK) or the chymotrypsin inhibitor N-a-tosyl-L-phenylalanine chloromethyl ketone (TPCK) did not significantly affect the LC50 of Cry1Ac protoxin. Enzyme activity was higher for LF than LF120 for trypsin-like proteases, but did not differ between strains for chymotrypsin-like proteases. The results here are consistent with previous reports indicating that reduced activation of protoxin is generally not a major mechanism of resistance to Bt proteins.
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Jizhen
authors.identifier: http://orcid.org/0000-0001-6487-4725
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 100193, China.
authors.forename: Gemei
authors.initials: G
authors.lastname: Liang
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Bingjie
authors.initials: B
authors.lastname: Wang
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhong
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Chen
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Myint Myint
authors.initials: MM
authors.lastname: Khaing
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Yuyuan
authors.initials: Y
authors.lastname: Guo
authors.affiliation: State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
authors.forename: Kongming
authors.initials: K
authors.lastname: Wu
authors.affiliation: Department of Entomology and BIO5 Institute, University of Arizona, Tucson, Arizona 85721, United States of America.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Tabashnik
mesh_terms: D000818:Animals; D001427:Bacterial Toxins / Q000494:pharmacology*; D007300:Insect Control; D007305:Insecticide Resistance; D007814:Larva / Q000187:drug effects; D009036:Moths / Q000187:drug effects*; D011498:Protein Precursors / Q000494:pharmacology*; D014107:Tosyllysine Chloromethyl Ketone / Q000494:pharmacology
chemical_list: C029103:Bacillus thuringiensis protoxin; D001427:Bacterial Toxins; D011498:Protein Precursors; D014107:Tosyllysine Chloromethyl Ketone