Activation of Bt Protoxin Cry1Ac in Resistant and Susceptible Cotton Bollworm
Khaing, Myint Myint
Tabashnik, Bruce E.
AffiliationUniv Arizona, Dept Entomol
Univ Arizona, Inst BIO5
MetadataShow full item record
PublisherPUBLIC LIBRARY SCIENCE
CitationActivation of Bt Protoxin Cry1Ac in Resistant and Susceptible Cotton Bollworm 2016, 11 (6):e0156560 PLOS ONE
Rights© 2016 Wei et al. This is an open access article distributed under the terms of the Creative Commons Attribution License.
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AbstractCrystalline (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.
VersionFinal published version
SponsorsKey Project for Breeding Genetically Modified Organisms [2016ZX08011-002]; National Natural Science Foundation of China