Background: Bacillus thuringiensis Cry toxins are used worldwide in the control of different insect pests important in agriculture or in human health. The Cry proteins are pore-forming toxins that affect the midgut cell of target insects. It was shown that non-toxic Cry1Ab helix α-4 mutants had a dominant negative (DN) phenotype inhibiting the toxicity of wildtype Cry1Ab when used in equimolar or sub-stoichiometric ratios (1∶1, 0.5∶1, mutant∶wt) indicating that oligomer formation is a key step in toxicity of Cry toxins.
Methodology/principal Findings: The DN Cry1Ab-D136N/T143D mutant that is able to block toxicity of Cry1Ab toxin, was used to analyze its capacity to block the activity against Manduca sexta larvae of other Cry1 toxins, such as Cry1Aa, Cry1Ac, Cry1Ca, Cry1Da, Cry1Ea and Cry1Fa. Cry1Ab-DN mutant inhibited toxicity of Cry1Aa, Cry1Ac and Cry1Fa. In addition, we isolated mutants in helix α-4 of Cry4Ba and Cry11Aa, and demonstrate that Cry4Ba-E159K and Cry11Aa-V142D are inactive and completely block the toxicity against Aedes aegypti of both wildtype toxins, when used at sub-stoichiometric ratios, confirming a DN phenotype. As controls we analyzed Cry1Ab-R99A or Cry11Aa-E97A mutants that are located in helix α-3 and are affected in toxin oligomerization. These mutants do not show a DN phenotype but were able to block toxicity when used in 10∶1 or 100∶1 ratios (mutant∶wt) probably by competition of binding with toxin receptors.
Conclusions/significance: We show that DN phenotype can be observed among different Cry toxins suggesting that may interact in vivo forming hetero-oligomers. The DN phenotype cannot be observed in mutants affected in oligomerization, suggesting that this step is important to inhibit toxicity of other toxins.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3095643 | PMC |
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0019952 | PLOS |
BMC Genomics
December 2024
Department of Entomology, University of Maryland, College Park, MD, 20742, USA.
Strong and shifting selective pressures of the Anthropocene are rapidly shaping phenomes and genomes of organisms worldwide. Crops expressing pesticidal proteins from Bacillus thuringiensis (Bt) represent one major selective force on insect genomes. Here we characterize a rapid response to selection by Bt crops in a major crop pest, Helicoverpa zea.
View Article and Find Full Text PDFPestic Biochem Physiol
December 2024
School of Life Sciences, Central China Normal University, Wuhan 430070, China. Electronic address:
Bacillus thuringiensis (Bt) produces Cry toxins that are used to control insect pests worldwide. However, evolution of insect resistance threatens the sustainable application of these toxins. In some cases, Cry toxin resistance has been linked to mutations affecting toxin receptors expression.
View Article and Find Full Text PDFPLoS Pathog
December 2024
Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México.
Int J Mol Sci
November 2024
Institute of Molecular Biosciences, Mahidol University, Salaya, Phuttamonthon 73170, Nakhon Pathom, Thailand.
Cry toxins from are effective biopesticides that kill lepidopteran pests, replacing chemical pesticides that indiscriminately attack both target and non-target organisms. However, resistance in susceptible pests is an emerging problem. also produces vegetative insecticidal protein (Vip3A), which can kill insect targets in the same group as Cry toxins but using different host receptors, making the combined application of Cry and Vip3A an exciting possibility.
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