Binding and Oligomerization of Modified and Native Bt Toxins in Resistant and Susceptible Pink Bollworm

• Published in: PloS one Vol. 10; no. 12; p. e0144086
• Main Authors: Ocelotl, Josue, Sánchez, Jorge, Arroyo, Raquel, García-Gómez, Blanca I, Gómez, Isabel, Unnithan, Gopalan C, Tabashnik, Bruce E, Bravo, Alejandra, Soberón, Mario
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 03-12-2015; Public Library of Science (PLoS)
• Subjects: Agrochemicals; Amino acids; Analysis; Animals; Bacillus thuringiensis; Bacillus thuringiensis - metabolism; Bacterial Proteins - pharmacology; Bacterial toxins; Binding; Cadherins; Chemical properties; Competition; Cotton; Cry1Ac toxin; Durability; Endotoxins - pharmacology; Genetic engineering; Helicoverpa armigera; Hemolysin Proteins - pharmacology; Insecticide resistance; Insecticide Resistance - genetics; Insecticides; Insecticides - pharmacology; Insects; Insertion; Laboratories; Larva - drug effects; Larva - genetics; Larva - metabolism; Larvae; Membrane vesicles; Membranes; Midgut; Mode of action; Moths - drug effects; Moths - genetics; Moths - metabolism; Mutation; Oligomerization; Oligomers; Pectinophora gossypiella; Pest control; Pest Control, Biological; Pests; Phosphatase; Physiological aspects; Protein binding; Proteins; Sprayers; Sprays; Toxicity; Toxins; Transgenic plants; United States
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0144086

Insecticidal proteins from Bacillus thuringiensis (Bt) are used extensively in sprays and transgenic crops for pest control, but their efficacy is reduced when pests evolve resistance. Better understanding of the mode of action of Bt toxins and the mechanisms of insect resistance is needed to enhance the durability of these important alternatives to conventional insecticides. Mode of action models agree that binding of Bt toxins to midgut proteins such as cadherin is essential for toxicity, but some details remain unresolved, such as the role of toxin oligomers. In this study, we evaluated how Bt toxin Cry1Ac and its genetically engineered counterpart Cry1AcMod interact with brush border membrane vesicles (BBMV) from resistant and susceptible larvae of Pectinophora gossypiella (pink bollworm), a global pest of cotton. Compared with Cry1Ac, Cry1AcMod lacks 56 amino acids at the amino-terminus including helix α-1; previous work showed that Cry1AcMod formed oligomers in vitro without cadherin and killed P. gossypiella larvae harboring cadherin mutations linked with >1000-fold resistance to Cry1Ac. Here we found that resistance to Cry1Ac was associated with reduced oligomer formation and insertion. In contrast, Cry1AcMod formed oligomers in BBMV from resistant larvae. These results confirm the role of cadherin in oligomerization of Cry1Ac in susceptible larvae and imply that forming oligomers without cadherin promotes toxicity of Cry1AcMod against resistant P. gossypiella larvae that have cadherin mutations.