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Updated: Apr 23, 2026
Rearing and Injection of Manduca sexta Larvae to Assess Bacterial Virulence
Published on: December 11, 2012
Bacillus thuringiensis Cry1AbMod toxin counters tolerance associated with low cadherin expression but not that
Isabel Gómez1, Biviana Flores1, Alejandra Bravo1
1Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. postal 510-3, Cuernavaca 62250, Morelos, Mexico.
Abstract:
To exert their toxic effect, Bacillus thuringiensis Cry1Ab toxin undergoes a sequential binding mechanism with different larval gut proteins including glycosyl-phosphatidyl-inositol anchored proteins like aminopeptidase-N (APN) or alkaline-phosphatase (ALP) and a transmembrane cadherin to form pre-pore structures that insert into the membrane. Cadherin binding induces oligomerization of the toxin by facilitating removal of the N-terminal region, while APN/ALP binding helps in oligomer membrane insertion. Cry1AbMod toxin was engineered to lack N-terminal region of the toxin and shown to counter resistance linked to cadherin mutations. In this manuscript we determined the toxicity of Cry1AbMod to Manduca sexta larvae silenced in the expression of cadherin, ALP or APN receptors. As previously reported Cry1Ab toxicity relied principally in ALP and cadherin in comparison to APN. Our data shows that Cry1AbMod counters resistance associated with low cadherin expression but was not effective against ALP silenced larvae. These results show that Cry1AbMod could be effective against resistance insects linked to mutations on binding molecules involved in toxin oligomerization but not against resistant insects linked to mutations on binding molecules involved in oligomer membrane insertion.
Insights
Bacillus thuringiensis Cry1AbMod toxin counters insect resistance linked to cadherin mutations but not alkaline phosphatase mutations. This engineered toxin is effective against specific insect gut protein binding alterations.
Area of Science:
- * Molecular biology
- * Insect toxicology
- * Biochemistry
Background:
- * Bacillus thuringiensis (Bt) Cry1Ab toxin requires sequential binding to larval gut proteins, including cadherin and glycosyl-phosphatidyl-inositol anchored proteins like aminopeptidase-N (APN) and alkaline phosphatase (ALP), to exert its toxic effect.
- * Cadherin binding facilitates toxin oligomerization, while APN/ALP binding aids membrane insertion, forming pre-pore structures.
- * Insect resistance to Bt toxins can arise from mutations in these gut protein receptors.
Purpose of the Study:
- * To evaluate the toxicity of engineered Cry1AbMod toxin, which lacks the N-terminal region, against Manduca sexta larvae with silenced expression of cadherin, ALP, or APN receptors.
- * To determine if Cry1AbMod can overcome resistance mechanisms associated with specific receptor mutations.
Main Methods:
- * Silencing of cadherin, ALP, and APN receptor gene expression in Manduca sexta larvae using RNA interference.
- * Assessment of Cry1AbMod toxicity in larvae with reduced expression of specific gut receptors.
- * Comparison of Cry1AbMod efficacy against Cry1Ab wild-type toxicity profiles.
Main Results:
- * Cry1AbMod demonstrated toxicity against Manduca sexta larvae with silenced cadherin expression, indicating efficacy against cadherin-mediated resistance.
- * Cry1AbMod was ineffective against larvae with silenced ALP expression, suggesting ALP is crucial for Cry1AbMod's action.
- * Cry1Ab toxicity was confirmed to rely primarily on ALP and cadherin, with less dependence on APN.
Conclusions:
- * The engineered Cry1AbMod toxin is effective against insect resistance linked to mutations affecting toxin oligomerization (e.g., cadherin binding).
- * Cry1AbMod is not effective against insect resistance linked to mutations affecting oligomer membrane insertion (e.g., ALP binding).
- * Cry1AbMod offers a potential strategy against specific Bt resistance mechanisms in agricultural pests.
