Bacillus thuringiensis Cry34Ab1/Cry35Ab1 interactions with western corn rootworm midgut membrane binding sites

Area of Science:

• Molecular biology and entomology
• Insect resistance management strategies
• Biotechnology in agriculture

Background:

• Bacillus thuringiensis (Bt) Cry34Ab1/Cry35Ab1 binary insecticidal proteins are used in transgenic corn to control western corn rootworm.
• Co-expression with non-transgenic refuges is a strategy to delay pest resistance.
• Understanding binding site interactions is crucial for predicting and managing cross-resistance.

Purpose of the Study:

• To investigate binding site interactions between Cry34Ab1/Cry35Ab1 and other coleopteran-active Bt proteins (Cry3Aa, Cry6Aa, Cry8Ba).
• To assess the potential for receptor-mediated cross-resistance in western corn rootworm.
• To evaluate the compatibility of Cry34Ab1/Cry35Ab1 with other Bt proteins for insect resistance management.

Main Methods:

• Competitive binding assays using radio-labeled proteins and western corn rootworm midgut brush border membrane vesicles (BBMV).
• Investigated binding of (125)I-Cry35Ab1, with and without Cry34Ab1, to BBMV in the presence of unlabeled competitor proteins.
• Assessed competitive binding of unlabeled Cry34Ab1 and Cry35Ab1 against (125)I-Cry3Aa and (125)I-Cry8Ba.

Main Results:

• (125)I-Cry35Ab1 specifically binds to western corn rootworm BBMV, with binding enhanced by Cry34Ab1.
• Cry34Ab1/Cry35Ab1 did not share binding sites with Cry3Aa, Cry6Aa, or Cry8Ba, as evidenced by lack of competitive binding.
• No competitive binding was observed when Cry3Aa or Cry8Ba were used with Cry34Ab1/Cry35Ab1, confirming distinct binding interactions.

Conclusions:

• Cry34Ab1/Cry35Ab1 exhibit distinct insecticidal mechanisms from Cry3Aa, Cry6Aa, and Cry8Ba, suggesting a low probability of cross-resistance.
• These findings support the compatibility of Cry34Ab1/Cry35Ab1 with Cry3Aa, Cry6Aa, or Cry8Ba for use in insect resistance management pyramids.
• The study provides a basis for deploying diverse Bt proteins in transgenic crops to effectively manage western corn rootworm populations.