Cadherins, aminopeptidases, glycolipids, alkaline phosphatases, and ATP binding cassette (ABC) transporters have all been proposed as functional receptors for Cry proteins from the bacterium Bacillus thuringiensis in Lepidoptera. The goal of our project is to identify and characterize Cry toxin binding proteins and test their role as functional Cry toxin receptors.

As insect models we use diverse lepidopteran species that are relevant agricultural pests, including Heliothis virescens (tobacco budworm), Helicoverpa zea (cotton bollworm), Spodoptera frugiperda (fall armyworm), Chrysodeixis includens (soybean looper) and Anticarsia gematalis (velvetbean caterpillar). We have also used alternative insect pests as they become available or are of interest to our group or collaborators. Because of their use in transgenic Bt crops, we have mostly focused on identifying receptors for Cry1Ac, Cry1Fa, and Cry2Ab toxins. More recently we have expanded our efforts to novel Cry proteins with potential use in new transgenic crops or Bt pesticides, such as Cry1I or Cry9 proteins.

We use diverse techniques to identify receptors, including but not limited to binding competition assays with radiolabeled Cry proteins, proteomics and blotting, affinity chromatography, and cloning followed by heterologous expression and cytotoxicity assays testing the fucntion of candidate Cry protein receptor genes. Identification of these receptors is crucial in identifying cros-resistance risks and designing monitoring as well as resistance management strategies.

Current Cry toxin binding site model for H. virescens larvae from binding competition assays. Predicted binding to unidentified sites is displayed with a broken line. These models are used to identify Cry proteins that do not share target sites in the insect midgut so that they can safely be combined in Bt crops or pesticides to delay evolution of resistance.