Functional Analysis Of The Midgut Cadherin Gene From Spodopteraexigua As A Functional Receptor Of Cry Protein

The wide range planting of transgenic Cry1 Ac Bt cotton effectively controls the damage of cotton bollworm, Helicoverpa armigera( Huber) and Pectinophora gossypiella( Saunders), and reduces the amount of pesticide usage and environmental pollution. However, a variety of target Lepidoptera pests have been reported have had resistance to the transgenic cotton. One international strategy to delay resistance to Bt crops and expand its target spectrum is to “pyramid” two or more Bt proteins that bind to distinct receptor proteins within the insect midgut, Cry2 A is one of the important proteins in Bt pyramid. Studies have shown that Cadherin is the main receptor of the Cry1 protein in Lepidopteran pests midgut, but the interaction between the cadherin protein and Cry2 is still unclear. Here, our research detected the binding capacity between cadherin protein and two Cry proteins( Cry1 Ac and Cry2Aa) through expressing CR7-MPED polypeptide fragments in vitro of beet armyworm cadherin(Se Cad1b), and both RNA interference and competitive binding analysis were applied to clarify the relationship between the beet armyworm Se Cad1 b and the two Cry proteins. The main findings are as follows:1. The polypeptide fragments Se Cad1 b, Se CR7-8F, Se CR9-MPED of Cadherin can bind with bio-Cry1 Ac and bio-Cry2 Aa.2. We find that the Se Cad1 b gene expression level significantly reduced after feeding beet armyworm ds RNA in 24 h, and the larval mortality to Cry1 Ac and Cry2 Aa significantly reduced after silencing the cadherin gene.3. Results of homologous and heterologous competitive binding asssays between the polypeptide fragments Se Cad1 b, Se CR7-8F, Se CR9-MPED of Cadherin and Cry1 Ac and Cry2 Aa proteins showed that there is no competitive binding between heterogous Cry proteins, while the homologous binding assay exists competitive binding.In summary, this study identified the Spodoptera exigua Cad1 b protein as a functional receptor of both Cry2 Aa and Cry1 Ac proteins, more over, Cry1 Ac and Cry2 Aa have different binding sites on the beet armyworm Se Cad1 b protein. The results lay the foundation for the study of Cry protein resistance mechanisms of the beet armyworm, and play a significant role for the research and development of Bt pyramid plants.