Cadherin Protein Is Involved in the Action of Bacillus thuringiensis Cry1Ac Toxin in Ostrinia furnacalis.

Wenzhong Jin,Xingliang Wang,Yuqian Zhai,Yidong Wu,Yihua Yang

doi:10.3390/toxins13090658

Abstract

Transgenic crops expressing Bacillus thuringiensis (Bt) insecticidal proteins have been extensively planted for insect pest control, but the evolution of Bt resistance in target pests threatens the sustainability of this approach. Mutations of cadherin in the midgut brush border membrane was associated with Cry1Ac resistance in several lepidoptera species, including the Asian corn borer, Ostrinia furnacalis, a major pest of maize in Asian–Western Pacific countries. However, the causality of O. furnacalis cadherin (OfCad) with Cry1Ac resistance remains to be clarified. In this study, in vitro and in vivo approaches were employed to examine the involvement of OfCad in mediating Cry1Ac toxicity. Sf9 cells transfected with OfCad showed significant immunofluorescent binding with Cry1Ac toxin and exhibited a concentration-dependent mortality effect when exposed to Cry1Ac. The OfCad knockout strain OfCad-KO, bearing homozygous 15.4 kb deletion of the OfCad gene generated by CRISPR/Cas9 mutagenesis, exhibited moderate-level resistance to Cry1Ac (14-fold) and low-level resistance to Cry1Aa (4.6-fold), but no significant changes in susceptibility to Cry1Ab and Cry1Fa, compared with the original NJ-S strain. The Cry1Ac resistance phenotype was inherited as autosomal, recessive mode, and significantly linked with the OfCad knockout in the OfCad-KO strain. These results demonstrate that the OfCad protein is a functional receptor for Cry1Ac, and disruption of OfCad confers a moderate Cry1Ac resistance in O. furnacalis. This study provides new insights into the mode of action of the Cry1Ac toxin and useful information for designing resistance monitoring and management strategies for O. furnacalis.

Highlights

The Gram-positive bacterium Bacillus thuringiensis (Bt) produces insecticidal toxins and has served as an excellent biological pesticide since its entomopathogenicity was discovered in the early 1900s [1]
We employ both in vitro and in vivo approaches to clarify whether O. furnacalis cadherin mediates Cry1Ac cytotoxicity and the development of resistance to Cry1Ac
Sf9 cells transfected with O. furnacalis cadherin (OfCad) showed significant binding with Cry1Ac toxin by immunolocalization analysis and exhibited a concentration-dependent mortality effect when treated by Cry1Ac

Summary

Introduction

The Gram-positive bacterium Bacillus thuringiensis (Bt) produces insecticidal toxins and has served as an excellent biological pesticide since its entomopathogenicity was discovered in the early 1900s [1]. Major advantages of Bt crops driving their adoption include its high efficacy at suppressing devastating pests, increased crop yield and farmer gains, and reduced synthetic pesticide usage, thereby benefiting human and environmental health [3,4,5,6]. Following the rapid spread of the fall armyworm (Spodoptera frugiperda) to the continents of Asia, the Pacific and Australia [13], extensive application of insecticides for emergency control might increase selection pressure on O. furnacalis. Undesirable consequences of pesticide use such as the evolution of resistance in insect pests, environmental pollution, and threats to human health should be carefully considered. An environmentally friendly and economically effective option for the control of major maize pests (O. furnacalis and S. frugiperda) is growing transgenic Bt maize. Bt maize was first commercially planted in 1996 and nowadays it is grown in 14 countries, and the global area has increased to 60.9 million hectares, including insect-resistant (Bt) and/or herbicide-tolerant transgenic maize [14]

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Conclusion