A P-Glycoprotein Is Linked to Resistance to the Bacillus thuringiensis Cry3Aa Toxin in a Leaf Beetle.

Yannick Pauchet,Anne Bretschneider,Sylvie Augustin,David Heckel

doi:10.3390/toxins8120362

Abstract

Chrysomela tremula is a polyvoltine oligophagous leaf beetle responsible for massive attacks on poplar trees. This beetle is an important model for understanding mechanisms of resistance to Bacillus thuringiensis (Bt) insecticidal toxins, because a resistant C. tremula strain has been found that can survive and reproduce on transgenic poplar trees expressing high levels of the Cry3Aa Bt toxin. Resistance to Cry3Aa in this strain is recessive and is controlled by a single autosomal locus. We used a larval midgut transcriptome for C. tremula to search for candidate resistance genes. We discovered a mutation in an ABC protein, member of the B subfamily homologous to P-glycoprotein, which is genetically linked to Cry3Aa resistance in C. tremula. Cultured insect cells heterologously expressing this ABC protein swell and lyse when incubated with Cry3Aa toxin. In light of previous findings in Lepidoptera implicating A subfamily ABC proteins as receptors for Cry2A toxins and C subfamily proteins as receptors for Cry1A and Cry1C toxins, this result suggests that ABC proteins may be targets of insecticidal three-domain Bt toxins in Coleoptera as well.

Highlights

Crystal (Cry) toxins produced during sporulation by the Gram-positive bacteriumBacillus thuringiensis (Bt) are highly potent against insects and for many years have been successfully used as biopesticides in agriculture
We demonstrate that the resistance to Cry3Aa in C. tremula is linked to the occurrence of a four-base-pair deletion in the open reading frame of CtABCB1 in resistant insects, and that insects homozygous for the presence of this deletion are resistant to Cry3Aa
We used a recent analysis of the tissue-specific expression of genes encoding ABC proteins in C. populi, a sister species of C. tremula, to identify ABC proteins expressed in the larval midgut

Summary

Introduction

Crystal (Cry) toxins produced during sporulation by the Gram-positive bacteriumBacillus thuringiensis (Bt) are highly potent against insects and for many years have been successfully used as biopesticides in agriculture. Different Cry toxins are highly specific to certain insect orders such as Lepidoptera, Diptera and Coleoptera [1]. The exponential increase in planting insect-resistant crop plants transformed to express Bt-derived insecticidal Cry proteins has enabled a substantial reduction in the use of chemical insecticides [2]. It has increased the selection pressure for target insects to develop resistance to these Bt crops. The western corn rootworm has recently developed resistance in the field to several transgenic maize lines expressing different Bt Cry toxins [3,4]. Efforts directed to understand the mode of action of Bt Cry toxins in insects and the associated resistance mechanisms are crucial to develop efficient crop pest management strategies

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