Constitutive activation of the midgut response to Bacillus thuringiensis in Bt-resistant Spodoptera exigua.

Patricia Hernández-Martínez,Baltasar Escriche,Salvador Herrero,Gloria Navarro-Cerrillo,Juan Ferré,Silvia Caccia,Ruud A De Maagd,William J Moar,Paulo Lee Ho

doi:10.1371/journal.pone.0012795

Patricia Hernández-Martínez, Baltasar Escriche + Show 7 more

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https://doi.org/10.1371/journal.pone.0012795

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Abstract

Bacillus thuringiensis is the most effective microbial control agent for controlling numerous species from different insect orders. The main threat for the long term use of B. thuringiensis in pest control is the ability of insects to develop resistance. Thus, the identification of insect genes involved in conferring resistance is of paramount importance. A colony of Spodoptera exigua (Lepidoptera: Noctuidae) was selected for 15 years in the laboratory for resistance to Xentari™, a B. thuringiensis-based insecticide, reaching a final resistance level of greater than 1,000-fold. Around 600 midgut ESTs were analyzed by DNA-macroarray in order to find differences in midgut gene expression between susceptible and resistant insects. Among the differentially expressed genes, repat and arylphorin were identified and their increased expression was correlated with B. thuringiensis resistance. We also found overlap among genes that were constitutively over-expressed in resistant insects with genes that were up-regulated in susceptible insects after exposure to Xentari™, suggesting a permanent activation of the response to Xentari™ in resistant insects. Increased aminopeptidase activity in the lumen of resistant insects in the absence of exposure to Xentari™ corroborated the hypothesis of permanent activation of response genes. Increase in midgut proliferation has been proposed as a mechanism of response to pathogens in the adult from several insect species. Analysis of S. exigua larvae revealed that midgut proliferation was neither increased in resistant insects nor induced by exposure of susceptible larvae to Xentari™, suggesting that mechanisms other than midgut proliferation are involved in the response to B. thuringiensis by S. exigua larvae.

Highlights

Bacillus thuringiensis-based biopesticides are employed for the control of numerous species from Lepidoptera, Diptera, and Coleoptera [1]
With the goal to find genes contributing to the resistance to B. thuringiensis containing multiple S. exigua-active compounds, we measured differential gene expression between a susceptible S. exigua colony and a colony that had developed high levels of resistance to a B. thuringiensis-based formulated product (XentariTM)
Neonate selection was discontinued after five days, resistance ratios obtained using both neonates and late instar larvae show that resistance was maintained during the entire larval stage, including the larval instar used in the macroarray analyses

Summary

Introduction

Bacillus thuringiensis-based biopesticides are employed for the control of numerous species from Lepidoptera, Diptera, and Coleoptera [1]. The most accepted and studied resistance mechanism is the reduction of Cry protein binding to the insect midgut In some cases, this reduced binding is associated with mutations or altered expression of genes encoding cadherin, aminopeptidase N or alkaline phosphatase receptors [8,9,10]. This reduced binding is associated with mutations or altered expression of genes encoding cadherin, aminopeptidase N or alkaline phosphatase receptors [8,9,10] These mechanisms that generally cause the highest levels of resistance have been usually found in insects selected for resistance to a single or few Cry proteins [4;11]. In Caenorhabditis elegans a defect in the synthesis of glycolipids that act as Cry5B receptors has been reported in Cry5B-resistant mutants [16;17]

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