Differential alteration of two aminopeptidases N associated with resistance to Bacillus thuringiensis toxin Cry1Ac in cabbage looper

Abstract

The soil bacterium Bacillus thuringiensis (Bt) is the most successfully used biopesticide in agriculture, and its insecticidal protein genes are the primary transgenes used for insect control in transgenic crops. However, evolution of insect resistance to Bt toxins threatens the long-term future of Bt applications. To date, cases of resistance to Bt toxins have been reported in agricultural situations in six insect species, but the molecular basis for these cases of resistance remains unclear. Here we report that the resistance to the Bt toxin Cry1Ac in the cabbage looper, Trichoplusia ni, evolved in greenhouses, is associated with differential alteration of two midgut aminopeptidases N, APN1 and APN6, conferred by a trans-regulatory mechanism. Biochemical, proteomic, and molecular analyses showed that in the Cry1Ac-resistant T. ni, APN1 was significantly down-regulated, whereas APN6 was significantly up-regulated. The Cry1Ac resistance was correlated with downregulation of APN1 but not with the up-regulation of APN6. The concurrent up-regulation of APN6 and down-regulation of APN1 might play a role in compensating for the loss of APN1 to minimize the fitness costs of the resistance. Along with identifying reduced expression of APN1 as the molecular basis of Bt resistance selected in an agricultural setting, our findings demonstrate the importance of APN1 to the mode of action of Bt toxin Cry1Ac.

Eliminating host-mediated effects demonstrates Bt maize producing Cry1F has no adverse effects on the parasitoid Cotesia marginiventris

“…Although no study was conducted to clarify the mechanisms of resistance to Cry1F protein of S. frugiperda, the midgut binding site (including cadherin, alkaline phosphatase and aminopeptidases N) modification to Cry proteins were the most probable mechanism (Ferré and Van Rie 2002, Jurat-Fuentes et al 2011, Tiewsiri and Wang 2011 that would not substantially alter the other characters of the resistant strain. Our previous studies had shown that Cry1F-resistant S. frugiperda were not affected by Cry1F when they fed on Cry1F maize, even though they contained a high dose of bioactive Cry1F protein (Tian et al 2012(Tian et al , 2013.…”

Microbial agents against Helicoverpa armigera: Where are we and where do we need to go?

“…The most common mechanism of resistance is by the disruption of binding of Bt toxin to receptors in the mid-gut membrane. This disruption might be either due to mutations in the receptors or changes in the expression of the receptors (Fuentes et al, 2011;Tiewsiri and Wang, 2011). The resistance mechanism associated with ABC transporter loci has also been reported (Baxter et al, 2011).…”

Biotechnological Approaches for the Control of Insect Pests in Crop Plants

“…This disruption may be caused either by mutations in the receptor that blocks binding (reviewed in [20]) or changes in expression of the receptors [152,153]. Mutations in cadherin genes are responsible for Bt resistance in Heliothis virescens [154], Helicoverpa armigera [155] and Pectinophora gossypiella [156].…”