Abstract
The vegetative insecticidal proteins (Vip), secreted by many Bacillus thuringiensis strains during their vegetative growth stage, are genetically distinct from known insecticidal crystal proteins (ICPs) and represent the second-generation insecticidal toxins. Compared with ICPs, the insecticidal mechanisms of Vip toxins are poorly understood. In particular, there has been no report of a definite receptor of Vip toxins to date. In the present study, we identified the scavenger receptor class C like protein (Sf-SR-C) from the Spodoptera frugiperda (Sf9) cells membrane proteins that bind to the biotin labeled Vip3Aa, via the affinity magnetic bead method coupled with HPLC-MS/MS. We then certified Vip3Aa protoxin could interact with Sf-SR-C in vitro and ex vivo. In addition, downregulation of SR-C expression in Sf9 cells and Spodoptera exigua larvae midgut reduced the toxicity of Vip3Aa to them. Coincidently, heterologous expression of Sf-SR-C in transgenic Drosophila midgut significantly enhanced the virulence of Vip3Aa to the Drosophila larvae. Moreover, the complement control protein domain and MAM domain of Sf-SR-C are involved in the interaction with Vip3Aa protoxin. Furthermore, endocytosis of Vip3Aa mediated by Sf-SR-C correlates with its insecticidal activity. Our results confirmed for the first time that Sf-SR-C acts as a receptor for Vip3Aa protoxin and provides an insight into the mode of action of Vip3Aa that will significantly facilitate the study of its insecticidal mechanism and application.
Highlights
IntroductionAs substitutes for chemical pesticides, are alternatives for insect control in crops
Microbial insecticides, as substitutes for chemical pesticides, are alternatives for insect control in crops
Scavenger receptor-C acts as the receptor for Vip3Aa role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Summary
As substitutes for chemical pesticides, are alternatives for insect control in crops. A signaling pathway model of the Cry toxin’s action has been reported [4, 5]. Several types of receptors for Cry toxins have been reported, such as aminopeptidase N (APN), the cadherinlike proteins, alkaline phosphatases, and ABC transporter [1, 7, 8]. Bt has been used successfully to control many crop pests by transgenic plant or traditional spray approaches, many pests are not sensitive to Cry toxins and a number of cases of insect resistance to Cry toxins have been reported as a result of laboratory or field selections [1,2,3]
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