Abstract
BackgroundRelatively recent evidence indicates that ABCC2 transporters play a main role in the mode of action of Bacillus thuringiensis (Bt) Cry1A-type proteins. Mapping of major Cry1A resistance genes has linked resistance to the ABCC2 locus in Heliothis virescens, Plutella xylostella, Trichoplusia ni and Bombyx mori, and mutations in this gene have been found in three of these Bt-resistant strains.ResultsWe have used a colony of Spodoptera exigua (Xen-R) highly resistant to a Bt commercial bioinsecticide to identify regions in the S. exigua genome containing loci for major resistance genes by using bulk segregant analysis (BSA). Results reveal a region containing three genes from the ABCC family (ABBC1, ABBC2 and ABBC3) and a mutation in one of them (ABBC2) as responsible for the resistance of S. exigua to the Bt commercial product and to its key Spodoptera-active ingredients, Cry1Ca. In contrast to all previously described mutations in ABCC2 genes that directly or indirectly affect the extracellular domains of the membrane protein, the ABCC2 mutation found in S. exigua affects an intracellular domain involved in ATP binding. Functional analyses of ABBC2 and ABBC3 support the role of both proteins in the mode of action of Bt toxins in S. exigua. Partial silencing of these genes with dsRNA decreased the susceptibility of wild type larvae to both Cry1Ac and Cry1Ca. In addition, reduction of ABBC2 and ABBC3 expression negatively affected some fitness components and induced up-regulation of arylphorin and repat5, genes that respond to Bt intoxication and that are found constitutively up-regulated in the Xen-R strain.ConclusionsThe current results show the involvement of different members of the ABCC family in the mode of action of B. thuringiensis proteins and expand the role of the ABCC2 transporter in B. thuringiensis resistance beyond the Cry1A family of proteins to include Cry1Ca.
Highlights
Recent evidence indicates that ABCC2 transporters play a main role in the mode of action of Bacillus thuringiensis (Bt) Cry1A-type proteins
Genes coding for insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have been transferred to plants to protect them from the attack of insect pests [1,2] and the global impact of this strategy has been unprecedented in plant biotechnology
Our approach using NGS and bulk segregant analysis (BSA) applied to S. exigua has pinpointed two genomic regions with high segregation distortion that have a high probability of containing genes involved in the resistance to B. thuringiensis
Summary
Recent evidence indicates that ABCC2 transporters play a main role in the mode of action of Bacillus thuringiensis (Bt) Cry1A-type proteins. All B. thuringiensis crystal proteins (Cry proteins) which are toxic to target insects share general traits in their mode of action: solubilization in the midgut, activation by gut proteases, binding to membrane surface proteins (generally referred to as ‘receptors’) [6,7]. Susceptible insects have epitopes in their membrane receptors that are recognized by sequences of the Cry proteins. This is probably the main reason why Cry proteins are not harmful to non-target insects [8]. The key role of membrane receptors has become evident when studying the biochemical basis of insect resistance to Cry toxins. Most cases of high level resistance to Cry1A proteins have been shown to be due to a decrease of toxin binding to midgut receptors [9]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
