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Isolation of transcripts from Diabrotica virgifera virgifera LeConte responsive to the Bacillus thuringiensis toxin Cry3Bb1
Citation:
SAYED, M., B. E. WIECHMAN, MARK E. SMITH, W. French, C. Nielsen, AND M. J. BAGLEY. Isolation of transcripts from Diabrotica virgifera virgifera LeConte responsive to the Bacillus thuringiensis toxin Cry3Bb1. Insect Molecular Biology. Blackwell Publishing, Malden, MA, 19(3):381-389, (2010).
Impact/Purpose:
This research effort is designed to provide the risk assessment community with modern genetic tools for evaluating long-term risks of genetically modified (GM) crops. Molecular population genetic data can potentially reveal information about long-term trends in both pest populations targeted by plant-incorporated pesticides (PIPs) and non-target populations. EPA regulations require specific pest management strategies to slow the evolution of resistance in target pest populations in order to prolong the environmental benefits of GM crops (i.e., reduced use of chemical pesticides). A key component of this research effort will be to provide detailed information on pest biology, including gene flow and mating patterns in the wild (within species and between closely related species), geographic and chromosomal distribution of resistance alleles, and the additive and non-additive effects of genetic variation on resistance under selective pressures in the field. These data will be used to improve and validate models of insect resistance development with the goal of implementing best agricultural practices for delaying or preventing the development of pest resistance. These methods will be evaluated as a necessary component in the process of developing novel PIPs. Monitoring resistance in the field is also a key component of Bt-crop stewardship mandated by the EPA. We will develop potential resistance markers using candidate resistance genes. Potential resistance markers will be used to develop a rapid molecular screening tool for field analysis of resistance in the field. Molecular monitoring would be preferable over regular field monitoring of crop damage due to resistant insects since molecular monitoring can detect resistance before economic damage and before resistance is wide spread. Molecular monitoring can potentially be an early indicatory of resistance development and allow time for remediation efforts. The objective of this task is to develop genetic methodologies for evaluating and decreasing ecological risks posed by genetically modified crops. This research has the following aims: measurement of population genetic parameters for target pest populations in order to inform pest resistance management models; genetic analysis of resistance/ tolerance to Bt-toxin in laboratory pest strains to investigate the genetic basis of Bt resistance.
Description:
Crystal proteins derived from Bacillus thuringiensis (Bt) have been widely used as a method of insect pest management for several decades. In recent years, a transgenic corn expressing the Cry3Bb1 toxin has been successfully used for protection against corn rootworm larvae (Genus Diatbrotica). The biological action of the Bt toxin in corn rootworms has not yet been clearly defined. Because develoment of resistance to Bt by corn rootworms will have huge economic and ecological costs, insight into larval response to Bt toxin is highly desirable. We identified 19 unique transcripts from western corn rootworm (D. virgifera virgifera LeConte) that are responsive to transgenic Cry3Bb1 by subtraction hybridization and quantitative RT-PCR. Putative identities of these genes were consistent with impacts on metabolism and development. Analysis of four highly modulated transcripts resulted in the characterization of novel genes coding for a cystein-rich secretory protein and a glutamine-rich membrane protein. A third gene encodes a nondescript 132 amino acid protein while the fourth remains uncharacterized. Expression patterns of these genes were strikingly different between susceptible and resistant western corn rootworm populations. These genes may provide useful targets for monitoring of Bt resistance in pest populations and could be developed as indicators for monitoring sublethal Bt exposure and effects on non-target insects.