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Functional Genomics Studies on Nuclear Receptors: Target Sites for Insecticide Development and Resistance Management
Department of Entomology
A number of insect pests are developing resistance against insecticides. There is a need to discover new insecticides as well as to understand resistance development by insect pests. A combination of post-genomic technologies (RNA interference, polymerase chain reaction and microarray analysis) will be used to determine the function of Nuclear receptors in the red flour beetle, Tribolium castaneum. We will determine protein:protein interactions of these NRs in two-hybrid assay in beetle cell line and develop reporter assays that can be used to screen for agonists and antagonists of NRs. We will also determine the role of select NRs (TcHR96, TcHNF4 and TcRXR) in development of resistance against insecticides by performing RNAi and microarray analysis in T. castaneum strain that showed resistance against synthetic pyrethroids (Pyr-R) in comparison with the susceptible Lab-S strain.
2011 Project Description
Cytochrome P450-mediated detoxification is one of the most important mechanisms involved in insecticide resistance. However, the molecular basis of this mechanism and the physiological functions of P450s associated with insecticide resistance remain largely unknown.
Here, we exploited the functional genomics and reverse genetic approaches to identify and characterize a P450 gene responsible for the majority of deltamethrin resistance observed in the QTC279 strain of Tribolium castaneum. We used recently completed whole-genome sequence of T. castaneum to prepare custom microarrays and identified a P450 gene, CYP6BQ9, which showed more than a 200-fold higher expression in the deltamethrin-resistant QTC279 strain when compared with its expression in the deltamethrin-susceptible Lab-S strain.
Functional studies using both double-strand RNA (dsRNA)-mediated knockdown in the expression of CYP6BQ9 and transgenic expression of CYP6BQ9 in Drosophila melanogaster showed that CYP6BQ9 confers deltamethrin resistance. Furthermore, CYP6BQ9 enzyme expressed in baculovirus metabolizes deltamethrin to 4-hydroxy deltamethrin. Strikingly, we also found that unlike many P450 genes involved in insecticide resistance that were reported previously, CYP6BQ9 is predominantly expressed in the brain, a part of the central nervous system (CNS) containing voltage-gated sodium channels targeted by deltamethrin.
Taken together, the current studies on the brain-specific insect P450 involved in deltamethrin resistance shed new light on the understanding of the molecular basis and evolution of insecticide resistance
The findings reported here will help in fighting insecticide resistance.
Palli S.R., Bai H. and Wigginton J. (2011) Insect genomics. In: Insect Molecular Biology and Biochemistry. Gilbert L.I. (eds) Academic Press PP 2-23.