Genetic and molecular analysis of a cytochrome P450 based pyrethroid resistance in the red flour beetle, Tribolium castaneum (Herbst)
Abstract
Detoxification by cytochrome P450 monooxygenases (P450s) is a major mechanism by which insect pests become resistant to insecticides. The purpose of the present study was to investigate the P450 basis of a high level pyrethroid resistance in the field derived Tribolium castaneum strain QTC279. QTC279 was shown to carry a major gene for pyrethroid resistance, PyrR, on linkage group 9 (LG9), approximately 20 cM from the morphological mutation pearl. Three-point mapping involving pearl and another mutant marker, cola, indicated a gene order of pearl-cola-PyrR. Initial toxicological studies indicated that the resistance conferred by PyrR was completely suppressed by the P450 inhibitor piperonyl butoxide. Moreover, microsomal preparations from pyrethroid resistant (R) strains contained higher levels of total P450 protein compared to those from the susceptible (S) strains, indicating that resistance was probably conferred, in part, by one or more P450 forms overexpressed in R strains. P450 gene fragments were cloned from R and S beetles to determine if any were differentially expressed. One P450 gene, CYP4Q4, was highly overexpressed in the R strains. This gene was positioned on LG9 relative to pearl, cola and the dominant LG9 mutation, Short elytra. The gene order was Short elytra-pearl-(cola, CYP4Q4). CYP4Q4 was found to be part of a gene cluster consisting of at least two other CYP4 genes that were not overexpressed in the R strains. Experimental matings were established to determine whether PyrR regulated CYP4Q4 expression as it conditioned pyrethroid resistance. Northern analysis revealed that highest levels of CYP4Q4 gene expression were seen only in the presence of the PyrR-R allele. The overexpression of CYP4Q4 appeared to be inherited as a completely dominant trait. Moreover, both pyrethroid resistance and overexpression of CYP4Q4 were observed irrespective of the CYP4Q4 alleles present in the beetles. The high constitutive overexpression of CYP4Q4 in QTC279, thus, appears to be controlled in trans by PyrR, indicating that PyrR may condition resistance by regulating the expression of at least one P450 gene.
Degree
Ph.D.
Advisors
Neal, Purdue University.
Subject Area
Entomology|Genetics
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