Year of Publication

2017

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture, Food and Environment

Department

Entomology

First Advisor

Dr. Subba Reddy Palli

Abstract

Insecticide resistance is a global problem. Insecticide resistance management is very important, considering the time, effort, and cost of discovering and developing a new insecticide. There are diverse resistance mechanisms, but enhanced detoxification through overexpression of cytochrome P450s and target site insensitivity through mutation in insecticide binding site are the two most common mechanisms. The xenobiotic detoxification is divided into three successive phases (I, II and III), which ensures the metabolism and excretion of the detrimental toxins. Each phase comprises of a specific group of metabolizing enzymes such as P450s (phase I), GSTs (phase II) and ABC transporters (phase III). The major goal of my research was to understand the molecular mechanism of insecticide resistance in two economically important coleopteran pests, Leptinotarsa decemlineata and Tribolium castaneum. The transcriptional regulation of the P450 genes mediating insecticide resistance in L. decemlineata (imidacloprid-resistant) and T. castaneum (deltamethrin-resistant) were studied and the xenobiotic trans and cis-elements identified. RNA interference (RNAi), and reporter assays revealed that the cytochrome P450 genes involved in insecticide resistance are regulated by transcription factor Cap n Collar ‘CncC’ and muscle aponeurosis fibromatosis ‘Maf’ belonging to the b-ZIP transcription factor family. Site-directed mutagenesis was employed to identify the binding site for CncC and Maf. Sequencing of RNA isolated from CncC knockdown T. castaneum identified genes regulated by CncC and involved in insecticide detoxification. RNAi and insecticide bioassays confirmed the function of select phase II (glutathione-S-transferases) and phase III (ABC transporters) identified by RNA sequencing. Overall, these data revealed that the xenobiotic transcription factor CncC is the master regulator of multiple genes that are involved in insecticide resistance.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2017.073

Available for download on Sunday, April 21, 2019

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