Comparative CYPomic analysis between the DDT susceptible and resistant Drosophila melanogaster strains 91-C and 91-R

Authors: SEONG, KEON MOOK - Michigan State University; Coates, Brad; BERENBAUM, MAY - University Of Illinois; CLARK, JOHN - University Of Massachusetts; PITTENDRIGH, BARRY - Michigan State University

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2018
Publication Date: 10/11/2018
Citation: Seong, K., Coates, B.S., Berenbaum, M.R., Clark, J.M., Pittendrigh, B.R. 2018. Comparative CYPomic analysis between the DDT susceptible and resistant Drosophila melanogaster strains 91-C and 91-R. Pest Management Science. 74(11):2530-2543. https://doi.org/10.1002/ps.4936.
DOI: https://doi.org/10.1002/ps.4936

Interpretive Summary: The adaptation of insect populations to chemical insecticides is a threat to sustainable agriculture practices worldwide, and the mechanisms by which insects adapt remain poorly understood. An ARS research in conjunction with university collaborators used a genomic approach to investigate the changes in a gene family, the cytochrome P450 monooxygenases, associated with the evolution of Dichlorodiphenyltrichloroethane (DDT) resistance within the fruit fly strain 91-R. This system serves as a model to study the evolution of insecticide resistance on a genome-wide scale, which can be used to gain insight into analogous traits among crop pest species. A combination of changes in gene expression and structural mutations were described across all P450 genes in the fruit fly, of which a subset showed constitutive changes between 91-R and a susceptible control strain, 91-C. These results show that directional selection can act upon multiple components of a biochemical pathway which might acted concertedly to provide high levels of resistance. The findings are pertinent university, government, and private sector scientists interested in understanding the mechanisms by which chemical insecticide resistance develops in insect populations.

Technical Abstract: The cytochrome P450 monooxygenases (P450s or CYPs) are involved in the biosynthesis and degradation of endogenous intracellular compounds and the detoxification of xenobiotics, including chemical insecticides. However, comparatively little is known about the genetic diversity of P450 genes within insects with respect to the evolution of chemical insecticide resistance. To partially address this knowledge gap, the impact of multigenerational dichloro-diphenyl-trichloroethane (DDT) selection on the fruit fly strain 91-R was used to model the diversity of P450 expression and allelic variation compared to a control strain, 91-C. RNA-Seq and quantitative real-time PCR estimated the significance of seven up- and three down-regulated P450 genes in the 91-R strain, of which 6 up-regulated transcripts were in the Cyp6 family previously implicated in metabolic resistance to insecticides in this species. The three transcripts down-regulated in 91-R belong to the Cyp4 and Cyp9 families. Nonsynonymous (amino acid-changing) mutations were found in 63 of 85 CYPs, but only 122 were fixed differently between 91-R and 91-C, and 16 P450 genes (18.4%) had amino acid changes within functional domains. Ten P450s proteins (11.5%) were truncated due to premature stop codons, of which three were fixed between strains. These results provide a genome-wide snapshot of functional and structural changes in P450 genes between strains 91-R and 91-C. Furthermore, a combination of changes in P450 protein-coding regions and transcript expression levels are associated with DDT resistance, and thereby suggest variation of this gene family in response to the long-term DDT selection.