Variation in Mitochondria-Derived Transcript Levels Associated With DDT Resistance in the 91-R Strain of Drosophila melanogaster (Diptera: Drosophilidae)

Abstract

The organochloride insecticide dichlorodiphenyltrichloroethane (DDT) and its metabolites can increase cellular levels of reactive oxygen species (ROS), cause mitochondrial dysfunction, and induce apoptosis. The highly DDT-resistant Drosophila melanogaster Meigen 1830 (Drosophila) strain, 91-R, and its susceptible control, 91-C, were used to investigate functional and structural changes among mitochondrial-derived pathways. Resequencing of mitochondrial genomes (mitogenomes) detected no structural differences between 91-R and 91-C, whereas RNA-seq suggested the differential expression of 221 mitochondrial-associated genes. Reverse transcriptase-quantitative PCR validation of 33 candidates confirmed that transcripts for six genes (Cyp12d1-p, Cyp12a4, cyt-c-d, COX5BL, COX7AL, CG17140) were significantly upregulated and two genes (Dif, Rel) were significantly downregulated in 91-R. Among the upregulated genes, four genes are duplicated within the reference genome (cyt-c-d, CG17140, COX5BL, and COX7AL). The predicted functions of the differentially expressed genes, or known functions of closely related genes, suggest that 91-R utilizes existing ROS regulation pathways of the mitochondria to combat increased ROS levels from exposure to DDT. This study represents, to our knowledge, the initial investigation of mitochondrial genome sequence variants and functional adaptations in responses to intense DDT selection and provides insights into potential adaptations of ROS management associated with DDT selection in Drosophila.

Fig. 1.

Candidate genes identified via RNA-seq analysis, which was replicated for four different reference sequences from 1) Compiled, 2) Nuclear, 3) DDT-Lit, and 4) Mitogenome gene sets. Black bars represent upregulated genes, and gray bars represent downregulated genes in the Drosophila melanogaster DDT-resistant strain 91-R compared to the DDT-susceptible strain 91-C.

Fig. 2.

Gene ontology (GO) annotations for a merged list of all 221 unique differentially expressed candidate genes for (a) molecular function, (b) biological process, and (c) cellular component, with the number of genes indicated after each GO annotation term. GO terms annotations obtained from flybase.org, and GO categories defined by the Gene Ontology Consortium (geneontology.org). Differentially expressed genes were determined via a comparison of the Drosophila melanogaster DDT-resistant strain 91-R and the DDT-susceptible strain 91-C.

Fig. 2.

Gene ontology (GO) annotations for a merged list of all 221 unique differentially expressed candidate genes for (a) molecular function, (b) biological process, and (c) cellular component, with the number of genes indicated after each GO annotation term. GO terms annotations obtained from flybase.org, and GO categories defined by the Gene Ontology Consortium (geneontology.org). Differentially expressed genes were determined via a comparison of the Drosophila melanogaster DDT-resistant strain 91-R and the DDT-susceptible strain 91-C.