Transcriptomic identification and characterization of genes commonly responding to sublethal concentrations of six...

Pretreatment with sublethal concentrations (LC₁₀) of six insecticides (chlorantraniliprole, cypermethrin, dinotefuran, indoxacarb, ivermectin, and spinosad) significantly elevated tolerance of the common fruit fly Drosophila melanogaster to lethal concentration of the respective insecticide. Commonly responding genes to sublethal treatments of the six insecticides were identified by transcriptome analysis based on a fold change >1.5 or < -1.5, and p < 0.05 as selection criteria. Following treatment with all the six insecticides, 26 transcripts were commonly over-transcribed, whereas 30 transcripts were commonly under-transcribed. Reliability of the transcriptome data was confirmed by quantitative PCR. A majority of the over-transcribed genes included those related to olfactory behavior, such as odorant-binding proteins, as well as immune-related genes, including attacin, diptericin, and immune-induced molecule 18. In contrast, genes belonging to the mitochondrial respiratory chain, such as mitochondrial NADH-ubiquinone oxidoreductase chain 1/3/4/5 and mitochondrial cytochrome b/c, were commonly under-transcribed. Furthermore, genes related to eggshell formation and motion were also under-transcribed, which may indicate a possible energy trade-off for xenobiotic stress. In summary, most of the differentially expressed genes were not directly related to well-known detoxification genes, suggesting that the roles of commonly expressed tolerance-related genes are not likely related to direct metabolic detoxification, but rather are associated with restoration of homeostasis.