Olive fly transcriptomics analysis implicates energy metabolism genes in spinosad resistance

Abstract

BackgroundThe olive fly, Bactrocera oleae, is the most devastating pest of cultivated olives. Its control has been traditionally based on insecticides, mainly organophosphates and pyrethroids. In recent years, the naturalyte spinosad is used against the olive fly. As with other insecticides, spinosad is subject to selection pressures that have led to resistance development. Mutations in the α6 subunit of the nicotinic acetylcholine receptor (nAChR) have been implicated in spinosad resistance in several species (e.g., Drosophila melanogaster) but excluded in others (e.g., Musca domestica). Yet, additional mechanisms involving enhanced metabolism of detoxification enzymes (such as P450 monooxygenases or mixed function oxidases) have also been reported. In order to clarify the spinosad resistance mechanisms in the olive fly, we searched for mutations in the α6-subunit of the nAChR and for up-regulated genes in the entire transcriptome of spinosad resistant olive flies.ResultsThe olive fly α6-subunit of the nAChR was cloned from the laboratory sensitive strain and a spinosad selected resistant line. The differences reflected silent nucleotide substitutions or conserved amino acid changes. Additionally, whole transcriptome analysis was performed in the two strains in order to reveal any underlying resistance mechanisms. Comparison of over 13,000 genes showed that in spinosad resistant flies nine genes were significantly over-expressed, whereas ~40 were under-expressed. Further functional analyses of the nine over-expressed and eleven under-expressed loci were performed. Four of these loci (Yolk protein 2, ATP Synthase FO subunit 6, Low affinity cationic amino acid transporter 2 and Serine protease 6) showed consistently higher expression both in the spinosad resistant strain and in wild flies from a resistant California population. On the other side, two storage protein genes (HexL1 and Lsp1) and two heat-shock protein genes (Hsp70 and Hsp23) were unfailingly under-expressed in resistant flies.ConclusionThe observed nucleotide differences in the nAChR-α6 subunit between the sensitive and spinosad resistant olive fly strains did not advocate for the involvement of receptor mutations in spinosad resistance. Instead, the transcriptome comparison between the two strains indicated that several immune system loci as well as elevated energy requirements of the resistant flies might be necessary to lever the detoxification process.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-714) contains supplementary material, which is available to authorized users.

Comparative transcriptome analyses of deltamethrin-susceptible and -resistant Culex pipiens pallens by RNA-seq

“…In general, the most represented GO and KEGG categories were “metabolic process” and “metabolic pathway”, which were widely acknowledged to involve in insecticide metabolism (Copley 2000; Sagri et al 2014). …”

De novo assembly of the olive fruit fly (Bactrocera oleae) genome with linked-reads and long-read technologies minimizes gaps and provides exceptional Y chromosome assembly

“…The tissues and/or organs included eggs, larvae, pupae, heads, testes among others ( Supplementary Table S9). RNA-seq data was collected from these tissues and stages since they were used to address other important questions of the B. oleae biology, such as the reproductive and the olfactory system [28,29]. Between 29 and 55 million reads per sample were generated and used to perform de novo transcript assembly using Trinity [77].…”

“…Despite its economic importance in olive producing countries, several peculiarities of the olive fruit fly's biology (e.g., difficulty in rearing, high natural homozygosity, lack of phenotypic mutations) made the development of classical genetics tools an impossible task. More recently, however, the olive fruit fly has been the subject of several molecular and transcriptomics studies [26][27][28] (Reviewed in Sagri et al [29]).…”

Housekeeping in Tephritid insects: the best gene choice for expression analyses in the medfly and the olive fly

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