BackgroundPhosphine is a valuable fumigant to control pest populations in stored grains and grain products. However, recent studies indicate a substantial increase in phosphine resistance in stored product pests worldwide.ResultsTo understand the molecular bases of phosphine resistance in insects, we used RNA-Seq to compare gene expression in phosphine-resistant and susceptible laboratory populations of the red flour beetle, Tribolium castaneum. Each population was evaluated as either phosphine-exposed or no phosphine (untreated controls) in triplicate biological replicates (12 samples total). Pairwise analysis indicated there were eight genes differentially expressed between susceptible and resistant insects not exposed to phosphine (i.e., basal expression) or those exposed to phopshine (>8-fold expression and 90 % C.I.). However, 214 genes were differentially expressed among all four treatment groups at a statistically significant level (ANOVA, p < 0.05). Increased expression of 44 cytochrome P450 genes was found in resistant vs. susceptible insects, and phosphine exposure resulted in additional increases of 21 of these genes, five of which were significant among all treatment groups (p < 0.05). Expression of two genes encoding anti-diruetic peptide was 2- to 8-fold reduced in phosphine-resistant insects, and when exposed to phosphine, expression was further reduced 36- to 500-fold compared to susceptible. Phosphine-resistant insects also displayed differential expression of cuticle, carbohydrate, protease, transporter, and many mitochondrial genes, among others. Gene ontology terms associated with mitochondrial functions (oxidation biological processes, monooxygenase and catalytic molecular functions, and iron, heme, and tetrapyyrole binding) were enriched in the significantly differentially expressed dataset. Sequence polymorphism was found in transcripts encoding a known phosphine resistance gene, dihydrolipoamide dehydrogenase, in both susceptible and resistant insects. Phosphine-resistant adults also were resistant to knockdown by the pyrethroid deltamethrin, likely due to the increased cytochrome P450 expression.ConclusionsOverall, genes associated with the mitochondria were differentially expressed in resistant insects, and these differences may contribute to a reduction in overall metabolism and energy production and/or compensation in resistant insects. These data provide the first gene expression data on the response of phosphine-resistant and -susceptible insects to phosphine exposure, and demonstrate that RNA-Seq is a valuable tool to examine differences in insects that respond differentially to environmental stimuli.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2121-0) contains supplementary material, which is available to authorized users.
BackgroundThe western corn rootworm, Diabrotica virgifera virgifera, is a pervasive pest of maize in North America and Europe, which has adapted to current pest management strategies. In advance of an assembled and annotated D. v. virgifera genome, we developed transcriptomic resources to use in identifying candidate genes likely to be involved in the evolution of resistance, starting with members of the ATP-binding cassette (ABC) transporter family.ResultsIn this study, 65 putative D. v. virgifera ABC (DvvABC) transporters were identified within a combined transcriptome assembly generated from embryonic, larval, adult male, and adult female RNA-sequence libraries. Phylogenetic analysis placed the deduced amino-acid sequences of the DvvABC transporters into eight subfamilies (A to H). To supplement our sequence data with functional analysis, we identified orthologs of Tribolium castaneum ABC genes which had previously been shown to exhibit overt RNA interference (RNAi) phenotypes. We identified eight such D. v. virgifera genes, and found that they were functionally similar to their T. castaneum counterparts. Interestingly, depletion of DvvABCB_39715 and DvvABCG_3712 transcripts in adult females produced detrimental reproductive and developmental phenotypes, demonstrating the potential of these genes as targets for RNAi-mediated insect control tactics.ConclusionsBy combining sequence data from four libraries covering three distinct life stages, we have produced a relatively comprehensive de novo transcriptome assembly for D. v. virgifera. Moreover, we have identified 65 members of the ABC transporter family and provided the first insights into the developmental and physiological roles of ABC transporters in this pest species.
Background The western corn rootworm, Diabrotica virgifera virgifera , is a pervasive pest of cultivated maize in North America and Europe, which has adapted to survive exposure to multiple insecticidal agents. Due to their role in insecticide transport, we sought to identify members of the ATP-binding cassette (ABC) transporter family in D. v. virgifera using a transcriptomics approach.Results In this study, 65 putative D. v. virgifera ABC ( Dvv ABC) transporters were identified within a combined transcriptome assembly generated from embryonic, larval, adult male, and adult female RNA-sequence libraries. Phylogenetic analysis placed the deduced amino-acid sequences of the Dvv ABC transporters into eight subfamilies (A to H). Of these, eight shared structural and functional conservation with Tribolium castaneum ABC transporter orthologs known to exhibit overt RNA interference (RNAi) knockdown phenotypes. Interestingly, depletion of DvvABCB_19147 and DvvABCG_3712 transcripts in adult females produced detrimental reproductive and developmental phenotypes (egg-laying or -hatching defects), demonstrating the potential of these genes as targets for RNAi-mediated insect control tactics.Conclusions By combining sequence data from four libraries covering three distinct life stages, we have produced a relatively comprehensive de novo transcriptome assembly for D. v. virgifera . Moreover, we have identified 65 members of the ABC transporter family, and provided the first insights into the developmental and physiological roles of ABC transporters in this pest species.
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