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Transcriptomic analysis of octanoic acid response in Drosophila sechellia using RNA-sequencing

ABSTRACT: The dietary specialist fruit fly Drosophila sechellia has evolved to specialize on the toxic fruit of its host plant Morinda citrifolia. Toxicity of Morinda fruit is primarily due to high levels of octanoic acid (OA). Using RNA interference (RNAi), prior work found that knockdown of Osiris family genes Osiris 6 (Osi6), Osi7, and Osi8 led to increased susceptibility to OA in adult D. melanogaster flies, likely representing genes underlying a Quantitative Trait Locus (QTL) for OA resistance in D. sechellia. While genes in this major effect locus are beginning to be revealed, prior work has shown at least five regions of the genome contribute to OA resistance. Here, we identify new candidate OA resistance genes by performing differential gene expression analysis using RNA sequencing (RNA-seq) on control and OA-exposed D. sechellia flies. We found 104 significantly differentially expressed genes with annotated orthologs in D. melanogaster, including six Osiris gene family members, consistent with previous functional studies and gene expression analyses. Gene ontology (GO) term enrichment showed significant enrichment for cuticle development in upregulated genes and significant enrichment of immune and defense responses in downregulated genes suggesting important aspects of the physiology of D. sechellia that may play a role in OA resistance. In addition, we identified 5 candidate OA resistance genes that potentially underlie QTL peaks outside of the major effect region, representing promising new candidate genes for future functional studies.

ORGANISM(S): Drosophila sechellia

PROVIDER: GSE104422 | GEO | 2017/10/28

SECONDARY ACCESSION(S): PRJNA412586

REPOSITORIES: GEO

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Project description:The underlying genetic basis of adaptive phenotypic changes are generally poorly understood, yet a growing number of case studies are beginning to shed light on important questions about the molecular nature and pleiotropy of such changes. We use Drosophila sechellia, a dietary specialist fruit fly that has evolved to specialize on a single toxic host plant: Morinda citrifolia, as a model for adaptive phenotypic change and seek to determine the genetic basis of traits associated with host specialization in this species. The fruit of M. citrifolia is toxic to other Drosophilids, primarily due to high levels of the defense chemical octanoic acid (OA) yet D. sechellia has evolved resistance to OA. Our prior work identified three Osiris family genes that reside in a fine-mapped QTL for OA resistance: Osiris 6 (Osi6), Osi7, and Osi8, that can alter OA resistance in adult D. melanogaster when knocked-down with RNA interference (RNAi) suggesting they may contribute to OA resistance in D. sechellia. Genetic mapping identified overlapping genomic regions involved in larval and adult OA resistance in D. sechellia, yet it remains unknown whether Osiris genes contribute to resistance in both life stages. Furthermore, because multiple genomic regions contribute to OA resistance, we aim to identify other gene(s) involved in this adaptation. Here, we identify candidate larval OA resistance genes using RNA-sequencing to measure genome-wide differential gene expression in D. sechellia larvae after exposure to OA and functionally test identified genes for a role in OA resistance. We then test the Osiris genes previously shown to alter adult OA resistance for effects on OA resistance in larvae. While the genes identified by RNA-seq we tested in larvae thus far do not influence OA resistance, we found that Osi8 knockdown decreased OA resistance in D. melanogaster larvae. These data suggest that evolved changes in Osi8 could impact OA resistance in multiple life stages while Osi6 and Osi7 may only impact adult resistance to OA.

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Transcriptomic analysis of octanoic acid response in Drosophila sechellia using RNA-sequencing

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