Transcriptomic Analysis of Octanoic Acid Response in<i>Drosophila sechellia</i>Using RNA-Sequencing

Abstract

The dietary specialist fruit fly <i>Drosophila sechellia</i> has evolved to specialize on the toxic fruit of its host plant <i>Morinda citrifolia</i> Toxicity of <i>Morinda</i> fruit is primarily due to high levels of octanoic acid (OA). Using RNA interference (RNAi), prior work found that knockdown of <i>Osiris</i> family genes <i>Osiris 6</i> (<i>Osi6</i>), <i>Osi7</i>, and <i>Osi8</i> led to increased susceptibility to OA in adult <i>D. melanogaster</i> flies, likely representing genes underlying a Quantitative Trait Locus (QTL) for OA resistance in <i>D. sechellia</i> 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 <i>D. sechellia</i> flies. We found 104 significantly differentially expressed genes with annotated orthologs in <i>D. melanogaster</i>, including six <i>Osiris</i> 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 <i>D. sechellia</i> that may play a role in OA resistance. In addition, we identified five candidate OA resistance genes that potentially underlie QTL peaks outside of the major effect region, representing promising new candidate genes for future functional studies.