Nasonia vitripennis venom causes targeted gene expression changes in its fly host

Abstract

Parasitoid wasps are diverse and ecologically important insects that use venom to modify their host's metabolism for the benefit of the parasitoid's offspring. Thus, the effects of venom can be considered an 'extended phenotype' of the wasp. The model parasitoid wasp Nasonia vitripennis has approximately 100 venom proteins, 23 of which do not have sequence similarity to known proteins. Envenomation by N. vitripennis has previously been shown to induce developmental arrest, selective apoptosis and alterations in lipid metabolism in flesh fly hosts. However, the full effects of Nasonia venom are still largely unknown. In this study, we used high throughput RNA sequencing (RNA-Seq) to characterize global changes in Sarcophaga bullata (Diptera) gene expression in response to envenomation by N. vitripennis. Surprisingly, we show that Nasonia venom targets a small subset of S. bullata loci, with ~2% genes being differentially expressed in response to envenomation. Strong upregulation of enhancer of split complex genes provides a potential molecular mechanism that could explain the observed neural cell death and developmental arrest in envenomated hosts. Significant increases in antimicrobial peptides and their corresponding regulatory genes provide evidence that venom could be selectively activating certain immune responses of the hosts. Further, we found differential expression of genes in several metabolic pathways, including glycolysis and gluconeogenesis that may be responsible for the decrease in pyruvate levels found in envenomated hosts. The targeting of Nasonia venom effects to a specific and limited set of genes provides insight into the interaction between the ectoparasitoid wasp and its host.

Keywords: enhancer of split; extended phenotype; parasitoid wasps; venom.

Fig. 1

Experimental design and comparisons conducted in present study. Each circle represents three replicates of five pooled hosts. (a) Comparisons to determine the effect of wounding by the ovipositor of Nasonia. (b) Comparisons within treatments to determine temporally changing gene expression. (c) Comparisons between treatments to determine the effects of Nasonia venom.

Fig. 2

Multidimensional scaling analysis showing clustering of treatment and replicates. Squares are replicates from envenomated host transcriptions and circles from normal developing host transcriptomes. The number in each designates the hours after envenomation the sample was collected.

Fig. 3

Comparing the number of differentially expressed genes in envenomated and normally developing hosts. (a) Number of significantly differentially expressed genes (adjusted P < 0.05) was determined by comparing 4-h hosts to each subsequent time point. (b) Overlap of differentially expressed genes among the temporally comparisons within envenomated and normally developing hosts as well as between the two treatments at each time point.

Fig. 4

Differential expression in fragments per kilobase per million (FPKM) of the enchancer of split complex between envenomated (solid line) and normally developing (dashed line) hosts at multiple time points.

Fig. 5

Changes in pyruvate metabolism in envenomated hosts. Metabolites measured in Mrinalini et al. (2014) are highlighted within circles, and genes measured in current study are labelled by their gene abbreviations listed below. Arrows indicate the direction of significantly changing genes or metabolites in envenomated hosts. ACO, aconitase; AR, aldose reductase; CS, citrate synthase; FUM, fumarase; IDH, isocitrate dehydrogenase;LDH, lactate dehydrogenase; MDH, malate dehydrogenase; ME, malic enzyme; OGDH, 2-oxoglutarate dehydrogenase complex; PC, pyruvate carboxylase; PDC, pyruvate dehydrogenase complex; PEPC, phosphoenolpyruvate carboxylase; PK, pyruvate kinase; SCS, succinyl CoA ligase; SDH, sorbitol dehydrogenase; SQR, succinate dehydrogenase.