Inhibition of Melanization by a Parasitoid Serine Protease Homolog Venom Protein Requires Both the Clip and the Non-Catalytic Protease-Like Domains

Transcriptome Analysis Reveals the Venom Genes of the Ectoparasitoid Habrobracon hebetor (Hymenoptera: Braconidae)

The ectoparasitoid Habrobracon hebetor (Hymenoptera: Braconidae) exhibits a broad parasitic capability towards various lepidopteran pests, with venom serving as a crucial virulent factor ensuring successful parasitization and subsequent host mortality. Analyzing the constituents of its venom is essential for elucidating the mechanisms underlying efficient host killing by this parasitoid and for exploring potentially functional venom proteins. Through a transcriptomic analysis, a total of 34 venom proteins were identified within the venom of H. hebetor, encompassing known components such as serine protease, metalloproteinase, esterase, and serine protease inhibitors commonly present in parasitoid venoms. Unique components like paralytic protein and ion transport peptide-like were identified, possibly specific to certain parasitoids, along with novel proteins with uncharacterized functions. Spatial gene expression profiling of the identified venom proteins using transcriptomic data, corroborated by quantitative PCR validation for 13 randomly selected proteins, revealed abundant expression levels in the venom apparatus, affirming them as genuine venom components. Notably, the paralytic protein exhibited prominent expression, with the highest FPKM (fragments per kilobase of transcript per million fragments mapped) value of 24,704.87 in the venom apparatus, indicative of its significant role in successful parasitism by H. hebetor. The identification of these venom proteins establishes a foundation for the further exploration of bioactive agents for pest management strategies.

The venom composition and parthenogenesis mechanism of the parasitoid wasp Microctonus hyperodae, a declining biocontrol agent

A biocontrol system in New Zealand using the endoparasitoid Microctonus hyperodae is failing, despite once being one of the most successful examples of classical biocontrol worldwide. Though it is of significant economic importance as a control agent, little is known about the genetics of M. hyperodae. In this study, RNA-seq was used to characterise two key traits of M. hyperodae in this system, the venom, critical for the initial success of biocontrol, and the asexual reproduction mode, which influenced biocontrol decline. Expanded characterisation of M. hyperodae venom revealed candidates involved in manipulating the host environment to source nutrition for the parasitoid egg, preventing a host immune response against the egg, as well as two components that may stimulate the host's innate immune system. Notably lacking from the venom-specific expression list was calreticulin, as it also had high expression in the ovaries. In-situ hybridisation revealed this ovarian expression was localised to the follicle cells, which may result in the deposition of calreticulin into the egg exochorion. Investigating the asexual reproduction of M. hyperodae revealed core meiosis-specific genes had conserved expression patterns with the highest expression in the ovaries, suggesting M. hyperodae parthenogenesis involves meiosis and that the potential for sexual reproduction may have been retained. Upregulation of genes involved in endoreduplication provides a potential mechanism for the restoration of diploidy in eggs after meiosis.

Knockout of Dicer-2 in the Sf9 cell line enhances the replication of Spodoptera frugiperda rhabdovirus and conditionally increases baculovirus replication

The Sf9 cell line, originally isolated from the ovarian tissue of Spodoptera frugiperda larvae, is widely used in academia and industry for the baculovirus-mediated production of recombinant proteins and virus-like particles. RNA interference (RNAi) is a conserved antiviral pathway present in eukaryotic organisms and is the primary antiviral defence mechanism in insects. Recent evidence has implicated RNAi as an antiviral response to baculovirus infection in Sf9 cells. To test this hypothesis, CRISPR/Cas9 technology was used to disable the RNAi pathway in Sf9 cells by knocking out Dicer-2, the protein responsible for cleaving viral double-stranded RNA precursors into short interfering RNAs. Infection of Dicer-2 knockout Sf9 cells with either the wild-type baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV), recombinant AcMNPV (rAcMNPV) expressing β-galactosidase (β-gal), or rAcMNPV expressing a wasp venom protein (Vn50) at a multiplicity of infection (m.o.i.) of 1 resulted in a modest increase in virus replication compared to control Sf9 cells under adherent culture conditions. In contrast, Dicer-2 knockout Sf9 monolayer or suspension cultures infected by the rAcMNPV expressing β-gal at higher m.o.i.s (3.5 and 20) did not exhibit increases in either viral DNA replication or β-gal production. Intriguingly, during long-term passaging in suspension, Dicer-2 knockout Sf9 cultures underwent transient crashes in cell proliferation and viability. It was discovered that these periods of low growth and viability coincided with a dramatic increase in the RNA levels of S. frugiperda rhabdovirus, a recently identified adventitious virus that persistently infects the Sf9 cell line, suggesting a role for Dicer-2 in managing chronic viral infections in this industrially relevant insect cell line.

A teratocyte-specific serpin from the endoparasitoid wasp Cotesia vestalis inhibits the prophenoloxidase-activating system of its host Plutella xylostella

Many endoparasitoids adopt several parasitic factors, such as venom, polydnavirus and teratocytes, to suppress the immune response of their associated hosts including melanization for successful parasitism. A teratocyte-specific expressed serpin gene, designated as CvT-serpin6, was identified from the parasitoid Cotesia vestalis. The immunoblot result suggested that CvT-serpin6 was secreted into extracellular space. qPCR results showed that CvT-serpin6 was mainly transcribed at later stages of parasitism, and the transcriptional abundance of CvT-serpin6 in teratocytes was significantly increased in response to the challenge of bacteria. Inhibitory assay indicated that recombinant CvT-serpin6 (rCvT-serpin6) could inhibit the activation of Plutella xylostella prophenoloxidase and ultimately resulted in the inhibition of melanization in P. xylostella haemolymph. Furthermore, we confirmed that rCvT-serpin6 could form SDS-stable complexes with activated PxPAP1 and PxPAP3 in a dose-dependent manner. Altogether, our results further shed insight into the molecular mechanisms that teratocytes involved in controlling host immune response.

An integrated transcriptomic and proteomic approach to identify the main Torymus sinensis venom components

During oviposition, ectoparasitoid wasps not only inject their eggs but also a complex mixture of proteins and peptides (venom) in order to regulate the host physiology to benefit their progeny. Although several endoparasitoid venom proteins have been identified, little is known about the components of ectoparasitoid venom. To characterize the protein composition of Torymus sinensis Kamijo (Hymenoptera: Torymidae) venom, we used an integrated transcriptomic and proteomic approach and identified 143 venom proteins. Moreover, focusing on venom gland transcriptome, we selected additional 52 transcripts encoding putative venom proteins. As in other parasitoid venoms, hydrolases, including proteases, phosphatases, esterases, and nucleases, constitute the most abundant families in T. sinensis venom, followed by protease inhibitors. These proteins are potentially involved in the complex parasitic syndrome, with different effects on the immune system, physiological processes and development of the host, and contribute to provide nutrients to the parasitoid progeny. Although additional in vivo studies are needed, initial findings offer important information about venom factors and their putative host effects, which are essential to ensure the success of parasitism.

Review of Venoms of Non-Polydnavirus Carrying Ichneumonoid Wasps

Parasitoids are predominantly insects that develop as larvae on or inside their host, also usually another insect, ultimately killing it after various periods of parasitism when both parasitoid larva and host are alive. The very large wasp superfamily Ichneumonoidea is composed of parasitoids of other insects and comprises a minimum of 100,000 species. The superfamily is dominated by two similarly sized families, Braconidae and Ichneumonidae, which are collectively divided into approximately 80 subfamilies. Of these, six have been shown to release DNA-containing virus-like particles, encoded within the wasp genome, classified in the virus family Polydnaviridae. Polydnaviruses infect and have profound effects on host physiology in conjunction with various venom and ovarial secretions, and have attracted an immense amount of research interest. Physiological interactions between the remaining ichneumonoids and their hosts result from adult venom gland secretions and in some cases, ovarian or larval secretions. Here we review the literature on the relatively few studies on the effects and chemistry of these ichneumonoid venoms and make suggestions for interesting future research areas. In particular, we highlight relatively or potentially easily culturable systems with features largely lacking in currently studied systems and whose study may lead to new insights into the roles of venom chemistry in host-parasitoid relationships as well as their evolution.

Venom serine proteinase homolog of the ectoparasitoid Scleroderma guani impairs host phenoloxidase cascade

The ant-like bethylid ectoparasitoid Scleroderma guani (Hymenoptera: Bethylidae) envenomates host to suppress immune response. Yet, the roles of its venom in inhibiting melanization of the host hemolymph have not been fully characterized. Here, we demonstrated that S. guani envenomation induced strong inhibition of melanization of the hemolymph from Tenebrio molitor (Coleoptera: Tenebrionidae), permitting the successful development of parasitoid offspring. To reveal venom component associated with such function, a serine proteinase homolog (SguaSPH) rich in the venom of S. guani was characterized. It was found that one of the catalytic triad residues for serine proteinase is absent in the amino acid sequence of SguaSPH. This venom component was abundantly expressed in venom apparatus and adult stages. By enzymatic assays, SguaSPH displayed low trypsin and no chymotrypsin activity, and was able to inhibit phenoloxidase activity in the hemolymph of Ostrinia furnacalis (Lepidoptera: Crambidae). The findings suggest that SguaSPH is essential for interfering with hemolymph melanization of S. guani envenomated host via phenoloxidase cascade disruption.

Superoxide dismutase from venom of the ectoparasitoid Scleroderma guani inhibits melanization of hemolymph

Superoxide dismutase (SOD) known as an important antioxidative stress protein has been recently found in venoms of several parasitoid wasps. However, its functions and characteristics as a virulent factor remain scarcely described. Here, we report the characterization of two venomous SOD genes (SguaSOD1 and SguaSOD3) from the ectoparasitoid, Scleroderma guani. The metal binding sites, cysteine amino acid positions and signature sequences of the SOD family were conserved within SguaSOD1 and SguaSOD3. Relatively high levels of their transcripts were observed in pupae followed a decrease in early adults, after which they had the highest transcriptions, indicating that their productions would be regulated in venom apparatus. Although the two genes showed lower expression in venom apparatus compared to head and thorax, the enzymatic assay revealed that SOD indeed had activity in venom. Further, we showed that recombinant SguaSOD3 suppressed melanization of host hemolymph, implying that this protein used as a virulent factor uniquely impacts the prophenoloxidase cascade.

Effects of ovarian fluid, venom and egg surface characteristics of Tetrastichus brontispae (Hymenoptera: Eulophidae) on the immune response of Octodonta nipae (Coleoptera: Chrysomelidae)

Although the importance of parasitoids as biocontrol agents has long been recognized, systematic studies of the physiological mechanisms are scarce, especially in those parasitoids that are able to successfully invade their hosts by activating host immune responses. This study explored this phenomenon by investigating the effects of ovarian fluid, venom and egg surface characteristics of Tetrastichus brontispae (Hymenoptera: Eulophidae) on host immunity. The results showed that the injection of venom alone induced higher phenoloxidase activity, while a mixture of ovarian plus venom fluids provoked higher granulocyte and plasmatocyte spreading ratios, highlighting the role that egg surface characteristics may play in successful parasitism. After thorough investigation, the presence of a hemomucin homologue was documented on the egg surface (which was named Tetrastichus brontispae adipocyte plasma membrane associated protein-like, TbAPMAP-like), while the absence of polydnaviruses, fibrous layers and virus-like filaments was confirmed. The higher encapsulation index of eggs incubated with TbAPMAP-like polyclonal antibody demonstrated the protection of the protein against encapsulation. These results contribute to our understanding of the mechanisms used by endoparasitoids to evade encapsulation during the early parasitism stage while enriching our knowledge of local active regulatory mechanisms. It is likely that this is the first study to determine the egg protective properties of TbAPMAP-like in host-parasite systems.

Venom Proteins from Parasitoid Wasps and Their Biological Functions

Parasitoid wasps are valuable biological control agents that suppress their host populations. Factors introduced by the female wasp at parasitization play significant roles in facilitating successful development of the parasitoid larva either inside (endoparasitoid) or outside (ectoparasitoid) the host. Wasp venoms consist of a complex cocktail of proteinacious and non-proteinacious components that may offer agrichemicals as well as pharmaceutical components to improve pest management or health related disorders. Undesirably, the constituents of only a small number of wasp venoms are known. In this article, we review the latest research on venom from parasitoid wasps with an emphasis on their biological function, applications and new approaches used in venom studies.