Identification of major Toxoneuron nigriceps venom proteins using an integrated transcriptomic/proteomic approach

The salivary gland transcriptome of Varroa destructor reveals suitable targets for RNAi-based mite control

The mite Varroa destructor Anderson and Trueman (Mesostigmata: Varroidae) has a dramatic impact on beekeeping and is one of the main causes of honey bee colony losses. This ectoparasite feeds on honey bees' liquid tissues, through a wound created on the host integument, determining weight loss and a reduction of lifespan, as well as the transmission of viral pathogens. However, despite its importance, the mite feeding strategy and the host regulation role by the salivary secretions have been poorly explored. Here, we contribute to fill this gap by identifying the salivary components of V. destructor, to study their functional importance for mite feeding and survival. The differential expression analysis identified 30 salivary gland genes encoding putatively secreted proteins, among which only 15 were found to be functionally annotated. These latter include proteins with putative anti-bacterial, anti-fungal, cytolytic, digestive and immunosuppressive function. The three most highly transcribed genes, coding for a chitin-binding domain protein, a Kazal domain serine protease inhibitor and a papain-like cysteine protease were selected to study their functional importance by reverse genetics. Knockdown (90%-99%) by RNA interference (RNAi) of the transcript of a chitin-binding domain protein, likely interfering with the immune reaction to facilitate mite feeding, was associated with a 40%-50% decrease of mite survival. This work expands our knowledge of the host regulation and nutritional exploitation strategies adopted by ectoparasites of arthropods and allows the identification of potential targets for RNAi, paving the way towards the development of new strategies for Varroa mite control.

Lipid Metabolism in Parasitoids and Parasitized Hosts

Parasitoids have an exceptional lifestyle where juvenile development is spent on or in a single host insect, but the adults are free-living. Unlike parasites, parasitoids kill the host. How parasitoids use such a limiting resource, particularly lipids, can affect chances to survive and reproduce. In part 1, we describe the parasitoid lifestyle, including typical developmental strategies. Lipid metabolism in parasitoids has been of interest to researchers since the 1960s and continues to fascinate ecologists, evolutionists, physiologists, and entomologists alike. One reason of this interest is that the majority of parasitoids do not accumulate triacylglycerols as adults. Early research revealed that some parasitoid larvae mimic the fatty acid composition of the host, which may result from a lack of de novo triacylglycerol synthesis. More recent work has focused on the evolution of lack of adult triacylglycerol accumulation and consequences for life history traits. In part 2 of this chapter, we discuss research efforts on lipid metabolism in parasitoids from the 1960s onwards. Parasitoids are also master manipulators of host physiology, including lipid metabolism, having evolved a range of mechanisms to affect the release, synthesis, transport, and take-up of lipids from the host. We lay out the effects of parasitism on host physiology in part 3 of this chapter.

Peeking into the Stingers: A Comprehensive SWATH-MS Study of the European Hornet Vespa crabro (Linnaeus, 1758) (Hymenoptera: Vespidae) Venom Sac Extracts

This study aimed to investigate the venom sac extracts (VSEs) of the European hornet (EH) Vespa crabro (Linnaeus, 1758) (Hymenoptera: Vespidae), focusing on the differences between stinging females, gynes (G), and workers (W), at the protein level. Using a quantitative "Sequential Window Acquisition of all Theoretical Fragment Ion Mass Spectra" (SWATH-MS) analysis, we identified and quantified a total of 240 proteins. Notably, within the group, 45.8% (n = 110) showed significant differential expression between VSE-G and VSE-W. In this set, 57.3% (n = 63) were upregulated and 42.7% (n = 47) downregulated in the G. Additionally, the two-hundred quantified proteins from the class Insecta belong to sixteen different species, six of them to the Hymenoptera/Apidae lineage, comprising seven proteins with known potential allergenicity. Thus, phospholipase A1 (Vesp v 1), phospholipase A1 verutoxin 2b (VT-2b), hyaluronidase A (Vesp v 2A), hyaluronidase B (Vesp v 2B), and venom allergen 5 (Vesp v 5) were significantly downregulated in the G, and vitellogenin (Vesp v 6) was upregulated. Overall, 46% of the VSE proteins showed differential expression, with a majority being upregulated in G. Data are available via ProteomeXchange with identifier PXD047955. These findings shed light on the proteomic differences in VSE between EH castes, potentially contributing to our understanding of their behavior and offering insights for allergy research.

Proteomic analyses of venom from a Spider Hawk, Pepsis decorata

Background

The composition of the venom from solitary wasps is poorly known, although these animals are considered sources of bioactive substances. Until the present moment, there is only one proteomic characterization of the venom of wasps of the family Pompilidae and this is the first proteomic characterization for the genus Pepsis.

Methods

To elucidate the components of Pepsis decorata venom, the present work sought to identify proteins using four different experimental conditions, namely: (A) crude venom; (B) reduced and alkylated venom; (C) trypsin-digested reduced and alkylated venom, and; (D) chymotrypsin-digested reduced and alkylated venom. Furthermore, three different mass spectrometers were used (Ion Trap-Time of Flight, Quadrupole-Time of Flight, and Linear Triple Quadruple).

Results

Proteomics analysis revealed the existence of different enzymes related to the insect's physiology in the venom composition. Besides toxins, angiotensin-converting enzyme (ACE), hyaluronidase, and Kunitz-type inhibitors were also identified.

Conclusion

The data showed that the venom of Pepsis decorata is mostly composed of proteins involved in the metabolism of arthropods, as occurs in parasitic wasps, although some classical toxins were recorded, and among them, for the first time, ACE was found in the venom of solitary wasps. This integrative approach expanded the range of compounds identified in protein analyses, proving to be efficient in the proteomic characterization of little-known species. It is our understanding that the current work will provide a solid base for future studies dealing with other Hymenoptera venoms.

An Overview of Ovarian Calyx Fluid Proteins of Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae): An Integrated Transcriptomic and Proteomic Approach

The larval stages of the tobacco budworm, Heliothis virescens (Fabricius) (Lepidoptera: Noctuidae), are parasitized by the endophagous parasitoid wasp, Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae). During the injections of eggs, this parasitoid wasp also injects into the host body the secretion of the venom gland and the calyx fluid, which contains a polydnavirus (T. nigriceps BracoVirus: TnBV) and the Ovarian calyx fluid Proteins (OPs). The effects of the OPs on the host immune system have recently been described. In particular, it has been demonstrated that the OPs cause hemocytes to undergo a number of changes, such as cellular oxidative stress, actin cytoskeleton modifications, vacuolization, and the inhibition of hemocyte encapsulation capacity, which results in both a loss of hemocyte functionality and cell death. In this study, by using a combined transcriptomic and proteomic analysis, the main components of T. nigriceps ovarian calyx fluid proteins were identified and their possible role in the parasitic syndrome was discussed. This study provides useful information to support the analysis of the function of ovarian calyx fluid proteins, to better understand T. nigriceps parasitization success and for a more thorough understanding of the components of ovarian calyx fluid proteins and their potential function in combination with other parasitoid factors.

Multi-Omic Identification of Venom Proteins Collected from Artificial Hosts of a Parasitoid Wasp

Habrobracon hebetor is a parasitoid wasp capable of infesting many lepidopteran larvae. It uses venom proteins to immobilize host larvae and prevent host larval development, thus playing an important role in the biocontrol of lepidopteran pests. To identify and characterize its venom proteins, we developed a novel venom collection method using an artificial host (ACV), i.e., encapsulated amino acid solution in paraffin membrane, allowing parasitoid wasps to inject venom. We performed protein full mass spectrometry analysis of putative venom proteins collected from ACV and venom reservoirs (VRs) (control). To verify the accuracy of proteomic data, we also collected venom glands (VGs), Dufour's glands (DGs) and ovaries (OVs), and performed transcriptome analysis. In this paper, we identified 204 proteins in ACV via proteomic analysis; compared ACV putative venom proteins with those identified in VG, VR, and DG via proteome and transcriptome approaches; and verified a set of them using quantitative real-time polymerase chain reaction. Finally, 201 ACV proteins were identified as potential venom proteins. In addition, we screened 152 and 148 putative venom proteins identified in the VG transcriptome and the VR proteome against those in ACV, and found only 26 and 25 putative venom proteins, respectively, were overlapped with those in ACV. Altogether, our data suggest proteome analysis of ACV in combination with proteome-transcriptome analysis of other organs/tissues will provide the most comprehensive identification of true venom proteins in parasitoid wasps.

Rho 1 participates in parasitoid wasp eggs maturation and host cellular immunity inhibition

Endoparasitoid wasps introduce venom into their host insects during the egg-laying stage. Venom proteins play various roles in the host physiology, development, immunity, and behavior manipulation and regulation. In this study, we identified a venom protein, MmRho1, a small guanine nucleotide-binding protein derived from ovary in the endoparasitoid wasp Microplitis mediator and found that knockdown of its expression by RNA interference caused down-regulation of vitellogenin and juvenile hormone, egg production, and cocoons formation in the female wasps. We demonstrated that MmRho1 entered the cotton bollworm's (host) hemocytes and suppressed cellular immune responses after parasitism using immunofluorescence staining. Furthermore, wasp MmRho1 interacted with the cotton bollworm's actin cytoskeleton rearrangement regulator diaphanous by yeast 2-hybrid and glutathione s-transferase pull-down. In conclusion, this study indicates that MmRho1 plays dual roles in wasp development and the suppression of the host insect cellular immune responses.

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.

Two venom serpins from the parasitoid wasp Microplitis mediator inhibit the host prophenoloxidase activation and antimicrobial peptide synthesis

Endoparasitoid wasps inject venom proteins into the hemocoel of host insects to ensure survival, growth, and development of their progenies by blocking host immunity. We previously identified ten serine protease inhibitors of the serpin superfamily in venom of the endoparasitoid wasp, Microplitis mediator, but it is unclear how these inhibitors may interact with host immune serine proteases. In this study, we investigated the functions of two serpins, MmvSPN-1 and MmvSPN-2, in the regulation of humoral immune responses in two hosts, the oriental armyworm Pseudaletia separate and the cotton bollworm Helicoverpa armigera, by dsRNA knockdown and biochemical assays using recombinant proteins. Knockdown of the two serpins resulted in increases in prophenoloxidase (PPO) activation and antimicrobial peptide (AMP) production in the hosts. After injection into the host hemocoel, the recombinant serpins inhibited PPO activation and AMP transcription. Mass spectrometry analysis of the pull-downs and in vitro reconstitution experiments revealed that HacSP29, a clip-domain serine protease in H. armigera, is the target of these two serpins. Therefore, these two inhibitors in the wasp venom may protect eggs from attacks by melanization and AMPs in the host insects.

Protein and volatile contents in the mandibular gland of the sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae)

The sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae) is an important sugarcane pest and mechanical injuries caused through the mandibles can allow pathogen infections. The mandibles of D. saccharalis, as well as other insects, are associated with mandibular glands with a possible function in food intake and mouthparts lubrication; however, the chemical composition of the secretion is poorly known and its elucidation is important for the comprehensive understanding of plant-insect interactions. This study characterized some proteins and volatiles in the mandibular glands of D. saccharalis larvae. MALDI-TOF/TOF mass spectrometry allowed the identification of 24 predicted proteins within 10 functional classes, including the transport and metabolism of carbohydrates, lipids, amino acids, and nucleotides; Posttranslational protein modifications; energy conversion; intracellular trafficking; transcription; translation; and cytoskeleton function. Metabolites identified from GC/MS analysis revealed the presence of hydrocarbons classified as alcohols, ether, alkanes, and esters with differences in their relative abundance. Linolenic acid, the most abundant metabolite found in this gland, when conjugated with amino acids, can be an elicitor in the plant-herbivore interaction. The results suggest the occurrence of digestive and defensive biochemical components, which may contribute to understanding of the multifunctional roles of the mandibular gland secretion of D. saccharalis larvae during feeding activity.

Proteotranscriptomics reveals the secretory dynamics of teratocytes, regulators of parasitization by an endoparasitoid wasp

Parasitoid wasps have evolved sophisticated mechanisms of host regulation that establish a favorable environment for the development of immature parasitoids. While maternal venom and symbiotic virus-like particles are well-known mechanisms of host regulation, another less-studied mechanism is the secretion of host regulation factors by cells called teratocytes, extra-embryonic cells released during parasitoid larval eclosion. Consequently, identification and characterization of teratocyte secretory products has not been reported in detail for any parasitoid wasp. We aimed to analyze teratocyte secretory products released into hemolymph of the larval sugarcane borer Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae) by its biological control agent, the koinobiont endoparasitoid wasp Cotesia flavipes Cameron, 1891 (Hymenoptera: Braconidae). Teratocytes were released upon eclosion of parasitoid larvae four days after parasitization (DAP) and increased in number and size until six DAP. Total D. saccharalis hemocyte viability was reduced immediately after parasitization until DAP 2, while total hemocyte count was lower from the third DAP, and phenoloxidase and lysozyme activity were disrupted compared to non-parasitized controls. To examine the secretory products of teratocytes, we generated a teratocyte transcriptome and compared its in silico translated open reading frames to mass spectra obtained from hemolymph from parasitized and unparasitized hosts. This led to the identification of 57 polypeptides secreted by teratocytes, the abundance of which we tracked over 0-10 DAP. Abundant teratocyte products included proteins similar to bracovirus proteins and multiple disulfide-rich peptides. Most teratocyte products accumulated in hemolymph, reaching their highest concentrations immediately before parasitoid pupation. Our results provide insights into host regulation by teratocytes and reveal molecules that may be useful in biotechnology.

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.

Identification and Functional Characterization of Toxoneuron nigriceps Ovarian Proteins Involved in the Early Suppression of Host Immune Response

The endophagous parasitoid Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) of the larval stages of the tobacco budworm Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae) injects the egg, the venom, the calyx fluid, which includes a Polydnavirus (T. nigriceps BracoVirus: TnBV) and the Ovarian Proteins (OPs) into the host body during oviposition. The host metabolism and immune system are disrupted prematurely shortly after parasitization by the combined action of the TnBV, venom, and OPs. OPs are involved in the early suppression of host immune response, before TnBV infects and expresses its genes in the host tissues. In this work, we evaluated the effect of HPLC fractions deriving from in toto OPs. Two fractions caused a reduction in hemocyte viability and were subsequently tested to detect changes in hemocyte morphology and functionality. The two fractions provoked severe oxidative stress and actin cytoskeleton disruption, which might explain the high rate of hemocyte mortality, loss of hemocyte functioning, and hence the host’s reduced hemocyte encapsulation ability. Moreover, through a transcriptome and proteomic approach we identify the proteins of the two fractions: eight proteins were identified that might be involved in the observed host hemocyte changes. Our findings will contribute to a better understanding of the secreted ovarian components and their role in parasitoid wasp strategy for evading host immune responses.

Amount of venom that Leptopilina species inject into Drosophila melanogaster larvae in relation to parasitic success

The Drosophila endoparasitoid wasps Leptopilina boulardi and L. heterotoma (Hymenoptera: Cynipidae) are pro-ovigenic species, i.e., females contain their lifetime number of mature eggs at emergence. They are therefore able to immediately parasitize many hosts when present. In response to parasitoid oviposition, the larval host D. melanogaster can mount an immune response, encapsulation, that can destroy the parasitoid eggs. This response is counteracted by the venom the wasp injects during oviposition. Here, we estimated the amount of venom injected into a D. melanogaster host larva using immunodetection of venom proteins and we attempted to correlate this amount with the number of eggs a female can lay on successive days. The venom reservoir of L. boulardi contains enough venom for at least 100 ovipositions while that of L. heterotoma contains venom for about 16 ovipositions. While a female L. boulardi may have enough venom for three days of parasitism when 20 or 40 larval hosts were presented each day, L. heterotoma certainly needs to synthesize new venom to parasitize the number of hosts offered. Interestingly, parasitism stopped (L. boulardi), egg protection (L. heterotoma) and egg hatching decreased (both species) after three days of parasitism. Thus, although venom does not appear to be a limiting factor for parasitism, our data suggest that it may have less effectiveness on the egg protection and on egg/host development after high repetitive egg laying.

Proteo-Transcriptomic Characterization of Sirex nitobei (Hymenoptera: Siricidae) Venom

The wood-boring woodwasp Sirex nitobei is a native pest in Asia, infecting and weakening the host trees in numerous ecological and commercial coniferous forest plantations. In China, hosts of S. nitobei are diverse, so the pest has spread to several provinces of China, resulting in considerable economic and ecological damage. During female oviposition, S. nitobei venom along with arthrospores of the symbiotic fungus Amylostereum areolatum or A. chaetica is injected into host trees, and the combination of these two biological factors causes the death of xylem host trees. The presence of venom alone causes only the yellowing and wilting of needles. In this study, we constructed the venom gland transcriptome of S. nitobei for the first time and a total of 15,036 unigenes were acquired. From the unigenes, 11,560 ORFs were identified and 537 encoding protein sequences with signal peptides at the N-terminus. Then, we used the venomics approach to characterize the venom composition of female S. nitobei and predicted 1095 proteins by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. We focused on seven proteins that were both highly expressed in the venom gland transcriptome and predicted in the crude venom proteome. These seven proteins are laccase-2, laccase-3, a protein belonging to the Kazal family, chitooligosaccharidolytic β-N-acetylglucosaminidase, beta-galactosidase, icarapin-like protein, and waprin-Thr1-like protein. Using quantitative real-time PCR (qRT-PCR), we also proved that the genes related to these seven proteins are specifically expressed in the venom glands. Finally, we revealed the functional role of S. nitobei venom in the physiological response of host trees. It can not only promote the colonization of symbiotic fungus but contribute to the development of eggs and larvae. This study provides a deeper understanding of the molecular mechanism of the woodwasp–pine interaction.

What Antarctic Plants Can Tell Us about Climate Changes: Temperature as a Driver for Metabolic Reprogramming

Global warming is strongly affecting the maritime Antarctica climate and the consequent melting of perennial snow and ice covers resulted in increased colonization by plants. Colobanthus quitensis is a vascular plant highly adapted to the harsh environmental conditions of Antarctic Peninsula and understanding how the plant is responding to global warming is a new challenging target for modern cell physiology. To this aim, we performed differential proteomic analysis on C. quitensis plants grown in natural conditions compared to plants grown for one year inside open top chambers (OTCs) which determine an increase of about 4 °C at midday, mimicking the effect of global warming. A thorough analysis of the up- and downregulated proteins highlighted an extensive metabolism reprogramming leading to enhanced photoprotection and oxidative stress control as well as reduced content of cell wall components. Overall, OTCs growth seems to be advantageous for C. quitensis plants which could benefit from a better CO₂ diffusion into the mesophyll and a reduced ROS-mediated photodamage.

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.

Role of Ovarian Proteins Secreted by Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) in the Early Suppression of Host Immune Response

Simple Summary

Toxoneuron nigriceps is an endoparasitoid of the tobacco budworm Heliothis virescens. Parasitoid strategies to survive involve different regulating factors that are injected into the host body together with the egg: the venom and the calyx fluid, containing a Polydnavirus (PDV) and Ovarian Proteins (OPs). The combination of these factors increases the success of parasitism. Although many studies have been reported on venom protein components and the knowledge on PDVs is increasing, little is known on OPs. These secretions are able to interfere early with the host cellular immune response, acting specifically on host haemocytes, cells involved in immune response. Our results show that OPs induce several alterations on haemocytes, including cellular oxidative stress condition and modifications of actin cytoskeleton, so inducing both a loss of haemocyte functionality and cell death. Overall, in synergy with PDV and venom, OPs positively contribute to the evasion of the host immune response by T. nigriceps.

Abstract

Toxoneuron nigriceps (Viereck) (Hymenoptera, Braconidae) is an endophagous parasitoid of the larval stages of the tobacco budworm, Heliothis virescens (Fabricius) (Lepidoptera, Noctuidae). During oviposition, T. nigriceps injects into the host body, along with the egg, the venom, the calyx fluid, which contains a Polydnavirus (T. nigriceps BracoVirus: TnBV), and the Ovarian Proteins (OPs). Although viral gene expression in the host reaches detectable levels after a few hours, a precocious disruption of the host metabolism and immune system is observed right after parasitization. This alteration appears to be induced by female secretions including TnBV venom and OPs. OPs, originating from the ovarian calyx cells, are involved in the induction of precocious symptoms in the host immune system alteration. It is known that OPs in braconid and ichneumonid wasps can interfere with the cellular immune response before Polydnavirus infects and expresses its genes in the host tissues. Here we show that T. nigriceps OPs induce several alterations on host haemocytes that trigger cell death. The OP injection induces an extensive oxidative stress and a disorganization of actin cytoskeleton and these alterations can explain the high-level of haemocyte mortality, the loss of haemocyte functionality, and so the reduction in encapsulation ability by the host.

Context-dependent venom deployment and protein composition in two assassin bugs

The Heteroptera are a diverse suborder of phytophagous, hematophagous, and zoophagous insects. The shift to zoophagy can be traced back to the transformation of salivary glands into venom glands, but the venom is used not only to kill and digest invertebrate prey but also as a defense strategy, mainly against vertebrates. In this study, we used an integrated transcriptomics and proteomics approach to compare the composition of venoms from the anterior main gland (AMG) and posterior main gland (PMG) of the reduviid bugs Platymeris biguttatus L. and Psytalla horrida Stål. In both species, the AMG and PMG secreted distinct protein mixtures with few interspecific differences. PMG venom consisted mostly of S1 proteases, redulysins, Ptu1-like peptides, and uncharacterized proteins, whereas AMG venom contained hemolysins and cystatins. There was a remarkable difference in biological activity between the AMG and PMG venoms, with only PMG venom conferring digestive, neurotoxic, hemolytic, antibacterial, and cytotoxic effects. Proteomic analysis of venom samples revealed the context-dependent use of AMG and PMG venom. Although both species secreted PMG venom alone to overwhelm their prey and facilitate digestion, the deployment of defensive venom was species-dependent. P. biguttatus almost exclusively used PMG venom for defense, whereas P. horrida secreted PMG venom in response to mild harassment but AMG venom in response to more intense harassment. This intriguing context-dependent use of defensive venom indicates that future research should focus on species-dependent differences in venom composition and defense strategies among predatory Heteroptera.

Reprograming of epigenetic mechanisms controlling host insect immunity and development in response to egg-laying by a parasitoid wasp

Parasitoids are insects that use other insects as hosts. They sabotage host cellular and humoral defences to promote the survival of their offspring by injecting viruses and venoms along with their eggs. Many pathogens and parasites disrupt host epigenetic mechanisms to overcome immune system defences, and we hypothesized that parasitoids may use the same strategy. We used the ichneumon wasp Pimpla turionellae as a model idiobiont parasitoid to test this hypothesis, with pupae of the greater wax moth Galleria mellonella as the host. We found that parasitoid infestation involves the suppression of host immunity-related effector genes and the modulation of host genes involved in developmental hormone signalling. The transcriptional reprogramming of host genes following the injection of parasitoid eggs was associated with changes in host epigenetic mechanisms. The introduction of parasitoids resulted in a transient decrease in host global DNA methylation and the modulation of acetylation ratios for specific histones. Genes encoding regulators of histone acetylation and deacetylation were mostly downregulated in the parasitized pupae, suggesting that parasitoids can suppress host transcription. We also detected a strong parasitoid-specific effect on host microRNAs regulating gene expression at the post-transcriptional level. Our data therefore support the hypothesis that parasitoids may favour the survival of their offspring by interfering with host epigenetic mechanisms to suppress the immune system and disrupt development.

An Integrated Proteomic and Transcriptomic Analysis Reveals the Venom Complexity of the Bullet Ant Paraponera clavata

A critical hurdle in ant venom proteomic investigations is the lack of databases to comprehensively and specifically identify the sequence and function of venom proteins and peptides. To resolve this, we used venom gland transcriptomics to generate a sequence database that was used to assign the tandem mass spectrometry (MS) fragmentation spectra of venom peptides and proteins to specific transcripts. This was performed alongside a shotgun liquid chromatography-mass spectrometry (LC-MS/MS) analysis of the venom to confirm that these assigned transcripts were expressed as proteins. Through the combined transcriptomic and proteomic investigation of Paraponera clavata venom, we identified four times the number of proteins previously identified using 2D-PAGE alone. In addition to this, by mining the transcriptomic data, we identified several novel peptide sequences for future pharmacological investigations, some of which conform with inhibitor cysteine knot motifs. These types of peptides have the potential to be developed into pharmaceutical or bioinsecticide peptides.

Insight into the Functional Diversification of Lipases in the Endoparasitoid Pteromalus puparum (Hymenoptera: Pteromalidae) by Genome-scale Annotation and Expression Analysis

Lipases play essential roles in digestion, transport, and processing of dietary lipids in insects. For parasitoid wasps with a unique life cycle, lipase functions could be multitudinous in particular. Pteromalus puparum is a pupal endoparasitoid of butterflies. The female adult deposits eggs into its host, along with multifunctional venom, and the developing larvae consume host as its main nutrition source. Parasitoid lipases are known to participate in the food digestion process, but the mechanism remains unclear. P. puparum genome and transcriptome data were interrogated. Multiple alignments and phylogenetic trees were constructed. We annotated a total of 64 predicted lipase genes belonging to five lipase families and suggested that eight venom and four salivary lipases could determine host nutrition environment post-parasitization. Many putative venom lipases were found with incomplete catalytic triads, relatively long β9 loops, and short lids. Data analysis reveals the loss of catalytic activities and weak triacylglycerol (TAG) hydrolytic activities of lipases in venom. Phylogenetic trees indicate various predicted functions of lipases in P. puparum. Our information enriches the database of parasitoid lipases and the knowledge of their functional diversification, providing novel insight into how parasitoid wasps manipulate host lipid storage by using venom lipases.

Profiling of quercetin glycosides and acyl glycosides in sun-dried peperoni di Senise peppers (Capsicum annuum L.) by a combination of LC-ESI(-)-MS/MS and polarity prediction in reversed-phase separations

Interest in targeted profiling of quercetin glycoconjugates occurring in edible foodstuffs continues to expand because of their recognized beneficial health effects. Quercetin derivatives encompass several thousands of chemically distinguishable compounds, among which there are several compounds with different glycosylations and acylations. Since reference standards and dedicated databases are not available, the mass spectrometric identification of quercetin glycoconjugates is challenging. A targeted liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) was applied for screening quercetin glycoconjugates in edible peperoni di Senise peppers (Capsicum annuum L.), protected by the European Union with the mark PGI (i.e., Protected Geographical Indication), and cultivated in Basilicata (Southern Italy). Chromatographic separation was accomplished by reversed-phase liquid chromatography (RPLC) using water/acetonitrile as the mobile phase and detection was performed on a linear ion trap mass spectrometer fitted with an electrospray ionization (ESI) source operating in negative ion mode. A correlation between experimental RP chromatographic retention time and those predicted by partition coefficients (log P) along with MS/MS data and an in-house developed database (named QUEdb) provided deep coverage for sixteen quercetin glycoconjugates. Among them, eleven quercetin glycoconjugates were already described in the literature and five were reported for the first time. These last acyl glycosidic quercetin derivatives were tentatively identified as quercetin-(galloyl-rhamnoside)-hexoside, [C₃₄H₃₃O₂₀]^- at m/z 761.1; quercetin-(sinapoyl-hexoside)-rhamnoside, [C₃₈H₃₉O₂₀]^- at m/z 815.4; quercetin-(galloyl-caffeoyl-hexoside)-rhamnoside, [C₄₃H₃₉O₂₃]^- at m/z 923.0; quercetin-(feruloyl-hexoside)-rhamnoside, [C₃₇H₃₇O₁₉]^- at m/z 785.1; and quercetin-(succinyl-rhamnoside)-rhamnoside, [C₃₁H₃₃O₁₈]^- at m/z 693.1. Graphical abstract.

Identification and Comparative Analysis of Venom Proteins in a Pupal Ectoparasitoid, Pachycrepoideus vindemmiae

Parasitoid wasps inject venom containing complex bioactive compounds to regulate the immune response and development of host arthropods and sometime paralyze host arthropods. Although extensive studies have been conducted on the identification of venom proteins in larval parasitoids, relatively few studies have examined the pupal parasitoids. In our current study, a combination of transcriptomic and proteomic methods was used to identify 64 putative venom proteins from Pachycrepoideus vindemmiae, an ectoparasitoid of Drosophila. Expression analysis revealed that 20 tested venom proteins have 419-fold higher mean expression in the venom apparatus than in other wasp tissues, indicating their specialization to venom. Comparisons of venom proteins from P. vindemmiae and other five species spanning three parasitoid families detected a core set of "ancient" orthologs in Pteromalidae. Thirty-five venom proteins of P. vindemmiae were assigned to the orthologous groups by reciprocal best matches with venoms of other pteromalids, while the remaining 29 were not. Of the 35 categories, twenty-seven have orthologous relationships with Nasonia vitripennis venom proteins and 25 with venoms of Pteromalus puparum. More distant relationships detected that five and two venom proteins of P. vindemmiae are orthologous with venoms of two Figitidae parasitoids and a Braconidae representative, respectively. Moreover, twenty-two venoms unique to P. vindemmiae were also detected, indicating considerable interspecific variation of venom proteins in parasitoids. Phylogenetic reconstruction based on a set of single-copy genes clustered P. vindemmiae with P. puparum, N. vitripennis, and other members of the family Pteromalidae. These findings provide strong evidence that P. vindemmiae venom proteins are well positioned for future functional and evolutionary studies.

Venomics of the ectoparasitoid wasp Bracon nigricans

BACKGROUND

Venom is one of the most important sources of regulation factors used by parasitic Hymenoptera to redirect host physiology in favour of the developing offspring. This has stimulated a number of studies, both at functional and "omics" level, which, however, are still quite limited for ectophagous parasitoids that permanently paralyze and suppress their victims (i.e., idiobiont parasitoids).

RESULTS

Here we present a combined transcriptomic and proteomic study of the venom of the generalist idiobiont wasp Bracon nigricans, an ectophagous larval parasitoid of different lepidopteran species, for which we recently described the host regulation strategy and the functional role of the venom in the induction of physiological changes in parasitized hosts. The experimental approach used led to the identification of the main components of B. nigricans venom involved in host regulation. Enzymes degrading lipids, proteins and carbohydrates are likely involved in the mobilization of storage nutrients from the fat body and may concurrently be responsible for the release of neurotoxic fatty acids inducing paralysis, and for the modulation of host immune responses.

CONCLUSION

The present work contributes to fill the gap of knowledge on venom composition in ectoparasitoid wasps, and, along with our previous physiological study on this species, provides the foundation on which to develop a functional model of host regulation, based both on physiological and molecular data. This paves the way towards a better understanding of parasitism evolution in the basal lineages of Hymenoptera and to the possible exploitation of venom as source of bioinsecticidal molecules.

Proteo-Transcriptomic Characterization of the Venom from the Endoparasitoid Wasp Pimpla turionellae with Aspects on Its Biology and Evolution

Within mega-diverse Hymenoptera, non-aculeate parasitic wasps represent 75% of all hymenopteran species. Their ovipositor dual-functionally injects venom and employs eggs into (endoparasitoids) or onto (ectoparasitoids) diverse host species. Few endoparasitoid wasps such as Pimpla turionellae paralyze the host and suppress its immune responses, such as encapsulation and melanization, to guarantee their offspring's survival. Here, the venom and its possible biology and function of P. turionellae are characterized in comparison to the few existing proteo-transcriptomic analyses on parasitoid wasp venoms. Multiple transcriptome assembly and custom-tailored search and annotation strategies were applied to identify parasitoid venom proteins. To avoid false-positive hits, only transcripts were finally discussed that survived strict filter settings, including the presence in the proteome and higher expression in the venom gland. P. turionella features a venom that is mostly composed of known, typical parasitoid enzymes, cysteine-rich peptides, and other proteins and peptides. Several venom proteins were identified and named, such as pimplin2, 3, and 4. However, the specification of many novel candidates remains difficult, and annotations ambiguous. Interestingly, we do not find pimplin, a paralytic factor in Pimpla hypochondriaca, but instead a new cysteine inhibitor knot (ICK) family (pimplin2), which is highly similar to known, neurotoxic asilid1 sequences from robber flies.

Regulation of the Larval Transcriptome of Diatraea saccharalis (Lepidoptera: Crambidae) by Maternal and Other Factors of the Parasitoid Cotesia flavipes (Hymenoptera: Braconidae)

Koinobiont endoparasitoid wasps regulate the host's physiology to their own benefit during their growth and development, using maternal, immature and/or derived-tissue weaponry. The tools used to subdue the wasps' hosts interfere directly with host transcription activity. The broad range of host tissues and pathways affected impedes our overall understanding of the host-regulation process during parasitoid development. Next-generation sequencing and de novo transcriptomes are helpful approaches to broad questions, including in non-model organisms. In the present study, we used Illumina sequencing to assemble a de novo reference transcriptome of the sugarcane borer Diatraea saccharalis, to investigate the regulation of host gene expression by the larval endoparasitoid Cotesia flavipes. We obtained 174,809,358 reads and assembled 144,116 transcripts, of which 44,325 were putatively identified as lepidopteran genes and represented a substantial number of pathways that are well described in other lepidopteran species. Comparative transcriptome analyses of unparasitized versus parasitized larvae identified 1,432 transcripts of D. saccharalis that were up-regulated under parasitization by C. flavipes, while 1,027 transcripts were down-regulated. Comparison of the transcriptomes of unparasitized and pseudoparasitized D. saccharalis larvae led to the identification of 1,253 up-regulated transcripts and 972 down-regulated transcripts in the pseudoparasitized larvae. Analysis of the differentially expressed transcripts showed that C. flavipes regulated several pathways, including the Ca+2 transduction signaling pathway, glycolysis/gluconeogenesis, chitin metabolism, and hormone biosynthesis and degradation, as well as the immune system, allowing us to identify key target genes involved in the metabolism and development of D. saccharalis.

Insights into the venom protein components of Microplitis mediator, an endoparasitoid wasp

Endoparasitoid wasps deliver a variety of maternal factors, such as venom proteins, viruses, and virus-like particles, from their venom and calyx fluid into hosts and thereby regulate the hosts' immune response, metabolism and development. The endoparasitoid, Microplitis mediator, is used as an important biological agent for controlling the devastating pest Helicoverpa armigera. In this study, using an integrated transcriptomic and proteomic analysis approach, we identified 75 putative venom proteins in M. mediator. The identified venom components were consistent with other known parasitoid wasps' venom proteins, including metalloproteases, serine protease inhibitors, and glycoside hydrolase family 18 enzymes. The metalloprotease and serpin family showed extensive gene duplications in venom apparatus. Isobaric tags for relative and absolute quantitation (iTRAQ) based quantitative proteomics revealed 521 proteins that were differentially expressed at 6 h and 24 h post-parasitism, including 10 wasp venom proteins that were released into the host hemolymph. Further analysis indicated that 511 differentially expressed proteins (DEP) from the host are primarily involved in the immune response, material metabolism, and extracellular matrix receptor interaction. Taken together, our results on parasitoid wasp venoms have the potential to enhance the application of endoparasitoid wasps for controlling insect pest.

Novel Factors of Viral Origin Inhibit TOR Pathway Gene Expression

Polydnaviruses (PDVs) are obligate symbionts of endoparasitoid wasps, which exclusively attack the larval stages of their lepidopteran hosts. The Polydnavirus is injected by the parasitoid female during oviposition to selectively infect host tissues by the expression of viral genes without undergoing replication. Toxoneuron nigriceps bracovirus (TnBV) is associated with Toxoneuron nigriceps (Hymenoptera: Braconidae) wasp, an endoparasitoid of the tobacco budworm larval stages, Heliothis virescens (Lepidoptera: Noctuidae). Previous studies showed that TnBV is responsible for alterations in host physiology. The arrest of ecdysteroidogenesis is the main alteration which occurs in last (fifth) instar larvae and, as a consequence, prevents pupation. TnBV induces the functional inactivation of H. virescens prothoracic glands (PGs), resulting in decreased protein synthesis and phosphorylation. Previous work showed the involvement of the PI3K/Akt/TOR pathway in H. virescens PG ecdysteroidogenesis. Here, we demonstrate that this cellular signaling is one of the targets of TnBV infection. Western blot analysis and enzyme immunoassay (EIA) showed that parasitism inhibits ecdysteroidogenesis and the phosphorylation of the two targets of TOR (4E-BP and S6K), despite the stimulation of PTTH contained in the brain extract. Using a transcriptomic approach, we identified viral genes selectively expressed in last instar H. virescens PGs, 48 h after parasitization, and evaluated expression levels of PI3K/Akt/TOR pathway genes in these tissues. The relative expression of selected genes belonging to the TOR pathway (tor, 4e-bp, and s6k) in PGs of parasitized larvae was further confirmed by qRT-PCR. The down-regulation of these genes in PGs of parasitized larvae supports the hypothesis of TnBV involvement in blocking ecdysteroidogenesis, through alterations of the PI3K/Akt/TOR pathway at the transcriptional level.

Parasitism and venom of ectoparasitoid Scleroderma guani impairs host cellular immunity

Venom is a prominently maternal virulent factor utilized by parasitoids to overcome hosts immune defense. With respect to roles of this toxic mixture involved in manipulating hosts immunity, great interest has been mostly restricted to Ichneumonoidea parasitoids associated with polydnavirus (PDV), of which venom is usually considered as a helper component to enhance the role of PDV, and limited Chalcidoidea species. In contrast, little information is available in other parasitoids, especially ectoparasitic species not carrying PDV. The ectoparasitoid Scleroderma guani injects venom into its host, Tenebrio molitor, implying its venom was involved in suppression of hosts immune response for successful parasitism. Thus, we investigated the effects of parasitism and venom of this parasitoid on counteracting the cellular immunity of its host by examining changes of hemocyte counts, and hemocyte spreading and encapsulation ability. Total hemocyte counts were elevated in parasitized and venom-injected pupae. The spreading behavior of both granulocytes and plasmatocytes was impaired by parasitization and venom. High concentration of venom led to more severely increased hemocyte counts and suppression of hemocyte spreading. The ability of hemocyte encapsulation was inhibited by venom in vitro. In addition to immediate effects observed, venom showed persistent interference in hosts cellular immunity. These results indicate that venom alone from S. guani plays a pivotal role in blocking hosts cellular immune response, serving as a regulator that guarantees the successful development of its progenies. The findings provide a foundation for further investigation of the underlying mechanisms in immune inhibitory action of S. guani venom.

First extensive characterization of the venom gland from an egg parasitoid: structure, transcriptome and functional role

The venom gland is a ubiquitous organ in Hymenoptera. In insect parasitoids, the venom gland has been shown to have multiple functions including regulation of host immune response, host paralysis, host castration and developmental alteration. However, the role played by the venom gland has been mainly studied in parasitoids developing in larval or pupal hosts while little is known for parasitoids developing in insect eggs. We conducted the first extensive characterization of the venom of the endoparasitoid Ooencyrtus telenomicida (Vassiliev), a species that develops in eggs of the stink bug Nezara viridula (L.). In particular we investigated the structure of the venom apparatus, its functional role and conducted a transcriptomic analysis of the venom gland. We found that injection of O. telenomicida venom induces: 1) a melanized-like process in N. viridula host eggs (host-parasitoid interaction), 2) impairment of the larval development of the competitor Trissolcus basalis (Wollaston) (parasitoid-parasitoid interaction). The O. telenomicida venom gland transcriptome reveals a majority of digestive enzymes (peptidases and glycosylases) and oxidoreductases (laccases) among the most expressed genes. The former enzymes are likely to be involved in degradation of the host resources for the specific benefit of the O. telenomicida offspring. In turn, alteration of host resources caused by these enzymes may negatively affect the larval development of the competitor T. basalis. We hypothesize that the melanization process induced by venom injection could be related to the presence of laccases, which are multicopper oxidases that belong to the phenoloxidases group. This work contributed to a better understanding of the venom in insect parasitoids and allowed to identify candidate genes whose functional role can be investigated in future studies.

Wasp venomic: Unravelling the toxins arsenal of Polybia paulista venom and its potential pharmaceutical applications

Polybia paulista (Hymenoptera: Vespidae) is a neotropical social wasp from southeast Brazil. As most social Hymenoptera, venom from P. paulista comprises a complex mixture of bioactive toxins ranging from low molecular weight compounds to peptides and proteins. Several efforts have been made to elucidate the molecular composition of the P. paulista venom. Data derived from proteomic, peptidomic and allergomic analyses has enhanced our understanding of the whole envenoming process caused by the insect sting. The combined use of bioinformatics, -omics- and molecular biology tools have allowed the identification, characterization, in vitro synthesis and recombinant expression of several wasp venom toxins. Some of these P. paulista - derived bioactive compounds have been evaluated for the rational design of antivenoms and the improvement of allergy specific diagnosis and immunotherapy. Molecular characterization of crude venom extract has enabled the description and isolation of novel toxins with potential biotechnological applications. Here, we review the different approaches that have been used to unravel the venom composition of P. paulista. We also describe the main groups of P. paulista - venom toxins currently identified and analyze their potential in the development of component-resolved diagnosis of allergy, and in the rational design of antivenoms and novel bioactive drugs.

Protein Discovery: Combined Transcriptomic and Proteomic Analyses of Venom from the Endoparasitoid Cotesia chilonis (Hymenoptera: Braconidae)

Many species of endoparasitoid wasps provide biological control services in agroecosystems. Although there is a great deal of information on the ecology and physiology of host/parasitoid interactions, relatively little is known about the protein composition of venom and how specific venom proteins influence physiological systems within host insects. This is a crucial gap in our knowledge because venom proteins act in modulating host physiology in ways that favor parasitoid development. Here, we identified 37 possible venom proteins from the polydnavirus-carrying endoparasitoid Cotesia chilonis by combining transcriptomic and proteomic analyses. The most abundant proteins were hydrolases, such as proteases, peptidases, esterases, glycosyl hydrolase, and endonucleases. Some components are classical parasitoid venom proteins with known functions, including extracellular superoxide dismutase 3, serine protease inhibitor and calreticulin. The venom contains novel proteins, not recorded from any other parasitoid species, including tolloid-like proteins, chitooligosaccharidolytic β-N-acetylglucosaminidase, FK506-binding protein 14, corticotropin-releasing factor-binding protein and vascular endothelial growth factor receptor 2. These new data generate hypotheses and provide a platform for functional analysis of venom components.

Comparative venomics of Psyttalia lounsburyi and P. concolor, two olive fruit fly parasitoids: a hypothetical role for a GH1 β-glucosidase

Venom composition of parasitoid wasps attracts increasing interest - notably molecules ensuring parasitism success on arthropod pests - but its variation within and among taxa is not yet understood. We have identified here the main venom proteins of two braconid wasps, Psyttalia lounsburyi (two strains from South Africa and Kenya) and P. concolor, olive fruit fly parasitoids that differ in host range. Among the shared abundant proteins, we found a GH1 β-glucosidase and a family of leucine-rich repeat (LRR) proteins. Olive is extremely rich in glycoside compounds that are hydrolyzed by β-glucosidases into defensive toxic products in response to phytophagous insect attacks. Assuming that Psyttalia host larvae sequester ingested glycosides, the injected venom GH1 β-glucosidase could induce the release of toxic compounds, thus participating in parasitism success by weakening the host. Venom LRR proteins are similar to truncated Toll-like receptors and may possibly scavenge the host immunity. The abundance of one of these LRR proteins in the venom of only one of the two P. lounsburyi strains evidences intraspecific variation in venom composition. Altogether, venom intra- and inter-specific variation in Psyttalia spp. were much lower than previously reported in the Leptopilina genus (Figitidae), suggesting it might depend upon the parasitoid taxa.