Functional analysis of a fatty acid binding protein produced by Aphidius ervi teratocytes

Insect Flight and Lipid Metabolism: Beyond the Classic Knowledge

Insects are the most successful animal group by various ecological and evolutionary metrics, including species count, adaptation diversity, biomass, and environmental influence. This book delves into the underlying reasons behind insects' dominance on Earth. Lipids play pivotal roles in insect biology, serving as fuel for physiological processes, signaling molecules, and structural components of biomembranes and providing waterproofing against dehydration, among other functions. The study of insect flight has been instrumental in advancing our understanding of insect metabolism, with the migratory locust (Locusta migratoria) and the tobacco hornworm (Manduca sexta) serving as prominent models. Throughout the 1980s and 1990s, numerous studies shed light on the role of adipokinetic hormone (AKH), a crucial neuropeptide in lipid mobilization, to support the extraordinary energy demands of insect flight. Remarkably, AKH was the first identified peptide hormone in insects. These pioneering works linking lipids and flight laid the groundwork for subsequent research characterizing the physiological roles of other neuroendocrine factors in energy substrate mobilization across diverse insect species. However, in the omics era, one may be surprised by the limited understanding of the complex cascade of events governing lipid supply to insect flight muscles. Thus, this chapter aims to provide a concise overview of the evolutionary significance of insect flight, emphasizing key advancements that expand our classical knowledge in this field. Ultimately, we hope this chapter serves as a modest tribute to the pioneering researchers of one of the most captivating areas in insect biology, inspiring further exploration into the myriad roles of lipids in insect biology.

The venom of Habrobracon hebetor induces alterations in host metabolism

The ability of parasitic wasps to manipulate a host's metabolism is under active investigation. Components of venom play a major role in this process. In the present work, we studied the effect of the venom of the ectoparasitic wasp Habrobracon hebetor on the metabolism of the greater wax moth host (Galleria mellonella). We identified and quantified 45 metabolites in the lymph (cell-free hemolymph) of wax moth larvae on the second day after H. hebetor venom injection, using NMR spectroscopy and liquid chromatography coupled with mass spectrometry. These metabolites included 22 amino acids, nine products of lipid metabolism (sugars, amines and alcohols) and four metabolic intermediates related to nitrogenous bases, nucleotides and nucleosides. An analysis of the larvae metabolome suggested that the venom causes suppression of the tricarboxylic acid cycle, an increase in the number of free amino acids in the lymph, an increase in the concentration of trehalose in the lymph simultaneously with a decrease in the amount of glucose, and destructive processes in the fat body tissue. Thus, this parasitoid venom not only immobilizes the prey but also modulates its metabolism, thereby providing optimal conditions for the development of larvae.

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.

Larvicidal activity of Acacia nilotica extracts against Culex pipiens and their suggested mode of action by molecular simulation docking

Mosquitoes are one of the deadliest and most hazardous animals on Earth, where they transmit several diseases that kill millions of people annually. There is an ongoing search almost everywhere in the world for more effective and contemporary ways to control mosquitoes other than pesticides. Phytochemicals are affordable, biodegradable biological agents that specialize in eliminating pests that represent a risk to public health. The effectiveness of Acacia nilotica methanol and aqueous leaf extracts against 4th instar larvae was evaluated. The results revealed that the methanol extract of A. nilotica had a noticeable influence on the mortality rate of mosquito larvae, especially at high concentrations. Not only did the mortality rate rise significantly, but the hatching of the mosquito eggs was potentially suppressed.Terpenes, fatty acids, esters, glycosides, pyrrolidine alkane, piperazine, and phenols were the most prevalent components in the methanol extract, while the aqueous extract of A. nilotica exclusively showed the presence of fatty acids. The insecticidal susceptibility tests of both aqueous and alcoholic extract of A. nilotica confirmed that the Acacia plant could serves as a secure and efficient substitute for chemical pesticides because of its promising effect on killing larvae and egg hatching delaying addition to their safety as one of the natural pesticides. Molecular docking study was performed using one of the crucial and life-controlling protein targets, fatty acid binding protein (FABP) and the most active ingredients as testing ligands to describe their binding ability. Most of the structurally related compounds to the co-crystallized ligand, OLA, like hexadecanoic acid furnished high binding affinity to the target protein with very strong and stable intermolecular hydrogen bonding and this is quite similar to OLA itself. Some other structural non-related compounds revealed extraordinarily strong binding abilities like Methoxy phenyl piperazine. Most of the binding reactivities of the majortested structures are due to high structure similarity between the positive control, OLA, and tested compounds. Such structure similarity reinforced with the binding abilities of some detected compounds in the A. nilotica extract could present a reasonable interpretation for its insecticidal activity via deactivating the FABP protein. The FABP4 enzyme inhibition activity was assessed for of both methanolic and aqueous of acacia plant extract and the inhibition results of methanol extract depicted noticeable potency if compared to orlistat, with half-maximal inhibitory concentration (IC50) of 0.681, and 0.535 µg/ml, respectively.

Honey Bee Larval Hemolymph as a Source of Key Nutrients and Proteins Offers a Promising Medium for Varroa destructor Artificial Rearing

Varroa destructor, a major ectoparasite of the Western honey bee Apis mellifera, is a widespread pest that damages colonies in the Northern Hemisphere. Throughout their lifecycle, V. destructor females feed on almost every developmental stage of their host, from the last larval instar to the adult. The parasite is thought to feed on hemolymph and fat body, although its exact diet and nutritional requirements are poorly known. Using artificial Parafilm™ dummies, we explored the nutrition of V. destructor females and assessed their survival when fed on hemolymph from bee larvae, pupae, or adults. We compared the results with mites fed on synthetic solutions or filtered larval hemolymph. The results showed that the parasites could survive for several days or weeks on different diets. Bee larval hemolymph yielded the highest survival rates, and filtered larval plasma was sufficient to maintain the mites for 14 days or more. This cell-free solution therefore theoretically contains all the necessary nutrients for mite survival. Because some bee proteins are known to be hijacked without being digested by the parasite, we decided to run a proteomic analysis of larval honey bee plasma to highlight the most common proteins in our samples. A list of 54 proteins was compiled, including several energy metabolism proteins such as Vitellogenin, Hexamerin, or Transferrins. These molecules represent key nutrient candidates that could be crucial for V. destructor survival.

Aphidius ervi venom regulates Buchnera contribution to host nutritional suitability

The association between the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and the endophagous parasitoid wasp Aphidius ervi Haliday (Hymenoptera: Braconidae) offers a unique model system for studying the molecular mechanisms underlying the complex interactions between the parasitoid, its host and the associated primary symbiont. Here, we investigate in vivo the functional role of the most abundant component of A. ervi venom, Ae-γ-glutamyl transpeptidase (Ae-γ-GT), which is known to induce host castration. Microinjections of double-stranded RNA into A. ervi pupae stably knocked down Ae-γ-GT1 and Ae-γ-GT2 paralogue genes in newly emerged females. These females were used to score the phenotypic changes both in parasitized hosts and in the parasitoid's progeny, as affected by a venom blend lacking Ae-γ-GT. Ae-γ-GT gene silencing enhanced growth both of host and parasitoid, supported by a higher load of the primary bacterial symbiont Buchnera aphidicola. Emerging adults showed a reduced survival and fecundity, suggesting a trade-off with body size. This demonstrates in vivo the primary role of Ae-γ-GT in host ovary degeneration and suggests that this protein counterbalances the proliferation of Buchnera likely triggered by other venom components. Our study provides a new approach to unravelling the complexity of aphid parasitoid venom in vivo, and sheds light on a novel role for Ae-γ-GT in host regulation.

Fatty acid binding protein is required for chitin biosynthesis in the wing of Drosophila melanogaster

Chitin, the major structural polysaccharide in arthropods such as insects and mites, is a linear polymer of N-acetylglucosamine units. The growth and development of insects are intimately coupled with chitin biosynthesis. The membrane-bound β-glycosyltransferase chitin synthase is known to catalyze the key polymerization step of N-acetylglucosamine. However, the additional proteins that might assist chitin synthase during chitin biosynthesis are not well understood. Recently, fatty acid binding protein (Fabp) has been suggested as a candidate that interacts with the chitin synthase Krotzkopf verkehrt (Kkv) in Drosophila melanogaster. Here, using split-ubiquitin membrane yeast two-hybrid and pull-down assays, we have demonstrated that the Fabp-B splice variant physically interacts with Kkv in vitro. The global knockdown of Fabp in D. melanogaster using RNA interference (RNAi) induced lethality at the larval stage. Moreover, in tissue-specific RNAi experiments, silenced Fabp expression in the epidermis and tracheal system caused a lethal larval phenotype. Fabp knockdown in the wings resulted in an abnormal wing development and uneven cuticular surface. In addition to reducing the chitin content in the first longitudinal vein of wings, Fabp silencing also caused the loss of procuticle laminate structures. This study revealed that Fabp plays an important role in chitin synthesis and contributes to a comprehensive understanding of the complex insect chitin biosynthesis.

Genome of the parasitoid wasp Cotesia chilonis sheds light on amino acid resource exploitation

Background

A fundamental feature of parasitism is the nutritional exploitation of host organisms by their parasites. Parasitoid wasps lay eggs on arthropod hosts, exploiting them for nutrition to support larval development by using diverse effectors aimed at regulating host metabolism. However, the genetic components and molecular mechanisms at the basis of such exploitation, especially the utilization of host amino acid resources, remain largely unknown. To address this question, here, we present a chromosome-level genome assembly of the parasitoid wasp Cotesia chilonis and reconstruct its amino acid biosynthetic pathway.

Results

Analyses of the amino acid synthetic pathway indicate that C. chilonis lost the ability to synthesize ten amino acids, which was confirmed by feeding experiments with amino acid-depleted media. Of the ten pathways, nine are known to have been lost in the common ancestor of animals. We find that the ability to synthesize arginine was also lost in C. chilonis because of the absence of two key genes in the arginine synthesis pathway. Further analyses of the genomes of 72 arthropods species show that the loss of arginine synthesis is common in arthropods. Metabolomic analyses by UPLC-MS/MS reveal that the temporal concentrations of arginine, serine, tyrosine, and alanine are significantly higher in host (Chilo suppressalis) hemolymph at 3 days after parasitism, whereas the temporal levels of 5-hydroxylysine, glutamic acid, methionine, and lysine are significantly lower. We sequence the transcriptomes of a parasitized host and non-parasitized control. Differential gene expression analyses using these transcriptomes indicate that parasitoid wasps inhibit amino acid utilization and activate protein degradation in the host, likely resulting in the increase of amino acid content in host hemolymph.

Conclusions

We sequenced the genome of a parasitoid wasp, C. chilonis, and revealed the features of trait loss in amino acid biosynthesis. Our work provides new insights into amino acid exploitation by parasitoid wasps, and this knowledge can specifically be used to design parasitoid artificial diets that potentially benefit mass rearing of parasitoids for pest control.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01313-3.

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 peroxisomal sterol carrier protein 2 (Scp2) contributes to lipid trafficking in differentiation and virulence of the insect pathogenic fungus Beauveria bassiana

Sterol carrier protein 2 (SCP2) represents a family of proteins binding a variety of lipids and plays essential roles in cellular physiology. However, its physiological roles are largely unknown in filamentous fungi. In this study, we functionally characterized an orthologous Scp2 gene in the filamentous insect pathogenic fungus Beauveria bassiana (BbScp2). BbScp2 was verified to be a peroxisomal protein and displayed different affinities to various lipids, with strong affinity to palmitic acid (PA) and ergosterol (ES). No significant binding activity was detected between protein and oleic acid (OA) or linoleic acid (LA). Ablation of BbScp2 did not cause significant effects on fungal growth on various carbon sources, but resulted in a modest reduction in conidial (49%) and blastospore yield (45%). In addition, exogenous lipids could recover the defectives in conidiation of ΔBbScp2 mutant strain. BbScp2 was required for the cytomembrane functionality in germlings, and its loss resulted in a more significant decrease in virulence indicated by cuticle infection assay than intrahemocoel injection assay. Our findings indicate that Scp2 links the lipid trafficking to the asexual differentiation and virulence of B. bassiana.

A serpin (CvT-serpin15) of teratocytes contributes to microbial-resistance in Plutella xylostella during Cotesia vestalis parasitism

BACKGROUND

Parasitic wasps are an important group of entomophagous insects for pest control. As parasitic wasps often lay eggs on or into their associated hosts, parasitoids evolve to utilize several factors including venom, polydnavirus (PDV) to alter host physiology for successful parasitism. Some taxa of endoparasitoids produce teratocytes, which are a type of cell that is released into host insects when wasp eggs hatch. Teratocytes display multifunction in parasitism such as host nutritional exploration, immune and developmental regulation, by secreting plenty of proteins into host hemocoel.

RESULTS

A serpin (CvT-serpin15) secreted by teratocytes was characterized. QPCR results showed the expressional level of CvT-serpin15 was upregulated following bacterial challenges. Enzyme activity experiment indicated the recombinant CvT-serpin15 protein could interfere with the growth of Gram-positive bacteria Staphylococcus aureus. The survival rate assay demonstrated CvT-serpin15 increased survival rate of Plutella xylostella infected by S. aureus.

CONCLUSION

CvT-serpin15 secreted by teratocytes would boost the host immune system when pathogens invade host hemocoel during parasitism, and ultimately protect the development of wasp larva from bacterial infection. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Variation in Parasitoid Virulence of Tetrastichus brontispae during the Targeting of Two Host Beetles

In host-parasitoid interactions, antagonistic relationship drives parasitoids to vary in virulence in facing different hosts, which makes these systems excellent models for stress-induced evolutionary studies. Venom compositions varied between two strains of Tetrastichus brontispae, Tb-Bl and Tb-On. Tb-Bl targets Brontispa longissima pupae as hosts, and Tb-On is a sub-population of Tb-Bl, which has been experimentally adapted to a new host, Octodonta nipae. Aiming to examine variation in parasitoid virulence of the two strains toward two hosts, we used reciprocal injection experiments to compare effect of venom/ovarian fluids from the two strains on cytotoxicity, inhibition of immunity and fat body lysis of the two hosts. We found that Tb-Onvenom was more virulent towards plasmatocyte spreading, granulocyte function and phenoloxidase activity than Tb-Blvenom. Tb-Blovary was able to suppress encapsulation and phagocytosis in both hosts; however, Tb-Onovary inhibition targeted only B. longissima. Our data suggest that the venom undergoes rapid evolution when facing different hosts, and that the wasp has good evolutionary plasticity.

Amino acid synthesis loss in parasitoid wasps and other hymenopterans

Insects utilize diverse food resources which can affect the evolution of their genomic repertoire, including leading to gene losses in different nutrient pathways. Here, we investigate gene loss in amino acid synthesis pathways, with special attention to hymenopterans and parasitoid wasps. Using comparative genomics, we find that synthesis capability for tryptophan, phenylalanine, tyrosine, and histidine was lost in holometabolous insects prior to hymenopteran divergence, while valine, leucine, and isoleucine were lost in the common ancestor of Hymenoptera. Subsequently, multiple loss events of lysine synthesis occurred independently in the Parasitoida and Aculeata. Experiments in the parasitoid Cotesia chilonis confirm that it has lost the ability to synthesize eight amino acids. Our findings provide insights into amino acid synthesis evolution, and specifically can be used to inform the design of parasitoid artificial diets for pest control.

A journey into the world of insect lipid metabolism

Lipid metabolism is fundamental to life. In insects, it is critical, during reproduction, flight, starvation, and diapause. The coordination center for insect lipid metabolism is the fat body, which is analogous to the vertebrate adipose tissue and liver. Fat body contains various different cell types; however, adipocytes and oenocytes are the primary cells related to lipid metabolism. Lipid metabolism starts with the hydrolysis of dietary lipids, absorption of lipid monomers, followed by lipid transport from midgut to the fat body, lipogenesis or lipolysis in the fat body, and lipid transport from fat body to other sites demanding energy. Lipid metabolism is under the control of hormones, transcription factors, secondary messengers and posttranscriptional modifications. Primarily, lipogenesis is under the control of insulin-like peptides that activate lipogenic transcription factors, such as sterol regulatory element-binding proteins, whereas lipolysis is coordinated by the adipokinetic hormone that activates lipolytic transcription factors, such as forkhead box class O and cAMP-response element-binding protein. Calcium is the primary-secondary messenger affecting lipid metabolism and has different outcomes depending on the site of lipogenesis or lipolysis. Phosphorylation is central to lipid metabolism and multiple phosphorylases are involved in lipid accumulation or hydrolysis. Although most of the knowledge of insect lipid metabolism comes from the studies on the model Drosophila; other insects, in particular those with obligatory or facultative diapause, also have great potential to study lipid metabolism. The use of these models would significantly improve our knowledge of insect lipid metabolism.

Aphidius ervi Teratocytes Release Enolase and Fatty Acid Binding Protein Through Exosomal Vesicles

The molecular bases of the host-parasitoid interactions in the biological system Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) and Aphidius ervi (Haliday) (Hymenoptera, Braconidae) have been elucidated allowing the identification of a gamma-glutamyl transpeptidase, the active component of maternal venom secretion, and teratocytes, the embryonic parasitic factors responsible for host physiology regulation after parasitization. Teratocytes, cells deriving from the dissociation of the serosa, the parasitoid embryonic membrane, are responsible for extra-oral digestion of host tissues in order to provide a suitable nutritional environment for the development of parasitoid larvae. Teratocytes rapidly grow in size without undergoing any cell division, synthesize, and release in the host hemolymph two proteins: a fatty acid binding protein (Ae-FABP) and an enolase (Ae-ENO). Ae-FABP is involved in transport of fatty acids deriving from host tissues to the parasitoid larva. Ae-ENO is an extracellular glycolytic enzyme that functions as a plasminogen like receptor inducing its activation to plasmin. Both Ae-FABP and Ae-ENO lack their signal peptides, and they are released in the extracellular environment through an unknown secretion pathway. Here, we investigated the unconventional mechanism by which teratocytes release Ae-FABP and Ae-ENO in the extracellular space. Our results, obtained using immunogold staining coupled with TEM and western blot analyses, show that these two proteins are localized in vesicles released by teratocytes. The specific dimension of these vesicles and the immunodetection of ALIX and HSP70, two exosome markers, strongly support the hypothesis that these vesicles are exosomes.

Lipid metabolism in insect disease vectors

More than a third of the world population is at constant risk of contracting some insect-transmitted disease, such as Dengue fever, Zika virus disease, malaria, Chagas' disease, African trypanosomiasis, and others. Independent of the life cycle of the pathogen causing the disease, the insect vector hematophagous habit is a common and crucial trait for the transmission of all these diseases. This lifestyle is unique, as hematophagous insects feed on blood, a diet that is rich in protein but relatively poor in lipids and carbohydrates, in huge amounts and low frequency. Another unique feature of these insects is that blood meal triggers essential metabolic processes, as molting and oogenesis and, in this way, regulates the expression of various genes that are involved in these events. In this paper, we review current knowledge of the physiology and biochemistry of lipid metabolism in insect disease vectors, comparing with classical models whenever possible. We address lipid digestion and absorption, hemolymphatic transport, and lipid storage by the fat body and ovary. In this context, both de novo fatty acid and triacylglycerol synthesis are discussed, including the related fatty acid activation process and the intracellular lipid binding proteins. As lipids are stored in order to be mobilized later on, e.g. for flight activity or survivorship, lipolysis and β-oxidation are also considered. All these events need to be finely regulated, and the role of hormones in this control is summarized. Finally, we also review information about infection, when vector insect physiology is affected, and there is a crosstalk between its immune system and lipid metabolism. There is not abundant information about lipid metabolism in vector insects, and significant current gaps in the field are indicated, as well as questions to be answered in the future.

Parasitic insect-derived miRNAs modulate host development

Parasitic wasps produce several factors including venom, polydnaviruses (PDVs) and specialized wasp cells named teratocytes that benefit the survival of offspring by altering the physiology of hosts. However, the underlying molecular mechanisms for the alterations remain unclear. Here we find that the teratocytes of Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella, and its associated bracovirus (CvBV) can produce miRNAs and deliver the products into the host via different ways. Certain miRNAs in the parasitized host are mainly produced by teratocytes, while the expression level of miRNAs encoded by CvBV can be 100-fold greater in parasitized hosts than non-parasitized ones. We further show that one teratocyte-produced miRNA (Cve-miR-281-3p) and one CvBV-produced miRNA (Cve-miR-novel22-5p-1) arrest host growth by modulating expression of the host ecdysone receptor (EcR). Altogether, our results show the first evidence of cross-species regulation by miRNAs in animal parasitism and their possible function in the alteration of host physiology during parasitism.

Cotesia vestalis teratocytes express a diversity of genes and exhibit novel immune functions in parasitism

Some endoparasitoid wasps lay eggs that produce cells called teratocytes. In this study, we sequenced and analyzed the transcriptome of teratocytes from the solitary endoparasitoid Cotesia vestalis (Braconidae), which parasitizes larval stage Plutella xylostella (Plutellidae). Results identified many teratocyte transcripts with potential functions in affecting host immune defenses, growth or metabolism. Characterization of teratocyte-secreted venom-like protein 8 (TSVP-8) indicated it inhibits melanization of host hemolymph in vitro, while two predicted anti-microbial peptides (CvT-def 1 and 3) inhibited the growth of bacteria. Results also showed the parasitized hosts lacking teratocytes experienced higher mortality after immune challenge by pathogens than hosts with teratocytes. Taken together, these findings indicate that C. vestalis teratocytes secrete products that alter host immune functions while also producing anti-microbial peptides with functions that help protect the host from infection by other organisms.

Extracellular matrix degradation via enolase/plasminogen interaction: Evidence for a mechanism conserved in Metazoa

BACKGROUND INFORMATION

While enolase is a ubiquitous metalloenzyme involved in the glycolytic pathway, it is also known as a multifunctional protein, since enolases anchored on the outer surface of the plasma membrane are involved in tissue invasion.

RESULTS

We have identified an extracellular enolase (Ae-ENO) produced by the teratocytes, embryonic cells of the insect parasitoid Aphidius ervi. We demonstrate that Ae-ENO, although lacking a signal peptide, accumulates in cytoplasmic vesicles oriented towards the cell membrane. Ae-ENO binds to and activates a plasminogen-like molecule inducing digestion of the host tissue and thereby ensuring successful parasitism.

CONCLUSIONS

These results support the hypothesis that plasminogen-like proteins exist in invertebrates. Interestingly the activation of a plasminogen-like protein is mediated by a mechanisms involving the surface enolase/fibrinolytic system considered, until now, exclusive of vertebrates, and that instead is conserved across species.

SIGNIFICANCE

To our knowledge, this is the first example of enolase mediated Plg-like binding and activation in insect cells, demonstrating the existence of an ECM degradation process via a Plg-like protein in invertebrates.

Host regulation and nutritional exploitation by parasitic wasps

The physiological alterations observed in naturally parasitized hosts are characterized by a number of reproductive and developmental changes. Some of these changes are also associated with alterations in host physiology that benefit the nutrition and development of wasp offspring. Here we review the breadth of host-parasitoid nutritional interactions, and discuss current understanding of underlying mechanisms. We also discuss priorities for future studies that could enhance understanding of basic questions about the parasitoid lifestyle and provide insights of value for insect control.

Identification of the main venom protein components of Aphidius ervi, a parasitoid wasp of the aphid model Acyrthosiphon pisum

Background

Endoparasitoid wasps are important natural enemies of the widely distributed aphid pests and are mainly used as biological control agents. However, despite the increased interest on aphid interaction networks, only sparse information is available on the factors used by parasitoids to modulate the aphid physiology. Our aim was here to identify the major protein components of the venom injected at oviposition by Aphidius ervi to ensure successful development in its aphid host, Acyrthosiphon pisum.

Results

A combined large-scale transcriptomic and proteomic approach allowed us to identify 16 putative venom proteins among which three γ-glutamyl transpeptidases (γ-GTs) were by far the most abundant. Two of the γ-GTs most likely correspond to alleles of the same gene, with one of these alleles previously described as involved in host castration. The third γ-GT was only distantly related to the others and may not be functional owing to the presence of mutations in the active site. Among the other abundant proteins in the venom, several were unique to A. ervi such as the molecular chaperone endoplasmin possibly involved in protecting proteins during their secretion and transport in the host. Abundant transcripts encoding three secreted cystein-rich toxin-like peptides whose function remains to be explored were also identified.

Conclusions

Our data further support the role of γ-GTs as key players in A. ervi success on aphid hosts. However, they also evidence that this wasp venom is a complex fluid that contains diverse, more or less specific, protein components. Their characterization will undoubtedly help deciphering parasitoid-aphid and parasitoid-aphid-symbiont interactions. Finally, this study also shed light on the quick evolution of venom components through processes such as duplication and convergent recruitment of virulence factors between unrelated organisms.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-342) contains supplementary material, which is available to authorized users.