Expression of immune-response genes in lepidopteran host is suppressed by venom from an endoparasitoid, Pteromalus puparum

Proteomic Analysis of Histone Crotonylation Suggests Diverse Functions in Myzus persicae

Myzus persicae is one of the most important economic pests of cultivated crops. In the present study, we used an integrated approach involving high-performance liquid chromatography fractionation, affinity enrichment, and mass spectrometry-based proteomics to carry out a comprehensive proteomic analysis of lysine crotonylation in M. persicae. Altogether, 7530 lysine crotonylation sites were identified in 2452 protein groups. Intensive bioinformatic analyses were then carried out to annotate those lysine crotonylated targets identified in terms of Gene Ontology annotation, domain annotation, subcellular localization, Kyoto Encyclopedia of Genes and Genomes pathway annotation, functional cluster analysis, etc. Analysis results showed that lysine-crotonylated proteins were involved in many biological processes, such as the amino acid metabolism, aminoacyl-tRNA biosynthesis, spliceosomes, ribosomes, and so forth. Notably, the interaction network showed that there were 199 crotonylated proteins involved in the amino acid metabolism and numerous crotonylation targets associated with fatty acid biosynthesis and degradation. The results provide a system-wide view of the entire M. persicae crotonylome and a rich data set for functional analysis of crotonylated proteins in this economically important pest, which marks an important beginning for the further research.

Characterization of a cell death-inducing endonuclease-like venom protein from the parasitoid wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

BACKGROUND

Parasitoid wasps are valuable natural enemies for controlling pests. To ensure successful parasitism, these wasps inject venoms along with their eggs that are deposited either into or on their hosts. Parasitoid venoms regulate host behaviors, development, metabolism and immune responses. Pteromalus puparum is a pupal endoparasitoid that parasitizes a number of butterflies, including the worldwide pest cabbage butterfly, Pieris rapae. Venom from P. puparum has a variety of effects on host hemocytes, including alteration of absolute and relative hemocyte counts, and inhibition of hemocyte spreading and encapsulation. In particular, P. puparum venom causes hemocyte cell death in vivo and in vitro.

RESULTS

Using assay-guided chromatography, a cell death-inducing venom fraction was identified and defined as P. puparum endonuclease-like venom protein (PpENVP). It belongs to the DNA/RNA nonspecific endonuclease family, which contains two conserved endonuclease activation sites. We analyzed its expression profiles and demonstrated that PpENVP inhibits gene expression in transfected cells relying on two activation sites. However, RNA interference of PpENVP did not significantly reduce P. puparum venom cytotoxicity, suggesting that PpENVP may not be the sole cytotoxic factor present.

CONCLUSION

Our results provide novel insight into the function of the P. puparum venom cocktail and identify a promising insecticide candidate endonuclease that targets insect hemocytes.

A chromosome-level genome assembly of the parasitoid wasp Pteromalus puparum

Parasitoid wasps represent a large proportion of hymenopteran species. They have complex evolutionary histories and are important biocontrol agents. To advance parasitoid research, a combination of Illumina short-read, PacBio long-read and Hi-C scaffolding technologies was used to develop a high-quality chromosome-level genome assembly for Pteromalus puparum, which is an important pupal endoparasitoid of caterpillar pests. The chromosome-level assembly has aided in studies of venom and detoxification genes. The assembled genome size is 338 Mb with a contig N50 of 38.7 kb and a scaffold N50 of 1.16 Mb. Hi-C analysis assembled scaffolds onto five chromosomes and raised the scaffold N50 to 65.8 Mb, with more than 96% of assembled bases located on chromosomes. Gene annotation was assisted by RNA sequencing for the two sexes and four different life stages. Analysis detected 98% of the BUSCO (Benchmarking Universal Single-Copy Orthologs) gene set, supporting a high-quality assembly and annotation. In total, 40.1% (135.6 Mb) of the assembly is composed of repetitive sequences, and 14,946 protein-coding genes were identified. Although venom genes play important roles in parasitoid biology, their spatial distribution on chromosomes was poorly understood. Mapping has revealed venom gene tandem arrays for serine proteases, pancreatic lipase-related proteins and kynurenine-oxoglutarate transaminases, which have amplified in the P. puparum lineage after divergence from its common ancestor with Nasonia vitripennis. In addition, there is a large expansion of P450 genes in P. puparum. These examples illustrate how chromosome-level genome assembly can provide a valuable resource for molecular, evolutionary and biocontrol studies of parasitoid wasps.

Insights into the venom protein components of the egg parasitoid Anastatus japonicus (Hymenoptera: Eupelmidae)

BACKGROUND

Parasitoid venom is composed of a complex mixture of various active substances with different biological functions and is injected in the host during the parasitoid oviposition. Anastatus japonicus (Hymenoptera: Eupelmidae) is an egg parasite of Tessaratoma papillosa (Hemiptera: Tessaratomidae). Although the venom of this egg parasitoid plays an important role in the parasitic process, relatively little work has been done to address the mechanism.

RESULTS

In the present study, proteomic analysis was performed to identify the proteins that play an important role in the parasitic process of A. japonicus. A total of 2084 proteins were identified, including 81 putative venom proteins, most of which were identified as Hexamerin, Chitinase 2, Calreticulin, Heat shock protein 83-like, Serine protease, Arginine kinase, Phosphoserine aminotransferase and Actin protein. Together the before (Be) and after (Af) parasitization venom contains 1628 proteins, including 212 DEPs with 181 and 31 significantly up-regulated and down-regulated respectively. In addition, 10 differentially expressed proteins (DEPs) with fold change ≥8.71 were subjected to RT-qPCR to validate the proteomic data. The differential expression analysis revealed that nine proteins were specifically present in the pre-parasitic venom, whereas 26 proteins were specific to the post-parasitic treatments. Results of RT-qPCR analysis showed high expression of the selected DEPs which further validated our proteomics data.

CONCLUSION

These new proteomic data greatly enrich our current knowledge about key venom proteins associated with parasitic process in A. japonicus and contribute to better understanding of the parasitic mechanisms leading to the development of new biological control strategies. © 2020 Society of Chemical Industry.

Lipidomics reveals how the endoparasitoid wasp Pteromalus puparum manipulates host energy stores for its young

Endoparasitoid wasps inject venom along with their eggs to adjust the physiological and nutritional environment inside their hosts to benefit the development of their offspring. In particular, wasp venoms are known to modify host lipid metabolism, lipid storage in the fat body, and release of lipids into the hemolymph, but how venoms accomplish these functions remains unclear. Here, we use an UPLC-MS-based lipidomics approach to analyze the identities and concentrations of lipids in both fat body and hemolymph of host cabbage butterfly (Pieris rapae) infected by the pupal endoparasitoid Pteromalus puparum. During infection, host fat body levels of highly unsaturated, soluble triacylglycerides (TAGs) increased while less unsaturated, less soluble forms decreased. Furthermore, in infected host hemolymph, overall levels of TAG and phospholipids (the major component of cell membranes) increased, suggesting that fat body cells are destroyed and their contents are dispersed. Altogether, these data suggest that wasp venom induces host fat body TAGs to be transformed into lower melting point (more liquid) forms and released into the host hemolymph following infection, allowing simple absorption and nutritional acquisition by wasp larvae. Finally, cholesteryl esters (CEs, a dietary lipid derived from cholesterol) increased in host hemolymph following infection with no concomitant decrease in host cholesterol, implying that the wasp may provide this necessary food resource to its offspring via its venom. This study provides novel insight into how parasitoid infection alters lipid metabolism in insect hosts, and begins to uncover the wasp venom proteins responsible for host physiological changes and offspring development.

Genome-wide characterization and transcriptomic analyses of neuropeptides and their receptors in an endoparasitoid wasp, Pteromalus puparum

In insects, neuropeptides constitute a group of signaling molecules that act in regulation of multiple physiological and behavioral processes by binding to their corresponding receptors. On the basis of the bioinformatic approaches, we screened the genomic and transcriptomic data of the parasitoid wasp, Pteromalus puparum, and annotated 36 neuropeptide precursor genes and 33 neuropeptide receptor genes. Compared to the number of precursor genes in Bombyx mori (Lepidoptera), Chilo suppressalis (Lepidoptera), Drosophila melanogaster (Diptera), Nilaparvata lugens (Hemiptera), Apis mellifera (Hymenoptera), and Tribolium castaneum (Coleoptera), P. puparum (Hymenoptera) has the lowest number of neuropeptide precursor genes. This lower number may relate to its parasitic life cycle. Transcriptomic data of embryos, larvae, pupae, adults, venom glands, salivary glands, ovaries, and the remaining carcass revealed stage-, sex-, and tissue-specific expression patterns of the neuropeptides, and their receptors. These data provided basic information about the identity and expression profiles of neuropeptides and their receptors that are required to functionally address their biological significance in an endoparasitoid wasp.

Genomic and transcriptomic analyses of glutathione S-transferases in an endoparasitoid wasp, Pteromalus puparum

Pteromalus puparum is a gregarious pupal endoparasitoid with a wide host range. It deposits eggs into pierid and papilionid butterfly pupae. Glutathione S-transferases (GSTs) are a family of multifunctional detoxification enzymes that act in xenobiotic metabolism in insects. Insect genome projects have facilitated identification and characterization of GST family members. We identified 20 putative GSTs in the P. puparum genome, including 19 cytosolic and one microsomal. Phylogenetic analysis showed that P. puparum GSTs are clustered into Hymenoptera-specific branches. Transcriptomic data of embryos, larvae, female pupae, male pupae, female adults, male adults, venom glands, carcass, salivary glands, and ovaries revealed stage-, sex-, and tissue-specific expression patterns of GSTs in P. puparum. This is the most comprehensive study of genome-wide identification, characterization, and expression profiling of GST family in hymenopterans. Our results provide valuable information for understanding the metabolic adaptation of this wasp.

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.

Understanding the genetic mechanism of resistance in aphid-treated alfalfa (Medicago sativa L.) through proteomic analysis

To minimize dependency on chemical pesticides, plant breeders are trying to emphasize on important agricultural pests for the development of pest resistant cultivars. However, the molecular approach and associated genetic tools conferring resistance have not been widely studied. In the current study, proteomic analysis of two of the alfalfa cultivars viz. a resistant (R) (Zhongmu-1) and a susceptible (S) (WL343), with (+ A) and without (- A) aphids rearing were carried out. Results indicated that 325 differentially expressed proteins (DEPs) up-regulated while 319 down-regulated with a pattern of R + A/R - A plants, whereas 371 up- and 583 down-regulated DEPs were identified in the S + A/S - A plants. Total number of DEPs found in (S + A/S - A) was around 19.7% greater than that of (R + A/R - A), whereas, the down-regulated DEPs of susceptible variety was 11.6% higher than the resistant cultivar. Applying the KEGG analysis, 96 and 142 DEPs were portrayed to 15 and 10 substantively augmented pathways for Zhongmu-1 and WL343, respectively. We also found that two of the shared pathways (carbon metabolism and pyruvate metabolism) are linking to important traits conferring resistance in alfalfa. Most importantly, the specific role of linoleic acid metabolism was found to be associated with jasmonic acid, flavonoid biosynthesis, and terpenoid backbone biosynthesis that might have been associated with the insect-resistant material synthesis in the resistant alfalfa cultivar. Our study suggested that both alfalfa cultivars (R, S) could govern protein expression through carbon and pyruvate metabolism. But only the resistant alfalfa cultivar (Zhongmu-1) can tune protein expression via linoleic acid metabolism and terpenoid backbone biosynthesis to induce the defensive protein expressions (e.g., jasmonic acid and flavonoid biosynthesis along with terpenoid backbone biosynthesis), to enhance plant defense capacity.

Oxidative stress and cytotoxicity elicited lipid peroxidation in hemocytes of Bombyx mori larva infested with dipteran parasitoid, Exorista bombycis

Parasitization of silkworm, Bombyx mori by invasive larva of dipteran parasitoid Exorista bombycis caused upto 20% revenue loss in sericulture. The parasitism was successful by suppressing host immune system however mechanism of immune suppression induced by E. bombycis is unknown which is unravelled here. The infestation induced cytotoxic symptoms in host hemocytes, such as vacuolated cytoplasm, porous plasma membrane, indented nuclei with condensed chromatin and dilated RER. One of the markers of necrosis is cell permeabilization, which can be measured as released lactate dehydrogenase (LDH). LDH level showed significantly (P<0.01) high release into extracellular medium in vitro after exposure of hemocytes to parasitoid larval tissue protein compared with control revealing membrane permeability and loss of cell integrity. At five minutes after exposure, cytotoxicity was 43% and was increased to 99% at 3h. The cytotoxicity is signalled by increased content of hydrogen peroxide (H2O2) causing lipid peroxidation followed by porosity in plasma membrane. A test for lipid peroxidation by measurement of lipid peroxidation breakdown product, malondialdehyde (MDA) revealed significant increase in peroxidation from one to 24 h post-invasion, with maximum at 12 h (P<0.008). Level of reactive oxygen species measured as H2O2 production increased from 6 to 12 h post-invasion and continued to increase significantly (P<0.03) reaching maximum at 48 h. These observations reveal that dipteran endoparasitoid invasion induced H2O2 production in the hemocytes causing cytotoxicity, lipid peroxidation and membrane porosity that suppressed both humoral- and cell-mediated immune responses of hemocytes in B. mori.

The genomic and transcriptomic analyses of serine proteases and their homologs in an endoparasitoid, Pteromalus puparum

In insects, serine proteases (SPs) and serine protease homologs (SPHs) constitute a large family of proteins involved in multiple physiological processes such as digestion, development, and immunity. Here we identified 145 SPs and 38 SPHs in the genome of an endoparasitoid, Pteromalus puparum. Gene duplication and tandem repeats were observed in this large SPs/SPHs family. We then analyzed the expression profiles of SP/SPH genes in response to different microbial infections (Gram-positive bacterium Micrococcus luteus, Gram-negative bacterium Escherichia coli, and entomopathogenic fungus Beauveria bassiana), as well as in different developmental stages and tissues. Some SPs/SPHs also displayed distinct expression patterns in venom gland, suggesting their specific physiological functions as venom proteins. Our finding lays groundwork for further research of SPs and SPHs expressed in the venom glands.

A novel negative-stranded RNA virus mediates sex ratio in its parasitoid host

Parasitoid wasps are important natural enemies of arthropod hosts in natural and agricultural ecosystems and are often associated with viruses or virion-like particles. Here, we report a novel negative-stranded RNA virus from a parasitoid wasp (Pteromalus puparum). The complete viral genome is 12,230 nucleotides in length, containing five non-overlapping, linearly arranged open reading frames. Phylogenetically, the virus clusters with and is a novel member of the mononegaviral family Nyamiviridae, here designated as Pteromalus puparum negative-strand RNA virus 1 (PpNSRV-1). PpNSRV-1 is present in various tissues and life stages of the parasitoid wasp, and is transmitted vertically through infected females and males. Virus infections in field populations of P. puparum wasps ranged from 16.7 to 37.5%, without linearly correlating with temperature. PpNSRV-1 increased adult longevity and impaired several fitness parameters of the wasp, but had no influence on successful parasitism. Strikingly, PpNSRV-1 mediated the offspring sex ratio by decreasing female offspring numbers. RNA interference knockdown of virus open reading frame I eliminated these PpNSRV-1-induced effects. Thus, we infer that PpNSRV-1 has complex effects on its insect host including sex ratio distortion towards males, as well as possible mutualistic benefits through increasing wasp longevity.

A Venom Serpin Splicing Isoform of the Endoparasitoid Wasp Pteromalus puparum Suppresses Host Prophenoloxidase Cascade by Forming Complexes with Host Hemolymph Proteinases

To ensure successful parasitism, parasitoid wasps inject venom along with their eggs into their hosts. The venom serves to suppress host immune responses, including melanization. Venom from Pteromalus puparum, a pupal endoparasitoid, inhibits melanization of host hemolymph in vitro in a dose-dependent manner. Using assay-guided fractionation, a serpin splicing isoform with phenoloxidase inhibitory activity was identified as P puparum serpin-1, venom isoform (PpS1V). This serpin gene has 16 predicted splicing isoforms that differ only in the C-terminal region. RT-PCR results show that the specific serpin isoform is differentially expressed in the venom gland. Recombinant PpS1V (rPpS1V) suppresses host prophenoloxidase (PPO) activation rather than inhibiting the phenoloxidase directly. Pulldown assays show that PpS1V forms complexes with two host hemolymph proteins, here named Pieris rapae hemolymph proteinase 8 (PrHP8) and P. rapae prophenoloxidase-activating proteinase 1 (PrPAP1), based on gene sequence blasting and phylogenetic analysis. The role of rPrPAP1 in the PPO activation cascade and its interaction with rPpS1V were confirmed. The stoichiometry of inhibition of PrPAP1 by PpS1V is 2.3. PpS1V also inhibits PPO activation in a non-natural host, Ostrinia furnacalis, through forming a complex with O. furnacalis serine protease 13 (OfSP13), an ortholog to PrPAP1. Our results identify a venom-enriched serpin isoform in P. puparum that inhibits host PPO activation, probably by forming a complex with host hemolymph proteinase PrPAP1.

Beneficial microorganisms for honey bees: problems and progresses

Nowadays, honey bees are stressed by a number of biotic and abiotic factors which may compromise to some extent the pollination service and the hive productivity. The EU ban of antibiotics as therapeutic agents against bee pathogens has stimulated the search for natural alternatives. The increasing knowledge on the composition and functions of the bee gut microbiota and the link between a balanced gut microbiota and health status have encouraged the research on the use of gut microorganisms to improve bee health. Somehow, we are assisting to the transfer of the "probiotic concept" into the bee science. In this review, we examine the role of the honey bee gut microbiota in bee health and critically describe the available applications of beneficial microorganisms as pest control agents and health support. Most of the strains, mainly belonging to the genera Lactobacillus, Bifidobacterium and Bacillus, are isolated from honey bee crop or gut, but some applications involve environmental strains or formulation for animal and human consumption. Overall, the obtained results show the favourable effect of applied microbial strains on bee health and productivity, in particular if strains of bee origin are used. However, it is actually not yet possible to conclude whether this strategy will ever work. In particular, many aspects regarding the overall setup of the experiments, the dose, the timing and the duration of the treatment need to be optimized, also considering the microbiological safety of the hive products (i.e. pollen and honey). In addition, a deep investigation about the effect on host immunity and physiology is envisaged. Lastly, the final users of the formulations, i.e. beekeepers, should be taken into account for the achievement of high-quality, cost-effective and easy-to-use products.

Venom of Parasitoid Pteromalus puparum Impairs Host Humoral Antimicrobial Activity by Decreasing Host Cecropin and Lysozyme Gene Expression

Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Here, we report that Pteromalus puparum venom impairs the antimicrobial activity of its host Pieris rapae. Inhibition zone results showed that bead injection induced the antimicrobial activity of the host hemolymph but that venom inhibited it. The cDNAs encoding cecropin and lysozyme were screened. Relative quantitative PCR results indicated that all of the microorganisms and bead injections up-regulated the transcript levels of the two genes but that venom down-regulated them. At 8 h post bead challenge, there was a peak in the transcript level of the cecropin gene, whereas the peak of lysozyme gene occurred at 24 h. The transcripts levels of the two genes were higher in the granulocytes and fat body than in other tissues. RNA interference decreased the transcript levels of the two genes and the antimicrobial activity of the pupal hemolymph. Venom injections similarly silenced the expression of the two genes during the first 8 h post-treatment in time- and dose-dependent manners, after which the silence effects abated. Additionally, recombinant cecropin and lysozyme had no significant effect on the emergence rate of pupae that were parasitized by P. puparum females. These findings suggest one mechanism of impairing host antimicrobial activity by parasitoid venom.

A Venom Gland Extracellular Chitin-Binding-Like Protein from Pupal Endoparasitoid Wasps, Pteromalus Puparum, Selectively Binds Chitin

Chitin-binding proteins (CBPs) are present in many species and they act in a variety of biological processes. We analyzed a Pteromalus puparum venom apparatus proteome and transcriptome and identified a partial gene encoding a possible CBP. Here, we report cloning a full-length cDNA of a sequence encoding a chitin-binding-like protein (PpCBP) from P. puparum, a pupal endoparasitoid of Pieris rapae. The cDNA encoded a 96-amino-acid protein, including a secretory signal peptide and a chitin-binding peritrophin-A domain. Phylogenetic analysis of chitin binding domains (CBDs) of cuticle proteins and peritrophic matrix proteins in selected insects revealed that the CBD of PpCBP clustered with the CBD of Nasonia vitripennis. The PpCBP is specifically expressed in the venom apparatus of P. puparum, mostly in the venom gland. PpCBP expression was highest at day one after adult eclosion and much lower for the following five days. We produced a recombinant PpCBP and binding assays showed the recombinant protein selectively binds chitin but not cellulose in vitro. We infer that PpCBP serves a structural role in the venom reservoir, or may be injected into the host to help wound healing of the host exoskeleton.

THE ENDOPARASITOID Pteromalus puparum INFLUENCES HOST GENE EXPRESSION WITHIN FIRST HOUR OF PARASITIZATION

The small cabbage butterfly, Pieris rapae, is an important pest of cruciferous corps, and Pteromalus puparum is a predominant pupal endoparasitoid wasp of this butterfly. For successful development of parasitoid offspring, female parasitoids usually introduce one or several kinds of maternal factors into the hemocoels during oviposition to suppress host immunity. To investigate the early changes in host immune-related genes following parasitization, we analyzed transcriptomes of parasitized and unparasitized, control, host pupae. Approximately 17.7 and 19.3 million paired-end reads were generated from nonparasitized and parasitized host pupae, and assembled de novo into 45,639 transcripts and 27,659 nonredundant unigenes. The average unigene length was 790 bp. A total 18,377 of 27,659 unigenes were annotated and we identified 557 differentially expressed unigenes in host pupae at 1 h after parasitization, of which 21 were immune-related. Parasitization led to downregulation of most pattern recognition receptors and upregulation of all serine protease inhibitors. The transcirptomic profile of P. rapae is considerably affected by parasitization. This study provides valuable sources for future investigations of the molecular interaction between P. puparum and its host P. rapae.

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.

The parasitoid, Cotesia flavipes (Cameron) (Hymenoptera: Braconidae), influences food consumption and utilization by larval Diatraea saccharalis (F.) (Lepidoptera: Crambidae)

Parasitoids exploit host insects for food and other resources; they alter host development and physiology to optimize conditions to favor parasitoid development. Parasitoids influence their hosts by injecting eggs, along with a variety of substances, including venoms, polydnaviruses, ovarian fluids, and other maternal factors, into hosts. These factors induce profound changes in hosts, such as behavior, metabolism, endocrine events, and immune defense. Because endoparasitoids develop and consume tissues from within their hosts, it is reasonable to suggest that internal parasitization would also influence host food consumption and metabolism. We report on the effects of parasitism by Cotesia flavipes on the food consumption and utilization of its host, Diatraea saccharalis. Cotesia flavipes reduces the host food consumption, but parasitized larvae considered a unit with their parasitoid's attained the same final weight as the nonparasitized larvae. Nutritional indices, midgut activities of carbohydrases, and trypsin of parasitized and nonparasitized D. saccharalis were assessed. Parasitized larvae had reduced relative food consumption, metabolic and growth rates, coupled with higher efficiency for conversion of the digested, but not ingested, food into body mass. Parasitism also affected food flux through the gut and protein contents in the midgut of parasitized larvae. The activity of α-amylase and trehalase in parasitized host was enhanced in the first day after parasitism relative to control larvae. Saccharase activity remained unchanged during larval development. Trypsin activity was reduced from the fifth to ninth day after parasitism. We argue on the mechanisms involved in host food processing after parasitism.

Parasitization by Scleroderma guani influences expression of superoxide dismutase genes in Tenebrio molitor

Superoxide dismutase (SOD) is an antioxidant enzyme involved in detoxifying reactive oxygen species. In this study, we identified genes encoding the extracellular and intracellular copper-zinc SODs (ecCuZnSOD and icCuZnSOD) and a manganese SOD (MnSOD) in the yellow mealworm beetle, Tenebrio molitor. The cDNAs for ecCuZnSOD, icCuZnSOD, and MnSOD, respectively, encode 24.55, 15.81, and 23.14 kDa polypeptides, which possess structural features typical of other insect SODs. They showed 20-94% identity to other known SOD sequences from Bombyx mori, Musca domestica, Nasonia vitripennis, Pediculus humanus corporis, and Tribolium castaneum. Expression of these genes was analyzed in selected tissues and developmental stages, and following exposure to Escherichia coli and parasitization by Scleroderma guani. We recorded expression of all three SODs in cuticle, fat body, and hemocytes and in the major developmental stages. Relatively higher expressions were detected in late-instar larvae and pupae, compared to other developmental stages. Transcriptional levels were upregulated following bacterial infection. Analysis of pupae parasitized by S. guani revealed that expression of T. molitor SOD genes was significantly induced following parasitization. We infer that these genes act in immune response and in host-parasitoid interactions.

Comparative proteomic analysis of Bombyx mori hemocytes treated with destruxin A

Destruxin A (DA), a cyclodepsipeptidic secondary metabolite of the entomopathogenic fungus, Metarhizium anisopliae, is an important anti-immunity agent against insect hemocytes. To understand the mechanism of the molecular responses to DA, fifth-instar larvae of the silkworm, Bombyx mori, were injected with 2 μg of DA. The proteomics of hemocytes were then investigated using two-dimensional electrophoresis and mass spectrometry, and validated qPCR. As a result, a total of 47 differently expressed protein spots were detected and 22 proteins in 26 spots were identified. There are eight immunity-related proteins, including three downregulated proteins (antitrypsin isoform 3, p50 protein, and calreticulin precursor) and five upregulated proteins (C-type lectin 10 precursor, serine proteinase-like protein, paralytic peptide, PPO-1, and PPO-2). Four resistance- and/or stress-related proteins (arginine kinase, carboxylesterase clade H, member 1, aminoacylase, and thiol peroxiredoxin) were upregulated. Ten proteins with other or unknown functions were also recorded. Five selected proteins were verified with qPCR. These results provide new insights into the molecular mechanism of host immune response to DA challenge.

Early changes in the pupal transcriptome of the flesh fly Sarcophagha crassipalpis to parasitization by the ectoparasitic wasp, Nasonia vitripennis

We investigated changes in the pupal transcriptome of the flesh fly Sarcophaga crassipalpis, 3 and 25 h after parasitization by the ectoparasitoid wasp, Nasonia vitripennis. These time points are prior to hatching of the wasp eggs, thus the results document host responses to venom injection, rather than feeding by the wasp larvae. Only a single gene appeared to be differentially expressed 3 h after parasitization. However, by 25 h, 128 genes were differentially expressed and expression patterns of a subsample of these genes were verified using RT-qPCR. Among the responsive genes were clusters of genes that altered the fly's metabolism, development, induced immune responses, elicited detoxification responses, and promoted programmed cell death. Envenomation thus clearly alters the metabolic landscape and developmental fate of the fly host prior to subsequent penetration of the pupal cuticle by the wasp larva. Overall, this study provides new insights into the specific action of ectoparasitoid venoms.

Inhibition of host cell encapsulation through inhibiting immune gene expression by the parasitic wasp venom calreticulin

Parasitoid wasps inject venom into the host to protect their offspring against host immune responses. In our previous study, we identified a calreticulin (CRT) in Pteromalus puparum venom. In this study, we expressed the wild-type and the coiled-coil domain deletion mutant P. puparum calreticulins (PpCRTs) in Escherichia coli and prepared polyclonal antibody in rabbit against PpCRT. Western blot analysis showed that PpCRT protein was not only present in the venom but also in all the tissues tested. Real time PCR results indicated that PpCRT mRNA was highly expressed in the venom gland. The transcript level of PpCRT in the venom gland was peaked at 2 days post-eclosion, while the PpCRT protein in the venom was maintained at a constant level. Both recombinant wild-type and mutant PpCRT proteins could bind to the surface of P. puparum eggs. Recombinant PpCRT inhibited hemocyte spreading and cellular encapsulation of the host Pieris rapae in vitro, and the coiled-coil domain is important for the inhibitory function of PpCRT. Immunocytochemistry results showed that PpCRT entered P. rapae hemocytes, and the coiled-coil domain played a role in this process. After injection of recombinant PpCRT into P. rapae pupae, real time PCR results showed that PpCRT inhibited transcript levels of host encapsulation-related genes, including calreticulin and scavenger receptor genes. In conclusion, our results suggest that P. puparum venom protects its offspring against host cellular immune responses via its functional component PpCRT to inhibit the expression of host cellular response-related genes.

Parasitization by Cotesia chilonis influences gene expression in fatbody and hemocytes of Chilo suppressalis

Background

During oviposition many parasitoid wasps inject various factors, such as polydnaviruses (PDVs), along with eggs that manipulate the physiology and development of their hosts. These manipulations are thought to benefit the parasites. However, the detailed mechanisms of insect host-parasitoid interactions are not fully understood at the molecular level. Based on recent findings that some parasitoids influence gene expression in their hosts, we posed the hypothesis that parasitization by a braconid wasp, Cotesia chilonis, influences the expression of genes responsible for development, metabolism and immune functions in the fatbody and hemocytes of its host, Chilo suppressalis.

Methodology/Principal Findings

We obtained 39,344,452 reads, which were assembled into 146,770 scaffolds, and 76,016 unigenes. Parasitization impacted gene expression in fatbody and hemocytes. Of these, 8096 fatbody or 5743 hemocyte unigenes were down-regulated, and 2572 fatbody or 1452 hemocyte unigenes were up-regulated. Gene ontology data showed that the majority of the differentially expressed genes are involved in enzyme-regulated activity, binding, transcription regulator activity and catalytic activity. qPCR results show that most anti-microbial peptide transcription levels were up-regulated after parasitization. Expression of bracovirus genes was detected in parasitized larvae with 19 unique sequences identified from six PDV gene families including ankyrin, CrV1 protein, cystatin, early-expressed (EP) proteins, lectin, and protein tyrosine phosphatase.

Conclusions

The current study supports our hypothesis that parasitization influences the expression of fatbody and hemocyte genes in the host, C. suppressalis. The general view is that manipulation of host metabolism and immunity benefits the development and emergence of the parasitoid offsprings. The accepted beneficial mechanisms include the direct impact of parasitoid-associated virulence factors such as venom and polydnavirus on host tissues (such as cell damage) and, more deeply, the ability of these factors to influence gene expression. We infer that insect parasitoids generally manipulate their environments, the internal milieu of their hosts.

Differential cellular gene expression in duck trachea infected with a highly or low pathogenic H5N1 avian influenza virus

Background

Avian influenza A (AI) viruses of subtypes H5 can cause serious disease outbreaks in poultry including panzootic due to H5N1 highly pathogenic (HP) viruses. These viruses are a threat not only for animal health but also public health due to their zoonotic potential. The domestic duck plays a major role in the epidemiological cycle of influenza virus subtypes H5 but little is known concerning host/pathogen interactions during influenza infection in duck species. In this study, a subtracted library from duck trachea (a primary site of influenza virus infection) was constructed to analyse and compare the host response after a highly or low pathogenic (LP) H5N1-infection.

Results

Here, we show that more than 200 different genes were differentially expressed in infected duck trachea to a significant degree. In addition, significant differentially expressed genes between LPAI- and HPAI-infected tracheas were observed. Gene ontology annotation was used and specific signalling pathways were identified. These pathways were different for LPAI and HPAI-infected tracheas, except for the CXCR4 signalling pathway which is implicated in immune response. A different modulation of genes in the CXCR4 signalling pathway and TRIM33 was induced in duck tracheas infected with a HPAI- or a LPAI-H5N1.

Conclusion

First, this study indicates that Suppressive Subtractive Hybridization (SSH) is an alternative approach to gain insights into the pathogenesis of influenza infection in ducks. Secondly, the results indicate that cellular gene expression in the duck trachea was differently modulated after infection with a LPAI-H5N1 or after infection with a HPAI-H5N1 virus. Such difference found in infected trachea, a primary infection site, could precede continuation of infection and could explain appearance of respiratory symptoms or not.

Venom of the ectoparasitoid, Nasonia vitripennis, influences gene expression in Musca domestica hemocytes

Insect hosts have evolved potent innate immunity against invasion by parasitoid wasps. Host/parasitoids live in co-evolutionary relationships. Nasonia vitripennis females inject venom into their dipteran hosts just prior to laying eggs on the host's outer integument. The parasitoid larvae are ectoparasitoids because they feed on their hosts within the puparium, but do not enter the host body. We investigated the influence of N. vitripennis venom on the gene expression profile of hemocytes of their hosts, pupae of the housefly, Musca domestica. We prepared venom by isolating venom glands and treated experimental host pupae with venom. We used suppression subtractive hybridization (SSH) to determine the influence of venom on hemocyte gene expression. At 1 h post treatment, we recorded decreases in transcript levels of 133 EST clones derived from forward a subtractive library of host hemocytes and upregulation in transcript levels of 111 EST clones from the reverse library. These genes are related to immune and stress response, cytoskeleton, cell cycle and apoptosis, metabolism, transport, and transcription/translation regulation. We verified the reliability of our data with reverse transcription quantitative real-time PCR analysis of randomly selected genes, and with assays of enzyme activities. These analyses showed that the expression level of all selected genes were downregulated after venom treatment. Outcomes of our experiments support the hypothesis that N. vitripennis venom influences the gene expression in host hemocytes. We conclude that the actions of venom on host gene expression influence host biology in ways that benefit the development and emergence of the next generation of parasitoids.

"It stings a bit but it cleans well": venoms of Hymenoptera and their antimicrobial potential

Venoms from Hymenoptera display a wide range of functions and biological roles. These notably include manipulation of the host, capture of prey and defense against competitors and predators thanks to endocrine and immune systems disruptors, neurotoxic, cytolytic and pain-inducing venom components. Recent works indicate that many hymenopteran species, whatever their life style, have also evolved a venom with properties which enable it to regulate microbial infections, both in stinging and stung animals. In contrast to biting insects and their salivary glands, stinging Hymenoptera seem to constitute an under-exploited ecological niche for agents of vector-borne disease. Few parasitic or mutualistic microorganisms have been reported to be hosted by venom-producing organs or to be transmitted to stung animals. This may result from the presence of potent antimicrobial molecules in venoms, histological features of venom apparatuses and selective effects of venoms on immune defenses of targeted organisms. The present paper reviews for the first time the venom antimicrobial potential of solitary and social Hymenoptera in molecular, ecological, and evolutionary perspectives.

Molecular cloning and functional study of calreticulin from a lepidopteran pest, Pieris rapae

Insects have an effective innate immune system to protect themselves from exogenous invaders. Calreticulin is a multifunctional protein mainly involved in directing proper conformation of proteins, controlling calcium level, and participating in immune responses. Previous suppression subtractive hybridization assay showed that the expression of Pieris rapae calreticulin (PrCRT) was suppressed after injection of Pteromalus puparum venom. In this study, we obtained a full length cDNA of PrCRT and expressed recombinant wild type and the N-domain deleted mutant PrCRT in bacteria. Real time quantitative PCR and western blot analyses showed that PrCRT mRNA and protein were expressed in hemocytes, Malpighian tubule, midgut, epidermis and fat body, with a higher level in hemocytes. PrCRT was probably located in endoplasmic reticulum distributing in the cytoplasm of hemocytes. Recombinant PrCRT was first able to attach and then enter the hemocytes by endocytosis. PrCRT mRNA in hemocytes was significantly induced after injection of yeast or beads, but did not change noticeably after injection of Escherichia coli or Micrococcus lysodeikticus. Recombinant PrCRT enhanced cellular encapsulation by P. rapae hemocytes in vitro, and the N-domain of PrCRT was required for encapsulation. RNAi of PrCRT by dsRNA injection impaired the ability of hemocytes to encapsulate beads. After parasitization by P. puparum, PrCRT mRNA and protein levels in P. rapae pupal hemocytes were significantly suppressed compared to non-parasitized control. Our results suggest that PrCRT is involved in cellular encapsulation and the pupal parasitoid P. puparum can decrease PrCRT expression to impair host cellular immune response.

Identification of mycosis-related genes in the eastern subterranean termite by suppression subtractive hybridization

The Eastern subterranean termite Reticulitermes flavipes (Isoptera, Rhinotermitidae) is a cosmopolitan, structural pest that is the target of research into termite innate immunity. In this study, we use suppression subtractive hybridization to construct a normalized cDNA library of genes excessively expressed upon fungal infection. At 24 h postinfection with Metarhizium anisopliae, the library revealed 182 expressed sequence tag (EST) clones that potentially represent immune responsive genes. The nucleotide sequence from a majority (97%) of ESTs assembled into a small number (n = 13) of contiguous sequences, with the remainder (n = 6) representing singletons. Our screen therefore captured as many as 19 different mRNAs highly expressed in response to the fungal pathogen at this time. Primary sequencing of all loci revealed that approximately half (n = 10) contained open reading frames with significant similarity to known proteins. These clones represent nuclear and mitochondrial coding genes, as well as putative long noncoding RNA genes. Quantitative polymerase chain reaction analysis of coding genes on independently infected groups of worker termites confirms in each case that the transcripts identified from the library are up-regulated postfungal infection. The genes identified here are relevant to future studies on termite biocontrol and social insect immunity.

Eicosanoids: Exploiting Insect Immunity to Improve Biological Control Programs

Insects, like all invertebrates, express robust innate, but not adaptive, immune reactions to infection and invasion. Insect immunity is usually resolved into three major components. The integument serves as a physical barrier to infections. Within the hemocoel, the circulating hemocytes are the temporal first line of defense, responsible for clearing the majority of infecting bacterial cells from circulation. Specific cellular defenses include phagocytosis, microaggregation of hemocytes with adhering bacteria, nodulation and encapsulation. Infections also stimulate the humoral component of immunity, which involves the induced expression of genes encoding antimicrobial peptides and activation of prophenoloxidase. These peptides appear in the hemolymph of challenged insects 6-12 hours after the challenge. Prostaglandins and other eicosanoids are crucial mediators of innate immune responses. Eicosanoid biosynthesis is stimulated by infection in insects. Inhibition of eicosanoid biosynthesis lethally renders experimental insects unable to clear bacterial infection from hemolymph. Eicosanoids mediate specific cell actions, including phagocytosis, microaggregation, nodulation, hemocyte migration, hemocyte spreading and the release of prophenoloxidase from oenocytoids. Some invaders have evolved mechanisms to suppress insect immunity; a few of them suppress immunity by targeting the first step in the eicosanoid biosynthesis pathways, the enzyme phospholipase A₂. We proposed research designed to cripple insect immunity as a technology to improve biological control of insects. We used dsRNA to silence insect genes encoding phospholipase A₂, and thereby inhibited the nodulation reaction to infection. The purpose of this article is to place our view of applying dsRNA technologies into the context of eicosanoid actions in insect immunity. The long-term significance of research in this area lies in developing new pest management technologies to contribute to food security in a world with a rapidly growing human population.

Pteromalus puparum venom impairs host cellular immune responses by decreasing expression of its scavenger receptor gene

Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Although there is a rich literature on these systems, parasitoid immune-disabling mechanisms have not been fully elucidated. Here we report on a newly discovered immune-disabling mechanism in the Pieris rapae/Pteromalus puparum host/parasitoid system. Because venom injections and parasitization suppresses host phagocytosis, we turned attention to the P. rapae scavenger receptor (Pr-SR), posing the hypothesis that P. puparum venom suppresses expression of the host Pr-SR gene. To test our hypothesis, we cloned a full-length cDNA of the Pr-SR. Multiple sequences alignment showed the deduced amino acid sequence of Pr-SR is similar to scavenger receptors of other lepidopterans. Bacterial and bead injections induced Pr-SR mRNA and protein expression, which peaked at 4h post-bead injection. Venom injection inhibited Pr-SR expression. Pr-SR was specifically expressed in granulocytes compared to plasmatocytes. We localized the Pr-SR protein in cytoplasm and cellular membrane, with no evidence of secretion into host plasma. Double-strand RNA designed to Pr-SR mRNA silenced expression of Pr-SR and significantly impaired host phagocytosis and encapsulation reactions. Venom injections similarly silenced Pr-SR expression during the first 8h post-treatment, after which the silencing effects gradually abated. We infer from these findings that one mechanism of impairing P. rapae hemocytic immune reactions is by silencing expression of Pr-SR.

Venom of parasitoid, Pteromalus puparum, suppresses host, Pieris rapae, immune promotion by decreasing host C-type lectin gene expression

Background

Insect hosts have evolved immunity against invasion by parasitoids, and in co-evolutionary response parasitoids have also developed strategies to overcome host immune systems. The mechanisms through which parasitoid venoms disrupt the promotion of host immunity are still unclear. We report here a new mechanism evolved by parasitoid Pteromalus puparum, whose venom inhibited the promotion of immunity in its host Pieris rapae (cabbage white butterfly).

Methodology/Principal Findings

A full-length cDNA encoding a C-type lectin (Pr-CTL) was isolated from P. rapae. Quantitative PCR and immunoblotting showed that injection of bacterial and inert beads induced expression of Pr-CTL, with peaks of mRNA and Pr-CTL protein levels at 4 and 8 h post beads challenge, respectively. In contrast, parasitoid venom suppressed Pr-CTL expression when co-injected with beads, in a time and dose-dependent manner. Immunolocalization and immunoblotting results showed that Pr-CTL was first detectable in vesicles present in cytoplasm of granulocytes in host hemolymph, and was then secreted from cells into circulatory fluid. Finally, the secreted Pr-CTL bound to cellular membranes of both granulocytes and plasmatocytes. Injection of double-stranded RNA specific for target gene decreased expression of Pr-CTL, and a few other host immune-related genes. Suppression of Pr-CTL expression also down-regulated antimicrobial and phenoloxidase activities, and reducing phagocytotic and encapsulation rates in host. The inhibitory effect of parasitoid venom on host encapsulation is consistent with its effect in suppressing Pr-CTL expression. Binding assay results showed that recombinant Pr-CTL directly attached to the surface of P. puparum egges. We infer that Pr-CTL may serve as an immune signalling co-effector, first binding to parasitoid eggs, regulating expression of a set of immune-related genes and promoting host immunity.

Conclusions/Significance

P. puparum venom inhibits promotion of host immune responses by silencing expression of host C-type lectin gene Pr-CTL, whose expression affected transcription of other host immune-related genes.

Parasitization by Macrocentrus cingulum (Hymenoptera: Braconidae) influences expression of prophenoloxidase in Asian corn borer Ostrinia furnacalis

A prophenoloxidase (PPO) cDNA (OfPPO) was cloned from the Asian corn borer Ostrinia furnacalis. Sequence analysis revealed a full length transcript of the OfPPO cDNA with 2,686 bp, containing a 2,079 bp open reading frame (ORF), a 73-bp 5'-untranslated region, and a 534-bp 3'-untranslated region with a poly(A) signal. The ORF encodes a 693-amino acid polypeptide, containing two distinct copper-binding regions, a plausible thiol ester site, two proteolytic activation sites, and a conserved C-terminal region, but lacks a signal peptide sequence. Expression of the OfPPO transcript in the plasma, hemocytes, fat body and midgut was inhibited by Macrocentrus cingulum at 4 h post-parasitization (pp). In situ hybridization analysis showed that the hemocytes, especially the oenocytoids, hybridized strongly with the DNA probes of the OfPPO gene. No signal was detected in the cuticular epithelium or fat body of the parasitized larvae. Colloidal gold particles were used to visualize the PPO by immunoelectron microscopy. The time course study revealed a decrease in the labeling of the OfPPO at 4, 6, 8, 12, and 1 day pp in the larval integument and midgut parasitized by M. cingulum. We infer from time course studies of OfPPO gene expression and PO enzymatic activity that OfPPO in the integument is released from hemocytes and that the OfPPO expression was influenced at the transcriptional, translational, and then the post-translational level by parasitization challenge.