Dynamics of the Interaction between Cotton Bollworm Helicoverpa armigera and Nucleopolyhedrovirus as Revealed by Integrated Transcriptomic and Proteomic Analyses

Molecular mechanism of Serratia marcescens Bizio infection in Reticulitermes chinensis Snyder based on full-length SMRT transcriptome sequencing

Reticulitermes chinensis Snyder is an important pest in forestry and construction and is widely distributed in China. We found that Serratia marcescens Bizio strain SM1 has insecticidal activity to R. chinensis, but the pathogenic mechanism of SM1 to R. chinensis is not clear. Therefore, full-length transcriptome sequencing was performed on R. chinensis infected with SM1 and the control group. A total of 230 differentially expressed genes were identified by comparing SM1 infection group and the control group, among which 103 were downregulated and 127 were upregulated. We found downregulated genes in nine metabolic pathway categories, among which carbohydrate metabolism had the most downregulated genes, followed by energy metabolism and amino acid metabolism. We also found that some downregulated genes were related to pattern recognition receptors, cellular immunity, and humoral immunity, indicating that R. chinensis immunity was negatively affected by SM1 infection. In addition, some genes in signal transduction and genetic information processing pathways were downregulated. In this study, high-throughput full-length transcriptome analysis was used to analyse the pathogenic mechanism of SM1 to R. chinensis. The results of this study provide useful information for exploring the relationship between SM1 and R. chinensis, and provide theoretical support for the future application of SM1 and the prevention and treatment of R. chinensis.

Transcriptomics and interactomics during the primary infection of an SfNPV baculovirus on Spodoptera frugiperda larvae

The fall armyworm (FAW), Spodoptera frugiperda, has been the most devastating pest of corn as well as of other crops in America, and more recently in Africa and Asia. The development of resistance to chemical insecticides led the search for environmentally friendly biological alternatives such as baculoviruses. This study focuses on the primary infection of the baculovirus SfNPV-Ar in the FAW's midgut epithelium, by analyzing the differential expression of transcripts in excised midguts at 6, 12, and 24 h post-infection (hpi), and predicted their interactions. Interaction of viral factors with the infected midgut tissue could alters various cellular processes, such as the apoptotic system due to the up-regulation observed of FABP at 6 hpi and of HSP90 at 24 hpi, along with the down-regulated PRX at 6 hpi and FABP transcripts between 12 and 24 hpi. Changes in transcript regulation could affect the cellular architecture of infected cells due to up-regulation of ARP 2/3 at 6 and 12 hpi, followed by down-regulation at 24 hpi. In relation to protein folding proteins, HSP90 was up-regulated at 24 hpi and PDI was down-regulated between 6 and 12 hpi. With respect to metabolism and cellular transport, AcilBP and ATPS0 were up regulated at 6 hpi and 12 hpi, respectively. In reference to transcription and translation up-regulation of RPL11 at 6 hpi and of FPN32 and RPL19 at 24 hpi was detected, as well as the down-regulation of RPL19 at 6 hpi, of PDI and RPL7 at 12 hpi, and of FABP at 24 hpi. In conclusion, gene regulation induced by viral infection could be related to the cytoskeleton and cellular metabolism as well as to oxidative stress, apoptosis, protein folding, translation, and ribosomal structure. The results presented in this work are an approach to understanding how the virus takes control of the general metabolism of the insect host during the primary infection period.

Integrated omic profiling of the medicinal mushroom Inonotus obliquus under submerged conditions

BACKGROUND

The Inonotus obliquus mushroom, a wondrous fungus boasting edible and medicinal qualities, has been widely used as a folk medicine and shown to have many potential pharmacological secondary metabolites. The purpose of this study was to supply a global landscape of genome-based integrated omic analysis of the fungus under lab-growth conditions.

RESULTS

This study presented a genome with high accuracy and completeness using the Pacbio Sequel II third-generation sequencing method. The de novo assembled fungal genome was 36.13 Mb, and contained 8352 predicted protein-coding genes, of which 365 carbohydrate-active enzyme (CAZyme)-coding genes and 19 biosynthetic gene clusters (BCGs) for secondary metabolites were identified. Comparative transcriptomic and proteomic analysis revealed a global view of differential metabolic change between seed and fermentation culture, and demonstrated positive correlations between transcription and expression levels of 157 differentially expressed genes involved in the metabolism of amino acids, fatty acids, secondary metabolites, antioxidant and immune responses. Facilitated by the widely targeted metabolomic approach, a total of 307 secondary substances were identified and quantified, with a significant increase in the production of antioxidant polyphenols.

CONCLUSION

This study provided the comprehensive analysis of the fungus Inonotus obliquus, and supplied fundamental information for further screening of promising target metabolites and exploring the link between the genome and metabolites.

Transcriptome analysis reveals that knocking out BmNPV iap2 induces apoptosis by inhibiting the oxidative phosphorylation pathway

Apoptosis is essential for the normal growth, development, and immunity defense of living organisms, and its function and mechanisms have been intensively studied. When viral infection occurs, apoptosis is triggered, causing programmed death of the infected cells. Meanwhile, viruses have also evolved countermeasures to inhibit apoptosis in host cells. We previously constructed a transgenic silkworm line with significantly improved resistance to Bombyx mori nucleopolyhedrovirus (BmNPV) by knocking out the BmNPV inhibitor of apoptosis 2 (iap2) gene. However, the mechanism of how IAP2 induces apoptosis still needs to be further investigated. Here, the transcriptomes of Cas9(-)/sgiap2 (-) and Cas9(+)/sgiap2(+) strains were analyzed at 48 h after BmNPV infection, and a total of 709 differential genes were obtained. A KEGG analysis revealed that the differentially expressed genes were enriched in the oxidative phosphorylation, proteasome, and ribosome pathways. In the oxidative phosphorylation pathway, 41 differentially expressed genes were downregulated, and 12 of these genes were verified by qRT-PCR. More importantly, the knockout of BmNPV iap2 led to the inhibition of the oxidative phosphorylation pathway, followed by activated oxidative stress triggered apoptosis, thereby inhibiting the replication of BmNPV in vitro and vivo. The results provide a basis for the analysis of the initiation of apoptosis that can inhibit virus proliferation, and the study presents new ideas for the subsequent creation of resistant material.

Metabolic reprogramming of Helicoverpa armigera larvae by HearNPV facilitates viral replication and host immune suppression

Baculoviruses are highly evolved parasites that genetically reprogram the developing phenotype of their host insect to produce a vessel for virus replication and dispersal. Here we show that larvae of Helicoverpa armigera infected with HearNPV accumulate glucose in the midgut, which reduces food consumption and alters the dynamics of pathways governing metabolism and immunity. We used transcriptomics to demonstrate the role of the insulin signalling pathway in regulating the HearNPV infection process. Dietary restriction decreased mortality of infected larvae and reduced viral replication prior to death, whereas dietary supplementation with glucose produced the opposite effects. The expression of most tricarboxylic acid cycle (TCA) and energy metabolism-related genes was reduced in infected larvae, whereas the expression of immunity-, glycolysis- and insulin-related genes was enhanced. Treatment of infected larvae with insulin increased their survival, reduced viral replication and inhibited climbing behaviour compared to a control treatment with DMSO, whereas RNAi suppression of the insulin receptor gene produced the opposite effects. Inhibition of glycolysis with dichloroacetate (DCA) promoted viral replication and accelerated larval death, but inhibition of the TCA cycle with 2-deoxyglucose (2-DG) did not, although both diminished climbing behaviour. This work demonstrates that successful baculovirus infections hinge on metabolic reprogramming of the host and concurrent suppression of immune responses in the larval midgut, with the insulin signalling pathway mediating a trade-off between glucose metabolism and virus resistance.

Dual roles and evolutionary implications of P26/poxin in antagonizing intracellular cGAS-STING and extracellular melanization immunity

P26, a homolog of the viral-encoded nuclease poxin that neutralizes the cGAS-STING innate immunity, is widely distributed in various invertebrate viruses, lepidopteran insects, and parasitoid wasps. P26/poxin from certain insect viruses also retains protease activity, though its biological role remains unknown. Given that many P26s contain a signal peptide, it is surmised that P26 may possess certain extracellular functions. Here, we report that a secretory baculoviral P26 suppresses melanization, a prominent insect innate immunity against pathogen invasion. P26 targets the cofactor of a prophenoloxidase-activating protease, and its inhibitory function is independent of nuclease activity. The analysis of P26/poxin homologs from different origins suggests that the ability to inhibit the extracellular melanization pathway is limited to P26s with a signal peptide and not shared by the homologs without it. These findings highlight the independent evolution of a single viral suppressor to perform dual roles in modulating immunity during virus-host adaptation.

Proteomics reveals the hemolymph components of partially fed Hyalomma asiaticum ticks

Hemolymph infection facilitates pathogen invasion of internal tick tissues. However, the overall protein composition of the hemolymph has not been analyzed for any tick species. Here, a gel based liquid chromatography tandem mass spectrometry method was used to characterize the hemolymph proteome of Hyalomma asiaticum females during blood feeding. A total of 311 proteins were identified. Hemelipoglyco-carrier proteins, apolipophorin-like proteins, and intracellular proteins were the most abundant proteins. Thirteen immunity-related proteins were identified, including peptidoglycan recognition protein (PGRP), Thioester-containing proteins (TEPs), clip‑serine proteinases, serpins and Dome. The presence of hemocytin, proclotting enzyme homologs, serpins, TEPs, factor D-like protein and the lack of coagulin, hemocyanin, and prophenoloxidase suggest ticks may possess a unique coagulation system, which is largely different from that of insects. Taken together, the study revealed the constitution, level, and possible functions of global hemolymph proteins in H. asiaticum and could facilitate the discovery of new targets for control of tick-borne pathogens.

Efficacy of Biopesticides in the Management of the Cotton Bollworm, Helicoverpa armigera (Noctuidae), under Field Conditions

Simple Summary

Cotton remains the most important cash crop in the world. The key insect pests of cotton include the African bollworm Helicoverpa armigera. This pest causes damage to crops estimated at greater than USD 2 billion per year worldwide. Excessive use of insecticides to control this pest has a negative effect on the environment, and is expensive for the farmers. The aim of this study is to explore the field efficacy of different biopesticides as an alternative to control H. armigera. Four biopesticides—namely, Eco-Bb^® (Beauveria bassiana), Bb endophyte (Beauveria bassiana), Bolldex^® (nucleopolyhedrovirus), and Delfin^® (Bacillus thuringiensis)—were evaluated and compared with the pyrethroid Karate^® (lambda-cyhalothrin) and an untreated control. Plots treated with Karate^® had significantly lower numbers of H. armigera larvae compared to the untreated control, and were comparable to the plots treated with Bolldex^®. On average, plots treated with Bolldex^® had a high seed cotton yield compared to the other treatments. Biopesticides showed a moderate reduction in the numbers of H. armigera larvae, and could thus be used within an integrated pest management programme.

Abstract

Cotton is one of the most valuable materials in the world, popularly used in the clothing industry and other products. However, its production is limited by the high infestation of insect pests. A study was conducted to evaluate the effects of different biopesticides on the control of the African bollworm (Helicoverpa armigera) under cotton field conditions. Four biopesticides—namely, Eco-Bb^® (Beauveria bassiana), Bb endophyte (Beauveria bassiana), Bolldex^® (Nucleopolyhedrovirus), and Delfin^® (Bacillus thuringiensis)—were evaluated and compared with the pyrethroid Karate^® (lambda-cyhalothrin) and an untreated control against H. armigera. Field trials were conducted at the Agriculture Research Council, Rustenburg, in the North West Province of South Africa during the 2017 and 2018 cotton seasons. The results revealed that in plots sprayed with Karate^® and Bolldex^®, the numbers of H. armigera were significantly reduced compared to the untreated controls. Plots treated with Bolldex^® had the lowest number of damaged bolls in 2017, while those treated with Karate^® had the lowest number of damaged bolls in 2018. All treated plots had significantly fewer damaged bolls when compared to the controls. A seed cotton yield of 5987 kg/ha was recorded in the plots that were treated with Bolldex^®—significantly higher than the yields from plots treated with Eco-Bb^®, Delfin^®, and Bb endophyte—in 2017. However, the yield in treatments with Eco-Bb^®, Delfin^®, and Bb endophyte was lower than that from the untreated controls during this season. In 2018, plots treated with Bolldex^® had the highest yield, at 6818 kg/ha, which was not different from the other treatments. The highest average seed cotton yield of 6400 kg/ha was recorded in the plots treated with Bolldex^®, followed by Karate^®. In summary, the efficacy of different biopesticides against H. armigera varied significantly, while the synthetic pesticide (Karate^®) and Bolldex^® resulted in more consistent control of this pest. The results suggest that biopesticides may, however, have the potential for use in the sustainable control of cotton bollworms as part of integrated pest management programmes, although further work is required to support this hypothesis.

Unraveling the innate immune responses of Bombyx mori hemolymph, fat body, and midgut to Bombyx mori nucleopolyhedrovirus oral infection by metabolomic analysis

Bombyx mori nucleopolyhedrovirus (BmNPV) infection causes a series of physiological and pathological changes in Bombyx mori (B. mori). Here, a metabolomic study of the innate immunity organs including hemolymph, fat body, and midgut of the silkworm strain Dazao following BmNPV challenge was conducted to reveal the metabolic variations in B. mori. Compared to the control, 4964 and 4942 features with 4077 and 4327 high-quality features were generated under positive and negative modes, respectively, from BmNPV-infected larvae. The principal component analysis and supervised learning method using partial least squares discrimination analysis demonstrated good analytical stability and experimental reproducibility of the metabolic profiles. Based on database annotations, a total of 296, 108, and 215 differential expressed metabolites (DEMs) were identified from BmNPV-infected group of hemolymph, fat body, and midgut, respectively, which were all mainly grouped into carboxylic acids and derivatives, fatty acyls, and glycerophospholipids. Kyoto Encyclopedia of Genes and Genomes Database enrichment analysis of the DEMs showed that amino acid metabolism was increased at 24 h after BmNPV infection. BmNPV induction was adopted to significantly alter a series of immune-related pathways including phospholipase D signaling pathway, FoxO signaling pathway, metabolism of xenobiotics by cytochrome P450, melanogenesis, membrane transport, carbohydrate metabolism, and lipid metabolism. The different levels of expression of several DEMs including l-glutamate, naphthalene, 3-succinoylpyridine 1-acyl-sn-glycerol 3-phosphate, and l-tyrosine which were involved in those pathways exhibited the immune responses of B. mori to BmNPV infection. Our findings are valuable for a better understanding of the antiviral mechanism of B. mori underlying the interaction between the silkworm and BmNPV.

Microbiota modulates gut immunity and promotes baculovirus infection in Helicoverpa armigera

Baculoviruses are natural enemies of agricultural and forest insect pests and play an important role in biological pest control. Oral infection by baculovirus in the insect midgut is necessary for establishing systemic infection and eventually killing the insect. Since the insect midgut continuously encounters microbiota, the gut microbiota could affect baculovirus infection. Here, we demonstrated that gut microbiota modulates immune responses and promotes baculovirus infection in the cotton bollworm, Helicoverpa armigera. After oral infection, numerous host immunity-related genes including genes encoding Toll and immune deficiency (IMD) pathway components were upregulated in the midgut. Elimination of the gut microbiota significantly increased the resistance to viral infection in H. armigera. Quantitative real-time reverse transcription polymerase chain reaction and proteomic analysis showed that downregulation of the antiviral factor prophenoloxidase (PPO) could be mediated by microbiota during infection. It implied that midgut microbiota diminishes the expression of PPO to facilitate viral infection in H. armigera. Our findings revealed that the microbiota plays an important role in modulating the resistance of H. armigera to baculovirus infection, providing new insights in applying biopesticide.

Functional characterization of two clip domain serine proteases in innate immune responses of Aedes aegypti

Background

Clip domain serine proteases (CLIPs), a very diverse group of proteolytic enzymes, play a crucial role in the innate immunity of insects. Innate immune responses are the first line of defense in mosquitoes against the invasion of pathogenic microorganisms. The Toll pathway, immunodeficiency (IMD) pathway and melanization are the main processes of innate immunity in Aedes aegypti. CLIPS are classified into five subfamilies—CLIPA, CLIPB, CLIPC, CLIPD, and CLIPE—based on their sequence specificity and phylogenetic relationships. We report the functional characterization of the genes that code for two CLIPs in Ae. aegypti (Ae): Ae-CLIPB15 and Ae-CLIPB22.

Methods

Clustal Omega was used for multiple amino acid sequence alignment of Ae-CLIPB15 and Ae-CLIPB22 with different CLIP genes from other insect species. The spatiotemporal expression profiles of Ae-CLIPB15 and Ae-CLIPB22 were examined. We determined whether Ae-CLIPB15 and Ae-CLIPB22 respond to microbial challenge and tissue injury. RNA interference (RNAi) was used to explore the function of Ae-CLIPB15 and Ae-CLIPB22 in the defense of Ae. aegypti against bacterial and fungal infections. The expression levels of nuclear factor kappa B (NF-κB) transcription factors REL1 and REL2 in the Toll pathway and IMD pathway after bacterial infection were investigated. Finally, the change in phenoloxidase (PO) activity in Ae-CLIPB15 and Ae-CLIPB22 knockdown adults was investigated.

Results

We performed spatiotemporal gene expression profiling of Ae-CLIPB15 and Ae-CLIPB22 genes in Ae. aegypti using quantitative real-time polymerase chain reaction. These genes were expressed in different stages and tissues. The messenger RNA (mRNA) levels for both genes were also up-regulated by Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus and fungal Beauveria bassiana infections, as well as in the tissue injury experiments. RNAi-mediated knockdown of Ae-CLIPB15 led to a significant decrease of PO activity in the hemolymph of Ae. aegypti, while other RNAi experiments revealed that both Ae-CLIPB15 and Ae-CLIPB22 were involved in immune defense against bacterial and fungal infections. The mRNA expression of NF-κB transcription factors REL1 and REL2 in the Toll pathway and IMD pathway differed between Ae-CLIPB15 and Ae-CLIPB22 knockdown mosquitoes infected with bacteria and wild type mosquitoes infected with bacteria.

Conclusions

Our findings suggest that Ae-CLIPB15 and Ae-CLIPB22 play a critical role in mosquito innate immunity, and that they are involved in immune responses to injury and infection. Their regulation of transcription factors and PO activity indicates that they also play a specific role in the regulation of innate immunity.

Graphical Abstract

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

BmNPV-induced hormone metabolic disorder in silkworm leads to enhanced locomotory behavior

Many parasites alter the host locomotory behaviors in a way that increases their fitness and progeny transmission. Baculoviruses can manipulate host physiology and alter the locomotory behavior by inducing 'hyperactivity' (increased locomotion) or 'tree-top disease' (climbing high up to the top before dying). However, the detailed molecular mechanism underlying virus-induced this hyperactive behavior remains elusive. In the present study, we showed that BmNPV invaded into silkworm brain tissue, resulting in severe brain damage. Moreover, BmNPV infection disturbed the insect hormone balance. The content of 20-hydroxyecdysone (20E) in hemolymph was much lower during the hyperactive stage, while the dopamine (DA) titer was higher than mock infection. Exogenous hormone treatment assays demonstrated that 20E inhibits virus-induced ELA (enhanced locomotory activity), while dopamine stimulates this behavior. More specificity, injection of dopamine or its agonist promote this hyperactive behavior in BmNPV-infected larvae. Taking together, our findings revealed the important role of hormone metabolism in BmNPV-induced ELA.

Global Metabolic Profiling of Baculovirus Infection in Silkworm Hemolymph Shows the Importance of Amino-Acid Metabolism

Viruses rely on host cell metabolism to provide the necessary energy and biosynthetic precursors for successful viral replication. Infection of the silkworm, Bombyx mori, by Bombyx mori nucleopolyhedrovirus (BmNPV), has been studied extensively in the past to unravel interactions between baculoviruses and their lepidopteran hosts. To understand the interaction between the host metabolic responses and BmNPV infection, we analyzed global metabolic changes associated with BmNPV infection in silkworm hemolymph. Our metabolic profiling data suggests that amino acid metabolism is strikingly altered during a time course of BmNPV infection. Amino acid consumption is increased during BmNPV infection at 24 h post infection (hpi), but their abundance recovered at 72 hpi. Central carbon metabolism, on the other hand, particularly glycolysis and glutaminolysis, did not show obvious changes during BmNPV infection. Pharmacologically inhibiting the glycolytic pathway and glutaminolysis also failed to reduce BmNPV replication, revealing that glycolysis and glutaminolysis are not essential during BmNPV infection. This study reveals a unique amino acid utilization process that is implemented during BmNPV infection. Our metabolomic analysis of BmNPV-infected silkworm provides insights as to how baculoviruses induce alterations in host metabolism during systemic infection.

Population structure of Cydia pomonella granulovirus isolates revealed by quantitative analysis of genetic variation

Genetic diversity of viruses is driven by genomic mutations and selection through its host, resulting in differences in virulence as well as host responses. For baculoviruses, which are naturally occurring pathogens of insects and which are frequently sprayed on hundred thousands to millions of hectares as biocontrol agents of insect pests, the phenomenon of virus-host co-evolution is of particular scientific interest and economic importance because high virulence of baculovirus products is essential and emergence of host resistance needs to be avoided as much as possible. In the present study, the population structure of twenty isolates of the Cydia pomonella granulovirus (CpGV), including twelve isolates from different geographic origins and eight commercial formulations, were studied on the basis of next-generation sequencing data and by analyzing the distribution of single nucleotide polymorphisms (SNPs). An entirely consensus sequence-free quantitative SNP analysis was applied for the identification of 753 variant SNP sites being specific for single as well as groups of CpGV isolates. Based on the quantitative SNP analysis, homogenous, heterogenous as well as mixed isolates were identified and their proportions of genotypes were deciphered, revealing a high genetic diversity of CpGV isolates from around the world. Based on hierarchical clustering on principal components (HCPC), six distinct isolate/group clusters were identified, representing the proposed main phylogenetic lineages of CpGV but comprising full genome information from virus mixtures. The relative location of different isolates in HCPC reflected the proportion of variable compositions of different genotypes. The established methods provide novel analysis tools to decipher the molecular complexity of genotype mixtures in baculovirus isolates, thus depicting the population structure of baculovirus isolates in a more adequate form than consensus based analyses.

Comparative genomic analysis of C-type lectin-domain genes in seven holometabolous insect species

C-type lectins (CTLs) recognize various glycoconjugates through carbohydrate recognition domains (CRDs) and they play important roles in immune responses. In this study, comparative genomic analysis of CTLs were performed in 7 holometabolous species. CTL-S1 to S8 and CTL-X1 to X4 orthologous groups existed in the 7 species, while CTL-X5 group with dual-CRD, CTL-S11 group with triple-CRD, CTL-S9 group with a long C-terminus and Lepidopteran specific CTL-S10 group were not conserved. SliCTL-S12 to S14 cluster was only present in Spodoptera litura, and CTL-S genes were expanded on chromosomes 2 L and 2 R in Drosophila melanogaster. Most IMLs were clustered into three groups and the numbers of IMLs vary among species due to gene duplications. D. melanogaster specific CTLs and Lepidopteran IMLs within each of the three groups evolved more rapidly with higher dN/dS ratios. Two CRDs in IMLs clustered into two clades, with conserved Cys4-Cys5 and Cys1-Cys2 bonds in the first and second CRDs, respectively. The CTL-S and CTL-X family members in S. litura were mainly expressed in the fat body of 5th but not 6th instar larvae, and responded differently to S. litura nucleopolyhedrovirus (SpltNPV) and Nomuraea rileyi infection. The transcription levels of SliCTLs that expressed in fat body but not highly expressed in hemocytes were decreased at the middle and late stages of SpltNPV infection, and the mRNA levels of SliCTLs highly or specifically expressed in hemocytes were mainly decreased by SpltlNPV, N. rileyi and Bacillus thuringiensis infection. These results provide valuable information for further exploration of CTL functions in host-pathogen interaction.

Transcriptome analysis of the innate immune system of Hyalomma asiaticum

Ticks are considered to be the second most important vectors of human infectious diseases. The innate immune system is the key factor that affects its vector competence. Hyalomma asiaticum is the primary vector of Crimean-Congo hemorrhagic fever virus (CCHFV). However, the immune system of H. asiaticum remains virtually unknown. Here, a high throughput full-length mRNA sequencing method was adopted to define the immunotranscriptome of H. asiaticum infected with the fungal pathogen Beauveria bassiana and gram-negative bacterium Enterobacter cloacae. The analysis yielded 22,300 isoforms with an average length of 3233 bps. In total, 68 potential immunity-related genes were identified based on similarity to the homologs known to be involved in immunity. These included most members of the Toll and JAK/STAT signaling pathways, but not the IMD signaling pathway. Moreover, two copies of Dicer-2 and five copies of Argonaute-2 were detected. These genes are postulated to be involved in the RNA interference (RNAi) pathway, which is an important defense against RNA viruses. Overall, this study provides the foundation for understanding the immune response of H. asiaticum to CCHFV.

Pattern recognition receptors from lepidopteran insects and their biological functions

Lepidopteran insects have potent innate immunity to fight against the invading pathogens. As the initiation step, pattern recognition receptors (PRRs) recognize and bind microbial surface configurations known as pathogen-associated molecular patterns (PAMPs). Aftermath, they initiate both cellular and humoral immune responses, including phagocytosis, agglutination, nodulation, encapsulation, prophenoloxidase activation, and synthesis of antimicrobial peptides. In this review, we summarize the recent findings concerning PRRs in lepidoptaeran insects, mostly agriculture pests including Helicoverpa armigera, Plutella xylostella, and Spodoptera exigua. We mainly focus on the function and phylogeny of C-type lectins (CTLs), peptidoglycan recognition proteins (PGRPs), β-1,3-glucan recognition proteins (βGRPs), and galectins (GALEs). It enriches our understanding of the immune system of lepidopteran insects and provides directions in the future research.

A RhoGAP venom protein from Microplitis mediator suppresses the cellular response of its host Helicoverpa armigera

Female parasitoid wasps normally inject virulence factors together with eggs into their host to counter host immunity defenses. A newly identified RhoGAP protein in the venom of Microplitis mediator compromises the cellular immunity of its host, Helicoverpa armigera. RhoGAP1 proteins entered H. armigera hemocytes, and the host cellular cytoskeleton was disrupted. Depletion of MmGAP1 by injection of dsRNA or antibody increased the wasp egg encapsulation rate. An immunoprecipitation assay of overexpressed MmGAP1 protein in a Helicoverpa cell line showed that MmGAP1 interacts with many cellular cytoskeleton associated proteins as well as Rho GTPases. A yeast two-hybrid and a pull-down assay demonstrated that MmGAP1 interacts with H. armigera RhoA and Cdc42. These results show that the RhoGAP protein in M. mediator can destroy the H. armigera hemocyte cellular cytoskeleton, restrain host cellular immune defense, and increase the probability of successful parasitism.

Identification of a Conserved Prophenoloxidase Activation Pathway in Cotton Bollworm Helicoverpa armigera

Melanization is a prominent insect humoral response for encapsulation of and killing invading pathogens. It is mediated by a protease cascade composed of a modular serine protease (SP), and clip domain SPs (cSPs), which converts prophenoloxidase (PPO) into active phenoloxidase (PO). To date, melanization pathway in cotton bollworm Helicoverpa armigera, an important agricultural pest, remains largely unclear. To biochemically reconstitute the pathway in vitro, the putative proteases along with modified proteases containing the factor Xa cleavage site were expressed by Drosophila S2 cell expression system. Purified recombinant proteins were used to examine their role in activating PPO. It is revealed that cascade is initiated by a modular SP-SP41, followed by cSP1 and cSP6. The three-step SP41/cSP1/cSP6 cascade could further activate PPO, and the PO activity was significantly enhanced in the presence of two cSP homologs (cSPHs), cSPH11 and cSPH50, suggesting the latter are cofactors for PPO activation. Moreover, baculovirus infection was efficiently blocked by the reconstituted PPO activation cascade, and the effect was boosted by cSPH11 and cSPH50. Taken together, we unraveled a conserved PPO activation cascade in H. armigera, which is similar to that exists in lepidopteran biochemical model Manduca sexta and highlighted its role in antagonizing viral infection.

Induction of DNA methyltransferase genes in Helicoverpa armigera following injection of pathogenic bacteria modulates expression of antimicrobial peptides and affects bacterial proliferation

Following pathogen attack in a host, widespread changes are induced in the host's gene expression, in particular those involved in the immune system, growth and survival. Epigenetic mechanisms have been suggested to be involved in the regulation of these changes through a number of mechanisms. DNA methylation is one of the important epigenetic processes that is carried out by DNA (cytosine-5) methyltransferase (DNMT) and alters expression of target genes. Here, we identified two putative sequences of DNMT (i.e. DNMT1 and DNMT2) from the transcriptome dataset of Helicoverpa armigera that showed high similarity to the homologous sequences in Bombyx mori. Domain architectures of DNMT1 and DNMT2 exhibit the unique pattern of DNMTs that highlights conserved function of these genes in different insects. To see if these genes play any role in bacterial infection, we challenged the fifth instar larvae of H. armigera by injecting Bacillus thuringiensis and Serratia marcescens cells into the hemolymph. Transcript levels of the DNMTs were analyzed by RT-qPCR. The results showed that the expression levels of DNMT1 and DNMT2 increased in the bacteria-injected larvae. Injection of the heat-killed bacteria also induced the expression of the DNMTs, but lower than that of the live bacteria. To determine whether these genes function during bacterial infection, we injected the inhibitor of DNMTs, 5-azacytidine (5-AZA), into the larvae and 24 h later, the bacterial cells were also injected into the larvae. Bacterial replication and larval mortality were analyzed in the treated and control insects. We found that 5-AZA reduced bacterial replication and also mortality of the bacterial-injected larvae regardless of the pathogenic bacterial species. Interestingly, the expression levels of antimicrobial peptides (AMPs) were also modulated following 5-AZA treatment. In conclusion, we showed that upregulation of the DNMTs in H. armigera following bacterial infections modulates AMPs and thereby affects the insect-bacteria interactions.

Specific genes related to nucleopolyhedrovirus in Bombyx mori susceptible and near-isogenic resistant strains through comparative transcriptome analysis

Bombyx mori nucleopolyhedrovirus (BmNPV) is one of the primary pathogens that causes severe economic losses to sericulture. Comparative transcriptomics analysis has been widely applied to explore the antiviral mechanism in resistant strains. Here, to identify genes involved in BmNPV infection, we identified differentially expressed genes (DEGs) and performed weighted gene co-expression network analysis (WGCNA) between two Bombyx mori strains: strain 871 (susceptible to BmNPV infection) and the near-isogenic strain 871C (resistant to BmNPV). Our results showed that 400 genes were associated with resistance in strain 871C, and 76 genes were related to susceptibility in strain 871. In addition, the correlation analysis of DEGs and WGCNA showed that 40 genes related to resistance were highly expressed in the resistant strain. Among them, gene BGIBMGA004291 was the most noticeable. We further identified the effect of gene BGIBMGA004291, which encoded a multiprotein bridge factor 2 (MBF2) family member (MBF2-10), on viral infection in cells. Our data suggested that MBF2-10 inhibited viral infection. Taken together, this study showed specific module trait correlations related to viral infection in strains 871 and 871C, and we identified a resistance-related gene. These findings suggested promising candidate genes with antiviral activity, aiding in the analysis of the antiviral molecular mechanisms in resistant strains.

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.

A Metalloprotease Homolog Venom Protein From a Parasitoid Wasp Suppresses the Toll Pathway in Host Hemocytes

Parasitoid wasps depend on a variety of maternal virulence factors to ensure successful parasitism. Encapsulation response carried out by host hemocytes is one of the major host immune responses toward limiting endoparasitoid wasp offspring production. We found that VRF1, a metalloprotease homolog venom protein identified from the endoparasitoid wasp, Microplitis mediator, could modulate egg encapsulation in its host, the cotton bollworm, Helicoverpa armigera. Here, we show that the VRF1 proenzyme is cleaved after parasitism, and that the C-terminal fragment containing the catalytic domain enters host hemocytes 6 h post-parasitism. Furthermore, using yeast two-hybrid and pull-down assays, VRF1 is shown to interact with the H. armigera NF-κB factor, Dorsal. We also show that overexpressed of VRF1 in an H. armigera cell line cleaved Dorsal in vivo. Taken together, our results have revealed a novel mechanism by which a component of endoparasitoid wasp venom interferes with the Toll signaling pathway in the host hemocytes.

Hemolymph protein profiles of subterranean termite Reticulitermes flavipes challenged with methicillin resistant Staphylococcus aureus or Pseudomonas aeruginosa

When the subterranean termite Reticulitermes flavipes is fed heat-killed methicillin resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa, the termite produces proteins with antibacterial activity against the inducer pathogen in its hemolymph. We used a proteomic approach to characterize the alterations in protein profiles caused by the inducer bacterium in the hemolymph of the termite. Nano-liquid chromatography-tandem mass spectrometry analysis identified a total of 221 proteins and approximately 70% of these proteins could be associated with biological processes and molecular functions. Challenges with these human pathogens induced a total of 57 proteins (35 in MRSA-challenged, 16 in P. aeruginosa-challenged, and 6 shared by both treatments) and suppressed 13 proteins by both pathogens. Quasi-Poisson likelihood modeling with false discovery rate adjustment identified a total of 18 and 40 proteins that were differentially expressed at least 2.5-fold in response to MRSA and P. aeruginosa-challenge, respectively. We selected 7 differentially expressed proteins and verified their gene expression levels via quantitative real-time RT-PCR. Our findings provide an initial insight into a putative termite immune response against MRSA and P. aeruginosa-challenge.

CTL14, a recognition receptor induced in late stage larvae, modulates anti-fungal immunity in cotton bollworm Helicoverpa armigera

C-type lectin (CTL) is usually considered as pattern recognition receptors in insect innate immunity. Here we found that CTL14 of Helicoverpa armigera was only activated in the fifth instar larvae not in the second instar by entomopathogen Beauveria bassiana infection. Recombinant CTL14 protein was found to form aggregates with zymosan and B. bassiana in vitro. Immunoprecipitation studies demonstrated that CTL14 interacted with serine proteinases (SP), serine proteinase inhibitor (serpin), prophenoloxidases (PPO) and vitellogenin (Vg) in the larval hemolymph. Furthermore, depletion of CTL14 using dsRNA led to dramatic decrease in the expression level of PPO1. Additionally, CTL14 depleted H. armigera decreased the resistance to fungal challenge. Taken together, our study showed the direct involvement of CTL14 in the anti-fungal immunity of H. armigera, which further explained the stronger immune responses in the fifth instar compared to the second instar larvae.

C-lysozyme contributes to antiviral immunity in Bombyx mori against nucleopolyhedrovirus infection

Lysozymes is a ubiquitous immune effector that is widely distributed in both vertebrates and invertebrates. Previous reports have shown that lysozymes significantly inhibit viral infections in vertebrates. However, the antiviral effects of lysozymes in invertebrates remain unclear. Here, we investigated the role of lysozymes in Bombyx mori (B. mori) response to viral infection by overexpressing B. mori C-lysozyme (BmC-LZM) in larvae and cells. We found that BmC-LZM was up-regulated in cells in response to viral infection. Indeed, the overexpressing of BmC-LZM significantly inhibited viral replication in cells during late-stage infection. However, this effect was reversed by BmC-LZM mRNA. BmC-LZM was successfully overexpressed in B. mori strain 871 using Baculovirus Expression Vector System (BEVS). This overexpression markedly reduced viral proliferation and increased larval survival percentage. Thus, BmC-LZM inhibited viral replication both in vivo and in vitro, indicating that BmC-LZM is involved in the insect immune response to viral infection. Our results provide a basis for further applications of lysozymes.

The interaction between baculoviruses and their insect hosts

Baculoviruses are double-stranded circular DNA viruses that infect arthropods via the midgut. Because of their superiority as eukaryotic expression systems and their importance as biopesticides, extensive research on the functions of baculovirus genes as well as on the host response to baculovirus infection has been carried out, including transcriptomic and proteomic analyses of the midgut. The morphological and cellular changes caused by baculovirus infection are also important to better understand the infection pathway. Thanks to these previous studies, we now have a clearer picture of the mechanisms of action of the virus and of host immunity. In this paper, we systematically reviewed studies on the interaction between baculoviruses and their insect hosts. By better understanding these interactions, baculoviruses can be developed for use as more efficient biopesticides to improve agricultural development in the future.

The immune strategies of mosquito Aedes aegypti against microbial infection

Yellow fever mosquito Aedes aegypti transmits many devastating arthropod-borne viruses (arboviruses), such as dengue virus, yellow fever virus, Chikungunya virus, and Zika virus, which cause great concern to human health. Mosquito control is an effective method to block the spread of infectious diseases. Ae. aegypti uses its innate immune system to fight against arboviruses, parasites, and fungi. In this review, we briefly summarize the recent findings in the immune response of Ae. aegypti against arboviral and entomopathogenic infections. This review enriches our understanding of the mosquito immune system and provides evidence to support the development of novel mosquito control strategies.

Two predominant MUPs, OBP3 and MUP13, are male pheromones in rats

BACKGROUND

In rats, urine-borne male pheromones comprise organic volatile compounds and major urinary proteins (MUPs). A number of volatile pheromones have been reported, but no MUP pheromones have been identified in rat urine.

RESULTS

We used sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing electrophoresis (IEF), nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) after in gel digestion of the proteins and quantitative real-time PCR (qRT-PCR) and showed that the levels of two MUPs, odorant-binding protein 3 (OBP3) (i.e. PGCL4) and MUP13 (i.e. PGCL1), in urine and their mRNAs in liver were higher in males than in females and were suppressed by orchidectomy and restored by testosterone treatment (T treatment). We then generated recombinant MUPs (rMUPs) and found that the sexual attractiveness of urine from castrated males to females significantly increased after the addition of either recombinant OBP3 (rOBP3) or recombinant MUP13 (rMUP13). Using c-Fos immunohistochemistry, we further examined neuronal activation in the brains of female rats after they sniffed rOBP3 or rMUP13. Both rOBP3 and rMUP13 activated the accessory olfactory bulb (AOB), medial preoptic area (MPA), bed nucleus of the stria terminalis (BST), medial amygdala (MeA), posteromedial cortical amygdala (PMCo) and ventromedial nucleus of the hypothalamus (VMH), which participate in the neural circuits responsible for pheromone-induced sexual behaviours. In particular, more c-Fos-immunopositive (c-Fos-ir) cells were observed in the posterior AOB than in the anterior AOB.

CONCLUSIONS

The expression of OBP3 and MUP13 was male-biased and androgen-dependent. They attracted females and activated brain areas related to sexual behaviours in female rats, suggesting that both OBP3 and MUP13 are male pheromones in rats. Particularly, an OBP excreted into urine was exemplified to be a chemical signal.

Inhibition of melanization by serpin-5 and serpin-9 promotes baculovirus infection in cotton bollworm Helicoverpa armigera

Melanization, an important insect defense mechanism, is mediated by clip-domain serine protease (cSP) cascades and is regulated by serpins. Here we show that proteolytic activation of prophenoloxidase (PPO) and PO-catalyzed melanization kill the baculovirus in vitro. Our quantitative proteomics and biochemical experiments revealed that baculovirus infection of the cotton bollworm, Helicoverpa armigera, reduced levels of most cascade members in the host hemolymph and PO activity. By contrast, serpin-9 and serpin-5 were sequentially upregulated after the viral infection. The H. armigera serpin-5 and serpin-9 regulate melanization by directly inhibiting their target proteases cSP4 and cSP6, respectively and cSP6 activates PPO purified from hemolymph. Furthermore, serpin-5/9-depleted insects exhibited high PO activities and showed resistance to baculovirus infection. Together, our results characterize a part of the melanization cascade in H. armigera, and suggest that natural insect virus baculovirus has evolved a distinct strategy to suppress the host immune system.

Melanization is one of important modules in insect defense system. It consists of a cascade of clip-domain serine proteases (cSPs) that converts the zymogen prophenoloxidase (PPO) to active phenoloxidase (PO), which is negatively regulated by serpins. PO then catalyses the formation of melanin that physically encapsulates certain pathogens. Parasites and bacteria have evolved to produce specific proteins or antibiotic to suppress the melanization response of host insects for survival. However, the mechanisms by which virus persists in the face of the insect melanization are poorly understood. In this study, we show that a DNA virus baculovirus infection of the cotton bollworm, Helicoverpa armigera, reduced the levels of most cascade members in the host hemolymph and PO activity. By contrast, serpin-9 and serpin-5 were sequentially upregulated after the viral infection. Our results also reveal that melanization kills baculovirus in vitro. Serpin-5 and serpin-9 regulate melanization by directly inhibiting their target proteases cSP4 and cSP6, respectively and cSP6 activates PPO purified from hemolymph. Moreover, serpin-5/9-depleted insects show resistance to baculovirus infection. Our findings have enriched the understanding of molecular mechanisms by which pathogens suppress the melanization response of host insect for survival.

Quantitative proteomics of Sf21 cells during Baculovirus infection reveals progressive host proteome changes and its regulation by viral miRNA

System level knowledge of alterations in host is crucial to elucidate the molecular events of viral pathogenesis and to develop strategies to block viral establishment and amplification. Here, we applied quantitative proteomics approach to study global proteome changes in the host; Spodoptera frugiperda upon infection by a baculovirus, Spodoptera litura NPV at two stages i.e. 12 h and 72 h post infection. At 12 hpi, >95% of host proteins remained stable, however at 72 hpi, 52% host proteins exhibited downregulation of 2-fold or more. Functional analysis revealed significant upregulation of transposition and proteasomal machinery while translation, transcription, protein export and oxidative phosphorylation pathways were adversely affected. An assessment of perturbed proteome after viral infection and viral miRNA expression led to the identification of 117 genes that are potential targets of 10 viral miRNAs. Using miRNA mimics, we confirmed the down regulation of 9 host genes. The results comprehensively show dynamics of host responses after viral infection.