Comparative transcriptome analysis of venom glands from Cotesia vestalis and Diadromus collaris, two endoparasitoids of the host Plutella xylostella

Parasitoid Serpins Evolve Novel Functions to Manipulate Host Homeostasis

Parasitoids introduce various virulence factors when parasitism occurs, and some taxa generate teratocytes to manipulate the host immune system and metabolic homeostasis for the survival and development of their progeny. Host-parasitoid interactions are extremely diverse and complex, yet the evolutionary dynamics are still poorly understood. A category of serpin genes, named CvT-serpins, was discovered to be specifically expressed and secreted by the teratocytes of Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella. Genomic and phylogenetic analysis indicated that the C. vestalis serpin genes are duplicated and most of them are clustered into 1 monophyletic clade. Intense positive selection was detected at the residues around the P1-P1' cleavage sites of the Cv-serpin reactive center loop domain. Functional analyses revealed that, in addition to the conserved function of melanization inhibition (CvT-serpins 1, 16, 18, and 21), CvT-serpins exhibited novel functions, i.e. bacteriostasis (CvT-serpins 3 and 5) and nutrient metabolism regulation (CvT-serpins 8 and 10). When the host-parasitoid system is challenged with foreign bacteria, CvT-serpins act as an immune regulator to reprogram the host immune system through sustained inhibition of host melanization while simultaneously functioning as immune effectors to compensate for this suppression. In addition, we provided evidence that CvT-serpin8 and 10 participate in the regulation of host trehalose and lipid levels by affecting genes involved in these metabolic pathways. These findings illustrate an exquisite tactic by which parasitoids win out in the parasite-host evolutionary arms race by manipulating host immune and nutrition homeostasis via adaptive gene evolution and neofunctionalization.

A serpin gene from a parasitoid wasp disrupts host immunity and exhibits adaptive alternative splicing

Alternative splicing (AS) is a major source of protein diversity in eukaryotes, but less is known about its evolution compared to gene duplication (GD). How AS and GD interact is also largely understudied. By constructing the evolutionary trajectory of the serpin gene PpSerpin-1 (Pteromalus puparum serpin 1) in parasitoids and other insects, we found that both AS and GD jointly contribute to serpin protein diversity. These two processes are negatively correlated and show divergent features in both protein and regulatory sequences. Parasitoid wasps exhibit higher numbers of serpin protein/domains than nonparasitoids, resulting from more GD but less AS in parasitoids. The potential roles of AS and GD in the evolution of parasitoid host-effector genes are discussed. Furthermore, we find that PpSerpin-1 shows an exon expansion of AS compared to other parasitoids, and that several isoforms are involved in the wasp immune response, have been recruited to both wasp venom and larval saliva, and suppress host immunity. Overall, our study provides an example of how a parasitoid serpin gene adapts to parasitism through AS, and sheds light on the differential features of AS and GD in the evolution of insect serpins and their associations with the parasitic life strategy.

Mining Amphibian and Insect Transcriptomes for Antimicrobial Peptide Sequences with rAMPage

Antibiotic resistance is a global health crisis increasing in prevalence every day. To combat this crisis, alternative antimicrobial therapeutics are urgently needed. Antimicrobial peptides (AMPs), a family of short defense proteins, are produced naturally by all organisms and hold great potential as effective alternatives to small molecule antibiotics. Here, we present rAMPage, a scalable bioinformatics discovery platform for identifying AMP sequences from RNA sequencing (RNA-seq) datasets. In our study, we demonstrate the utility and scalability of rAMPage, running it on 84 publicly available RNA-seq datasets from 75 amphibian and insect species—species known to have rich AMP repertoires. Across these datasets, we identified 1137 putative AMPs, 1024 of which were deemed novel by a homology search in cataloged AMPs in public databases. We selected 21 peptide sequences from this set for antimicrobial susceptibility testing against Escherichia coli and Staphylococcus aureus and observed that seven of them have high antimicrobial activity. Our study illustrates how in silico methods such as rAMPage can enable the fast and efficient discovery of novel antimicrobial peptides as an effective first step in the strenuous process of antimicrobial drug development.

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

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

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Comparative Transcriptome Analysis Reveals Sex-Based Differences during the Development of the Adult Parasitic Wasp Cotesia vestalis (Hymenoptera: Braconidae)

The endoparasitic wasp Cotesia vestalis is an important biological agent for controlling the population of Plutella xylostella, a major pest of cruciferous crops worldwide. Though the genome of C. vestalis has recently been reported, molecular mechanisms associated with sexual development have not been comprehensively studied. Here, we combined PacBio Iso-Seq and Illumina RNA-Seq to perform genome-wide profiling of pharate adult and adult development of male and female C. vestalis. Taking advantage of Iso-Seq full-length reads, we identified 14,466 novel transcripts as well as 8770 lncRNAs, with many lncRNAs showing a sex- and stage-specific expression pattern. The differentially expressed gene (DEG) analyses showed 2125 stage-specific and 326 sex-specific expressed genes. We also found that 4819 genes showed 11,856 alternative splicing events through combining the Iso-Seq and RNA-Seq data. The results of comparative analyses showed that most genes were alternatively spliced across developmental stages, and alternative splicing (AS) events were more prevalent in females than in males. Furthermore, we identified six sex-determining genes in this parasitic wasp and verified their sex-specific alternative splicing profiles. Specifically, the characterization of feminizer and doublesex splicing between male and female implies a conserved regulation mechanism of sexual development in parasitic wasps.

Symbiotic bracovirus of a parasite manipulates host lipid metabolism via tachykinin signaling

Parasites alter host energy homeostasis for their own development, but the mechanisms underlying this phenomenon remain largely unknown. Here, we show that Cotesia vestalis, an endoparasitic wasp of Plutella xylostella larvae, stimulates a reduction of host lipid levels. This process requires excess secretion of P. xylostella tachykinin (PxTK) peptides from enteroendocrine cells (EEs) in the midgut of the parasitized host larvae. We found that parasitization upregulates PxTK signaling to suppress lipogenesis in midgut enterocytes (ECs) in a non-cell-autonomous manner, and the reduced host lipid level benefits the development of wasp offspring and their subsequent parasitic ability. We further found that a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for PxTK induction, which in turn reduces the systemic lipid level of the host. Taken together, these findings illustrate a novel mechanism for parasite manipulation of host energy homeostasis by a symbiotic bracovirus gene to promote the development and increase the parasitic efficiency of an agriculturally important wasp species.

Parasitic wasps are ubiquitous on earth and diverse. They lay eggs in or on the bodies of their hosts, and they have evolved adaptive strategies to regulate the energy metabolism of their hosts to match their own specific nutrition requirements. Here, we found that Cotesia vestalis, a solitary endoparasitoid of Plutella xylostella, uses symbiotic bracovirus as a weapon to manipulate host systemic lipid levels. Specifically, a C. vestalis bracovirus (CvBV) gene, CvBV 9–2, is responsible for the induction of PxTK, which in turn suppresses lipogenesis in the midgut of the parasitized host, leading to a nutritional lipid level suitable for the development and subsequent parasitic efficiency of C. vestalis wasps. Our study provides innovative insights into the mechanisms by which parasitic wasps manipulate host lipid homeostasis and may help to expand our knowledge of other parasitic systems.

Review of Venoms of Non-Polydnavirus Carrying Ichneumonoid Wasps

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

The genomes of two parasitic wasps that parasitize the diamondback moth

BACKGROUND

Parasitic insects are well-known biological control agents for arthropod pests worldwide. They are capable of regulating their host's physiology, development and behaviour. However, many of the molecular mechanisms involved in host-parasitoid interaction remain unknown.

RESULTS

We sequenced the genomes of two parasitic wasps (Cotesia vestalis, and Diadromus collaris) that parasitize the diamondback moth Plutella xylostella using Illumina and Pacbio sequencing platforms. Genome assembly using SOAPdenovo produced a 178 Mb draft genome for C. vestalis and a 399 Mb draft genome for D. collaris. A total set that contained 11,278 and 15,328 protein-coding genes for C. vestalis and D. collaris, respectively, were predicted using evidence (homology-based and transcriptome-based) and de novo prediction methodology. Phylogenetic analysis showed that the braconid C. vestalis and the ichneumonid D. collaris diverged approximately 124 million years ago. These two wasps exhibit gene gains and losses that in some cases reflect their shared life history as parasitic wasps and in other cases are unique to particular species. Gene families with functions in development, nutrient acquisition from hosts, and metabolism have expanded in each wasp species, while genes required for biosynthesis of some amino acids and steroids have been lost, since these nutrients can be directly obtained from the host. Both wasp species encode a relative higher number of neprilysins (NEPs) thus far reported in arthropod genomes while several genes encoding immune-related proteins and detoxification enzymes were lost in both wasp genomes.

CONCLUSIONS

We present the annotated genome sequence of two parasitic wasps C. vestalis and D. collaris, which parasitize a common host, the diamondback moth, P. xylostella. These data will provide a fundamental source for studying the mechanism of host control and will be used in parasitoid comparative genomics to study the origin and diversification of the parasitic lifestyle.

Analysis of the Gynaephora qinghaiensis pupae immune transcriptome in response to parasitization by Thektogaster sp

As a pest on the Qinghai-Tibet Plateau, Gynaephora qinghaiensis causes severe damage to grassland vegetation and its pupae are also natural hosts of Thektogaster sp. To successfully parasitize, endoparasitoids generally introduce or secrete multiple parasitic factors into the host body during the spawning stage to suppress the host immune response. To study the parasitic effects of Thektogaster sp. on G. qinghaiensis, a transcriptome analysis of immune-related genes in parasitized and nonparasitized G. qinghaiensis pupae was performed. A total of 371,260,704 clean reads were assembled into 118,144 unigenes with an average length of 884.33 base pairs. Of these, 23,660 unigenes were annotated in at least one database and 94,484 unigenes were not annotated in any databases. These findings indicated that the majority of the genetic resources (79.97% of all unigenes) in Gynaephora should be further explored. Parasitization significantly affected the transcriptional profile of G. qinghaiensis pupae. The present study identified 12,322 differentially expressed genes and 57 immune-related genes were identified in parasitized G. qinghaiensis pupae. Most immune-related genes were downregulated, potentially resulting from the inhibitory effect of Thektogaster sp. on G. qinghaiensis pupae after parasitization. Overall, the transcriptome analysis sheds valuable light on the molecular mechanisms of G. qinghaiensis parasitization by Thektogaster sp. and promotes the development of novel biocontrol strategies for Gynaephora based on immune defense.

Biocontrol characteristics of the fruit fly pupal parasitoid Trichopria drosophilae (Hymenoptera: Diapriidae) emerging from different hosts

Trichopria drosophilae (Hymenoptera: Diapriidae) is an important pupal endoparasitoid of Drosophila melanogaster Meigen (Diptera: Drosophilidae) and some other fruit fly species, such as D. suzukii, a very important invasive and economic pest. Studies of T. drosophilae suggest that this could be a good biological control agent for fruit fly pests. In this research, we compared the parasitic characteristics of T. drosophilae reared in D. melanogaster (TD_m) with those reared in D. hydei (TD_h). TD_h had a larger size than TD_m. The number of maximum mature eggs of a female TD_h was 133.6 ± 6.9, compared with the significantly lower value of 104.8 ± 11.4 for TD_m. Mated TD_h female wasp continuously produced female offspring up to 6 days after mating, compared with only 3 days for TD_m. In addition, the offspring female ratio of TD_h, i.e., 82.32%, was significantly higher than that of TD_m, i.e., 61.37%. Under starvation treatment, TD_h survived longer than TD_m. TD_h also survived longer than TD^m at high temperatures, such as 37 °C, although they both survived well at low temperatures, such as 18 °C and 4 °C. Old-age TD_h females maintained a high parasitism rate and offspring female ratio, while they were declined in old-age TD_m. Overall, TD_h had an advantage in terms of body size, fecundity, stress resistance ability and the parasitism rate compared with TD_m. Therefore, T. drosophilae from D. hydei could improve biocontrol efficacy with enormous economic benefits in the field, especially in the control of many frugivorous Drosophilidae species worldwide.

Venomics reveals novel ion transport peptide-likes (ITPLs) from the parasitoid wasp Tetrastichus brontispae

Despite substantial advances in uncovering constituents of parasitoid venoms due to their potential applications as insecticides and pharmaceuticals, most of these studies are primarily restricted to braconid and ichneumonid wasps. Little information is available regarding virulent factors from venom of Eulophidae. In order to provide insight into the venom components of this family and parasitoid venom evolution, a venom protein repertoire (venomics) of the endoparasitoid wasp, Tetrastichus brontispae was deciphered using a proteomic approach. A large number of diverse venom proteins/peptides were identified, including novel proteins and those proteins commonly found in the venoms of other parasitoids such as serine protease, esterase, dipeptidyl peptidase IV, acid phosphatase, major royal jelly protein, superoxide dismutase, and venom allergen 3/5. Three ion transport peptide-likes (ITPLs) were abundantly detected in T. brontispae venom. Of these, two of them are reported as a novel form for the first time, with the characteristics of lengthened amino acid sequences and additional cysteine residues. These venom ITPLs are obviously apart from other general members within the crustacean hyperglycemic hormone/ion transport peptide (CHH/ITP) family. It implies that they would evolve unique functions essential for parasitism success.

Combined Venom Gland Transcriptomic and Venom Peptidomic Analysis of the Predatory Ant Odontomachus monticola

Ants (hymenoptera: Formicidae) have adapted to many different environments and have become some of the most prolific and successful insects. To date, 13,258 ant species have been reported. They have been classified into 333 genera and 17 subfamilies. Except for a few Formicinae, Dolichoderinae, and members of other subfamilies, most ant species have a sting with venom. The venoms are composed of formic acid, alkaloids, hydrocarbons, amines, peptides, and proteins. Unlike the venoms of other animals such as snakes and spiders, ant venoms have seldom been analyzed comprehensively, and their compositions are not yet completely known. In this study, we used both transcriptomic and peptidomic analyses to study the composition of the venom produced by the predatory ant species Odontomachus monticola. The transcriptome analysis yielded 49,639 contigs, of which 92 encoded toxin-like peptides and proteins with 18,106,338 mapped reads. We identified six pilosulin-like peptides by transcriptomic analysis in the venom gland. Further, we found intact pilosulin-like peptide 1 and truncated pilosulin-like peptides 2 and 3 by peptidomic analysis in the venom. Our findings related to ant venom peptides and proteins may lead the way towards development and application of novel pharmaceutical and biopesticidal resources.