Prediction of a peptidome for the western tarnished plant bug Lygus hesperus

Identification of neuropeptides and their G protein-coupled receptors in the predatory stink bug, Arma custos (Hemiptera: Pentatomidae)

The predatory stink bug Arma custos has been selected as an effective biological control agent and has been successfully massly bred and released into fields for the control of a diverse insect pests. As a zoophytophagous generalist, A. custos relies on a complex neuropeptide signaling system to prey on distinct food and adapt to different environments. However, information about neuropeptide signaling genes in A. custos has not been reported to date. In the present study, a total of 57 neuropeptide precursor transcripts and 41 potential neuropeptide G protein-coupled receptor (GPCR) transcripts were found mainly using our sequenced transcriptome data. Furthermore, a number of neuropeptides and their GPCR receptors that were enriched in guts and salivary glands of A. custos were identified, which might play critical roles in feeding and digestion. Our study provides basic information for an in-depth understanding of biological and ecological characteristics of the predatory bug and would aid in the development of better pest management strategies based on the effective utilization and protection of beneficial natural enemies.

Transcriptome analysis reveals salivary gland-specific neuropeptide signaling genes in the predatory stink bug, Picromerus lewisi

Predatory stink bugs derive from phytophagous stink bugs and evolved enhanced predation skills. Neuropeptides are a diverse class of ancient signaling molecules that regulate physiological processes and behavior in animals, including stink bugs. Neuropeptide evolution might be important for the development of predation because neuropeptides can be converted to venoms that impact prey. However, information on neuropeptide signaling genes in predatory stink bugs is lacking. In the present study, neuropeptide signaling genes of Picromerus lewisi, an important predatory stink bug and an effective biological agent, were comprehensively identified by transcriptome analysis, with a total of 59 neuropeptide precursor genes and 58 potential neuropeptide receptor genes found. In addition, several neuropeptides and their receptors enriched in salivary glands of P. lewisi were identified. The present study and subsequent functional research contribute to an in-depth understanding of the biology and behavior of the predatory bugs and can provide basic information for the development of better pest management strategies, possibly including neuropeptide receptors as insecticide targets and salivary gland derived venom toxins as novel killing moleculars.

Molecular and Functional Characterization of Pyrokinin-Like Peptides in the Western Tarnished Plant Bug Lygus hesperus (Hemiptera: Miridae)

Simple Summary

Neuropeptides regulate most insect biological functions. One such group of peptides, the pyrokinins (PKs), are distinguished by a C-terminal FXPRLamide. While widely distributed in most insects, they are poorly characterized in plant bugs. To address this limitation, we identified the PK transcript in the western tarnished plant bug (Lygus hesperus) and examined its expression. The Lygus PK transcript is predicted to yield three PK-like peptides but only two (LyghePKa and LyghePKb) have the characteristic C-terminal amide. The transcript is expressed throughout development and is most abundant in heads. A custom FXPRLamide antibody revealed immunoreactive cells throughout the Lygus central nervous system consistent with typical neuropeptide expression. To assess potential functional roles of the peptides, a fluorescence-based Ca²⁺ influx assay using cultured insect cells stably expressing a moth PK receptor was performed. LyghePKa was unable to stimulate receptor activation, whereas LyghePKb triggered a robust response. The in vivo pheromonotropic activity of the two peptides was likewise assessed using three different moth species. Like the cell culture system, only the LyghePKb peptide was active. The study suggests evolutionary divergence of the PK gene in plant bugs and provides critical insights into likely biological functions in the western tarnished plant bug.

Abstract

The pyrokinin (PK) family of insect neuropeptides, characterized by C termini consisting of either WFGPRLamide (i.e., PK1) or FXPRLamide (i.e., PK2), are encoded on the capa and pk genes. Although implicated in diverse biological functions, characterization of PKs in hemipteran pests has been largely limited to genomic, transcriptomic, and/or peptidomic datasets. The Lygus hesperus (western tarnished plant bug) PK transcript encodes a prepropeptide predicted to yield three PK2 FXPRLamide-like peptides with C-terminal sequences characterized by FQPRSamide (LyghePKa), FAPRLamide (LyghePKb), and a non-amidated YSPRF. The transcript is expressed throughout L. hesperus development with greatest abundance in adult heads. PRXamide-like immunoreactivity, which recognizes both pk- and capa-derived peptides, is localized to cells in the cerebral ganglia, gnathal ganglia/suboesophageal ganglion, thoracic ganglia, and abdominal ganglia. Immunoreactivity in the abdominal ganglia is largely consistent with capa-derived peptide expression, whereas the atypical fourth pair of immunoreactive cells may reflect pk-based expression. In vitro activation of a PK receptor heterologously expressed in cultured insect cells was only observed in response to LyghePKb, while no effects were observed with LyghePKa. Similarly, in vivo pheromonotropic effects were only observed following LyghePKb injections. Comparison of PK2 prepropeptides from multiple hemipterans suggests mirid-specific diversification of the pk gene.

Filling in the gaps: A reevaluation of the Lygus hesperus peptidome using an expanded de novo assembled transcriptome and molecular cloning

Peptides are the largest and most diverse class of molecules modulating physiology and behavior. Previously, we predicted a peptidome for the western tarnished plant bug, Lygus hesperus, using transcriptomic data produced from whole individuals. A potential limitation of that analysis was the masking of underrepresented genes, in particular tissue-specific transcripts. Here, we reassessed the L. hesperus peptidome using a more comprehensive dataset comprised of the previous transcriptomic data as well as tissue-specific reads produced from heads and accessory glands. This augmented assembly significantly improves coverage depth providing confirmatory transcripts for essentially all of the previously identified families and new transcripts encoding a number of new peptide precursors corresponding to 14 peptide families. Several families not targeted in our initial study were identified in the expanded assembly, including agatoxin-like peptide, CNMamide, neuropeptide-like precursor 1, and periviscerokinin. To increase confidence in the in silico data, open reading frames of a subset of the newly identified transcripts were amplified using RT-PCR and sequence validated. Further PCR-based profiling of the putative L. hesperus agatoxin-like peptide precursor revealed evidence of alternative splicing with near ubiquitous expression across L. hesperus development, suggesting the peptide serves functional roles beyond that of a toxin. The peptides predicted here, in combination with those identified in our earlier study, expand the L. hesperus peptidome to 42 family members and provide an improved platform for initiating molecular and physiological investigations into peptidergic functionality in this non-model agricultural pest.

Assessment of midgut enteroendocrine peptide complement in the honey bee, Apis mellifera

Peptides modulate physiological/behavioral control systems in all animals. In arthropods, midgut epithelial endocrine cells are one of the largest sources of these signaling agents. At present, little is known about the identity of the peptides that form arthropod midgut enteroendocrine peptidomes. While many techniques can be used for peptide structural identification, in silico transcriptome mining is one that has been used extensively for arthropod neuropeptidome prediction; this strategy has yet to be used for large-scale arthropod enteroendocrine peptide discovery. Here, a tissue-specific transcriptome was used to assess putative enteroendocrine peptide complement in the honey bee, Apis mellifera, midgut. Searches for transcripts encoding members of 42 peptide families were conducted, with evidence of expression for 15 groups found in the assembly: adipokinetic hormone, allatostatin A, allatostatin C, bursicon, CCHamide, CNMamide, diuretic hormone 31, diuretic hormone 44, insulin-like peptide, myosuppressin, neuropeptide F, pigment dispersing hormone, pyrokinin, short neuropeptide F, and tachykinin-related peptide. The proteins deduced from the midgut transcripts are identical in sequence, or nearly so, to those of Apis pre/preprohormones deposited previously into NCBI, providing increased confidence in the accuracy of the reported data. Seventy-five peptides were predicted from the deduced precursor proteins, 26 being members of known peptide families. Comparisons to previously published mass spectrometric data support the existence of many of the predicted Apis peptides. This study is the first prediction of an arthropod midgut peptidome using transcriptomics, and provides a powerful new resource for investigating enteroendocrine peptide signaling within/from the Apis midgut, a species of significant ecological/economic importance.

RNA interference-mediated knockdown of eye coloration genes in the western tarnished plant bug (Lygus hesperus Knight)

Insect eye coloration arises from the accumulation of various pigments. A number of genes that function in the biosynthesis (vermilion, cinnabar, and cardinal) and importation (karmoisin, white, scarlet, and brown) of these pigments, and their precursors, have been identified in diverse species and used as markers for transgenesis and gene editing. To examine their suitability as visible markers in Lygus hesperus Knight (western tarnished plant bug), transcriptomic data were screened for sequences exhibiting homology with the Drosophila melanogaster proteins. Complete open reading frames encoding putative homologs for all seven genes were identified. Bioinformatic-based sequence and phylogenetic analyses supported initial annotations as eye coloration genes. Consistent with their proposed role, each of the genes was expressed in adult heads as well as throughout nymphal and adult development. Adult eyes of those injected with double-stranded RNAs (dsRNAs) for karmoisin, vermilion, cinnabar, cardinal, and scarlet were characterized by a red band along the medial margin extending from the rostral terminus to the antenna. In contrast, eyes of insects injected with dsRNAs for both white and brown were a uniform light brown. White knockdown also produced cuticular and behavioral defects. Based on its expression profile and robust visible phenotype, cardinal would likely prove to be the most suitable marker for developing gene editing methods in Lygus species.

AMGSEFLamide, a member of a broadly conserved peptide family, modulates multiple neural networks in Homarus americanus

Recent genomic/transcriptomic studies have identified a novel peptide family whose members share the carboxyl terminal sequence -GSEFLamide. However, the presence/identity of the predicted isoforms of this peptide group have yet to be confirmed biochemically, and no physiological function has yet been ascribed to any member of this peptide family. To determine the extent to which GSEFLamides are conserved within the Arthropoda, we searched publicly accessible databases for genomic/transcriptomic evidence of their presence. GSEFLamides appear to be highly conserved within the Arthropoda, with the possible exception of the Insecta, in which sequence evidence was limited to the more basal orders. One crustacean in which GSEFLamides have been predicted using transcriptomics is the lobster, Homarus americanus Expression of the previously published transcriptome-derived sequences was confirmed by reverse transcription (RT)-PCR of brain and eyestalk ganglia cDNAs; mass spectral analyses confirmed the presence of all six of the predicted GSEFLamide isoforms - IGSEFLamide, MGSEFLamide, AMGSEFLamide, VMGSEFLamide, ALGSEFLamide and AVGSEFLamide - in H. americanus brain extracts. AMGSEFLamide, of which there are multiple copies in the cloned transcripts, was the most abundant isoform detected in the brain. Because the GSEFLamides are present in the lobster nervous system, we hypothesized that they might function as neuromodulators, as is common for neuropeptides. We thus asked whether AMGSEFLamide modulates the rhythmic outputs of the cardiac ganglion and the stomatogastric ganglion. Physiological recordings showed that AMGSEFLamide potently modulates the motor patterns produced by both ganglia, suggesting that the GSEFLamides may serve as important and conserved modulators of rhythmic motor activity in arthropods.

Molecular cloning and characterization of the SIFamide precursor and receptor in a hymenopteran insect, Bombus terrestris

SIFamides (SIFa) are a family of neuropeptides that are highly conserved among arthropods. In insects, this peptide is mainly expressed in four medial interneurons in the pars intercerebralis and affects sexual behavior, sleep regulation and pupal mortality. Furthermore, an influence on the hatching rate has been observed. The first SIFa receptor (SIFR) was pharmacologically characterized in Drosophila melanogaster and is homologous to the vertebrate gonadotropin-inhibitory hormone (GnIH) receptor (NPFFR). In this study, we pharmacologically characterized the SIFR of the buff-tailed bumblebee Bombus terrestris. We demonstrated an intracellular increase in calcium ions and cyclic AMP (cAMP) upon ligand binding with an EC₅₀ value in the picomolar and nanomolar range, respectively. In addition, we studied the agonistic properties of a range of related and modified peptides. By means of quantitative real time PCR (qPCR), we examined the relative transcript levels of Bomte-SIFa and Bomte-SIFR in a variety of tissues.

In silico prediction of neuropeptides in Hymenoptera parasitoid wasps

Parasitoid wasps of the order Hymenoptera, the most diverse groups of animals, are important natural enemies of arthropod hosts in natural ecosystems and can be used in biological control. To date, only one neuropeptidome of a parasitoid wasp, Nasonia vitripennis, has been identified. This study aimed to identify more neuropeptides of parasitoid wasps, by using a well-established workflow that was previously adopted for predicting insect neuropeptide sequences. Based on publicly accessible databases, totally 517 neuropeptide precursors from 24 parasitoid wasp species were identified; these included five neuropeptides (CNMamide, FMRFamide-like, ITG-like, ion transport peptide-like and orcokinin B) that were identified for the first time in parasitoid wasps, to our knowledge. Next, these neuropeptides from parasitoid wasps were compared with those from other insect species. Phylogenetic analysis suggested the divergence of AST-CCC within Hymenoptera. Further, the encoding patterns of CAPA/PK family genes were found to be different between Hymenoptera species and other insect species. Some neuropeptides that were not found in some parasitoid superfamilies (e.g., sulfakinin), or considerably divergent between different parasitoid superfamilies (e.g., sNPF) might be related to distinct physiological processes in the parasitoid life. Information of neuropeptide sequences in parasitoid wasps can be useful for better understanding the phylogenetic relationships of Hymenoptera and further elucidating the physiological functions of neuropeptide signaling systems in parasitoid wasps.

Prediction of a peptidome for the ecotoxicological model Hyalella azteca (Crustacea; Amphipoda) using a de novo assembled transcriptome

Due to its sensitivity to many environmental and anthropogenic stressors, including a wide range of chemical compounds, Hyalella azteca, a freshwater amphipod, has emerged as one of the most commonly used invertebrates for ecotoxicological assessment.Peptidergic signaling systems are key components in the control of organism-environment interactions, and there is a growing literature suggesting that they are targets of a number of aquatic toxicants.Interestingly, and despite its model species status in the field of ecotoxicology, little is known about the peptide hormones of H. azteca.Here, a transcriptome was produced for this species using the de novo assembler Trinity and mined for sequences encoding putative peptide precursors; the transcriptome was assembled from 460,291,636 raw reads and consists of 133,486 unique transcripts.Seventy-six sequences encoding peptide pre/preprohormones were identified from this transcriptome, allowing for the prediction of 202 distinct peptides, which included members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, ecdysis-triggering hormone, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone, GSEFLamide, inotocin, leucokinin, myosuppressin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide, sulfakinin, tachykinin-related peptide and trissin families.These peptides expand the known peptidome for H. azteca approximately nine-fold, forming a strong foundation for future studies of peptidergic control, including disruption by aquatic toxicants, in this important ecotoxicological model.

Neuropeptide discovery in Proasellus cavaticus: Prediction of the first large-scale peptidome for a member of the Isopoda using a publicly accessible transcriptome

In silico transcriptome mining is one of the most effective methods for neuropeptide discovery in crustaceans, particularly for species that are small, rare or from geographically inaccessible habitats that make obtaining the large pools of tissue needed for other peptide discovery platforms impractical. Via this approach, large peptidomes have recently been described for members of many of the higher crustacean taxa, one notable exception being the Isopoda; no peptidome has been predicted for any member of this malacostracan order. Using a publicly accessible transcriptome for the isopod Proasellus cavaticus, a subcentimeter subterranean ground water dweller, the first in silico-predicted peptidome for a member of the Isopoda is presented here. BLAST searches employing known arthropod neuropeptide pre/preprohormone queries identified 49 transcripts as encoding putative homologs within the P. cavaticus transcriptome. The proteins deduced from these transcripts allowed for the prediction of 171 distinct mature neuropeptides. The P. cavaticus peptidome includes members of the adipokinetic hormone-corazonin-like peptide, allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon α, bursicon β, CCHamide, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, diuretic hormone 31, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone α2, leucokinin, myosuppressin, neuroparsin, neuropeptide F, pigment dispersing hormone, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, sulfakinin, tachykinin-related peptide and trissin families, as well as many linker/precursor-related sequences that may or may not represent additional bioactive molecules. Interestingly, many of the predicted P. cavaticus neuropeptides possess structures identical (or nearly so) to those previously described from members of several other malacostracan orders, i.e., the Decapoda, Amphipoda and Euphausiacea, a finding that suggests broad phylogenetic conservation of bioactive peptide structures, and possibly functions, may exist within the Malacostraca.