Identification of three protein disulfide isomerase members from Haemaphysalis longicornis tick

Dual roles for a tick protein disulfide isomerase during the life cycle of the Lyme disease agent

The protein disulfide isomerase (PDI) family is a group of enzymes that have thiol-disulfide oxidoreductase, disulfide isomerase, and redox-dependent chaperone activities. PDIs facilitate diverse infections in mammalian hosts by directly binding to pathogens, immunomodulation, or enabling microbial invasion of host cells. PDI homologs within pathogens are also potential virulence factors. However, whether PDIs within blood-feeding ticks influence microbial infection remains unknown. In this study, we investigated the role of Ixodes scapularis PDIs, on the Lyme disease agent, Borrelia burgdorferi. I. scapularis has five PDIs (IsPDIs), and IsPDIA6 gene expression is reduced upon B. burgdorferi infection in the tick. IsPDIA6-mediated trypsin inhibitor gene expression contributes to B. burgdorferi colonization within the tick midgut. IsPDIA6 is also secreted into the host during tick feeding, alters cytokine/chemokine expression at the tick bite site, and influences the initial stage of bacterial infection in mice. These data demonstrate that a PDI from a blood-feeding vector plays a role in the life cycle of an extracellular pathogen.

IMPORTANCE

Vector-borne diseases are a leading cause of death and illness worldwide, and more than 80% of the global population live in areas at risk from at least one major vector-borne disease. In this study, we demonstrate a dual role of a specific Ixodes tick protein disulfide isomerase (PDI) in inhibiting the ability of the Lyme disease agent to colonize ticks and also in enhancing the initial stage of spirochete infection of mice. This study represents a novel conceptual advancement that a PDI from a blood-feeding vector plays important roles in the life cycle of an extracellular pathogen.

A conserved protein disulfide isomerase enhances plant resistance against herbivores

Herbivore-associated molecular patterns (HAMPs) enable plants to recognize herbivores and may help plants adjust their defense responses. Here, we report on herbivore-induced changes in a protein disulfide isomerase (PDI) widely distributed across arthropods. PDI from the spider mite Tetranychus evansi (TePDI), a mesophyll-feeding agricultural pest worldwide, triggered immunity in multiple Solanaceae plants. TePDI-mediated cell death in Nicotiana benthamiana required the plant signaling proteins SGT1 (suppressor of the G2 allele of skp1) and HSP90 (heat shock protein 90), but was suppressed by spider mite effectors Te28 and Te84. Moreover, PDIs from phylogenetically distinct herbivorous and nonherbivorous arthropods triggered plant immunity. Finally, although PDI-induced plant defenses impaired the performance of spider mites on plants, RNAi experiments revealed that PDI genes are essential for the survival of mites and whiteflies. Our findings indicate that plants recognize evolutionarily conserved HAMPs to activate plant defense and resist pest damage, pointing to opportunities for broad-spectrum pest management.

Protein profiling of hemolymph in Haemaphysalis flava ticks

Background

Tick hemolymph bathes internal organs, acts as an exchange medium for nutrients and cellular metabolites, and offers protection against pathogens. Hemolymph is abundant in proteins. However, there has been limited integrated protein analysis in tick hemolymph thus far. Moreover, there are difficulties in differentiating tick-derived proteins from the host source. The aim of this study was to profile the tick/host protein components in the hemolymph of Haemaphysalis flava.

Methods

Hemolymph from adult engorged H. flava females was collected by leg amputation from the Erinaceus europaeus host. Hemolymph proteins were extracted by a filter-aided sample preparation protocol, digested by trypsin, and assayed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). MS raw data were searched against the UniProt Erinaceidae database and H. flava protein database for host- and tick-derived protein identification. Protein abundance was further quantified by intensity-based absolute quantification (iBAQ).

Results

Proteins extracted from hemolymph unevenly varied in size with intense bands between 100 and 130 kDa. In total, 312 proteins were identified in the present study. Therein 40 proteins were identified to be host-derived proteins, of which 18 were high-confidence proteins. Top 10 abundant host-derived proteins included hemoglobin subunit-α and subunit-β, albumin, serotransferrin-like, ubiquitin-like, haptoglobin, α-1-antitrypsin-like protein, histone H2B, apolipoprotein A-I, and C3-β. In contrast, 169 were high-confidence tick-derived proteins. These proteins were classified into six categories based on reported functions in ticks, i.e., enzymes, enzyme inhibitors, transporters, immune-related proteins, muscle proteins, and heat shock proteins. The abundance of Vg, microplusin and α-2-macroglobulin was the highest among tick-derived proteins as indicated by iBAQ.

Conclusions

Numerous tick- and host-derived proteins were identified in hemolymph. The protein profile of H. flava hemolymph revealed a sophisticated protein system in the physiological processes of anticoagulation, digestion of blood meal, and innate immunity. More investigations are needed to characterize tick-derived proteins in hemolymph.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05287-7.

Data from expressed sequence tags from the organs and embryos of parthenogenetic Haemaphysalis longicornis

Objectives

Haemaphysalis longicornis is the most important tick species in Japan and has a wide range of vector capacity. Due to its veterinary and medical importance, this tick species has been used as a model for tick/vector biological studies. To identify the key molecules associated with physiological processes during blood feeding and embryogenesis, full-length cDNA libraries were constructed using the fat body, hemocytes-containing hemolymph, midgut, ovary and salivary glands of fed females and embryos of the laboratory colony of parthenogenetic H. longicornis. The sequences of cDNA from the salivary glands had been already released. However, the related information is still poor, and the other expressed sequence tags have not yet been deposited.

Data description

A total of 39,113 expressed sequence tags were obtained and deposited at the DNA DataBank of Japan. There were 7745 sequences from embryos, 7385 from the fat body, 8303 from the hemolymph including hemocytes, 7385 from the midgut, and 8295 from the ovary. The data, including expressed sequence tags from the salivary glands was summarized into Microsoft Excel files. Sharing this data resource with the tick research community will be valuable for the identification of novel genes and advance the progress of tick research.

An Ixodes scapularis Protein Disulfide Isomerase Contributes to Borrelia burgdorferi Colonization of the Vector

Borrelia burgdorferi causes Lyme disease, the most common tick-transmitted illness in North America. When Ixodes scapularis feed on an infected vertebrate host, spirochetes enter the tick gut along with the bloodmeal and colonize the vector. Here, we show that a secreted tick protein, I. scapularis protein disulfide isomerase A3 (IsPDIA3), enhances B. burgdorferi colonization of the tick gut. I. scapularis ticks in which ispdiA3 has been knocked down using RNA interference have decreased spirochete colonization of the tick gut after engorging on B. burgdorferi-infected mice. Moreover, administration of IsPDIA3 antiserum to B. burgdorferi-infected mice reduced the ability of spirochetes to colonize the tick when feeding on these animals. We show that IsPDIA3 modulates inflammatory responses at the tick bite site, potentially facilitating spirochete survival at the vector-host interface as it exits the vertebrate host to enter the tick gut. These data provide functional insights into the complex interactions between B. burgdorferi and its arthropod vector and suggest additional targets to interfere with the spirochete life cycle.

The root-knot nematode effector MiPDI1 targets a stress-associated protein (SAP) to establish disease in Solanaceae and Arabidopsis

Large amounts of effectors are secreted by the oesophageal glands of plant-parasitic nematodes, but their molecular mode of action remains largely unknown. We characterized a Meloidogyne incognita protein disulphide isomerase (PDI)-like effector protein (MiPDI1) that facilitates nematode parasitism. In situ hybridization showed that MiPDI1 was expressed specifically in the subventral glands of M. incognita. It was significantly upregulated during parasitic stages. Immunolocalization demonstrated MiPDI1 secretion in planta during nematode migration and within the feeding cells. Host-induced silencing of the MiPDI1 gene affected the ability of the nematode to infect the host, whereas MiPDI1 expression in Arabidopsis increased susceptibility to M. incognita, providing evidence for a key role of MiPDI1 in M. incognita parasitism. Yeast two-hybrid, bimolecular fluorescence complementation and coimmunoprecipitation assays showed that MiPDI1 interacted with a tomato stress-associated protein (SlSAP12) orthologous to the redox-regulated AtSAP12, which plays an important role in plant responses to abiotic and biotic stresses. SAP12 silencing or knocking out in Nicotiana benthamiana and Arabidopsis increased susceptibility to M. incognita. Our results suggest that MiPDI1 acts as a pathogenicity factor promoting disease by fine-tuning SAP-mediated responses at the interface of redox signalling, defence and stress acclimation in Solanaceae and Arabidopsis.

Secretome Analysis and In Planta Expression of Salivary Proteins Identify Candidate Effectors from the Brown Planthopper Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a phloem sap-feeding insect. During feeding on rice plants, BPH secretes salivary proteins with potential effector functions, which may play a critical role in the plant-insect interactions. However, a limited number of BPH effector proteins have been identified to date. Here, we sequenced the salivary gland transcriptomes of five BPH populations and subsequently established a N. lugens secretome consisting of 1,140 protein-encoding genes. Secretome analysis revealed the presence of both conserved and rapidly evolving salivary proteins. A screen for potential effectors that elicit responses in the plant was performed via the transient expression analysis of 64 BPH salivary proteins in Nicotiana benthamiana leaves and rice protoplasts. The salivary proteins Nl12, Nl16, Nl28, and Nl43 induced cell death, whereas Nl40 induced chlorosis and Nl32 induced a dwarf phenotype in N. benthamiana, indicating effector properties of these proteins. Ectopic expression of the six salivary proteins in N. benthamiana upregulated expression of defense-related genes and callose deposition. Tissue expression analysis showed a higher expression level of the six candidate effectors in salivary glands than in other tissues. Subcellular localization and analysis of the domain required for cell death showed a diverse structure of the six effectors. Nl28, Nl40, and Nl43 are N. lugens specific; in contrast, Nl12, Nl16, and Nl32 are conserved among insects. The Nl40 family has numerous isoforms produced by alternative splicing, exemplifying rapid evolution and expansion of effector proteins in the BPH. Our results suggest a potential large effector repertoire in BPH and a higher level of effector conservation exist in BPH compared with that in plant pathogens.

De novo assembly and analysis of midgut transcriptome of the argasid tick Ornithodoros erraticus and identification of genes differentially expressed after blood feeding

Ticks are hematophagous vectors of great medical and veterinary importance because they transmit numerous pathogenic microorganisms to humans and animals. The argasid Ornithodoros erraticus is the main vector of tick-borne human relapsing fever and African swine fever in the Mediterranean Basin. Tick enterocytes express bioactive molecules that perform key functions in blood digestion, feeding, toxic waste processing and pathogen transmission. To explore new strategies for tick control, in this work we have obtained and compared the midgut transcriptomes of O. erraticus female ticks before and after a blood meal and identified the genes whose expression is differentially regulated after feeding. The transcript sequences were annotated, functionally and structurally characterised and their expression levels compared between both physiological conditions (unfed females and fed females at 2 days post-engorgement). Up to 29,025 transcripts were assembled, and 9290 of them corresponded to differentially expressed genes (DEGs) after feeding. Of these, 4656 genes were upregulated and nearly the same number of genes was downregulated in fed females compared to unfed females. BLASTN and BLASTX analyses of the 29,025 transcripts allowed the annotation of 9072 transcripts/proteins. Among them, the most numerous were those with catalytic and binding activities and those involved in diverse metabolic pathways and cellular processes. The analyses of functional groups of upregulated DEGs potentially related to the digestion of proteins, carbohydrates and lipids, and the genes involved in the defence response and response to oxidative stress, confirm that these processes are narrowly regulated in ticks, highlighting their complexity and importance in tick biology. The expression patterns of six genes throughout the blood digestion period revealed significant differences between these patterns, strongly suggesting that the transcriptome composition is highly dynamic and subjected to important variation along the trophogonic cycle. This may guide future studies aimed at improving the understanding of the molecular physiology of tick digestion and digestion-related processes. The current work provides a more robust and comprehensive understanding of the argasid tick digestive system.

Molecular characterization and analysis of a novel protein disulfide isomerase-like protein of Eimeria tenella

Protein disulfide isomerase (PDI) and PDI-like proteins are members of the thioredoxin superfamily. They contain thioredoxin-like domains and catalyze the physiological oxidation, reduction and isomerization of protein disulfide bonds, which are involved in cell function and development in prokaryotes and eukaryotes. In this study, EtPDIL, a novel PDI-like gene of Eimeria tenella, was cloned using rapid amplification of cDNA ends (RACE) according to the expressed sequence tag (EST). The EtPDIL cDNA contained 1129 nucleotides encoding 216 amino acids. The deduced EtPDIL protein belonged to thioredoxin-like superfamily and had a single predicted thioredoxin domain with a non-classical thioredoxin-like motif (SXXC). BLAST analysis showed that the EtPDIL protein was 55–59% identical to PDI-like proteins of other apicomplexan parasites. The transcript and protein levels of EtPDIL at different development stages were investigated by real-time quantitative PCR and western blot. The messenger RNA and protein levels of EtPDIL were higher in sporulated oocysts than in unsporulated oocysts, sporozoites or merozoites. Protein expression was barely detectable in unsporulated oocysts. Western blots showed that rabbit antiserum against recombinant EtPDIL recognized only a native 24 kDa protein from parasites. Immunolocalization with EtPDIL antibody showed that EtPDIL had a disperse distribution in the cytoplasm of whole sporozoites and merozoites. After sporozoites were incubated in complete medium, EtPDIL protein concentrated at the anterior of the sporozoites and appeared on the surface of parasites. Specific staining was more intense and mainly located on the parasite surface after merozoites released from mature schizonts invaded DF-1 cells. After development of parasites in DF-1 cells, staining intensified in trophozoites, immature schizonts and mature schizonts. Antibody inhibition of EtPDIL function reduced the ability of E. tenella to invade DF-1 cells. These results suggested that EtPDIL might be involved in sporulation in external environments and in host cell adhesion, invasion and development of E. tenella.

Insights into the insect salivary gland proteome: diet-associated changes in caterpillar labial salivary proteins

The primary function of salivary glands is fluid and protein secretion during feeding. Compared to mammalian systems, little is known about salivary protein secretion processes and the effect of diet on the salivary proteome in insect models. Therefore, the effect of diet nutritional quality on caterpillar labial salivary gland proteins was investigated using an unbiased global proteomic approach by nanoLC/ESI/tandem MS. Caterpillars of the beet armyworm, Spodoptera exigua Hübner, were fed one of three diets: an artificial diet containing their self-selected protein to carbohydrate (p:c) ratio (22p:20c), an artificial diet containing a higher nutritional content but the same p:c ratio (33p:30c) or the plant Medicago truncatula Gaertn. As expected, most identified proteins were associated with secretory processes and not influenced by diet. However, some diet-specific differences were observed. Nutrient stress-associated proteins, such as peptidyl-propyl cis-trans isomerase and glucose-regulated protein94/endoplasmin, and glyceraldehyde 3-phosphate dehydrogenase were identified in the labial salivary glands of caterpillars fed nutritionally poor diets, suggesting a link between nutritional status and vesicular exocytosis. Heat shock proteins and proteins involved in endoplasmic reticulum-associated protein degradation were also abundant in the labial salivary glands of these caterpillars. In comparison, proteins associated with development, such as arylphorin, were found in labial salivary glands of caterpillars fed 33p:30c. These results suggest that caterpillars fed balanced or nutritionally-poor diets have accelerated secretion pathways compared to those fed a protein-rich diet.

Molecular cloning and expression pattern analysis of two novel disulfide isomerases in shrimp

Protein disulfide isomerase (PDI) catalyzes formation and isomerization of disulfide bridges and has chaperone activity. Currently, increasing evidence suggests the significance of PDI in immune and stress responses. To clarify the role of PDIs in the innate immunity of shrimp, two PDI genes were isolated and identified from Fenneropenaeus chinensis (fleshy prawn). FcPDI1 is 1878bp in length and encodes a protein of 383 amino acids. It has 18-amino acid signal peptide, 3 thioredoxin domains with 3 active sites of CGHC, and KEDL retention signal at its C-end. FcPDI1 is an atypical PDI. The open reading frame of FcPDI2 encodes a 497-amino acid protein and shows the classical domain organization a-b-b'-a'. Phylogenic analysis and multiple alignments show that FcPDI1 is similar to PDI that contains 3 thioredoxin domains from other species including invertebrates and vertebrates. FcPDI2, LvPDI, and insect PDIs are grouped into one cluster and are similar to PDIs having a-b-b'-a' domain organization. Tissue distribution shows that FcPDI1 and FcPDI2 were expressed in all detected tissues at the mRNA level. Changes in FcPDI1 and FcPDI2 expression at the mRNA level in hemocytes, hepatopancreas, gills, and ovaries upon Vibrio or white spot syndrome virus challenge were also analyzed. The results suggest that FcPDI1 and FcPDI2 might have roles in the innate immunity of shrimp. FcPDI1 was also successfully expressed in Escherichia coli and the recombinant FcPDI1 showed insulin reductase activity. Results show that FcPDI might play an important role in the innate immunity of shrimp.

Transcriptome analysis of the synganglion from the brown dog tick, Rhipicephalus sanguineus

Tick control strategies rely heavily on chemicals (acaricides), most of which target the central nervous system. With increasing resistance, new acaricides are urgently needed but knowledge of tick neurobiology is surprisingly limited, notably the number of neural-specific gene sequences. One thousand and eight expressed sequence tags (ESTs) were obtained from a normalized cDNA library from Rhipicephalus sanguineus synganglia. Putative functional identities were assigned to 44% whereas 34% were unknown/novel sequences. Of particular interest were ESTs encoding a chitinase-like enzyme, an acetylcholinesterase and four transmembrane receptors including two glutamate-gated chloride channel receptors, a leucokinin-like receptor and a nicotinic acetylcholine receptor alpha-subunit. This study highlights the benefits of using both neural tissues and normalized libraries in an EST-approach for identifying potential acaricide targets expressed as rare transcripts.

A second protein disulfide isomerase plays a protective role against nitrosative and nutritional stresses in Schizosaccharomyces pombe

In the present work, a second gene encoding protein disulfide isomerase (PDI2) was cloned and characterized from Schizosaccharomyces pombe, and its regulation was studied. The structural gene encoding PDI2 was amplified from the genomic DNA using PCR, and ligated into the E. coli-yeast shuttle vector pRS316 to generate the recombinant plasmid pYPDI2. The determined DNA sequence carries 2,578 bp and is able to encode a protein of 726 amino acid sequence with CGAC at the putative active site. The fission yeast cells harboring pYPDI2 contained 1.62- and 2.73-fold higher PDI activity than the control yeast cells in exponential and stationary phases, respectively, indicating that the cloned gene is in vivo functioning. The PDI2 mRNA levels in both vector control and pYPDI2-containing yeast cells were found to be significantly higher in the stationary phase than in the exponential phase, suggesting that expression of the PDI2 gene is under stationary control. The yeast cells harboring pYPDI2 showed enhanced survival on minimal media plates containing nitric oxide (NO)-generating sodium nitroprusside (SNP) and no nitrogen. The synthesis of β-galactosidase from the PDI2-lacZ fusion gene was markedly enhanced in the Pap1-positive KP1 cells by SNP and nitrogen starvation. However, the enhancement in the synthesis of β-galactosidase from the PDI2-lacZ fusion gene by SNP and nitrogen starvation appeared to be relatively reduced in the Pap1-negative TP108-3C cells than in the Pap1-positive KP1 cells. The PDI2 mRNA level was elevated by SNP and nitrogen starvation in the Pap1-positive cells but not in the Pap1-negative cells. In brief, the S. pombe PDI2 plays a protective role against nitrosative and nutritional stresses, and is positively regulated by NO and nitrogen starvation in a Pap1-dependent manner.

Blocking the secretion of saliva by silencing the HlYkt6 gene in the tick Haemaphysalis longicornis

Soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs) have been identified as the key components of the protein complexes that facilitate vesicle traffic, of which Ykt6 (from Saccharomyces cerevisiae, v-SNARE) is proved to be a multifunctional protein in the membrane fusion. In the present study, a tick homologue of Ykt6 (HlYkt6, predicted 22.6 kDa), was isolated from the ixodid tick Haemaphysalis longicornis. RT-PCR and Western blot analysis indicated that the gene and the encoded protein were expressed ubiquitously in different tissues of the partially fed adult tick. Silencing of the HlYkt6 gene resulted in a significant decrease of the engorged body weight (82.9 +/- 26.8 mg vs. 232.17 +/- 59.1 mg in the PBS-injected control group and 178.7 +/- 57.0 mg in the GFP dsRNA-injected control group) and high mortality of replete ticks (100% in tested group vs. 4.8% in the PBS and 20.4% in GFP dsRNA-injected control groups). Disruption of HlYkt6 mRNA led to the suppression of saliva secretion, and a lower anticoagulant activity of the released liquid from the glands (APTT time: 25.25 +/- 1.50 s) than that of the control groups (39.25 +/- 0.50 s in the PBS-treated group and 40.0 +/- 1.41 s in the GFP dsRNA-treated group). These results suggest the vital role of the HlYkt6 protein in the exocytosis of saliva proteins, the feeding and survival of ticks.