Effects of rrm1 on NNV Resistance Revealed by RNA-seq and Gene Editing.

Viral nervous necrosis (VNN) disease caused by the nervous necrosis virus (NNV) is a major disease, leading to a huge economic loss in aquaculture. Previous GWAS and QTL mapping have identified a major QTL for NNV resistance in linkage group 20 in Asian seabass. However, no causative gene for NNV resistance has been identified. In this study, RNA-seq from brains of Asian seabass fingerlings challenged with NNV at four time points (5, 10, 15 and 20 days post-challenge) identified 1228, 245, 189 and 134 DEGs, respectively. Eight DEGs, including rrm1, were located in the major QTL for NNV resistance. An association study in 445 survived and 608 dead fingerlings after NNV challenge revealed that the SNP in rrm1 were significantly associated with NNV resistance. Therefore, rrm1 was selected for functional analysis, as a candidate gene for NNV resistance. The expression of rrm1 was significantly increased in the gill, liver, spleen and muscle, and was suppressed in the brain, gut and skin after NNV challenge. The rrm1 protein was localized in the nuclear membrane. Over-expression of rrm1 significantly decreased viral RNA and titer in NNV-infected Asian seabass cells, whereas knock-down of rrm1 significantly increased viral RNA and titer in NNV-infected Asian seabass cells. The rrm1 knockout heterozygous zebrafish was more susceptible to NNV infection. Our study suggests that rrm1 is one of the causative genes for NNV resistance and the SNP in the gene may be applied for accelerating genetic improvement for NNV resistance.

Heat Stress Reduces the Susceptibility of Caenorhabditis elegans to Orsay Virus Infection.

The nematode Caenorhabditis elegans has been a versatile model for understanding the molecular responses to abiotic stress and pathogens. In particular, the response to heat stress and virus infection has been studied in detail. The Orsay virus (OrV) is a natural virus of C. elegans and infection leads to intracellular infection and proteostatic stress, which activates the intracellular pathogen response (IPR). IPR related gene expression is regulated by the genes pals-22 and pals-25, which also control thermotolerance and immunity against other natural pathogens. So far, we have a limited understanding of the molecular responses upon the combined exposure to heat stress and virus infection. We test the hypothesis that the response of C. elegans to OrV infection and heat stress are co-regulated and may affect each other. We conducted a combined heat-stress-virus infection assay and found that after applying heat stress, the susceptibility of C. elegans to OrV was decreased. This difference was found across different wild types of C. elegans. Transcriptome analysis revealed a list of potential candidate genes associated with heat stress and OrV infection. Subsequent mutant screens suggest that pals-22 provides a link between viral response and heat stress, leading to enhanced OrV tolerance of C. elegans after heat stress.

NK-lysin peptides ameliorate viral encephalopathy and retinopathy disease signs and provide partial protection against nodavirus infection in European sea bass.

Antimicrobial peptides (AMP) comprise a wide range of small molecules with direct antibacterial activity and immunostimulatory role and are proposed as promising substitutes of the antibiotics. Additionally, they also exert a role against other pathogens such as viruses and fungi less evaluated. NK-lysin, a human granulysin orthologue, possess a double function, taking part in the innate immunity as AMP and also as direct effector in the cell-mediated cytotoxic (CMC) response. This molecule is suggested as a pivotal molecule involved in the defence upon nervous necrosis virus (NNV), an epizootic virus provoking serious problems in welfare and health status in Asian and Mediterranean fish destined to human consumption. Having proved that NK-lysin derived peptides (NKLPs) have a direct antiviral activity against NNV in vitro, we aimed to evaluate their potential use as a prophylactic treatment for European sea bass (Dicentrarchus labrax), one of the most susceptible cultured-fish species. Thus, intramuscular injection of synthetic NKLPs resulted in a very low transcriptional response of some innate and adaptive immune markers. However, the injection of NKLPs ameliorated disease signs and increased fish survival upon challenge with pathogenic NNV. Although NKLPs showed promising results in treatments against NNV, more efforts are needed to understand their mechanisms of action and their applicability to the aquaculture industry.

First Report on Natural Infection of Nodavirus in an Echinodermata, Sea Cucumber (Apostichopus japonicas).

Cross-species transmission of emerging viruses happens occasionally due to epidemiological, biological, and ecological factors, and it has caused more concern recently. Covert mortality nodavirus (CMNV) was revealed to be a unique shrimp virus that could cross species barrier to infect vertebrate fish. In the present study, CMNV reverse transcription-nested PCR (RT-nPCR)-positive samples were identified from farmed sea cucumber (Apostichopus japonicas) in the CMNV host range investigation. The amplicons of RT-nPCR from sea cucumber were sequenced, and its sequences showed 100% identity with the RNA-dependent RNA polymerase gene of the original CMNV isolate. Histopathological analysis revealed pathologic changes, including karyopyknosis and vacuolation of the epithelial cells, in the sea cucumber intestinal tissue. The extensive positive hybridization signals with CMNV probe were shown in the damaged epithelial cells in the in situ hybridization assay. Meanwhile, transmission electron microscopy analysis revealed CMNV-like virus particles in the intestine epithelium. All the results indicated that the sea cucumber, an Echinodermata, is a new host of CMNV. This study supplied further evidence of the wide host range of CMNV and also reminded us to pay close attention to its potential risk to threaten different aquaculture animal species.

Punctuated Loci on Chromosome IV Determine Natural Variation in Orsay Virus Susceptibility of Caenorhabditis elegans Strains Bristol N2 and Hawaiian CB4856.

Host-pathogen interactions play a major role in evolutionary selection and shape natural genetic variation. The genetically distinct Caenorhabditis elegans strains, Bristol N2 and Hawaiian CB4856, are differentially susceptible to the Orsay virus (OrV). Here, we report the dissection of the genetic architecture of susceptibility to OrV infection. We compare OrV infection in the relatively resistant wild-type CB4856 strain to the more susceptible canonical N2 strain. To gain insight into the genetic architecture of viral susceptibility, 52 fully sequenced recombinant inbred lines (CB4856 × N2 RILs) were exposed to OrV. This led to the identification of two loci on chromosome IV associated with OrV resistance. To verify the two loci and gain additional insight into the genetic architecture controlling virus infection, introgression lines (ILs) that together cover chromosome IV, were exposed to OrV. Of the 27 ILs used, 17 had an CB4856 introgression in an N2 background, and 10 had an N2 introgression in a CB4856 background. Infection of the ILs confirmed and fine-mapped the locus underlying variation in OrV susceptibility, and we found that a single nucleotide polymorphism in cul-6 may contribute to the difference in OrV susceptibility between N2 and CB4856. An allele swap experiment showed the strain CB4856 became as susceptible as the N2 strain by having an N2 cul-6 allele, although having the CB4856 cul-6 allele did not increase resistance in N2. In addition, we found that multiple strains with nonoverlapping introgressions showed a distinct infection phenotype from the parental strain, indicating that there are punctuated locations on chromosome IV determining OrV susceptibility. Thus, our findings reveal the genetic complexity of OrV susceptibility in C. elegans and suggest that viral susceptibility is governed by multiple genes.IMPORTANCE Genetic variation determines the viral susceptibility of hosts. Yet, pinpointing which genetic variants determine viral susceptibility remains challenging. Here, we have exploited the genetic tractability of the model organism Caenorhabditis elegans to dissect the genetic architecture of Orsay virus infection. Our results provide novel insight into natural determinants of Orsay virus infection.

Sites responsible for infectivity and antigenicity on nervous necrosis virus (NNV) appear to be distinct.

Nervous necrosis virus (NNV) is a pathogenic fish-virus belonging to the genus Betanodavirus (Nodaviridae). Surface protrusions on NNV particles play a crucial role in both antigenicity and infectivity. We exposed purified NNV particles to different physicochemical conditions to investigate the effects on antigenicity and infectivity, in order to reveal information regarding the conformational stability and spatial relationships of NNV neutralizing-antibody binding sites and cell receptor binding sites. Treatment with PBS at 37 °C, drastically reduced NNV antigenicity by 66-79% on day one, whereas its infectivity declined gradually from 107.6 to 105.8 TCID50/ml over 10 days. When NNV was treated with carbonate/bicarbonate buffers at different pHs, both antigenicity and infectivity of NNV declined due to higher pH. However, the rate of decline with respect to antigenicity was more moderate than for infectivity. NNV antigenicity declined 75-84% after treatment with 2.0 M urea, however, there was no reduction observed in infectivity. The antibodies used in antigenicity experiments have high NNV-neutralizing titers and recognize conformational epitopes on surface protrusions. The maintenance of NNV infectivity means that receptor binding sites are functionally preserved. Therefore, it seems highly likely that NNV neutralizing-antibody binding sites and receptor binding sites are independently located on surface protrusions.

Immunogene expression analysis in betanodavirus infected-Senegalese sole using an OpenArray® platform.

The transcriptomic response of Senegalese sole (Solea senegalensis) triggered by two betanodaviruses with different virulence to that fish species has been assessed using an OpenArray® platform based on TaqMan™ quantitative PCR. The transcription of 112 genes per sample has been evaluated at two sampling times in two organs (head kidney and eye/brain-pooled samples). Those genes were involved in several roles or pathways, such as viral recognition, regulation of type I (IFN-1)-dependent immune responses, JAK-STAT cascade, interferon stimulated genes, protein ubiquitination, virus responsive genes, complement system, inflammatory response, other immune system effectors, regulation of T-cell proliferation, and proteolysis and apoptosis. The highly virulent isolate, wSs160.3, a wild type reassortant containing a RGNNV-type RNA1 and a SJNNV-type RNA2 segments, induced the expression of a higher number of genes in both tested organs than the moderately virulent strain, a recombinant harbouring mutations in the protruding domain of the capsid protein. The number of differentially expressed genes was higher 2 days after the infection with the wild type isolate than at 3 days post-inoculation. The wild type isolate also elicited an exacerbated interferon 1 response, which, instead of protecting sole against the infection, increases the disease severity by the induction of apoptosis and inflammation-derived immunopathology, although inflammation seems to be modulated by the complement system. Furthermore, results derived from this study suggest a potential important role for some genes with high expression after infection with the highly virulent virus, such as rtp3, sacs and isg15. On the other hand, the infection with the mutant does not induce immune response, probably due to an altered recognition by the host, which is supported by a different viral recognition pathway, involving myd88 and tbkbp1.

Balancing Selection of the Intracellular Pathogen Response in Natural Caenorhabditis elegans Populations.

Genetic variation in host populations may lead to differential viral susceptibilities. Here, we investigate the role of natural genetic variation in the Intracellular Pathogen Response (IPR), an important antiviral pathway in the model organism Caenorhabditis elegans against Orsay virus (OrV). The IPR involves transcriptional activity of 80 genes including the pals-genes. We examine the genetic variation in the pals-family for traces of selection and explore the molecular and phenotypic effects of having distinct pals-gene alleles. Genetic analysis of 330 global C. elegans strains reveals that genetic diversity within the IPR-related pals-genes can be categorized in a few haplotypes worldwide. Importantly, two key IPR regulators, pals-22 and pals-25, are in a genomic region carrying signatures of balancing selection, suggesting that different evolutionary strategies exist in IPR regulation. We infected eleven C. elegans strains that represent three distinct pals-22 pals-25 haplotypes with Orsay virus to determine their susceptibility. For two of these strains, N2 and CB4856, the transcriptional response to infection was also measured. The results indicate that pals-22 pals-25 haplotype shapes the defense against OrV and host genetic variation can result in constitutive activation of IPR genes. Our work presents evidence for balancing genetic selection of immunity genes in C. elegans and provides a novel perspective on the functional diversity that can develop within a main antiviral response in natural host populations.

Investigation of routes of entry and dispersal pattern of RGNNV in tissues of European sea bass, Dicentrarchus labrax.

Viral encephalopathy and retinopathy (VER) is a serious neuropathological fish disease affecting in the Mediterranean aquaculture mainly European sea bass, Dicentrarchus labrax. It is well known that betanodaviruses are neurotropic viruses that replicate in nerve tissues, preferentially brain and retina. However, routes of entry and progression of the virus in the central nervous system (CNS) remain unclear. The role of four tissues-eye, oesophagus, gills and skin-as possible gateways of a betanodavirus, the redspotted grouper nervous necrosis virus (RGNNV), was investigated after experimental challenges performed on European seabass juveniles. The dispersal pattern of Betanodavirus at primarily stages of the disease was also assessed, using a real-time qPCR assay. The development of typical clinical signs of VER, the presence of characteristic histopathological lesions in the brain and retina and the detection of viral RNA in the tissues of all experimental groups ascertained that successful invasion of RGNNV under all experimental routes was achieved. Transneuronal spread along pathways known to be connected to the initial site of entry seems to be the predominant scenario of viral progression in the CNS. Furthermore, viraemia appeared only after the installation of the infection in the brain.

Fish RIP1 Mediates Innate Antiviral Immune Responses Induced by SGIV and RGNNV Infection.

Receptor interacting protein 1 (RIP1) is an essential sensor of cellular stress, which may respond to apoptosis or cell survival and participate in antiviral pathways. To investigate the roles of fish RIP1 in Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV) infection, a RIP1 homolog from orange-spotted grouper (Epinephelus coioides) (EcRIP1) was cloned and characterized. EcRIP1 encoded a 679 amino acid protein that shares 83.28% identity with that of Perca flavescens and contained a homologous N-terminal kinase (S-TKc) domain, a RIP isotype interaction motif (RHIM), and a C-terminal domain (DD). EcRIP1 was predominantly detected in immune tissues, and its expression was induced by RGNNV or SGIV infection in vitro. Subcellular localization showed that EcRIP1 was distributed in the cytoplasm with point-like uniform and dot-like aggregation forms. Overexpression of EcRIP1 inhibited SGIV and RGNNV replication and positively regulated the expression levels of interferon (IFN) and IFN-stimulated genes and pro-inflammatory factors. EcRIP1 may interact with grouper tumor necrosis factor receptor type 1-associated DEATH domain protein (EcTRADD) to promote SGIV-induced apoptosis, and interact with grouper Toll/interleukin-1 receptor (TIR) domain containing adapter inducing interferon-ß (EcTRIF) and participate in Myeloid Differentiation Factor 88 (MyD88)-independent toll-like receptor (TLR) signaling. EcRIP1 may also interact with grouper tumor necrosis factor receptor-associated factors (TRAFs) as intracellular linker proteins and mediate the signaling of various downstream signaling pathways, including NF-κB and IFN. These results suggest that EcRIP1 may inhibit SGIV and RGNNV infection by regulating apoptosis and various signaling molecules. Our study offers new insights into the regulatory mechanism of RIP1-related signaling, and provides a novel perspective on fish diseases mediated by RIP1.

Huntingtin-interacting protein family members have a conserved pro-viral function from Caenorhabditis elegans to humans.

Huntingtin-interacting protein family members are evolutionarily conserved from yeast to humans, and they are known to be key factors in clathrin-mediated endocytosis. Here we identified the Caenorhabditis elegans protein huntingtin-interacting protein-related 1 (HIPR-1) as a host factor essential for Orsay virus infection of C. elegans Ablation of HIPR-1 resulted in a greater than 10,000-fold reduction in viral RNA, which could be rescued by ectopic expression of HIPR-1. Viral RNA replication from an endogenous transgene replicon system was not affected by lack of HIPR-1, suggesting that HIPR-1 plays a role during an early, prereplication virus life-cycle stage. Ectopic expression of HIPR-1 mutants demonstrated that neither the clathrin light chain-binding domain nor the clathrin heavy chain-binding motif were needed for virus infection, whereas the inositol phospholipid-binding and F-actin-binding domains were essential. In human cell culture, deletion of the human HIP orthologs HIP1 and HIP1R led to decreased infection by Coxsackie B3 virus. Finally, ectopic expression of a chimeric HIPR-1 harboring the human HIP1 ANTH (AP180 N-terminal homology) domain rescued Orsay infection in C. elegans, demonstrating conservation of its function through evolution. Collectively, these findings further our knowledge of cellular factors impacting viral infection in C. elegans and humans.

Differential immunogene expression profile of European sea bass (Dicentrarchus labrax, L.) in response to highly and low virulent NNV.

European sea bass is highly susceptible to the nervous necrosis virus, RGNNV genotype, whereas natural outbreaks caused by the SJNNV genotype have not been recorded. The onset and severity of an infectious disease depend on pathogen virulence factors and the host immune response. The importance of RGNNV capsid protein amino acids 247 and 270 as virulence factors has been previously demonstrated in European sea bass; however, sea bass immune response against nodaviruses with different levels of virulence has been poorly characterized. Knowing the differences between the immune response against both kinds of isolates may be key to get more insight into the host mechanisms responsible for NNV virulence. For this reason, this study analyses the transcription of immunogenes differentially expressed in European sea bass inoculated with nodaviruses with different virulence: a RGNNV virus obtained by reverse genetics (rDl956), highly virulent to sea bass, and a mutated virus (Mut247+270Dl956, RGNNV virus displaying SJNNV-type amino acids at positions 247 and 270 of the capsid protein), presenting lower virulence. This study has been performed in brain and head kidney, and the main differences between the immunogene responses triggered by both viruses have been observed in brain. The immunogene response in this organ is stronger after inoculation with the most virulent virus, and the main differences involved genes related with IFN I system, inflammatory response, cell-mediated response, and apoptosis. The lower virulence of Mut247+270Dl956 to European sea bass can be associated with a delayed IFN I response, as well as an early and transitory inflammation and cell-mediated responses, suggesting that those can be pivotal elements in controlling the viral infection, and therefore, their functional activity could be analysed in future studies. In addition, this study supports the role of capsid amino acids at positions 247 and 270 as important determinants of RGNNV virulence to European sea bass.

Modelling the effect of vaccination on transmission dynamics of nervous necrosis virus in grouper larvae Epinephelus coioides.

Nervous necrosis virus (NNV) infection in susceptible grouper larvae has been reported to cause high mortalities, leading to great economic losses in aquaculture industry. Although the effects of NNV vaccines on grouper have been broadly investigated, vaccination strategies have not been fully established. To this end, we introduced the parsimonious epidemiological models that explored the assessment of key epidemiological parameters and how they changed when vaccinations showed the effects. We showed that the models capture the published cumulative mortality data accurately. We estimated a basic reproduction number R0  = 2.44 for NNV transmission in grouper larvae without vaccination. To effectively control NNV transmission by vaccination, a model for disease control was also generalized to attain the goals of controlled reproduction number less than 1. Our results indicated that at least 60% of grouper population needed to be immunized for ~75 min. Our data-driven modelling approach that links the transmission dynamics of NNV and vaccination strategies for grouper has the potential to support evidence-based planning and adaptation of integrated control measures. We encourage that the epidemiology-based framework introduced here can be further implemented for establishing effective vaccination and mitigation actions aimed at controlling diseases in fish farming practices.

Characterization of CD4-Positive Lymphocytes in the Antiviral Response of Olive Flounder (Paralichthys oliveceus) to Nervous Necrosis Virus.

The presence of CD4 T lymphocytes has been described for several teleost species, while many of the main T cell subsets have not been characterized at a cellular level, because of a lack of suitable tools for their identification, e.g., monoclonal antibodies (mAbs) against cell markers. We previously described the tissue distribution and immune response related to CD3ε and CD4-1 T cells in olive flounder (Paralichthys oliveceus) in response to a viral infection. In the present study, we successfully produce an mAb against CD4-2 T lymphocytes from olive flounder and confirmed its specificity using immuno-blotting, immunofluorescence staining, flow cytometry analysis and reverse transcription polymerase chain reaction (RT-PCR). Using these mAbs, we were able to demonstrate that the CD3ε T cell populations contain both types of CD4+ cells, with the majority of the CD4 T cell subpopulations being CD4-1+/CD4-2+ cells, determined using two-color flow cytometry analysis. We also examined the functional activity of the CD4-1 and CD4-2 cells in vivo in response to a viral infection, with the numbers of both types of CD4 T cells increasing significantly during the virus infection. Collectively, these findings suggest that the CD4 T lymphocytes in olive flounder are equivalent to the helper T cells in mammals in terms of their properties and function, and it is the CD4-2 T lymphocytes rather than the CD4-1 T cells that play an important role in the Th1 immune response against viral infections in olive flounder.

Capsid amino acids at positions 247 and 270 are involved in the virulence of betanodaviruses to European sea bass.

European sea bass (Dicentrarchus labrax) is severely affected by nervous necrosis disease, caused by nervous necrosis virus (NNV). Two out of the four genotypes of this virus (red-spotted grouper nervous necrosis virus, RGNNV; and striped jack nervous necrosis virus, SJNNV) have been detected in sea bass, although showing different levels of virulence to this fish species. Thus, sea bass is highly susceptible to RGNNV, whereas outbreaks caused by SJNNV have not been reported in this fish species. The role of the capsid protein (Cp) amino acids 247 and 270 in the virulence of a RGNNV isolate to sea bass has been evaluated by the generation of recombinant RGNNV viruses harbouring SJNNV-type amino acids in the above mentioned positions (Mut247Dl965, Mut270Dl965 and Mut247 + 270Dl965). Viral in vitro and in vivo replication, virus virulence and fish immune response triggered by these viruses have been analysed. Mutated viruses replicated on E-11 cells, although showing some differences compared to the wild type virus, suggesting that the mutations can affect the viral cell recognition and entry. In vivo, fish mortality caused by mutated viruses was 75% lower, and viral replication in sea bass brain was altered compared to non-mutated virus. Regarding sea bass immune response, mutated viruses triggered a lower induction of IFN I system and inflammatory response-related genes. Furthermore, mutations caused changes in viral serological properties (especially the mutation in amino acid 270), inducing higher seroconversion and changing antigen recognition.

Noda-Like RNA Viruses Infecting Caenorhabditis Nematodes: Sympatry, Diversity, and Reassortment.

Three RNA viruses related to nodaviruses were previously described to naturally infect the nematode Caenorhabditis elegans and its relative, Caenorhabditis briggsae Here, we report on a collection of more than 50 viral variants from wild-caught Caenorhabditis. We describe the discovery of a new related virus, the Melník virus, infecting C. briggsae, which similarly infects intestinal cells. In France, a frequent pattern of coinfection of C. briggsae by the Santeuil virus and Le Blanc virus was observed at the level of an individual nematode and even a single cell. We do not find evidence of reassortment between the RNA1 and RNA2 molecules of Santeuil and Le Blanc viruses. However, by studying patterns of evolution of each virus, reassortments of RNA1 and RNA2 among variants of each virus were identified. We develop assays to test the relative infectivity and competitive ability of the viral variants and detect an interaction between host genotype and Santeuil virus genotype, such that the result depends on the host strain.IMPORTANCE The roundworm Caenorhabditis elegans is a laboratory model organism in biology. We study natural populations of this small animal and its relative, C. briggsae, and the viruses that infect them. We previously discovered three RNA viruses related to nodaviruses and here describe a fourth one, called the Melník virus. These viruses have a genome composed of two RNA molecules. We find that two viruses may infect the same animal and the same cell. The two RNA molecules may be exchanged between variants of a given viral species. We study the diversity of each viral species and devise an assay of their infectivity and competitive ability. Using this assay, we show that the outcome of the competition also depends on the host.

Altered conformational structures of nervous necrosis virus surface protrusions and free coat proteins after incubation at moderate-low temperatures.

Nervous necrosis virus (NNV) is a pathogenic fish virus belonging to family Nodaviridae. The objective of this study was to analyze stabilities of NNV surface protrusion and free coat protein (CP) conformational structures by analyzing changes of NNV infectivity and antigenicity after incubation at moderate-low temperatures. When cultured NNV suspension was incubated at 45 °C, its infectivity declined gradually but its antigenicity maintained. In contrast, both infectivity and antigenicity of purified NNV declined after incubation at 45 °C. After heat-treatment, surface protrusions of NNV particles disappeared completely, although viral particle structures maintained. Therefore, the reduction in NNV infectivity appeared to specifically occur as a result of heat-denaturation of virus surface protrusions. The loss of NNV infectivity in the presence of fetal bovine serum (FBS) was delayed compared to virus heated in the absence of FBS, demonstrating that FBS could function as a stabilizer for conformational structures of NNV surface protrusions. Moreover, the stabilizing function of FBS changed depending on salt concentration. Continued maintenance of antigenicity for heated cultured NNV suspension containing free-CPs may suggest that conformational structures corresponding to protrusion-domain of free-CP are more heat-stable than those of surface protrusions on NNV particles.

Meta-analysis suggests evidence of novel stress-related pathway components in Orsay virus - Caenorhabditis elegans viral model.

The genetic model organism, Caenorhabditis elegans (C. elegans), shares many genes with humans and is the best-annotated of the eukaryotic genome. Therefore, the identification of new genes and pathways is unlikely. Nevertheless, host-pathogen interaction studies from viruses, recently discovered in the environment, has created new opportunity to discover these pathways. For example, the exogenous RNAi response in C. elegans by the Orsay virus as seen in plants and other eukaryotes is not systemic and transgenerational, suggesting different RNAi pathways between these organisms. Using a bioinformatics meta-analysis approach, we show that the top 17 genes differentially-expressed during C. elegans infection by Orsay virus are functionally uncharacterized genes. Furthermore, functional annotation using similarity search and comparative modeling, was able to predict folds correctly, but could not assign easily function to the majority. However, we could identify gene expression studies that showed a similar pattern of gene expression related to toxicity, stress and immune response. Those results were strengthened using protein-protein interaction network analysis. This study shows that novel molecular pathway components, of viral innate immune response, can be identified and provides models that can be further used as a framework for experimental studies. Whether these features are reminiscent of an ancient mechanism evolutionarily conserved, or part of a novel pathway, remain to be established. These results reaffirm the tremendous value of this approach to broaden our understanding of viral immunity in C. elegans.

Complete genome sequence and pathogenic analysis of a new betanodavirus isolated from shellfish.

We determined the complete genomic RNA sequence of a new type of betanodavirus Korea shellfish nervous necrosis virus (KSNNV) isolated from shellfish. Compared with other isolates representing four genotypes of betanodaviruses, the identity of the whole nucleotide sequence of the virus was in the range of 76%-83% with the presence of specific genetic motifs and formed a separate new branch in the phylogenetic analysis. In pathogenic analysis by immersion method, KSNNV-KOR1 shows 100% cumulative mortality like SFRG10/2012BGGa1 (RGNNV) in newly hatched sevenband grouper and mandarin fish, which is clearly different from those found in negative control groups. There were no significant differences in increasing rates of mortality and viral intra-tissue concentration of larval fishes infected with KSNNV-KOR1 at both 20 and 25°C water temperature. Histopathological examination of each fish species in the moribund stage revealed the presence of clear vacuoles in both brain and retinal tissues similar to typical histopathology features of RGNNV. In the present study, we first report a new betanodavirus from shellfish as the aetiological agent of viral nervous necrosis disease in fish with complete genomic nucleotide sequence and pathogenic analysis.

The Dietary Restriction-Like Gene drl-1, Which Encodes a Putative Serine/Threonine Kinase, Is Essential for Orsay Virus Infection in Caenorhabditis elegans.

Orsay virus is the only known natural virus pathogen of Caenorhabditis elegans, and its discovery has enabled virus-host interaction studies in this model organism. Host genes required for viral infection remain understudied. We previously established a forward genetic screen based on a virus-inducible green fluorescent protein transcriptional reporter to identify novel host factors essential for virus infection. Here, we report the essential role in Orsay virus infection of the dietary restriction-like (drl-1) gene, which encodes a serine/threonine kinase similar to the mammalian MEKK3 kinase. Ablation of drl-1 led to a >10,000-fold reduction in Orsay virus RNA levels, which could be rescued by ectopic expression of DRL-1. DRL-1 was dispensable for Orsay replication from an endogenous transgene replicon, suggesting that DRL-1 affects a prereplication stage of the Orsay life cycle. Thus, this study demonstrates the power of C. elegans as a model to identify novel virus-host interactions essential for virus infection.IMPORTANCE The recent discovery of Orsay virus, the only known natural virus of Caenorhabditis elegans, provides a unique opportunity to study virus-host interactions that mediate infection in a genetically tractable multicellular model organism. As viruses remain a global threat to human health, better insights into cellular components that enable virus infection and replication can ultimately lead to the development of new targets for antiviral therapeutics.