Efficient generation of recombinant eggplant mottled dwarf virus and expression of foreign proteins in solanaceous hosts.

Reverse genetics systems have only been successfully developed for a few plant rhabdoviruses. Additional systems are needed for molecular virology studies of these diverse viruses and development of viral vectors for biotechnological applications. Eggplant mottled dwarf virus (EMDV) is responsible for significant agricultural losses in various crops throughout the Mediterranean region and the Middle East. In this study, we report efficient recovery of infectious EMDV from cloned DNAs and engineering of EMDV-based vectors for the expression of foreign proteins in tobacco, eggplant, pepper, and potato plants. Furthermore, we show that the EMDV-based vectors are capable of simultaneously expressing multiple foreign proteins. The developed EMDV reverse genetics system offers a versatile tool for studying virus pathology and plant-virus interactions and for expressing foreign proteins in a range of solanaceous crops.

Nonarboviral Equine Encephalitides.

Several viruses transmitted by biological vectors or through direct contact, air, or ingestion cause neurologic disease in equids. Of interest are viruses of the Togaviridae, Flaviviridae, Rhabdoviridae, Herpesviridae, Bornaviridae, and Bunyaviridae families. Variable degree of inflammation is present with these viruses but lack of an inflammatory response does not rule out their presence. The goal of this article is to provide an overview on pathophysiologic and clinical aspects of nonarboviral equine encephalitides, specifically on lyssaviruses (rabies) and bornaviruses (Borna disease).

Divergent Rhabdovirus Discovered in a Patient with New-Onset Nodding Syndrome.

A divergent rhabdovirus was discovered in the bloodstream of a 15-year-old girl with Nodding syndrome from Mundri West County in South Sudan. Nodding syndrome is a progressive degenerative neuropathy of unknown cause affecting thousands of individuals in Sub-Saharan Africa. The index case was previously healthy until she developed head-nodding seizures four months prior to presentation. Virus discovery by VIDISCA-NGS on the patient's plasma detected multiple sequence reads belonging to a divergent rhabdovirus. The viral load was 3.85 × 103 copies/mL in the patient's plasma and undetectable in her cerebrospinal fluid. Further genome walking allowed for the characterization of full coding sequences of all the viral proteins (N, P, M, U1, U2, G, U3, and L). We tentatively named the virus "Mundri virus" (MUNV) and classified it as a novel virus species based on the high divergence from other known viruses (all proteins had less than 43% amino acid identity). Phylogenetic analysis revealed that MUNV forms a monophyletic clade with several human-infecting tibroviruses prevalent in Central Africa. A bioinformatic machine-learning algorithm predicted MUNV to be an arbovirus (bagged prediction strength (BPS) of 0.9) transmitted by midges (BPS 0.4) with an artiodactyl host reservoir (BPS 0.9). An association between MUNV infection and Nodding syndrome was evaluated in a case-control study of 72 patients with Nodding syndrome (including the index case) matched to 65 healthy households and 48 community controls. No subject, besides the index case, was positive for MUNV RNA in their plasma. A serological assay detecting MUNV anti-nucleocapsid found, respectively, in 28%, 22%, and 16% of cases, household controls and community controls to be seropositive with no significant differences between cases and either control group. This suggests that MUNV commonly infects children in South Sudan yet may not be causally associated with Nodding syndrome.

Components and Architecture of the Rhabdovirus Ribonucleoprotein Complex.

Rhabdoviruses, as single-stranded, negative-sense RNA viruses within the order Mononegavirales, are characterised by bullet-shaped or bacteroid particles that contain a helical ribonucleoprotein complex (RNP). Here, we review the components of the RNP and its higher-order structural assembly.

Lyssavirus Vaccine with a Chimeric Glycoprotein Protects across Phylogroups.

Rabies is nearly 100% lethal in the absence of treatment, killing an estimated 59,000 people annually. Vaccines and biologics are highly efficacious when administered properly. Sixteen rabies-related viruses (lyssaviruses) are similarly lethal, but some are divergent enough to evade protection from current vaccines and biologics, which are based only on the classical rabies virus (RABV). Here we present the development and characterization of LyssaVax, a vaccine featuring a structurally designed, functional chimeric glycoprotein (G) containing immunologically important domains from both RABV G and the highly divergent Mokola virus (MOKV) G. LyssaVax elicits high titers of antibodies specific to both RABV and MOKV Gs in mice. Immune sera also neutralize a range of wild-type lyssaviruses across the major phylogroups. LyssaVax-immunized mice are protected against challenge with recombinant RABV and MOKV. Altogether, LyssaVax demonstrates the utility of structural modeling in vaccine design and constitutes a broadened lyssavirus vaccine candidate.

A Neuron-Specific Antiviral Mechanism Modulates the Persistent Infection of Rice Rhabdoviruses in Leafhopper Vectors.

Many plant rhabdoviruses are neurotropic and can persistently infect the central nervous system (CNS) of their insect vectors without causing significant cytopathology. The mechanisms by which the insect CNS resists infection by plant rhabdoviruses are largely unknown. Here, we report that the neural factor Hikaru genki homolog of the leafhopper Nephotettix cincticeps (NcHig) limits the spread of the nucleorhabdovirus rice yellow stunt virus (RYSV) in vector CNS. NcHig is predominantly expressed in the CNS of N. cincticeps, and the knockdown of NcHig expression by RNA interference enhances RYSV infection of the CNS. Furthermore, immuno-blockade of NcHig function by microinjection of N. cincticeps with NcHig antibody also enhances viral infection of the CNS. Thus, we conclude that the neuron-specific factor NcHig can control RYSV propagation in the CNS. Interestingly, we find the Hig homolog of the leafhopper Recilia dorsalis also has antiviral activity during the persistent infection of the cytorhabdovirus rice stripe mosaic virus (RSMV) in vector CNS. We further determine that RYSV and RSMV matrix proteins specifically interact with the complement control protein (CCP) domains of Higs. Thus, the matrix protein-binding ability of Hig is potentially essential for its antiviral activity in rice leafhoppers. Our results demonstrate an evolutionarily conserved antiviral mechanism for Hig to mediate the persistent infection of rice rhabdoviruses in the CNS of leafhopper vectors.

Identification and phylogenetic characterization of bovine ephemeral fever virus (BEFV) of Middle Eastern lineage associated with 2018-2019 outbreaks in India.

Bovine ephemeral fever virus (BEFV) is an evolving arbovirus reported across tropical, subtropical and temperate climatic zones globally. This study reveals prominent BEFV outbreaks in India, emerging annually during monsoons in subtropical areas accompanied by a congenial abundance of the vector population. PCR-based detection of viral genomic RNA in the blood samples collected during outbreaks of 2018-2019 for the first time confirmed the presence of BEFV in India. Phylogenetic analysis based on the glycoprotein gene of BEFV showed the current isolates to have high sequence homology with Middle Eastern lineage with nearly 97%, identity to Turkey (BEFV Ad12/TUR) and Israel (Israel 2006) isolates.

Structure of the Vesicular Stomatitis Virus L Protein in Complex with Its Phosphoprotein Cofactor.

The large (L) proteins of non-segmented, negative-strand RNA viruses are multifunctional enzymes that produce capped, methylated, and polyadenylated mRNA and replicate the viral genome. A phosphoprotein (P), required for efficient RNA-dependent RNA polymerization from the viral ribonucleoprotein (RNP) template, regulates the function and conformation of the L protein. We report the structure of vesicular stomatitis virus L in complex with its P cofactor determined by electron cryomicroscopy at 3.0 Å resolution, enabling us to visualize bound segments of P. The contacts of three P segments with multiple L domains show how P induces a closed, compact, initiation-competent conformation. Binding of P to L positions its N-terminal domain adjacent to a putative RNA exit channel for efficient encapsidation of newly synthesized genomes with the nucleoprotein and orients its C-terminal domain to interact with an RNP template. The model shows that a conserved tryptophan in the priming loop can support the initiating 5' nucleotide.

Plant Viruses in Plant Molecular Pharming: Toward the Use of Enveloped Viruses.

Plant molecular pharming has emerged as a reliable platform for recombinant protein expression providing a safe and low-cost alternative to bacterial and mammalian cells-based systems. Simultaneously, plant viruses have evolved from pathogens to molecular tools for recombinant protein expression, chimaeric viral vaccine production, and lately, as nanoagents for drug delivery. This review summarizes the genesis of viral vectors and agroinfection, the development of non-enveloped viruses for various biotechnological applications, and the on-going research on enveloped plant viruses.

Integrated Transcriptomic and Proteomic Analysis of Red Blood Cells from Rainbow Trout Challenged with VHSV Point Towards Novel Immunomodulant Targets.

Teleost red blood cells (RBCs) are nucleated and therefore can propagate cellular responses to exogenous stimuli. RBCs can mount an immune response against a variety of fish viruses, including the viral septicemia hemorrhagic virus (VHSV), which is one of the most prevalent fish viruses resulting in aquaculture losses. In this work, RBCs from blood and head kidney samples of rainbow trout challenged with VHSV were analyzed via transcriptomic and proteomic analyses. We detected an overrepresentation of differentially expressed genes (DEGs) related to the type I interferon response and signaling in RBCs from the head kidney and related to complement activation in RBCs from blood. Antigen processing and presentation of peptide antigen was overrepresented in RBCs from both tissues. DEGs shared by both tissues showed an opposite expression profile. In summary, this work has demonstrated that teleost RBCs can modulate the immune response during an in vivo viral infection, thus implicating RBCs as cell targets for the development of novel immunomodulants.

Dichorhaviruses in their Host Plants and Mite Vectors.

A group of related bacilliform, nuclear viruses with a bisegmented negative-sense RNA genome that are transmitted by Brevipalpus mites likely in a circulative-propagative manner were recently classified in the new genus Dichorhavirus, family Rhabdoviridae. These viruses cause localized lesions on leaves, stems, and fruits of economically significant horticultural and ornamental plant species. Among its members, orchid fleck virus, citrus leprosis virus N, and coffee ringspot virus are most prominent. This chapter summarizes the current knowledge about these viruses, available detection techniques, and their interactions with their plant hosts and mite vectors.

ICTV Virus Taxonomy Profile: Rhabdoviridae.

The family Rhabdoviridae comprises viruses with negative-sense (-) single-stranded RNA genomes of 10.8-16.1 kb. Virions are typically enveloped with bullet-shaped or bacilliform morphology but can also be non-enveloped filaments. Rhabdoviruses infect plants and animals including mammals, birds, reptiles and fish, as well as arthropods which serve as single hosts or act as biological vectors for transmission to animals or plants. Rhabdoviruses include important pathogens of humans, livestock, fish and agricultural crops. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of Rhabdoviridae, which is available at www.ictv.global/report/rhabdoviridae.

Replicon RNA Viral Vectors as Vaccines.

Single-stranded RNA viruses of both positive and negative polarity have been used as vectors for vaccine development. In this context, alphaviruses, flaviviruses, measles virus and rhabdoviruses have been engineered for expression of surface protein genes and antigens. Administration of replicon RNA vectors has resulted in strong immune responses and generation of neutralizing antibodies in various animal models. Immunization of mice, chicken, pigs and primates with virus-like particles, naked RNA or layered DNA/RNA plasmids has provided protection against challenges with lethal doses of infectious agents and administered tumor cells. Both prophylactic and therapeutic efficacy has been achieved in cancer immunotherapy. Moreover, recombinant particles and replicon RNAs have been encapsulated by liposomes to improve delivery and targeting. Replicon RNA vectors have also been subjected to clinical trials. Overall, immunization with self-replicating RNA viruses provides high transient expression levels of antigens resulting in generation of neutralizing antibody responses and protection against lethal challenges under safe conditions.

Developments in Plant Negative-Strand RNA Virus Reverse Genetics.

Twenty years ago, breakthroughs for reverse genetics analyses of negative-strand RNA (NSR) viruses were achieved by devising conditions for generation of infectious viruses in susceptible cells. Recombinant strategies have subsequently been engineered for members of all vertebrate NSR virus families, and research arising from these advances has profoundly increased understanding of infection cycles, pathogenesis, and complexities of host interactions of animal NSR viruses. These strategies also permitted development of many applications, including attenuated vaccines and delivery vehicles for therapeutic and biotechnology proteins. However, for a variety of reasons, it was difficult to devise procedures for reverse genetics analyses of plant NSR viruses. In this review, we discuss advances that have circumvented these problems and resulted in construction of a recombinant system for Sonchus yellow net nucleorhabdovirus. We also discuss possible extensions to other plant NSR viruses as well as the applications that may emanate from recombinant analyses of these pathogens.

Epithelial cell lines of the cotton rat (Sigmodon hispidus) are highly susceptible in vitro models to zoonotic Bunya-, Rhabdo-, and Flaviviruses.

BACKGROUND: Small mammals such as bats and rodents have been increasingly recognized as reservoirs of novel potentially zoonotic pathogens. However, few in vitro model systems to date allow assessment of zoonotic viruses in a relevant host context. The cotton rat (Sigmodon hispidus) is a New World rodent species that has a long-standing history as an experimental animal model due to its unique susceptibility to human viruses. Furthermore, wild cotton rats are associated with a large variety of known or potentially zoonotic pathogens. METHODS: A method for the isolation and culture of airway epithelial cell lines recently developed for bats was applied for the generation of rodent airway and renal epithelial cell lines from the cotton rat. Continuous cell lines were characterized for their epithelial properties as well as for their interferon competence. Susceptibility to members of zoonotic Bunya-, Rhabdo-, and Flaviviridae, in particular Rift Valley fever virus (RVFV), vesicular stomatitis virus (VSV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) was tested. Furthermore, novel arthropod-derived viruses belonging to the families Bunya-, Rhabdo-, and Mesoniviridae were tested. RESULTS: We successfully established airway and kidney epithelial cell lines from the cotton rat, and characterized their epithelial properties. Cells were shown to be interferon-competent. Viral infection assays showed high-titre viral replication of RVFV, VSV, WNV, and TBEV, as well as production of infectious virus particles. No viral replication was observed for novel arthropod-derived members of the Bunya-, Rhabdo-, and Mesoniviridae families in these cell lines. CONCLUSION: In the current study, we showed that newly established cell lines from the cotton rat can serve as host-specific in vitro models for viral infection experiments. These cell lines may also serve as novel tools for virus isolation, as well as for the investigation of virus-host interactions in a relevant host species.

Ensemble Structure of the Highly Flexible Complex Formed between Vesicular Stomatitis Virus Unassembled Nucleoprotein and its Phosphoprotein Chaperone.

Nucleocapsid assembly is an essential process in the replication of the non-segmented, negative-sense RNA viruses (NNVs). Unassembled nucleoprotein (N(0)) is maintained in an RNA-free and monomeric form by its viral chaperone, the phosphoprotein (P), forming the N(0)-P complex. Our earlier work solved the structure of vesicular stomatitis virus complex formed between an N-terminally truncated N (NΔ21) and a peptide of P (P60) encompassing the N(0)-binding site, but how the full-length P interacts with N(0) remained unknown. Here, we combine several experimental biophysical methods including size exclusion chromatography with detection by light scattering and refractometry, small-angle X-ray and neutron scattering and nuclear magnetic resonance spectroscopy with molecular dynamics simulation and computational modeling to characterize the NΔ21(0)-PFL complex formed with dimeric full-length P. We show that for multi-molecular complexes, simultaneous multiple-curve fitting using small-angle neutron scattering data collected at varying contrast levels provides additional information and can help refine structural ensembles. We demonstrate that (a) vesicular stomatitis virus PFL conserves its high flexibility within the NΔ21(0)-PFL complex and interacts with NΔ21(0) only through its N-terminal extremity; (b) each protomer of P can chaperone one N(0) client protein, leading to the formation of complexes with stoichiometries 1N:P2 and 2N:P2; and (c) phosphorylation of residues Ser60, Thr62 and Ser64 provides no additional interactions with N(0) but creates a metal binding site in PNTR. A comparison with the structures of Nipah virus and Ebola virus N(0)-P core complex suggests a mechanism for the control of nucleocapsid assembly that is common to all NNVs.

Resistance to Rhabdoviridae Infection and Subversion of Antiviral Responses.

Interferon (IFN) treatment induces the expression of hundreds of IFN-stimulated genes (ISGs). However, only a selection of their products have been demonstrated to be responsible for the inhibition of rhabdovirus replication in cultured cells; and only a few have been shown to play a role in mediating the antiviral response in vivo using gene knockout mouse models. IFNs inhibit rhabdovirus replication at different stages via the induction of a variety of ISGs. This review will discuss how individual ISG products confer resistance to rhabdoviruses by blocking viral entry, degrading single stranded viral RNA, inhibiting viral translation or preventing release of virions from the cell. Furthermore, this review will highlight how these viruses counteract the host IFN system.

Predicting the host protein interactors of Chandipura virus using a structural similarity-based approach.

Chandipura virus (CHPV), alike other pathogens, exploits the cellular infrastructure of their hosts through complex network of interactions for successful infection. CHPV being a recently emerged pediatric encephalitic virus, the mechanisms involved in the establishment of viral persistence are still ill defined. Because the protein interface between CHPV and its host provides one means by which the virus invades and seize control of their human host machinery, the authors in this study have employed computational methods to create a network of putative protein-protein interactions between CHPV and its human host to shed light on the hitherto less-known CHPV biology. On the basis of the 2105 potential interactions predicted among 1650 human proteins and the five proteins of CHPV, the authors decipher the probable mode by which the virus manipulates the biological pathways of its host toward its own end and replicates while evading the immune system. Identification of such conserved set of putative interactions that allow the virus to take control of the host has the potential to deepen our understanding of the virus-specific remodeling processes of the host cell and illuminate new arenas of disease intervention.