Development and application of sugarcane streak mosaic virus vectors

Sugarcane streak mosaic virus (SCSMV) is one of the major pathogens of sugarcane in the world. Molecular studies and disease management of SCSMV are hindered by the lack of efficient infectious clones. In this study, we successfully constructed Agrobacterium infiltration based infectious clone of SCSMV with different variants. Infectious clones of wild type SCSMV could efficiently infect Nicotiana benthamiana and sugarcane plants resulting in streak and mosaic symptoms on systemic leaves which were further confirmed with RT-PCR and serological assays. SCSMV variants of less adenylation displayed attenuated pathogenicity on N.benthamiana. SCSMV-based recombinant heterologous EGFP protein vector was also developed. The EGFP-tagged recombinant SCSMV could highly expressed in vegetative organs including roots. These infectious clones of SCSMV could be further developed for platform tools for both biotechnological studies and management of SCSMV disease.

Development of full-length infectious cDNA clones and host range identification of an echinacea strain of tobacco streak virus

Tobacco streak virus induces severe diseases on a wide range of plants and becomes an emerging threat to crop yields. However, the infectious clones of TSV remain to be developed for reverse genetics studies. Here, we obtained the full genome sequence of a TSV-CNB isolate and analyzed the phylogenetic characteristics. Subsequently, we developed the full-length infectious cDNA clones of TSV-CNB driven by 35 S promoter using yeast homologous recombination. Furthermore, the host range of TSV-CNB isolate was determined by Agrobacterium infiltration and mechanical inoculation. The results reveal that TSV-CNB can infect 10 plant species in 5 families including Glycine max, Vigna radiate, Lactuca sativa var. Ramosa, Dahlia pinnate, E. purpurea, Calendula officinalis, Helianthus annuus, Nicotiana. Benthamiana, Nicotiana tabacum and Chenopodium quinoa. Taken together, the TSV infectious clones will be a useful tool for future studies on viral pathogenesis and host-virus interactions.

Engineering of stable infectious cDNA constructs of a fluorescently tagged tomato chlorosis virus

Tomato chlorosis virus (ToCV) is an emerging pathogen that cause severe yellow leaf disorder syndrome in tomato plants. In this study, we aimed to generate a recombinant ToCV tagged with green fluorescent protein (GFP) to enable real-time monitoring of viral infection in living plants. Transformation of the full-length cDNA construct of ToCV RNA1 into Escherichia coli resulted in instability issues, which were successfully overcome by inserting a plant intron into RNA1. Subsequently, a GFP tag was engineered into a cDNA construct of ToCV RNA2. The resulting recombinant ToCV-GFP could systemically infect Nicotiana benthamiana plants, and GFP expression was observed along the major veins. Utilizing ToCV-GFP, we also showed that ToCV engages in antagonistic relationships with two different tomato-infecting viruses in mixed infections in N. benthamiana. This study demonstrates the potential of ToCV-GFP as a valuable tool for the visual tracking of infection and movement of criniviruses in living plants.

Construction and characterization of an infectious cDNA clone of human rhinovirus A89

Rhinoviruses (RVs) are major causes of the common cold and are related to severe respiratory tract diseases, leading to a considerable economic burden and impacts on public health. Available and stable viral resources of rhinoviruses for laboratory use are important for promoting studies on rhinoviruses and further vaccine or therapeutic drug development. Reverse genetic technology can be useful to produce rhinoviruses and will help to promote studies on their pathogenesis and virulence. In this study, rhinovirus A89, an RV-A species that has been found to be highly involved in hospitalization triggered by RV infections, was selected to construct an infectious clone based on its sequence as a representative. The viral mRNA produced by a T7 RNA transcript system was transfected into H1-HeLa cells, and the rescued RV-A89 viruses were harvested and confirmed by sequencing. The rescued RV-A89 induced a similar cytopathic effect (CPE) and shared almost identical growth kinetics curves with parental RV-A89. Moreover, 9A7, a prescreened monoclonal antibody against the parental RV-A89, had a good and specific reaction with the rescued RV-A89, and further characterization showed almost the same morphology and protein composition of both viruses; thus, recombinant RV-A89 with similar biological characterization and virulence to the parental virus was obtained. In summary, the infectious clone of RV-A89 was successfully established, and the development of reverse genetic technology for rhinovirus will provide a framework for further studies on rhinoviruses.

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.

Reverse Genetics of Hepatitis C Virus Using an RNA Polymerase I-Mediated Transcription

The reverse genetics system commonly used for the production of hepatitis C virus (HCV), which is a major causative agent of liver diseases, involves introduction of the viral genomic RNA synthesized in vitro into human hepatoma cells by electroporation. As an alternative methodology, we describe a cell culture system based on transfection with an expression plasmid containing a full-length HCV cDNA clone flanked by RNA polymerase I promoter and terminator sequences to generate infectious virus particles from transfected cells.

Construction of an Agrobacterium-mediated infectious cDNA clone of melon aphid-borne yellows virus

Melon aphid-borne yellows virus (MABYV), a member of the genus Polerovirus in the family Solemoviridae, has widely spread in recent years and cause yellowing disease on cucurbits. Here, we obtained the complete genome sequence of MABYV bottle guard (Lagenaria siceraria) isolate MABYV-KF, and constructed its infectious cDNA clone under the control of the cauliflower mosaic virus (CaMV) 35S promoter by Gibson assembly. The 5,677 nt of its genome shared more than 94.00% sequence identity with the two known MABYV isolates. The inoculation results showed that MABYV infectious cDNA clone could systemically infect bottle guard, cucumber and muskmelon plants, and cause typical yellowing symptom. The virus progeny from the infectious clone could be transmitted between bottle guard plants by aphid. Further analyses revealed that point mutations in the F-box-like motif (Pro57) and C-terminal conserved sequence (Phe211) of P0 cause low viral accumulations in systematic leaves and failed to induce symptom. The infectious clone will be potentially a tool in the investigation of viral pathogenesis, virus-virus interaction and virus-host/-vector interactions.

Recovery of a Far-Eastern Strain of Tick-Borne Encephalitis Virus with a Full-Length Infectious cDNA Clone

Tick-borne encephalitis virus (TBEV) is a pathogenic virus known to cause central nervous system (CNS) diseases in humans, and has become an increasing public health threat nowadays. The rates of TBEV infection in the endemic countries are increasing. However, there is no effective antiviral against the disease. This underscores the urgent need for tools to study the emergence and pathogenesis of TBEV and to accelerate the development of vaccines and antivirals. In this study, we reported an infectious cDNA clone of TBEV that was isolated in China (the WH2012 strain). A beta-globin intron was inserted in the coding region of nonstructural protein 1 (NS1) gene to improve the stability of viral genome in bacteria. In mammalian cells, the inserted intron was excised and spliced precisely, which did not lead to the generation of inserted mutants. High titers of infectious progeny viruses were generated after the transfection of the infectious clone. The cDNA-derived TBEV replicated efficiently, and caused typical cytopathic effect (CPE) and plaques in BHK-21 cells. In addition, the CPE and growth curve of cDNA-derived virus were similar to that of its parental isolate in cells. Together, we have constructed the first infectious TBEV cDNA clone in China, and the clone can be used to investigate the genetic determinants of TBEV virulence and disease pathogenesis, and to develop countermeasures against the virus.

Development and application of a full-length infectious clone of potato virus Y isolate belonging to SYR-I strain

Potato virus Y (PVY) causes huge damage to potato and tobacco production worldwide. The complete genome sequence of GZ, a PVY isolate (strain SYR-I) from Guizhou province, China, was cloned into the binary vector pCambia0390. Three introns were individually inserted into the P3 and CI ORFs to produce plasmid pCamPVY-GZ. The plasmid could infect plants of Nicotiana benthamiana, N. tabacum via agroinfiltration and plants of pepper and potato by mechanical inoculation. The green fluorescence protein gene of Aequoria victoriae was cloned into the encoding regions between nuclear inclusion body 'b' and coat protein genes in pCamPVY-GZ to produce pCamPVY-GZ-GFP, which could infect plants of N. benthamiana, N. tabacum, potato and tomato, and produce green fluorescence in the systemic leaves of inoculated plants. Mutations were introduced to pCamPVY-GZ to make the lysine (K) 391 and glutamic acid (E)410 of helper component-proteinase to arginine (R) and asparagic acid (E), respectively. Unlike wild type PVY-GZ, the mutant PVY-K391R/E410D could not induce veinal necrosis in N. tabacum plants. With an interval of 14 days, mutant PVY-K391R/E410D could protect N. tabacum plants from the infection of severe PVY strain. The results presented here provide a promising alternate for the prevention of diseases caused by PVY.

E and prM proteins of genotype V Japanese encephalitis virus are required for its increased virulence in mice

We previously showed that the Japanese encephalitis virus (JEV) genotype V (GV) strain Muar exhibits significantly higher virulence in mice than the genotype I (GI) JEV strain Mie/41/2002. In this study, we attempted to identify the region responsible for the increased virulence of GV JEV using recombinant intertypic and single mutant JEVs. Intertypic viruses containing the GV E region in the Mie/41/2002 backbone showed increased pathogenicity in mice. The amino acid at position 123 in the E protein (E123) of the Mie/41/2002 and GV JEVs was serine and histidine, respectively. A serine-to-histidine substitution at E123 of the Mie/41/2002 increased its virulence. However, histidine-to-serine changes at E123 in the intertypic mutants with the GV E region remained highly virulent. GV Muar prM-bearing mutants were also highly pathogenic in mice. Our results suggest that the E and prM proteins of GV JEV are responsible for the highly virulent characteristics of GV JEV.

Construction and biological characterization of an Agrobacterium-mediated infectious cDNA of squash mosaic virus

Squash mosaic virus (SqMV), a member of the species Squash mosaic virus in the genus Comovirus (family Comoviridae), is an important seed-borne virus that causes serious economic losses in cucurbit crops. Here, we constructed infectious cDNA clones of SqMV genomic RNAs (RNA1 and RNA2) under the control of the cauliflower mosaic virus (CaMV) 35S promoter by Gibson assembly. The infectious cDNA clones of SqMV could infect zucchini squash (Cucurbita pepo) plants systemically by agrobacterium-mediated inoculation. The virus progeny from the infectious clones showed no difference from the wild type in terms of pathogenicity and symptom induction. It could be mechanically transmitted to zucchini squash (Cucurbita pepo), pumpkin (Cucurbita moschata), cucumber (Cucumis sativus), and muskmelon (Cucumis melo) but not watermelon (Citrullus lanatus) or Nicotiana benthamiana. This is the first report of construction of a SqMV infection clone and will facilitate the investigation of viral pathogenesis and host interactions.

Construction and characterization of an infectious cDNA clone of potato virus S developed from selected populations that survived genetic bottlenecks

BACKGROUND

Infectious cDNA clones are a powerful tool for studies on RNA viruses using reverse genetics. Potato virus S (PVS) is a carlavirus with a worldwide distribution. Although the complete genome sequences of many PVS isolates have been reported, the construction of an infectious cDNA clone of PVS is yet to be reported. The aim of this study is the development and molecular characterization of an infectious cDNA clone of PVS.

METHODS

A full-length cDNA clone pPVS-H-FL-AB was constructed by connecting eight cDNA clones of PVS isolate H95. Capped RNA transcripts from pPVS-H-FL-AB and a modified clone pPVS-H-FL-H, containing the consensus genome sequence of PVS-H95, proved to be non-infectious. Therefore, a full-length cDNA clone pPVS-H-FL-β was reconstructed from PVS-H00, isolated from PVS-H95 populations by repeating a single local lesion isolation in Chenopodium quinoa three times; PVS-H00 appeared to be a selected variant that survived genetic bottlenecks. The sequence of cDNA clone pPVS-H-FL-β was determined as the genome sequence of PVS-H00 and compared with the consensus sequence of PVS-H95 genome.

RESULTS

All Nicotiana occidentalis plants inoculated with ≥0.2 μg capped RNA transcripts from pPVS-H-FL-β developed symptoms on upper leaves, as observed with PVS-H00 inoculation. Similar levels of viral genomic and subgenomic RNAs and coat protein were detected in systemically infected leaves. Sequence comparison of PVS-H95 and PVS-H00 revealed 370 nucleotide polymorphisms (4.4% of the entire genome sequence), causing 91 amino acid substitutions in six open reading frames (ORFs). The infectivity of chimeric RNAs derived from recombinants between the two cDNA clones revealed that the lack of infectivity of pPVS-H-FL-H transcripts was due to ORF1, which encodes replicase and harbors 80 amino acid substitutions compared with pPVS-H-FL-β. Approximately 71.3% amino acid substitutions in replicase were located within the variable region of unknown function between the putative methyltransferase and ovarian tumor-like protease domains.

CONCLUSIONS

This is the first report of the development of an infectious cDNA clone of PVS. Our analyses suggest that PVS population within a plant exists as quasispecies and the replicase sequence diversity of PVS obstruct the construction of a full-length infectious cDNA clone.

Successful infection of BALB/c mice by a swine hepatitis E virus clone constructed with reverse genetics

Background

Hepatitis E virus (HEV) is a leading cause of hepatitis worldwide. However, its infection biology and pathogenesis remain largely elusive. Furthermore, no proven medication is available for treating hepatitis E. Robust experimental models are urgently required to advance the research of HEV infection. Because of the lacking of a sophisticated small animal model, this study aimed to establish a mouse model of HEV infection.

Methods

We constructed a full-length swine HEV cDNA clone of genotype 4 (named as pGEM-HEV) by reverse genetics approach. And we inoculated with HEV RNA in BALB/c mice to establish small animal model for HEV infection and pathogenesis studies.

Results

The capped RNA transcripts of pGEM-HEV prepared in vitro were replication-competent in HepG2 cells. Importantly, BALB/c mice intravenously inoculated with RNA transcripts of pGEM-HEV developed an active infection as shown by shedding viruses in feces, detectable negative strand of HEV in the liver, spleen and kidney, and causing liver inflammation.

Conclusion

In this study, we successfully established of BALB/c mice-based small animal model for HEV provides an opportunity to further understand HEV pathogenesis and to develop effective antiviral medications.

Insertion position as well as the inserted TRS and gene sequences differentially affect the retention of foreign gene expression by simian hemorrhagic fever virus (SHFV)

Recombinant SHFV infectious cDNA clones expressing a foreign gene from an additional sg mRNA were constructed. Two 3' genomic region sites, between ORF4' and ORF2b and between ORF4 and ORF5, were utilized for insertion of the myxoma M013 gene with a C-terminal V5 tag followed by one of the three inserted transcription regulatory sequences (TRS), TRS2', TRS4' or TRS7. M013 insertion at the ORF4'/ORF2b site but not the ORF4/ORF5 site generated progeny virus but only the recombinant virus with an inserted TRS2' retained the entire M013 gene through passage four. Insertion of an auto-fluorescent protein gene, iLOV, with an inserted TRS2' at the ORF4'/ORF2b site, generated viable progeny virus. iLOV expression was maintained through passage eight. Although regulation of SHFV subgenomic RNA synthesis is complex, the ORF4'/ORF2b site, which is located between the two sets of minor structural proteins, is able to tolerate foreign gene insertion.

Development of infectious cDNA clones of Grapevine leafroll-associated virus 3 and analyses of the 5' non-translated region for replication and virion formation

Infectious cDNA clones were developed for Grapevine leafroll-associated virus 3 (GLRaV-3, genus Ampelovirus, family Closteroviridae). In vitro RNA transcripts generated from cDNA clones showed replication via the production of 3'-coterminal subgenomic (sg) mRNAs in Nicotiana benthamiana protoplasts. The detection of sgRNAs and the recovery of progeny recombinant virions from N. benthamiana leaves agroinfiltrated with full-length cDNA clones confirmed RNA replication and virion formation. The 5' non-translated region (5' NTR) of GLRaV-3 was exchangeable between genetic variants and complement the corresponding cognate RNA functions in trans. Mutational analysis of the 5' NTR in minireplicon cDNA clones showed that the conserved 40 nucleotides at the 5'-terminus were indispensable for replication, compared to downstream variable portion of the 5' NTR. Some of the functional mutations in the 5' NTR were tolerated in full-length cDNA clones and produced sgRNAs and virions in N. benthamiana leaves, whereas other mutations affected replication and virion formation.

A reverse genetics system for enterovirus D68 using human RNA polymerase I

Human enterovirus D68 (EV-D68) is a highly contagious virus, which causes respiratory tract infections. However, no effective vaccines are currently available for controlling EV-D68 infection. Here, we developed a reverse genetics system to recover EV-D68 minireplicons and infectious EV-D68 from transfected plasmids using the RNA polymerase I (Pol I) promoter. The EV-D68 minireplicons contained the luciferase reporter gene, which flanked by the non-coding regions of the EV-D68 RNA. The luciferase signals could be detected in cells after transfection and Pol I promoter-mediated luciferase signal was significantly stronger than that mediated by the T7 promoter. Furthermore, recombinant viruses were generated by transfecting plasmids that contained the genomic RNA segments of EV-D68, under the control of Pol I promoter into 293T cells or RD cells. On plaque morphology and growth kinetics, the rescued virus and parental virus were indistinguishable. In addition, we showed that the G394C mutation disrupts the viral 5'-UTR structure and suppresses the viral cap-independent translation. This reverse genetics system for EV-D68 recovery can greatly facilitate research into EV-D68 biology. Moreover, this system could accelerate the development of EV-D68 vaccines and anti-EV-D68 drugs.

Development and Characterization of an Infectious cDNA Clone of Equine Arteritis Virus

Development and characterization of several infectious cDNA clones of equine arteritis virus (EAV) have been described in the literature. Here we describe the assembly of the full-length infectious cDNA clone of the virulent Bucyrus strain (VBS; ATCC VR-796) of EAV in a plasmid vector. This system allows generation of infectious in vitro-transcribed (IVT) RNA from the linearized plasmid that can be transfected or electroporated into mammalian cells to produce infectious recombinant progeny virus. This is an efficient reverse genetics system that allows easy manipulation of EAV genomes to study molecular biology of the virus and pathogenesis of equine viral arteritis.

Construction of a high-yield dengue virus by replacing nonstructural proteins 3-4B without increasing virulence

Producing virus at high yield is critically important for development of whole virion inactivated vaccines or live attenuated vaccines. Most dengue virus (DENV) clinical isolates, however, replicate at low levels in cultured cells, which limits their use for vaccine development. The present study examined differences between low-replicating DENV clinical isolates and high-replicating laboratory strains with the aim of engineering high-yield DENV clinical isolates. Construction of a series of recombinant chimeric viruses derived from a high-replicating laboratory DENV type 4 (DENV-4) H241 strain and a clinical isolate revealed that the NS3-NS4B region of H241 conferred a replication advantage in cultured cells. Furthermore, northern blot analysis revealed that this advantage was due to more efficient synthesis of viral RNA. Importantly, replacement of the NS3-NS4B region of H241 did not increase virulence in mice, suggesting that viral production can be increased safely. This study provided information that will facilitate engineering of safe and high-yield viruses that can be used for vaccine development.

Construction of infectious clones of lychnis ringspot virus and evaluation of its relationship with barley stripe mosaic virus by reassortment of genomic RNA segments

Lychnis ringspot virus (LRSV, genus Hordeivirus) was first isolated in 1959, and has been shown to infect several dicot plants in nature. However, due to the lack of infectious cDNA clones, the biological properties and mechanisms underlying LRSV infection are obscure. In this work, we constructed infectious cDNA clones of LRSV and have compiled the complete LRSV genomic (g) RNA sequence. Comparison of nucleotide and amino acid sequences between LRSV and barley stripe mosaic virus (BSMV), the type member of genus Hordeivirus, reveals that despite belonging to the same genus, and replicating in chloroplasts, the viruses are only distantly related. This could be further indicated by the failure of different LRSV/BSMV reassortants to infect N. benthamiana. LRSV infectious cDNA clones provide a useful tool for studies of biological diversity among hordeiviruses, and also may contribute to the understanding of seed transmission in dicot plants.

Pig BVDV-2 non-structural protein (Npro) links to cellular antiviral response in vitro

In this study, we constructed for the first time a full-length cDNA clone of pig-original bovine viral diarrhea virus 2 (BVDV-2) strain SH-28, modified the cDNA clone (pASH28) for mutant pASHΔN^pro and derived virus strain vASHΔN^pro by deleting the genomic region encoding the N^pro polypeptide, and examined significance of protein N^pro for antiviral responses in vitro. Data showed that N^pro-deletion mutant virus vASHΔN^pro led to significant overexpression of oligo adenylate synthetase (OAS), myxovirus-resistant protein 1 (Mx1), and ubiquitin-like protein 15 (ISG15). Data also revealed that overexpression of N^pro, but not NS2 and NS3 proteins, resulted in significant down-regulation of OAS, Mx1, and ISG15 production (p ≤ 0.05) in bovine cells as well as porcine cells transfected with N^pro recombinant eukaryotic expression plasmids. N^pro (but not NS2 and NS3) was also found to inhibit poly(IC) from inducing production of type I interferon (IFN-I). These results indicated that protein N^pro may play multiple roles in regulating antiviral response in host cells interfered by pig BVDV-2 strain, and provided useful information to understand better the mechanism of BVDV-2 persistent infection in pigs.

A determinant of disease symptom severity is located in RNA2 of broad bean wilt virus 2

Broad bean wilt virus 2 (BBWV2), which belongs to the genus Fabavirus, is a destructive pathogen of many economically important horticultural and ornamental crops. In this study, we constructed infectious full-length cDNA clones of two distinct isolates of BBWV2 under control of the cauliflower mosaic virus 35S promoter. BBWV2-PAP1 isolated from paprika (Capsicum annuum var. gulosum) induces severe disease symptoms in various pepper varieties, whereas BBWV2-RP1 isolated from red pepper (Capsicum annuum L.) causes mild symptoms. Agrobacterium-mediated inoculation of the infectious cDNA clones of BBWV2-PAP1 and RP1 resulted in the same symptoms as the original virus isolates. The infectious cDNA clones of BBWV2-PAP1 and RP1 were used to examine the symptoms induced by pseudorecombinants between the two isolates to localize in which of the two genomic RNAs are the symptom severity determinants in BBWV2. The pseudorecombinant of RP1-RNA1 and PAP1-RNA2 induced severe symptoms, similar to those caused by the parental isolate PAP1, whereas the pseudorecombinant of PAP1-RNA1 and RP1-RNA2 induced mild symptoms, similar to those caused by the parental isolate RP1. Our results suggest that BBWV2 RNA2 contains a symptom determinant(s) capable of enhancing symptom severity.

Reverse Genetics Approaches for Chikungunya Virus

Reverse genetic systems based on an infectious cDNA clone, a double-stranded copy of the viral genome carried on a plasmid vector, have greatly enhanced the understanding of RNA virus biology by facilitating genetic manipulation of viral RNA genomes. To date, infectious cDNA clones of Chikungunya virus (CHIKV) have been constructed using different combinations of plasmid vectors and/or bacterial host strains. Here, we describe our approaches for the construction of infectious cDNA clones of CHIKV and the protocol for genetic manipulation of the clones by site-directed mutagenesis.

Replacement of pr gene with Japanese encephalitis virus pr using reverse genetics reduces antibody-dependent enhancement of dengue virus 2 infection

Severe dengue is more likely found during secondary heterologous dengue virus (DENV) infection or primary infection of infants born to dengue-immune mothers and led to the hypothesis of antibody-dependent enhancement (ADE). It has been reported that pre-membrane (prM)-reactive antibodies do not efficiently neutralize DENV infection but instead potently promote ADE infection. Meanwhile, these enhancing anti-prM antibodies mainly react with the precursor (pr) peptide. To evaluate the effect of pr gene substitution on neutralization and ADE of DENV infection, a novel chimeric dengue virus (JEVpr/DENV2) was rationally constructed by replacing the DENV pr gene with Japanese encephalitis virus (JEV) pr gene, based on the full-length infectious complementary DNA (cDNA) clone of DENV2 ZS01/01. We found that chimeric JEVpr/DENV2 showed reduced virulence and good immunogenicity. In addition, anti-JEVpr/DENV2 sera showed broad cross-reactivity and efficient neutralizing activity with all four DENV serotypes and immature DENV2 (ImDENV2). Most importantly, compared with anti-DENV2 sera, anti-JEVpr/DENV2 sera showed significantly reduced enhancing activity of DENV infection in K562 cells. These results suggest that the ADE activities could be reduced by replacing the DENV pr gene with JEV pr gene. These findings may help us better understand the pathogenesis of DENV infection and provide a reference for the development of a vaccine against DENV.

Construction and characterization of an infectious cDNA clone of Echovirus 25

Echovirus 25 (E-25) is a member of the enterovirus family and a common pathogen that induces hand, foot, and mouth disease (HFMD), meningitis, skin rash, and respiratory illnesses. In this study, we constructed and characterized an infectious full-length E-25 cDNA clone derived from the XM0297 strain, which was the first subgenotype D6 strain isolated in Xiamen, China. The 5'-Untranslated Regions (5'-UTR), P3 (3A-3B, 3D) and P3 (3C) regions of this E-25 (XM0297) strain were highly similar to EV-B77, E-16 and E-13, respectively. Our data demonstrate that the rescued E-25 viruses exhibited similar growth kinetics to the prototype virus strain XM0297. We observed the rescued viral particles using transmission electron microscope (TEM) and found them to possess an icosahedral structure, with a diameter of approximately 30 nm. The cross neutralization test demonstrated that the E-25 (XM0297) strain immune serum could not neutralize EV-A71, CV-A16 or CV-B3; likewise, the EV-A71 and CV-A16 immune serum could not neutralize E-25 (XM0297). The availability of this infectious clone will greatly enhance future virological investigations and possible vaccine development against E-25.

A positively charged lysine residue at VP2 131 position allows for the enhanced adaptability of foot-and-mouth disease virus serotype A in BHK-21 cells

Field outbreak strains of foot-and-mouth disease virus (FMDV) infect host cells through certain Arg-Gly-Asp (RGD) dependent integrin family of cellular receptors. In contrast, FMDV adapted in non-host cell cultures are reported to acquire the ability to infect cells via heparin sulphate (HS) or other unidentified cell surface molecules. It has been reported that during the serial passage of FMDV serotype A in BHK-21 cell culture, VP2 E131K (E2131K) substitution was fixed within the heparin sulphate binding site. The fixation of positively charged residue at position VP2 131 of serotype A is considered to associate with the ability to utilise alternative receptor. In this study, an infectious full-length cDNA clone for Indian FMDV vaccine strain A IND 40/2000 was constructed. Through site-directed mutagenesis on the cDNA clone, recombinant virus containing positive charged amino acid residue at position VP2 131 was rescued. The recombinant mutated virus was shown to have specific and strong affinity for HS and demonstrated an enhanced infectivity in BHK-21 cell line. The introduction of lysine residue at VP2 131 position that allows cell culture adaptation of FMDV serotype A could be exploited for the generation of vaccine seed stocks with improved growth properties in BHK-21 cell line.

Sequences outside that of residues 93-102 of 3A protein can contribute to the ability of foot-and-mouth disease virus (FMDV) to replicate in bovine-derived cells

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease of cloven-hoofed animals. During 2010 and 2011, there was an epidemic of the Mya-98 lineage of the Southeast Asia (SEA) topotype in East Asia, including China. Changes in the FMDV 3A protein have been previously reported to be associated with the inability of FMDV to grow in bovine cells and cause disease in cattle. In this paper, we report the generation of a full-length infectious cDNA clone of FMDV O/SEA/Mya-98 strain O/GZSB/2011 for the first time along with two genetically modified viruses with deletion at positions 93-102 and 133-143 in 3A based on the established infectious clone. All the recombinant viruses grew well and displayed growth properties and plaque phenotypes similar to those of the parental virus in baby hamster kidney (BHK-21) cells, porcine kidney (PK-15) cells, and primary fetal porcine kidney (FPK) cells. While the recombinant viruses rvGZSB and rvSBΔ133-143 exhibited similar growth properties and plaque phenotypes with the parental virus in primary fetal bovine kidney (FBK) cells, the recombinant virus rvSBΔ93-102, containing deletion at positions 93-102 in 3A, grew at a slower rate and had a smaller plaque size phenotype in FBK cells than that of the parental virus. Therefore, the results suggest that the deletion at positions 93-102 of 3A protein does not affect FMDV replication efficiency in BHK-21, PK-15 and FPK cells, but affects virus replication efficiency in FBK cells, although, cannot alone account for the inability to replicate in bovine cells.