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PubMed2026

The Q653R substitution in the spike protein is associated with attenuation of a GVI-1 infectious bronchitis virus strain.

The GVI-1 genotype of infectious bronchitis virus (IBV) has become increasingly prevalent in Asia. In this study, a highly pathogenic GVI-1 strain (GVI-1-WT) was attenuated by 110 serial passages in embryonated chicken eggs, yielding an attenuated strain (GVI-1-E110). Comparative genomic analysis identified two amino acid substitutions, S523I, Q653R and a nine-amino-acid truncation in the spike (S) protein. To evaluate the contribution of the two point mutations to virulence attenuation, recombinant viruses carrying Q653R and S523I substitutions were generated using a reverse genetics system based on the GVI-1-WT strain as the backbone. Their replication and pathogenicity were assessed in embryonated eggs and specific pathogen-free chickens. The Q653R substitution was associated with reduced viral replication in embryonated chicken eggs and pathogenicity in specific pathogen-free chickens, whereas the S523I mutation alone showed a limited effect but enhanced attenuation when combined with Q653R. However, the attenuation phenotype of the recombinant viruses did not fully recapitulate that of the passaged strain GVI-1-E110, suggesting that additional mutations, including the identified truncation and mutations in replicase-associated genes outside the S protein, may also contribute to virulence attenuation. This study indicates that spike protein mutations are involved in the attenuation of GVI-1 IBV strains, and provides insights into the molecular basis of IBV attenuation during serial passage. Further studies are required to elucidate the underlying mechanisms and to evaluate their potential relevance for vaccine development.

GVI-1 genotype↗
PubMed2026

Field-isolate recombinant tick-borne encephalitis viruses define reporter-stability guidelines for antiviral testing in flaviviruses.

As arthropod-borne viruses continue to threaten populations globally, there is a pressing need for experimental systems that enable rapid antiviral discovery. Reverse-genetics platforms producing recombinant reporter orthoflaviviruses have been developed to address this gap. Here, we present two new recombinant tick-borne encephalitis viruses (TBEVrec) generated on a European-subtype Haselmühl Tiho1 isolate backbone. A reporter gene, either eGFP or Nluc, was inserted in the capsid-coding region of the genome downstream of the capsid RNA regulatory signal and separated from the complete viral polyprotein by a 2A self-cleaving peptide. TBEVrec was better rescued using the circular polymerase extension reaction (CPER) than with the infectious subgenomic amplicon (ISA) method. TBEVrec replicated efficiently in relevant human cell lines, with comparable replication to wild-type TBEV in a neuronal cell line and moderately reduced titers and RNA levels in immune-derived cell lines. Using either eGFP or Nluc, we illustrate how TBEVrec enabled high-content RNAi screening, highlighting Nucleolin and PRKD1 as potential TBEV host factors, and drug testing on a benchtop plate reader. Nanopore sequencing of the eGFP insert revealed that the reporter is excised without affecting flanking regions. Comparative analysis of eGFP and Nluc further shows that this instability is time- and cell type-dependent, and that Nluc is comparatively more stable. From these observations, we outline safeguards and design principles that are broadly applicable both to the rescue of existing constructs and to the design of future recombinant reporter virus platforms.

CPER↗
PubMed2027

Production of Viral Particles from a Chikungunya Virus Infectious Clone.

Chikungunya virus (CHIKV) is a positive-sense single-stranded RNA virus, which poses challenges for its study and genetic manipulation. Because direct mutagenesis of viral RNA genomes is technically impractical, reverse genetics systems are essential tools for investigating viral biology. To enable such approaches, infectious clones containing a full-length cDNA copy of the viral genome are constructed. The cDNA is positioned under the control of a bacteriophage RNA polymerase promoter, allowing commercial RNA polymerases to use the linearized plasmid as a template for the in vitro transcription of full-length viral genomic RNA (gRNA). Importantly, positive-sense viral genomes serve as mRNAs for the translation of viral proteins in a cellular environment, meaning that these transcripts contain all the information required to initiate viral replication. Following transfection into permissive cultured cells, viral proteins are expressed, enabling genome replication and, ultimately, the recovery of infectious particles from the cell supernatant. Here, we describe a detailed procedure for generating CHIKV particles through plasmid linearization, in vitro transcription, and subsequent RNA transfection.

Chikungunya virus↗
PubMed2026

Meiotic Origins of Non-Mosaic Klinefelter Syndrome (47, XXY): Mechanisms, Dimorphism, and Emerging Genetic Susceptibility.

BACKGROUND: Non-mosaic Klinefelter syndrome (47,XXY) arises from sex-specific meiotic mechanisms leading to nondisjunction during gametogenesis. In maternal cases, errors occur predominantly during meiosis I, frequently involving X chromosomes that lack crossovers or exhibit crossovers outside optimal chromosomal locations; this nondisjunction is further exacerbated by advancing maternal age and the subsequent deterioration of cohesins. Conversely, paternal 47,XXY stems primarily from the failure of obligate recombination within the pseudoautosomal region, which is critical for accurate XY segregation. OBJECTIVE: Drawing on the latest literature, this review transitions from a descriptive account of non-mosaic Klinefelter syndrome (nKS) toward a comprehensive analysis of mechanistic and genomic evidence, establishing a unified framework of sex-specific meiotic vulnerability. METHODS: We synthesized recent findings from forward genetic approaches in mouse models with data from human observational and reverse-genetic studies, delineating an updated view of the established and putative mechanisms that modulate sex chromosome segregation. RESULTS: We frame XX and XY nondisjunction as a genetically modulated process rather than a purely stochastic event. The integrated evidence supports a unified framework in which maternal and paternal mechanisms converge primarily on meiotic recombination failure but differ in timing, chromosomal context, and genetic modulation. CONCLUSIONS: From a clinical standpoint, identifying the molecular drivers of sex chromosome aneuploidy will enhance genetic counseling and risk stratification. Such insights are poised to facilitate informed reproductive decision-making and timely therapeutic support, ultimately reducing the burden of nKS comorbidities and improving patients' quality of life.

aneuploidy↗
PubMed2025

Genomics control of biostimulant-induced stress tolerance and crop yield enhancement.

Biostimulants are changing modern agriculture, as they have the potential to secure healthy and sustainable food production while preserving the environment. They have two main biological effects: growth promotion and stress protection. Both effects can lead to enhancement of the yield and improvement of the marketable grade of the produce in crops, without compromising crop quality. Their use increased exponentially in the past decade, as they are highly efficient, ecologically friendly (non-toxic, biodegradable), and applicable to all major crops. While exponential data on the physiological mechanisms of stress protection is accumulating in recent years, the information as to how biostimulants act at the molecular level is still rather limited. Here we review the growing evidence of the biostimulants role in stress protection and yield enhancement of crops, as well as the recent transcriptomic and metabolomic data, which indicate biostimulants' molecular mode of action. In particular, we outline the role of genes encoding signaling components, plant hormones (abscisic acid, brassinosteroids, and ethylene), genes encoding transcription factors from ERF, WRKY, NAC, and MYB families, and genes related to growth, photosynthesis, and stress response. Finally, we describe strategies to study the genetic and genomics control of biostimulants mode of action, with foci on stress tolerance and yield enhancement. In Arabidopsis, established systems for biostimulants-induced protection against drought and oxidative stress will allow both forward and reverse genetics approaches to identify key genes from the biostimulants network. Mutations in such genes compromise the stress-protective effect of biostimulants. In major crops such as pepper and tomato, large Genome Wide Association Studies (GWAS) panels can be utilized to study crops responses to biostimulants in terms of drought tolerance, fruit qualities, and yield in order to pinpoint genes controlling biostimulants-induced stress protection and yield enhancement. The combination of these approaches allows identification and verification of important genes involved in the pathways of biostimulant-induced stress protection and yield enhancement, as well as deciphering parts of the intricate biostimulant-signaling network.

Crops, Agricultural↗
PubMed2026

Integrated analysis uncovers exogenous induction and molecular regulation of erinacine A accumulation in Hericium erinaceus.

Erinacine A, a cyathane-type diterpenoid mainly from Hericium erinaceus mycelia, exhibits prominent neurotrophic and neuroprotective activities, making it a promising candidate for managing neurodegenerative diseases. However, its low abundance and unclear genetic regulatory mechanisms hinder its application as a nutraceutical. This study aimed to decipher its regulatory mechanisms and enhance production. Four exogenous inducers were screened, with salicylic acid (SA) and ergosterol (ERG) significantly increasing erinacine A content by 62.21% and 146.70% at 20 days, respectively. Transcriptome and WGCNA of inducer-treated sample identified darkorange and magenta modules associated with erinacine A biosynthesis, with the eri gene cluster enriched in the darkorange module and eriG and eriF as hub genes. Forward genetic analysis via QTL mapping of the HeD127 dikaryon population revealed significant phenotypic variation in erinacine A content (0.341-13.085 mg/g) and identified two loci (erA-1 and erA-2) explaining 18.63% of phenotypic variation. Integrating these forward and reverse genetic analyses revealed that salicylic acid and ergosterol synergistically regulate core carbon metabolic pathways to augment acetyl-CoA supply for the mevalonate pathway, suppressed competitive metabolism, enhanced diterpene skeleton construction and structural modification. These results deepen our understanding of the genetic and molecular basis governing accumulation of erinacine A, and facilitate its application in neuroprotective pharmaceuticals.

Diterpenes↗
PubMed2025

Genetic crosses reveal genomic loci responsible for virulence in Cryptosporidium parvum infection.

The relationship between parasite genotype and pathogenesis is largely unknown for Cryptosporidium, a leading cause of diarrheal disease in children. An array of parasites with similar genomes produces varied disease outcomes in different hosts. Here, we isolate and characterize Cryptosporidium parvum strains that show marked differences in virulence and persistence in mice. Taking advantage of the sexual life cycle of this eukaryotic pathogen, we use genetic crosses to discover the underlying chromosomal loci. Whole-genome sequencing and bulk segregant analysis of infection-selected progeny mapped three loci on chromosomes 2, 6, and 7 associated with the ability to colonize and persist in mice and the positions of drug resistance genes. The chromosome 6 locus encodes the hyper-polymorphic surface glycoprotein GP60. Reverse genetic studies in both parental strains demonstrate that GP60 controls parasite burden and virulence, but not persistence, and reveal the dominance of the less virulent allele, suggesting it restricts virulence.

Cryptosporidium parvum↗
PubMed2026

Aphid symbiotic virus engineered for in vivo expression of insecticidal effectors.

Microbial pesticides are eco-friendly alternatives to chemical pesticides. However, few viral pesticides have been developed. Insects harbor diverse symbiotic viruses, which have the potential to be engineered for translational applications in pest control. Here, we engineered Acyrthosiphon pisum virus (APV), a symbiotic virus of the pea aphid, to deliver anti-aphid effectors using reverse genetics technology. A cytomegalovirus (CMV) promoter-driven APV infectious clone was successfully rescued in pea aphids with the assistance of nanocarrier star polymer (SPc). Based on this infectious clone, the protein coding sequence of chymotrypsin inhibitor variant 8 (Chy8) and the double-stranded RNA sequence targeting the aphid clip-domain serine protease (SPLP) were separately assembled into the APV genome to generate APV-Chy8 and APV-dsSPLP infectious clones, respectively. The recombinant APV clones reduced aphid relative survival rates by 34% and 17% by microinjection, respectively. To enhance the transcriptional efficiency, the APV-Chy8 and APV-dsSPLP clones were transcribed in vitro using the T7 promoter. The in vitro-synthesized APV-Chy8 and APV-dsSPLP clones reduced aphid relative survival rates by 48% and 45% by microinjection, respectively. These results demonstrate that engineered APV can deliver cargos and reduce aphid survival under injection-based experimental conditions, highlighting the potential of symbiotic virus-based vectors for delivering insecticidal effectors.

Animals↗
PubMed2001

Bunyamwera bunyavirus nonstructural protein NSs is a nonessential gene product that contributes to viral pathogenesis.

Bunyamwera virus (family Bunyaviridae, genus Bunyavirus) contains a tripartite negative-sense RNA genome. The smallest RNA segment, S, encodes the nucleocapsid protein N and a nonstructural protein, NSs, in overlapping reading frames. We have generated a mutant virus lacking NSs, called BUNdelNSs, by reverse genetics. Compared with the wild-type (wt) virus, BUNdelNSs exhibited a smaller plaque size and generated titers of virus approximately 1 log lower. In mammalian cells, the mutant expressed greatly increased levels of N protein; significantly, the marked inhibition of host cell protein synthesis shown by wt virus was considerably impaired by BUNdelNSs. When inoculated by the intracerebral route BUNdelNSs killed BALB/c mice with a slower time course than wt and exhibited a reduced cell-to-cell spread, and titers of virus in the brain were lower. In addition, the abrogation of NSs expression changed Bunyamwera virus from a noninducer to an inducer of an interferon-beta promoter. These results suggest that, although not essential for growth in tissue culture or in mice, the bunyavirus NSs protein has several functions in the virus life cycle and contributes to viral pathogenesis.

Aedes↗
PubMed2025

Orthobunyavirus neurovirulence is a complex trait involving all three genome segments.

La Crosse orthobunyavirus (LACV) is a tri-segmented negative sense RNA virus and is the leading cause of pediatric arboviral encephalitis in the USA. The viral factors that mediate LACV's ability to replicate and cause damage and disease in the brain (neurovirulence) are not fully understood. We previously characterized the neurovirulence of LACV and closely related Inkoo virus (INKV) and discovered they have opposing neurovirulence phenotypes in mice and human neuronal cells: LACV has high neurovirulence and INKV has low neurovirulence. We therefore generated reassortant viruses between LACV and INKV to map the genome segments that mediate LACV's high neurovirulence phenotype. We recovered all six possible reassortant viruses of the L, M, and S genome segments using coinfection and reverse genetics approaches. We evaluated the neurovirulence of these reassortant viruses in mice in vivo and in human neuronal cells in vitro. Our results show that no single LACV genome segment alone was sufficient to cause wildtype LACV-like neurological disease in mice, and in fact all six reassortant viruses were attenuated from wildtype LACV. We found that the LACV M and S segments together were the primary drivers of neurological disease in mice, whereas the LACV L segment played a minor role. Our in vitro results indicate that the LACV M segment is crucial for efficient replication in neurons, but the LACV L segment appears to mediate slightly more efficient neuronal replication than the INKV L segment. The LACV M and S segments together induced wildtype LACV-like levels of neuronal death, indicating the LACV M and S are the primary mediators of neuronal death, and the L segment is not required. Together, these results indicate that LACV neurovirulence is a complex trait mediated by viral proteins on all three genome segments.

Journal Article↗
PubMed2026

A sequence-based classifier distinguishes phenotype-associated genes from other gene models in plants.

Only a small fraction of annotated plant genes possess experimentally validated associations with specific phenotypes. Phenotype-associated genes have distinct structural, molecular, and evolutionary characteristics compared with nonvalidated gene models. Here, we develop a simple classifier that uses sequence and evolutionary features, which can be generated for any species with an annotated reference genome assembly, to accurately distinguish phenotype-associated genes from both the overall population of annotated gene models and a specific set of genes identified as being tolerant of premature stop mutations. A model trained solely on genes from maize (Zea mays) identifies and prioritizes rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana) genes that are highly enriched in genes with experimentally validated links to phenotypes in both of these evolutionarily distant species. Gene models predicted to have a higher probability of being linked to phenotypes display patterns consistent with known biological properties of phenotype-associated genes. Notably, the sets of genes predicted to have a high probability of being linked to phenotype variation do not consist exclusively of well-characterized gene families but included many uncharacterized gene families carrying domains of unknown function. The quantitative scores generated by this model offer a valuable resource for prioritizing and exploring the vast number of uncharacterized gene models in plants, reducing the risk of failure in future reverse genetic efforts and potentially accelerating gene discovery and functional annotation in crops.

Phenotype↗
PubMed2025

Phylogeny, chromosomal mapping and expression analyses of wheat CLAVATA pathway components suggest differential selection on receptor-like kinases, CLEs and T3 WOXes.

Ensuring continuous global food security is a major challenge of the 21st century. Wheat contributes approximately 20% of the total calories consumed by humans, and an estimated 60% increase in production will be required by 2050 to meet forecast global demand. In cereals like wheat, inflorescence (ear) size and branching patterns determine the number of flowers (florets) and grains produced, and these aspects of plant architecture are regulated by the activity of stem cells in the growing shoot tips. CLAVATA peptide and receptor-like kinase signalling regulates angiosperm stem cell activity, and as changes in CLAVATA function can improve crop yields, CLAVATA is a key target for reverse engineering. Here, we identify components of the wheat CLAVATA pathway using genome searches against Triticum aestivum and its wild relatives Triticum turgidum ssp. durum, Triticum turgidum ssp. dicoccoides, Triticum urartu and Aegilops tauschii. Using phylogenetic and synteny analysis, we determine the relationship between homoeologues and infer patterns of gene family evolution. Whilst CLAVATA1, BARELY ANY MERISTEM, RECEPTOR-LIKE PROTEIN KINASE 2, CORYNE and CLAVATA2 receptor-like kinase homologues are mainly present as single genome copies as in other grasses, CLAVATA3-like but not TRACHEARY ELEMENT DIFFERENTIATION FACTOR (TDIF)-like peptide encoding genes and WUSCHEL-LIKE HOMEOBOX (WOX) genes have expanded copy numbers with many gene gains and losses during evolution. Our results highlight wheat CLAVATA pathway components for reverse genetic analysis and indicate potential differential selection on wheat receptor-like kinases, their peptide ligands and WOXes.

Triticum↗
PubMed2002

Bunyamwera bunyavirus nonstructural protein NSs counteracts the induction of alpha/beta interferon.

Production of alpha/beta interferons (IFN-alpha/beta) in response to viral infection is one of the main defense mechanisms of the innate immune system. Many viruses therefore encode factors that subvert the IFN system to enhance their virulence. Bunyamwera virus (BUN) is the prototype of the Bunyaviridae family. By using reverse genetics, we previously produced a recombinant virus lacking the nonstructural protein NSs (BUNdelNSs) and showed that NSs is a nonessential gene product that contributes to viral pathogenesis. Here we demonstrate that BUNdelNSs is a strong inducer of IFN-alpha/beta, whereas in cells infected with the wild-type counterpart expressing NSs (wild-type BUN), neither IFN nor IFN mRNA could be detected. IFN induction by BUNdelNSs correlated with activation of NF-kappaB and was dependent on virally produced double-stranded RNA and on the IFN transcription factor IRF-3. Furthermore, both in cultured cells and in mice lacking a functional IFN-alpha/beta system, BUNdelNSs replicated to wild-type BUN levels, whereas in IFN-competent systems, wild-type BUN grew more efficiently. These results suggest that BUN NSs is an IFN induction antagonist that blocks the transcriptional activation of IFN-alpha/beta in order to increase the virulence of Bunyamwera virus.

Animals↗
PubMed2005

Attenuation of bunyavirus replication by rearrangement of viral coding and noncoding sequences.

Bunyamwera virus (BUN) is the prototype virus of the family Bunyaviridae. BUN has a tripartite negative-sense RNA genome comprising small (S), medium (M), and large (L) segments. Partially complementary untranslated regions (UTRs) flank the coding region of each segment. The terminal 11 nucleotides of these UTRs are conserved between the three segments, while the internal regions are unique. The UTRs direct replication and transcription of viral RNA and are sufficient to allow encapsidation of viral RNA into ribonucleoprotein complexes. To investigate the segment-specific functions of the UTRs, we have used reverse genetics to recover a recombinant virus (called BUN MLM) in which the L segment open reading frame (ORF) is flanked by the M segment UTRs. Compared to wild-type virus, BUN MLM virus shows growth attenuation in cultured mammalian cells and a slower disease progression in mice, produces small plaques, expresses reduced levels of L mRNA and L (RNA polymerase) protein, synthesizes less L genomic and antigenomic RNA, and has an increased particle-to-PFU ratio. Our data suggest that the packaging of BUN RNAs is not segment specific. In addition, the phenotype of BUN MLM virus supports the finding that BUN UTRs differ in their regulation of RNA synthesis but suggests that the interplay between each segment UTR and its cognate ORF may contribute to that regulation. Since BUN MLM virus is attenuated due to an essentially irreversible mutation, the rearrangement of UTRs is a feasible strategy for vaccine design for the more pathogenic members of the Bunyaviridae.

Animals↗
PubMed2026

Systematic mapping of insertion-tolerant regions enables capsid engineering of an infectious RNA phage.

RNA phages are attractive platforms for the design of programmable bioparticles, but their development has been constrained by limited knowledge of genomic sites that can tolerate sequence insertion. Here, we combined MuA transposase-mediated in vitro insertion mutagenesis with our established reverse genetics systems to systematically identify insertion-tolerant regions (ITRs) in the RNA phages MS2 and PP7. Screening of 4,555 MS2 and 2,228 PP7 random insertion clones identified 29 and 26 non-redundant ITRs, respectively. We further analyzed and compared these ITRs in the context of RNA genome organization and virion architecture. Both phages contained ITRs within the maturation protein, whereas only PP7 tolerated insertions within the coat protein (CP). On the basis of structural location and plaque-forming capacity, an ITR situated between Gly74 and Glu75 (GGC^GAG) in the PP7 CP was selected for further study. Infectious phage particles generated from complementary DNA clones retained the 15-bp insertion at both the RNA and protein levels. Engineered PP7 phages carrying an Arg-Gly-Asp motif inserted into the CP at this ITR displayed enhanced in vivo clearance in a Drosophila model, despite having in vitro stability comparable to that of the wild type. These findings provide the first example of CP engineering in an infectious RNA phage and establish a framework for engineering RNA phages for biological and biotechnological applications.IMPORTANCEA major obstacle to developing RNA phages as synthetic biology platforms is the lack of design principles for genomic insertion. Here, we address this limitation by establishing a mutagenesis-and-recovery workflow that systematically identifies insertion-tolerant regions (ITRs) in the RNA phages MS2 and PP7. The resulting maps reveal distinct structural constraints in the two phages and enable rational engineering of a peptide-display site in the PP7 capsid. Using this approach, we generated an engineered infectious phage with a modified capsid, thereby providing the first demonstration of capsid engineering in an infectious RNA phage, to our knowledge. This study lays the groundwork for the rational design of live RNA phage virions as tractable and engineerable scaffolds for future biological and biotechnological applications.

Animals↗
PubMed2026

A bireporter recombinant SARS-CoV-2 Omicron BA.5 for in vitro and in vivo studies.

The continuous emergence of variants of concern (VoCs) represents a significant challenge to effectively control severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although FDA-approved vaccines and antivirals have been successfully developed and implemented for the prophylactic and therapeutic intervention of SARS-CoV-2 infection, recent VoCs could escape protection garnered by previous vaccine and antiviral approaches. Determining the efficacy of prophylactics and/or therapeutics against recent VoCs will assist in efficiently controlling currently circulating SARS-CoV-2 strains. We used our previously described bacterial artificial chromosome-based reverse genetics approach for Omicron BA.5 to generate a recombinant SARS-CoV-2 BA.5 encoding a fusion of ZsGreen to Nanoluciferase (rBA.5 ZsG-Nluc) from the locus of the viral nucleocapsid (N) protein separated by the porcine teschovirus-1 2A proteolytic cleavage site. The rBA.5 ZsG-Nluc replicates to levels comparable to recombinant BA.5 wild type (rBA.5 WT) and expresses high levels of ZsG and Nluc in cultured cells. This facilitates tracking viral infection and the identification of antivirals and neutralizing antibodies with EC50 and NT50 values, respectively, similar to those obtained with rBA.5 WT. Importantly, in Keratin-18 human angiotensin-converting enzyme-2 mice, rBA.5 ZsG-Nluc retains the same pathogenicity and ability to replicate in the lungs of infected mice as rBA.5 WT. Using rBA.5 ZsG-Nluc, we detected Nluc activity systemically and Nluc and ZsG expression in the lungs of infected mice using an in vivo imaging system. Our results demonstrate the feasibility of using rBA.5 ZsG-Nluc to track viral infections and identify prophylactics and therapeutics against recent SARS-CoV-2 VoCs in vitro, ex vivo, and in vivo.IMPORTANCESevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative virus of the coronavirus disease 2019 pandemic, is continually evolving to escape immunity acquired by previous natural infections or vaccinations. Moreover, recent SARS-CoV-2 variants of concern (VoCs) have acquired antiviral-resistant mutations to FDA-approved drugs. The emergence of these VoCs highlights the importance of identifying new prophylactics and therapeutics against currently circulating SARS-CoV-2 strains. We generated a recombinant bireporter Omicron BA.5 SARS-CoV-2 (rBA.5 ZsG-Nluc) that expresses reporter proteins, which are useful for cellular and whole animal studies, and has similar viral replication and pathogenicity to a wild-type recombinant Omicron BA.5 SARS-CoV-2. In Keratin-18 human angiotensin-converting enzyme-2 mice, rBA.5 ZsG-Nluc infection can be tracked systemically or in the lungs of infected mice using an in vivo imaging system. We establish a proof-of-concept platform of rBA.5 ZsG-Nluc in combination with an ancestral SARS-CoV-2 strain expressing mCherry to simultaneously identify antivirals and neutralizing antibodies against original and recent SARS-CoV-2 strains.

SARS-CoV-2↗
PubMed2025

Key virulence factors responsible for differences in pathogenicity between clinically proven live-attenuated Japanese encephalitis vaccine SA14-14-2 and its pre-attenuated highly virulent parent SA14.

Japanese encephalitis virus (JEV), a neuroinvasive and neurovirulent orthoflavivirus, can be prevented in humans with the SA14-14-2 vaccine, a live-attenuated version derived from the wild-type SA14 strain. To determine the viral factors responsible for the differences in pathogenicity between SA14 and SA14-14-2, we initially established a reverse genetics system that includes a pair of full-length infectious cDNAs for both strains. Using this cDNA pair, we then systematically exchanged genomic regions between SA14 and SA14-14-2 to generate 20 chimeric viruses and evaluated their replication capability in cell culture and their pathogenic potential in mice. Our findings revealed the following: (i) The single envelope (E) protein of SA14-14-2, which contains nine mutations (eight in the ectodomain and one in the stem region), is both necessary and sufficient to render SA14 non-neuroinvasive and non-neurovirulent. (ii) Conversely, the E protein of SA14 alone is necessary for SA14-14-2 to become highly neurovirulent, but it is not sufficient to make it highly neuroinvasive. (iii) The limited neuroinvasiveness of an SA14-14-2 derivative that contains the E gene of SA14 significantly increases (approaching that of the wild-type strain) when two viral nonstructural proteins are replaced by their counterparts from SA14: (a) NS1/1', which has four mutations on the external surface of the core β-ladder domain; and (b) NS2A, which has two mutations in the N-terminal region, including two non-transmembrane α-helices. In line with their roles in viral pathogenicity, the E, NS1/1', and NS2A genes all contribute to the enhanced spread of the virus in cell culture. Collectively, our data reveal for the first time that the E protein of JEV has a dual function: It is the master regulator of viral neurovirulence and also the primary initiator of viral neuroinvasion. After the initial E-mediated neuroinvasion, the NS1/1' and NS2A proteins act as secondary promoters, further amplifying viral neuroinvasiveness.

Animals↗
PubMed2025

Natural self-attenuation of pathogenic viruses by deleting the silencing suppressor coding sequence for long-term plant-virus coexistence.

Potyviridae is the largest family of plant-infecting RNA viruses. All members of the family (potyvirids) have single-stranded positive-sense RNA genomes, with polyprotein processing as the expression strategy. The 5'-proximal regions of all potyvirids, except bymoviruses, encode two types of leader proteases: the serine protease P1 and the cysteine protease HCPro. However, their arrangement and sequence composition vary greatly among genera or even species. The leader proteases play multiple important roles in different potyvirid-host combinations, including RNA silencing suppression and virus transmission. Here, we report that viruses in the genus Arepavirus, which encode two HCPro leader proteases in tandem (HCPro1-HCPro2), can naturally lose the coding sequences for these two proteins during infection. Notably, this loss is associated with a shift in foliage symptoms from severe necrosis to mild chlorosis or even asymptomatic infections. Further analysis revealed that the deleted region is flanked by two short repeated sequences in the parental isolates, suggesting that recombination during virus replication likely drives this genomic deletion. Reverse genetic approaches confirmed that the loss of leader proteases weakens RNA silencing suppression and other critical functions. A field survey of areca palm trees displaying varied symptom severity identified a transitional stage in which full-length viruses and deletion mutants coexist in the same tree. Based on these findings, we propose a scenario in which full-length isolates drive robust infections and facilitate plant-to-plant transmission, eventually giving rise to leader protease-less variants that mitigate excessive damage to host trees, allowing long-term coexistence with the perennial host. To our knowledge, this is the first report of potyvirid self-attenuation via coding sequence loss.

Plant Diseases↗