Diversity and Pathobiology of an Ilarvirus Unexpectedly Detected in Diverse Plants and Global Sequencing Data.

High-throughput sequencing (HTS) and sequence mining tools revolutionized virus detection and discovery in recent years, and implementing them with classical plant virology techniques results in a powerful approach to characterize viruses. An example of a virus discovered through HTS is Solanum nigrum ilarvirus 1 (SnIV1) (Bromoviridae), which was recently reported in various solanaceous plants from France, Slovenia, Greece, and South Africa. It was likewise detected in grapevines (Vitaceae) and several Fabaceae and Rosaceae plant species. Such a diverse set of source organisms is atypical for ilarviruses, thus warranting further investigation. In this study, modern and classical virological tools were combined to accelerate the characterization of SnIV1. Through HTS-based virome surveys, mining of sequence read archive datasets, and a literature search, SnIV1 was further identified from diverse plant and non-plant sources globally. SnIV1 isolates showed relatively low variability compared with other phylogenetically related ilarviruses. Phylogenetic analyses showed a distinct basal clade of isolates from Europe, whereas the rest formed clades of mixed geographic origin. Furthermore, systemic infection of SnIV1 in Solanum villosum and its mechanical and graft transmissibility to solanaceous species were demonstrated. Near-identical SnIV1 genomes from the inoculum (S. villosum) and inoculated Nicotiana benthamiana were sequenced, thus partially fulfilling Koch's postulates. SnIV1 was shown to be seed-transmitted and potentially pollen-borne, has spherical virions, and possibly induces histopathological changes in infected N. benthamiana leaf tissues. Overall, this study provides information to better understand the diversity, global presence, and pathobiology of SnIV1; however, its possible emergence as a destructive pathogen remains uncertain. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

[Research progress in the etiology of hepatitis type E virus].

Hepatitis type E virus (HEV) is a significant infectious zoonotic disease that causes hepatitis E. The disease is primarily transmitted via the fecal-oral route through contaminated water or food and is transmissible between species and genera. The causative agent for the disease is the hepatitis type E virus, which is a member of the Hepadnaviridae family and a single-stranded RNA virus. Its 7.2 kb genome mainly contains three open reading frames (ORFs): ORF1 encodes a non-structural polyprotein that mediates viral replication and transcription; ORF2 encodes a capsid protein and free antigen that induce neutralizing antibodies; ORF3 partially overlaps with ORF2 and encodes a small multifunctional protein involved in virion formation and release. HEV has a unique dual life cycle: it is excreted into feces in the form of naked virions but circulates in the blood in the form of "quasi-enveloped" particles. The two kinds of virus particles adsorb and penetrate the host cell in distinct ways, then internalize and decapsulate to replicate the genome, thereby producing more virion and releasing it outside the cell to mediate the virus's spread. This paper reviews the morphological characteristics, genome structure, encoded proteins, and function of HEV virus-like particles in order to provide a theoretical basis for basic research and comprehensive disease prevention and control.

Research progress in the etiology of hepatitis type E virus / 中华肝脏病杂志

Hepatitis type E virus (HEV) is a significant infectious zoonotic disease that causes hepatitis E. The disease is primarily transmitted via the fecal-oral route through contaminated water or food and is transmissible between species and genera. The causative agent for the disease is the hepatitis type E virus, which is a member of the Hepadnaviridae family and a single-stranded RNA virus. Its 7.2 kb genome mainly contains three open reading frames (ORFs): ORF1 encodes a non-structural polyprotein that mediates viral replication and transcription; ORF2 encodes a capsid protein and free antigen that induce neutralizing antibodies; ORF3 partially overlaps with ORF2 and encodes a small multifunctional protein involved in virion formation and release. HEV has a unique dual life cycle: it is excreted into feces in the form of naked virions but circulates in the blood in the form of "quasi-enveloped" particles. The two kinds of virus particles adsorb and penetrate the host cell in distinct ways, then internalize and decapsulate to replicate the genome, thereby producing more virion and releasing it outside the cell to mediate the virus's spread. This paper reviews the morphological characteristics, genome structure, encoded proteins, and function of HEV virus-like particles in order to provide a theoretical basis for basic research and comprehensive disease prevention and control.

The protein encoded by the duck plague virus UL14 gene regulates virion morphogenesis and affects viral replication.

To investigate the pivotal roles of the duck plague virus (DPV) tegument protein UL14 in viral replication, we generated 2 mutated viruses of DPV by using the bacterial artifcial chromosome system, the UL14-null mutant virus (CHv-BAC-ΔUL14) and the corresponding revertant virus (CHv-BAC-ΔUL14R). We found that the CHv-BAC-ΔUL14 viruses exhibited impaired virion morphogenesis in transmission electron microscopy (TEM) studies. Furthermore, CHv-BAC-ΔUL14 exhibited a plaque size reduction in duck embryo fibroblasts (DEFs). Finally, CHv-BAC-ΔUL14 exhibited a significant viral growth defect. Taken together, our findings suggest that DPV UL14 protein regulates viral morphogenesis for efficient viral replication.

A Novel Lineage of Cile-Like Viruses Discloses the Phylogenetic Continuum Across the Family Kitaviridae.

An increasing number of plant species have been recognized or considered likely reservoirs of viruses transmitted by Brevipalpus mites. A tiny fraction of these viruses, primarily those causing severe economic burden to prominent crops, have been fully characterized. In this study, based on high-throughput sequencing, transmission electron microscopy analyses of virions in plant-infected tissues, viral transmission experiments, and the morphoanatomical identification of the involved Brevipalpus mites, we describe molecular and biological features of viruses representing three new tentative species of the family Kitaviridae. The genomes of Solanum violifolium ringspot virus (SvRSV, previously partially characterized), Ligustrum chlorotic spot virus (LigCSV), and Ligustrum leprosis virus (LigLV) have five open reading frames (ORFs) > 500 nts, two distributed in RNA1 and three in RNA2. RNA1 of these three viruses display the same genomic organization found in RNA1 of typical cileviruses, while their RNA2 are shorter, possessing only orthologs of genes p61, p32, and p24. LigCSV and LigLV are more closely related to each other than to SvRSV, but the identities between their genomic RNAs were lower than 70%. In gene-by-gene comparisons, ORFs from LigCSV and LigLV had the highest sequence identity values (nt sequences: 70-76% and deduced amino acid sequences: 74-83%). The next higher identity values were with ORFs from typical cileviruses, with values below 66%. Virions of LigLV (≈ 40 nm × 55 nm) and LigCSV (≈ 54 nm × 66 nm) appear almost spherical, contrasting with the bacilliform shape of SvRSV virions (≈ 47 nm × 101 nm). Mites collected from the virus-infected plants were identified as Brevipalpus papayensis, B. tucuman, and B. obovatus. Viruliferous B. papayensis mites successfully transmitted LigCSV to Arabidopsis thaliana. SvRSV, LigCSV, and LigLV seem to represent novel sub-lineages of kitaviruses that descent on parallel evolutionary branches from a common ancestor shared with the tentative cile-like virus hibiscus yellow blotch virus and typical cileviruses. Biological and molecular data, notably, the phylogenetic reconstruction based on the RdRp proteins in which strong support for monophyly of the family Kitaviridae is observed, mark an advance in the understanding of kitavirids.

Ionic Strength-Dependent, Reversible Pleomorphism of Recombinant Newcastle Disease Virus.

A genetically modified, recombinant form of Newcastle disease virus (rNDV) undergoes ionic strength-dependent changes in morphology, as observed by cryo-electron microscopy (cEM). In hypotonic solutions with ionic strengths ranging from < 0.01 to 0.02 M, rNDV virions are spherical or predominantly spherical. In isotonic and hypertonic solutions, rNDV displays pleomorphism and contains a mixed population of spherical and elongated particles, indicating that a change from spherical to elongated shape is induced with increasing salt concentration. This ionic strength-dependent transition is largely reversible, as determined by cEM. Concomitantly, we measured infectious titers of these same rNDV samples at different ionic strengths using a fluorescent focus assay (FFA). The infectivity of oncolytic rNDV was found to be independent of ionic strength, ranging from 0.01 M to approximately 0.5 M. These structural and functional observations, in combination, suggest that infectivity (and, by inference, oncolytic activity) of rNDV virions is fully maintained in their pleomorphic forms.IMPORTANCE Oncolytic viruses are being developed for cancer therapy, as they selectively target, infect, and kill cancer cells. NDV is particularly attractive because while it is pathogenic to avians (e.g., chickens), it does not cause significant viremia in humans. We have developed a genetically modified recombinant NDV (rNDV) that has much reduced pathogenicity in chickens but is highly oncolytic. The morphology of rNDV transitions from spherical at very low salt concentrations to a heterogeneous population of spherical and elongated virions in isotonic (physiologic salt concentration) and hypertonic solutions. The infectivity (cell-killing activity by infecting cells) of rNDV is unaltered by changes in salt concentration despite morphological changes. These observations are significant for purification and formulation of rNDV, as exposure to different salt concentrations may be needed. Importantly, at physiological salt concentration, relevant to clinical testing, infectivity and, therefore, oncolytic activity will not be compromised despite morphological heterogeneity.

Genomic, Morphological and Biological Traits of the Viruses Infecting Major Fruit Trees.

Banana trees, citrus fruit trees, pome fruit trees, grapevines, mango trees, and stone fruit trees are major fruit trees cultured worldwide and correspond to nearly 90% of the global production of woody fruit trees. In light of the above, the present manuscript summarizes the viruses that infect the major fruit trees, including their taxonomy and morphology, and highlights selected viruses that significantly affect fruit production, including their genomic and biological features. The results showed that a total of 163 viruses, belonging to 45 genera classified into 23 families have been reported to infect the major woody fruit trees. It is clear that there is higher accumulation of viruses in grapevine (80/163) compared to the other fruit trees (each corresponding to less than 35/163), while only one virus species has been reported infecting mango. Most of the viruses (over 70%) infecting woody fruit trees are positive-sense single-stranded RNA (+ssRNA), and the remainder belong to the -ssRNA, ssRNA-RT, dsRNA, ssDNA and dsDNA-RT groups (each corresponding to less than 8%). Most of the viruses are icosahedral or isometric (79/163), and their diameter ranges from 16 to 80 nm with the majority being 25-30 nm. Cross-infection has occurred in a high frequency among pome and stone fruit trees, whereas no or little cross-infection has occurred among banana, citrus and grapevine. The viruses infecting woody fruit trees are mostly transmitted by vegetative propagation, grafting, and root grafting in orchards and are usually vectored by mealybug, soft scale, aphids, mites or thrips. These viruses cause adverse effects in their fruit tree hosts, inducing a wide range of symptoms and significant damage, such as reduced yield, quality, vigor and longevity.