An induced hypersensitive-like response limits expression of foreign peptides via a recombinant TMV-based vector in a susceptible tobacco

Practical use of tobravirus-based vector to produce SARS-CoV-2 antigens in plants

A plant-based heterologous expression system is an attractive option for recombinant protein production because it is based on a eukaryotic system of high feasibility, and low biological risks. Frequently, binary vector systems are used for transient gene-expression in plants. However, plant virus vector-based systems offer advantages for higher protein yields due to their self-replicating machinery. In the present study, we show an efficient protocol using a plant virus vector based on a tobravirus, pepper ringspot virus, that was employed for transient expression of severe acute respiratory syndrome coronavirus 2 partial gene fragments of the spike (named S1-N) and the nucleocapsid (named N) proteins in Nicotiana benthamiana plants. Purified proteins yield of 40~60µg/g of fresh leaves were obtained. Both proteins, S1-N and N, showed high and specific reactivities against convalescent patients' sera by the enzyme-linked immunosorbent assay format. The advantages and critical points in using this plant virus vector are discussed. DATA AVAILABILITY: All data generated and analyzed during this study are included in this published article and supporting materials.

Non-structural Functions of Hordeivirus Capsid Protein Identified in Plants Infected by a Chimeric Tobamovirus

Capsid proteins (CPs) of (+)RNA-containing plant viruses are multifunctional proteins involved in many stages of viral infection cycle, in addition to their main function of virus capsid formation. For example, the tobamoviral CP ensures virus systemic transport in plants and defines the virus-host interactions, thereby influencing the virus host range, virus infectivity, pathogenicity, and manifestation of infection symptoms. Hordeiviruses and tobamoviruses belong to the Virgaviridae family and have rod-shaped virions with a helical symmetry; their CPs are similar in structure. However, no non-structural functions of hordeiviral CPs have been described so far. In this study, we assayed possible non-structural functions of CP from the barley stripe mosaic virus (BSMV) (hordeivirus). To do this, the genome of turnip vein clearing virus (TVCV) (tobamovirus) was modified by substituting the TVCV CP gene with the BSMV CP gene or its mutants. We found that BSMV CP efficiently replaced TVCV CP at all stages of viral infection. In particular, BSMV CP performed the role of tobamoviral CP in the long-distance transport of the chimeric virus, acted as a hypersensitive response elicitor, and served as a pathogenicity determinant that influenced the symptoms of the viral infection. The chimeric tobamovirus coding for the C-terminally truncated BSMV CP displayed an increased infectivity and was transported in plants in a form of atypical virions (ribonucleoprotein complexes).

Citrus leprosis virus C Infection Results in Hypersensitive-Like Response, Suppression of the JA/ET Plant Defense Pathway and Promotion of the Colonization of Its Mite Vector

Leprosis is a serious disease of citrus caused by Citrus leprosis virus C (CiLV-C, genus Cilevirus) whose transmission is mediated by false spider mites of the genus Brevipalpus. CiLV-C infection does not systemically spread in any of its known host plants, thus remaining restricted to local lesions around the feeding sites of viruliferous mites. To get insight into this unusual pathosystem, we evaluated the expression profiles of genes involved in defense mechanisms of Arabidopsis thaliana and Citrus sinensis upon infestation with non-viruliferous and viruliferous mites by using reverse-transcription qPCR. These results were analyzed together with the production of reactive oxygen species (ROS) and the appearance of dead cells as assessed by histochemical assays. After interaction with non-viruliferous mites, plants locally accumulated ROS and triggered the salicylic acid (SA) and jasmonate/ethylene (JA/ET) pathways. ERF branch of the JA/ET pathways was highly activated. In contrast, JA pathway genes were markedly suppressed upon the CiLV-C infection mediated by viruliferous mites. Viral infection also intensified the ROS burst and cell death, and enhanced the expression of genes involved in the RNA silencing mechanism and SA pathway. After 13 days of infestation of two sets of Arabidopsis plants with non-viruliferous and viruliferous mites, the number of mites in the CiLV-C infected Arabidopsis plants was significantly higher than in those infested with the non-viruliferous ones. Oviposition of the viruliferous mites occurred preferentially in the CiLV-C infected leaves. Based on these results, we postulated the first model of plant/Brevipalpus mite/cilevirus interaction in which cells surrounding the feeding sites of viruliferous mites typify the outcome of a hypersensitive-like response, whereas viral infection induces changes in the behavior of its vector.

Structure and Noncanonical Activities of Coat Proteins of Helical Plant Viruses

The main function of virus coat protein is formation of the capsid that protects the virus genome against degradation. However, besides the structural function, coat proteins have many additional important activities in the infection cycle of the virus and in the defense response of host plants to viral infection. This review focuses on noncanonical functions of coat proteins of helical RNA-containing plant viruses with positive genome polarity. Analysis of data on the structural organization of coat proteins of helical viruses has demonstrated that the presence of intrinsically disordered regions within the protein structure plays an important role in implementation of nonstructural functions and largely determines the multifunctionality of coat proteins.

Presentation of peptides from Bacillus anthracis protective antigen on Tobacco Mosaic Virus as an epitope targeted anthrax vaccine

The current anthrax vaccine requires improvements for rapidly invoking longer-lasting neutralizing antibody responses with fewer doses from a well-defined formulation. Designing antigens that target neutralizing antibody epitopes of anthrax protective antigen, a component of anthrax toxin, may offer a solution for achieving a vaccine that can induce strong and long lasting antibody responses with fewer boosters. Here we report implementation of a strategy for developing epitope focused virus nanoparticle vaccines against anthrax by using immunogenic virus particles to present peptides derived from anthrax toxin previously identified in (1) neutralizing antibody epitope mapping studies, (2) toxin crystal structure analyses to identify functional regions, and (3) toxin mutational analyses. We successfully expressed two of three peptide epitopes from anthrax toxin that, in previous reports, bound antibodies that were partially neutralizing against toxin activity, discovered cross-reactivity between vaccine constructs and toxin specific antibodies raised in goats against native toxin and showed that antibodies induced by our vaccine constructs also cross-react with native toxin. While protection against intoxication in cellular and animal studies were not as effective as in previous studies, partial toxin neutralization was observed in animals, demonstrating the feasibility of using plant-virus nanoparticles as a platform for epitope defined anthrax vaccines.

Engineered Tobacco mosaic virus mutants with distinct physical characteristics in planta and enhanced metallization properties

Tobacco mosaic virus mutants were engineered to alter either the stability or surface chemistry of the virion: within the coat protein, glutamic acid was exchanged for glutamine in a buried portion to enhance the inter-subunit binding stability (E50Q), or a hexahistidine tract was fused to the surface-exposed carboxy terminus of the coat protein (6xHis). Both mutant viruses were expected to possess specific metal ion affinities. They accumulated to high titers in plants, induced distinct phenotypes, and their physical properties during purification differed from each other and from wild type (wt) virus. Whereas 6xHis and wt virions contained RNA, the majority of E50Q protein assembled essentially without RNA into rods which frequently exceeded 2 μm in length. Electroless deposition of nickel metallized the outer surface of 6xHis virions, but the central channel of E50Q rods, with significantly more nanowires of increased length in comparison to those formed in wtTMV.