The emerging key features of latency in tobamoviruses

Abstract text (incl. figure legends and references)

Introduction

Tobacco mosaic virus (TMV), the first plant virus imaged in electron microscopy, is the type member of the genus Tobamovirus, family Virgaviridae.

Typically, tobamoviruses cause systemic infections with severe symptoms on the host leading to major yield loss. For new emerging and highly virulent members such as the tomato brown rugose fruit virus infecting tomato quarantine measures, apply.

The diseased phenotype can consist of mosaic patterns, leaf mottling and/or deformations in early infection stages that develop to reduced growth and necrosis in new emerging leaves. All diseased tissues are associated with major disruptions and reorganizations in their ultrastructure.

The tropical plant Hoya ssp. is susceptible to both virulent as well as latent tobamoviruses. Hoya tobamovirus 2 (HoTV-2 ) has been isolated from asymptomatic hoya plants (Gaafar et al., 2020) and serves as model system to investigate the ultrastructure of latent, asymptomatic tobamovirus infections.

Objectives

Analysis of serological relationship of HoTV-2 with other tobamoviruses Identification of cellular features during latent (HoTV-2) compared to virulent (TMV) tobamovirus infections. Characterization of viral interferences in mixed infections comprising HoTV-2 and TMV Analyses of cellular ultrastructure in compatible and resistant tobacco species Identification of HoTV-2 virions and viral RNA respectively in associated compartments of infected cells using IEM

Material and Methods

HoTV-2 was isolated from infected hoya plants using a bioassay. Therefore, healthy Nicotiana ssp. were mechanically inoculated with HoTV-2 infected hoya leaves. Negative stain and ISEM were used for virus detection in plant sap homogenates (Richert-Pöggeler et al., 2018; Gaafar et al., 2020). Embedding and generation of ultrathin sections were performed as described in (Erokhina et al., 2017).

Results

HoTV-2 is serological cross-reacting with Youcai mosaic virus (YoMV) antiserum (DSMZ, Germany) but not with other tested tobamoviruses. Whereas phenotypically no differences of systemic HoTV-2 infections are visible when the virus is transmitted among asterid hosts from its primary host (Apocynyceae, Gentianales) to susceptible Nicotiana ssp. (Solanaceae, Solanales), the cellular ultrastructure indicates differences in viral replication. Only in Solanales virus particles were detected. The number of virions was significantly reduced in latent (HoTV-2) compared to virulent (TMV) tobamovirus infections. YoMV antiserum can be used in IEM, but lacks specificty for efficient immunogold labeling.

Conclusions

Ultrastructural analysis provided evidence that the asymptomatic phenotype is associated with reduced viral replication.

References

Erokhina, T. N., Lazareva, E. A., Richert-Pöggeler, K. R., Sheval, E. V., Solovyev, A. G., and Morozov, S. Y. (2017). Subcellular Localization and Detection of Tobacco mosaic virus ORF6 Protein by Immunoelectron Microscopy. Biochemistry (Mosc) 82, 60–66. doi: 10.1134/S0006297917010060

Gaafar, Y., Richert-Pöggeler, K. R., Hartrick, J., Lüddecke, P., Maaß, C., Schuhmann, S., et al. (2020). A new tobamovirus infecting Hoya spp. New Dis. Rep. 42, 10. doi: 10.5197/j.2044-0588.2020.042.010

Richert-Pöggeler, K. R., Franzke, K., Hipp, K., and Kleespies, R. G. (2018). Electron Microscopy Methods for Virus Diagnosis and High Resolution Analysis of Viruses. Front Microbiol 9, 3255. doi: 10.3389/fmicb.2018.03255