The Tombusviridae is a relatively large and diverse family of plant viruses that have small single‐stranded, positive‐sense, RNA (ribonucleic acid) genomes which have been grouped together owing to the high degree of sequence identity displayed by their RNA‐dependent RNA polymerases. Tombusvirid virion structures, gene expression strategies, replication, RNA recombination, virus movement and the support of satellite viruses/defective‐interfering RNAs have been particularly well characterised. All genera (with the exception of the Umbraviruses) produce spherical virions with capsid proteins that can be subdivided by the presence (or absence) of a C‐terminal protruding domain. Transmission of several members by fungal zoospores in a species‐specific manner has been reported while aphid transmission of Umbraviruses is completely dependent on a helper virus from the Luteoviridae. The virions of several members have been utilised for biotechnology purposes.

Key Concepts

  • Various genera most likely arose through RNA recombination.
  • Tombusviridae species replicate to high titres within their host cells.
  • RNA genomes are small with a limited number of gene products that serve multiple functions.
  • RNA–RNA interactions control gene expression in several genera.
  • Viral‐encoded suppressors of RNA silencing act at several different stages in the response cascade.
  • Virions (if present) are non‐enveloped and extremely stable.
  • Several members are transmitted through soil by specific fungal zoospores.

Keywords: RNA plant viruses; virus structure; satellites; soil and fungus transmission; gene expression strategies; RNA–RNA interactions

Figure 1. Genomic organisation of type members from each genus of the family Tombusviridae. Virus abbreviations are those from Table. Boxes represent known and predicted open reading frames with the sizes of the respective proteins (or readthrough products) indicated above or below. Colours indicate both protein function and extensive amino acid sequence conservation (with the exception of Other Functions; see legend). RT, translational readthrough of termination codon and −1 FS, −1 ribosomal frameshifting event.
Figure 2. Electron micrograph of Red clover necrotic mosaic virus particles. Copyright Tim L. Sit and Steven A. Lommel.
Figure 3. Structure and organisation of the tomato bushy stunt virus particle. (a) Three‐dimensional arrangement of the capsid protein (CP) domains. (b) Linear arrangement. The number of amino acid residues is indicated below each domain. R, RNA‐binding domain; a, arm region; S, shell domain; h, hinge sequence and P, protruding domain. (c) Spatial arrangement of the CP subunits within the virus particle. A conformation, red; B conformation, blue and C conformation, green. Reproduced with permission from S. C. Harrison, A. J. Olson, C. E. Schutt, F. K. Winkler, G. Bricogne (1978),Tomato bushy stunt virus at 2.9 Å resolution, Nature, vol 276, Issue 5686 © Nature Publishing Group.


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Further Reading

Lee KK and Johnson JE (2003) Complementary approaches to structure determination of icosahedral viruses. Current Opinion in Structural Biology 13: 558–569.

Nagy PD, Pogany J and Lin JY (2014) How yeast can be used as a genetic platform to explore virus‐host interactions: from 'omics' to functional studies. Trends in Microbiology 22: 309–316.

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Taliansky ME and Robinson DJ (2003) Molecular biology of umbraviruses: phantom warriors. Journal of General Virology 84: 1951–1960.

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Sit, Tim L, and Lommel, Steven A(Nov 2015) Tombusviridae. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000756.pub3]