Plant Viruses with Rod‐Shaped Virions


Plant viruses that form rigid, rod‐shaped particles are found in eight genera. All of these viruses have single‐stranded ribonucleic acid (RNA) genomes that, with one exception, are positive‐sense. Most plant viruses with rod‐shaped particles are found in the six genera that form the Virgaviridae family with approximately half of all the definitive species in the Tobamovirus genus. The virus particles are formed from single structural proteins that encapsidate the genomic RNAs in nonenveloped, helical arrays. Despite their morphological similarities these viruses have diverse molecular and biological properties. While the tobamoviruses have nonsegmented genomes and are mechanically transmitted, the other viruses have segmented genomes and are transmitted by a variety of mechanisms: seed transmission, nematode vectors and plasmodiophorid vectors. Many of the viruses are important disease agents of crop species.

Key Concepts:

  • Aside from the anomalous Varicosavirus genus, all viruses with rod‐shaped virions are single‐stranded, positive‐sense ribonucleic acid (RNA) viruses that replicate in the cytoplasm of host plant cells.

  • The rod‐shaped virions are formed from helical arrays of a single form of coat protein subunit and their length is dependent on the size of the encapsidated RNAs.

  • Apart from species within the Tobamovirus genus, all viruses with rod‐shaped virions have segmented genomes divided between multiple RNAs.

  • The plant viruses with rod‐shaped virions use a variety of mechanisms to translate the multiple open reading frames in their genomes, including leaky‐readthrough translation, the use of 3′ coterminal subgenomic RNAs and leaky‐initiation of translation by scanning ribosomes.

  • The intercellular movement of these viruses within host plants is achieved through the use of a single Tobacco mosaic virus‐like movement protein or a ‘triple gene block’ of movement proteins.

  • The principle mechanism of transmission for all species within a genus varies between genera: the species within four genera are primarily plasmodiophorid transmitted, whereas those in three other genera are primarily mechanically transmitted, seed transmitted or nematode transmitted.

  • All the genera containing viruses with rod‐shaped virions include species that cause economically important diseases that are controlled through the use of virus‐free seed/vegetative stocks, good sanitary practices and resistant crop cultivars.

Keywords: Virgaviridae; Tobamovirus; Tobravirus; Hordeivirus; soil‐borne viruses; plasmodiophorid‐transmitted viruses

Figure 1.

Electron micrograph of Tobacco rattle virus particles showing central ‘canal’. Bar represents 50 nm.

Figure 2.

Arrangement of open reading frames (ORFs) in the genome of a representative member of each of the genera of plant viruses with rod‐shaped virions: (a) Tobacco mosaic virus (genus Tobamovirus); (b) Barley stripe mosaic virus (genus Hordeivirus); (c) Tobacco rattle virus (genus Tobravirus); (d) Soil‐borne wheat mosaic virus (genus Furovirus); (e) Potato mop‐top virus (genus Pomovirus); (f) Peanut clump virus (genus Pecluvirus) and (g) Beet necrotic yellow vein virus (genus Benyvirus). The functions of the ORF products are indicated as follows: red, genes for replication‐associated proteins; blue, genes for proteins involved in virus cell‐to‐cell movement; green, virus coat protein genes; grey, genes for proteins probably involved in transmission by vectors; yellow, genes for proteins that act as pathogenicity factors and silencing suppressors. Leaky termination codons where translational readthrough occurs are marked with an arrow.



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Further Reading

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Reddy DVR, Bragard C, Sreenivasulu P and Delfosse P (2008) Pecluvirus. In: Mahy BWJ and van Regenmortel MHV (eds) Encyclopedia of Virology (Third Edition), vol. 4, pp. 291–296. Oxford: Academic Press.

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Torrance L (2008) Pomovirus. In: Mahy BWJ and van Regenmortel MHV (eds) Encyclopedia of Virology (Third Edition), vol. 4, pp. 282–287. Oxford: Academic Press.

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Chapman, Sean N(Mar 2013) Plant Viruses with Rod‐Shaped Virions. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000753.pub3]