# ICTV Virus Taxonomy Profile: Spinareoviridae 2022

Jelle Matthijnssens, Houssam Attoui, Krisztián Bányai, Corina P D Brussaard, Pranav Danthi, Mariana del Vas, Terence S Dermody, Roy Duncan, Qín Fāng, Reimar Johne, et al.

► To cite this version:

Jelle Matthijnssens, Houssam Attoui, Krisztián Bányai, Corina P D Brussaard, Pranav Danthi, et al. ICTV Virus Taxonomy Profile: Spinareoviridae 2022. Journal of General Virology, 2022, 103, 10.1099/jgv.0.001781. hal-04356109

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# ICTV Virus Taxonomy Profile: Spinareoviridae 2022

Jelle Matthijnssens¹*, Houssam Attoui², Krisztián Bányai³, Corina P. D. Brussaard⁴, Pranav Danthi⁵, Mariana del Vas⁶, Terence S. Dermody⁷, Roy Duncan⁸, Qín Fāng (方勤)⁹, Reimar Johne¹⁰, Peter P. C. Mertens¹¹, Fauziah Mohd Jaafar¹², John T. Patton⁵, Takahide Sasaya (笹谷孝英)¹³, Nobuhiro Suzuki (鈴木信弘)¹⁴, Taiyun Wei (魏太云)¹⁵ and ICTV Report Consortium

## Abstract

Spinareoviridae is a large family of icosahedral viruses that are usually regarded as non-enveloped with segmented (9–12 linear segments) dsRNA genomes of 23–29 kbp. Spinareovirids have a broad host range, infecting animals, fungi and plants. Some have important pathogenic potential for humans (e.g. Colorado tick fever virus), livestock (e.g. avian orthoreoviruses), fish (e.g. aquaréviruses) and plants (e.g. rice ragged stunt virus and rice black streaked dwarf virus). This is a summary of the ICTV Report on the family Spinareoviridae, which is available at ictv.global/report/spinareoviridae.

<table><caption>**Table 1.** Characteristics of members of the family Spinareoviridae</caption><tr><td>Example:</td><td>mammalian orthoreovirus-3 Dearing (T3D; HM159613-22), species Mammalian orthoreovirus, genus Orthoreovirus</td></tr><tr><td>Virion</td><td>Non-enveloped, icosahedral, 60–85 nm virions composed of 1–3 concentric capsid protein layers</td></tr><tr><td>Genome</td><td>23–29 kbp of segmented linear dsRNA, with each of the 9–12 segments ranging from 0.5 to 4.8 kbp</td></tr><tr><td>Replication</td><td>Replication occurs in the cytoplasm in electron-dense structures called viroplasms, viral inclusions or viral factories</td></tr><tr><td>Translation</td><td>From full-length transcribed mRNAs that possess a 5'-terminal cap but no poly(A)-tail</td></tr><tr><td>Host range</td><td>Mammals, aquatic animals (fish, mammals, crustaceans, molluscs), birds, reptiles, arthropods, fungi and plants</td></tr><tr><td>Taxonomy</td><td>Realm Riboviria, kingdom Orthornavirae, phylum Duplornaviricota, class Resentoviricetes, order Reovirales: >8 genera and >55 species</td></tr></table>

## VIRION

Spinareovirid particles are icosahedral (Table 1). The protein capsid is organized as 1–3 concentric layers of capsid proteins, with an overall diameter of 50–85 nm [1]. Members of the family Spinareoviridae have spikes or turrets at the 12 icosahedral vertices of the subviral particle (Fig. 1), in contrast to members of the family Sedoreoviridae, which have an almost spherical or ‘smooth’ appearance.

## GENOME

Spinareovirids contain 9–12 segments of linear dsRNA comprising 23–29 kbp in total, with individual segments ranging from 0.5 to 4.8 kbp. The positive-sense strands of each duplex are modified with a 5'-terminal type 1 cap structure but no 3'-poly(A) tail. The viral RNAs are mostly monocistronic with relatively short 5'- and 3'-non-coding regions, although some segments have a second or third functional ORF [2, 3].

Received 15 June 2022; Accepted 20 June 2022; Published 17 November 2022

**Author affiliations:** ¹University of Leuven, Leuven, Belgium; ²National Institute for Agricultural Research (INRA), Maisons Alfort, France; ³Veterinary Medical Research Institute, Budapest, H-1143, Hungary; ⁴NIOZ Royal Netherlands Institute for Sea Research & University of Utrecht, Texel, The Netherlands; ⁵Indiana University, Bloomington, USA; ⁶Instituto de Agrobiotecnología y Biología Molecular (IABIMO), Buenos Aires, Argentina; ⁷University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA; ⁸Dalhousie University, Halifax, Nova Scotia, Canada; ⁹Wuhan Institute of Virology, Wuhan, PR China; ¹⁰German Federal Institute for Risk Assessment, Berlin, Germany; ¹¹University of Nottingham, Leicestershire, UK; ¹²Ecole Nationale Vétérinaire d'Alfort, Maisons Alfort, France; ¹³National Agriculture and Food Research Organization, Fukuyama, Japan; ¹⁴Okayama University, Kurashiki, Japan; ¹⁵Fujian Agriculture and Forestry University, Fuzhou, PR China.

*Correspondence: Jelle Matthijnssens, jelle.matthijnssens@kuleuven.be

Keywords: ICTV report; taxonomy; Spinareoviridae; Reovirales.

001781 © 2022 The Authors

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<figure><img src="image_6.png" /><figcaption>**Fig. 1.** Spinareovirid particle structure coloured according to functional similarity (blue – core shell, green – middle layer, yellow – outer capsid, purple – RNA capping, red – membrane penetration, orange – receptor binding) (shown schematically). (a) Subviral particle. (b) Virion. The diameter of the mature virion is approximately 80 nm (excluding spikes). Adapted from [7].</figcaption></figure>

## REPLICATION

Virus entry into cells varies between genera but usually results in loss of outer-capsid components. The resulting transcriptionally active particles are released into the cytoplasm. The 5'-capped mRNAs are synthesized by structural enzymatic components of the viral particle and released into the cytoplasm through pores

<figure><img src="image_7.png" /><figcaption>**Fig. 2.** Spinareovirus phylogeny based on RNA-directed RNA polymerase amino acid sequences. For details see online Report.</figcaption></figure>

## References

1. Jaafar FM, Attoui H, Mertens PPC, de Micco P, de Lamballerie X. Structural organization of an encephalitic human isolate of Banna virus (genus *Seadornavirus*, family *Reoviridae*). *J Gen Virol* 2005;86:1147–1157.

2. Marzachi C, Boccardo G, Milne R, Isogai M, Uyeda I. (eds). Genome structure and variability of Fijiviruses. In: *Semin Virol*. Elsevier; 1995.

3. Yang Y, Gaspard G, McMullen N, Duncan R. Polycistronic genome segment evolution and gain and loss of FAST protein function during fusogenic orthoreovirus speciation. *Viruses* 2020;12:E702.

at the five-fold icosahedral vertices of the virion. Viral inclu- sions, also known as viral factories, are distributed throughout the cytoplasm. These neo-organelles are sites of viral mRNA synthesis, genome replication and particle assembly [4]. Sets of a single copy of each capped mRNA are incorporated into progeny virus particles [5]. These mRNAs serve as templates for negative-strand synthesis, thereby reconstituting genomic encapsidated dsRNAs. Progeny virions are released without compromising cell viability (e.g. budding) or following cell lysis, depending on the cell type [6].

## TAXONOMY

Current taxonomy: [ictv.global/taxonomy](https://www.icтов global/taxonomy). The family *Spinareoviridae* includes multiple genera (Fig. 2) and >55 species of viruses infecting mammals, aquatic animals (fish, mammals, crustaceans, molluscs), birds, reptiles, arthropods, fungi and plants. The number of genome segments (9–12) is character- istic of viruses within a single genus, although members of the genus *Mycoreovirus* can have either 11 or 12 segments. Other factors distinguishing different genera are host (and vector) range, disease signs and capsid structure. The amino acid sequence of the relatively conserved RNA-directed RNA polymerase can be used for comparison across taxonomic boundaries. Among members of a species, protein and RNA sequences are relatively conserved, being serologically cross- reactive and including specific RNA packaging signals. This high degree of functional and structural compatibility allows viable progeny virus strains to be generated by reassortment between viruses of the same species.

## RESOURCES

Full ICTV Report on the family *Spinareoviridae*: [ictv.global/report/spinareoviridae](https://www.icтов global/report/spinareoviridae)

### Funding information

Production of this summary, the online chapter and associated resources, was supported by the Microbiology Society.

### Acknowledgements

Members of the ICTV (10th) Report Consortium are Stuart G. Siddell, Elliot J. Lefkowitz, Sead Sabanadzovic, Peter Simmonds, F. Murilo Zerbini, Donald B. Smith and Jens H. Kuhn.

### Conflicts of interest

The authors declare that there are no conflicts of interest.

4. Boehme KW, Ikizler M, Kobayashi T, Dermody TS. Reverse genetics for mammalian reovirus. *Methods* 2011;55:109–113.

5. Borodavka A, Desselberger U, Patton JT. Genome packaging in multi-segmented dsRNA viruses: distinct mechanisms with similar outcomes. *Curr Opin Virol* 2018;33:106–112.

6. Roth AN, Aravamudhan P, Fernández de Castro I, Tenorio R, Risco C, et al. Ins and outs of reovirus: vesicular trafficking in viral entry and egress. *Trends Microbiol* 2021;29:363–375.

7. Trask SD, McDonald SM, Patton JT. Structural insights into the coupling of virion assembly and rotavirus replication. *Nat Rev Microbiol* 2012;10:165–177.