Abstract
Fusariviridae is a family of mono-segmented, positive-sense RNA viruses with genome sizes of 5.9–10.7 kb. Most genomic RNAs are bicistronic, but exceptions have up to four predicted ORFs. In bicistronic genomes, the 5′-proximal ORF codes for a single protein with both RNA-directed RNA polymerase (RdRP) and RNA helicase (Hel) domains; little is known about the protein encoded by the second ORF. Fusarivirids do not appear to form virions. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Fusariviridae, which is available at ictv.global/report/fusariviridae.
Keywords: Fusariviridae, ICTV Report, Taxonomy
Virion
No true virions are associated with fusarivirids (Table 1).
Table 1. Characteristics of members of the family Fusariviridae.
| Example: | Fusarium graminearum dsRNA mycovirus 1 (AY533037), species Alphafusarivirus fusarii, genus Alphafusarivirus |
| Virion | Thought to be capsidless since no virions can be purified on a sucrose density gradient |
| Genome | 5.9–10.7 kb mono-segmented, positive-sense RNA |
| Replication | Unknown |
| Translation | For Fusarium graminearum dsRNA mycovirus 1, expression of downstream ORFs is from subgenomic RNAs. There is no evidence for such molecules for Rosellinia necatrix fusarivirus 1 |
| Host range | Experimentally confirmed hosts are members of the kingdom Fungi and in one case a confirmed stramenopiles oomycetes host |
| Taxonomy | Realm Riboviria, kingdom Orthornavirae, phylum Pisuviricota, class Duploviricetes, order Durnavirales: several genera and >30 species |
Genome
Fusarivirids can be monocistronic (Lentinula edodes fusarivirus 1) [1], bicistronic (Rosellinia necatrix fusarivirus 1) [2], tricistronic (Pleospora tiphycola fusarivirus 1) [3] or quadricistronic (Rhizoctonia solani fusarivirus 1) [4] (Fig. 1). The largest ORF always codes for a single protein with both RNA-directed RNA polymerase (RdRP) and RNA helicase (Hel) domains. The second ORF encodes a protein that contains a motif from a structural maintenance of chromosomes (SMC) protein (PDB entry code: 6YUF) [5,6]. Accessory ORFs are often genus-specific. In the largest quadricistronic fusarivirids a second helicase domain is also present [7].
Fig. 1. Genome organisation of representative fusariviruses. RdRP, RNA-directed RNA polymerase domain, Hel, Helicase domain, SMC, structural maintenance of chromosomes domain.
Replication
During replication, the abundant replicative form of dsRNA accumulates intracellularly.
Pathogenicity
A comparison of colony morphology between virus-free and virus-infected isogenic strains suggests that infections of Rosellinia necatrix with Rosellinia necatrix fusarivirus 1 is asymptomatic and does not cause hypovirulence on apple rootstocks [2]. Lack of symptoms has also been observed for Sclerotinia sclerotiorum fusarivirus 1 [8]. Fusarium graminearum virus 1 strain SD4 causes hypovirulence and eliminates deoxynivalenol synthesis in Fusarium graminearum [9].
Taxonomy
Current taxonomy: ictv.global/taxonomy. The family Fusariviridae (Fig. 2) is included in the pisuviricot class Duploviricetes, order Durnavirales, together with a number of families mostly with dsRNA genomes, with the exception of the most closely related family (Hypoviridae), members of which have a ssRNA genome [2,10].
Fig. 2. Phylogenetic analysis of fusarivirus RdRP protein sequences. Numbers at nodes indicated percentage bootstrap support. For details of viruses and methods see full Fusariviridae ICTV Report.
Resources
Full ICTV Report on the family Fusariviridae: http://www.ictv.global/report/xxxxhttp://www.ictv.global/report/fusariviridae.
Acknowledgements
We thank Evelien Adriaenssens, Holly Hughes, Elliot J. Lefkowitz, Sead Sabanadzovic, Peter Simmonds, Dann Turner, F. Murilo Zerbini, Luisa Rubino, Arvind Varsani (ICTV Report Editors) and Donald B. Smith (Managing Editor, ICTV Report).
Abbreviations
- Hel
RNA helicase
- RdRP
RNA-directed RNA polymerase
- SMC
a structural maintenance of chromosomes protein
Footnotes
Funding: Production of this Profile, the ICTV Report, and associated resources was supported by the Microbiology Society.
Contributor Information
Sotaro Chiba, Email: chiba@nuagr1.agr.nagoya-u.ac.jp.
Nobuhiro Suzuki, Email: nsuzuki@okayama-u.ac.jp.
Leonardo Velasco, Email: leonardo.velasco@juntadeandalucia.es.
María A. Ayllón, Email: mariaangeles.ayllon@upm.es.
Shin-Yi Lee-Marzano, Email: ShinYi.Marzano@usda.gov.
Liying Sun, Email: sunliying@nwafu.edu.cn.
Sead Sabanadzovic, Email: ssabanadzovic@entomology.msstate.edu.
Massimo Turina, Email: massimo.turina@ipsp.cnr.it.
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