Abstract
The family Botourmiaviridae includes viruses with a mono- or multi-segmented positive-sense RNA genome that infect plants and filamentous fungi. The family includes the genera Ourmiavirus (plant viruses), Botoulivirus, Betabotoulivirus, Magoulivirus, Scleroulivirus, Betascleroulivirus, Gammascleroulivirus, Deltascleroulivirus, Epsilonscleroulivirus, Penoulivirus, Rhizoulivirus and Betarhizoulivirus (fungal viruses). This summary is based on the International Committee on Taxonomy of Viruses (ICTV) Report on the family Botourmiaviridae, which is available at ictv.global/report/botourmiaviridae.
Keywords: Botourmiaviridae, ICTV report, taxonomy
Virion
Members of the genus Ourmiavirus are plant viruses with non-enveloped bacilliform virions composed of a single 23.8 kDa coat protein. Electron microscopy reveals particles with conical ends (apparently hemi-icosahedral) and cylindrical bodies that are 18 nm in diameter (Table 1, Fig. 1). Most particles consist of two discs (giving a particle length of 30 nm), while others have three (37 nm) or, more rarely, four (45.5 nm) or six discs (62 nm). Members of other genera are non-encapsidated mycoviruses.
Table 1. Characteristics of members of the family Botourmiaviridae.
| Example | Ourmia melon virus VE9 (RNA1: EU770623; RNA2: EU770624; RNA3: EU770625), species Ourmia melon virus, genus Ourmiavirus |
|---|---|
| Virion | Bacilliform (18×30–62 nm) with a 23.8 kDa CP (Ourmiavirus) or non-encapsidated (members of other genera) |
| Genome | Positive-sense, mono-segmented RNA of approximately 2–5 kb (members of 11 genera) or tri-segmented RNA genome of 2.8, 1.1 and 0.97 kb (Ourmiavirus) |
| Replication | Cytoplasmic; virion assembly is coupled to active replication (Ourmiavirus) |
| Translation | From genomic RNA; each genomic segment is monocistronic |
| Host range | Plants (Ourmiavirus only) and fungi |
| Taxonomy | Realm Riboviria, kingdom Orthornavirae, phylum Lenarviricota, class Miaviricetes, order Ourlivirales, family Botourmiaviridae; >10 genera with >150 species |
Fig. 1. Virion morphology. Negative-contrast electron micrograph (uranyl acetate) of purified particles of Ourmia melon virus (bar, 100 nm).
Genome
The genome of ourmiaviruses consists of three segments of positive-sense RNA (2814, 1064 and 974 nt for Ourmia melon virus) [1], encoding an RNA-directed RNA polymerase (RdRP, 97.5 kDa; RNA1), a movement protein (MP, 31.6 kDa; RNA2) and a coat protein (CP, 23.8 kDa; RNA3) (Fig. 2) [2]. Members of genera other than Ourmiavirus have a single genome segment of 1671–5234 nt encoding an RdRP [3,5]. Unlike other members of the family, the genomes of the magoulivirus, Magnaporthe oryzae ourmia-like virus 1; the scleroulivirus, Magnaporthe oryzae botourmiavirus 9 and the gammascleroulivirus, Magnaporthe oryzae botourmiavirus 6 are polyadenylated at the 3′-end [6,7].
Fig. 2. Genome organization of representative isolates of the family Botourmiaviridae.
Replication
Ourmiavirus replication is dependent on the viral RdRP. The synthesis of the ourmiavirus CP from actively replicating RNA3 is necessary for both virion assembly and systemic infection of the host [2]. The ourmiavirus MP determines symptoms and forms tubular structures involved in cell-to-cell movement [8] and may undergo post-translational modification. Replication of mycoviruses (genera other than Ourmiavirus) is strictly dependent on the virus RdRP.
Pathogenicity
Members of the genus Ourmiavirus infect plants; Ourmia melon virus infects melon, producing chlorotic spots and irregular ringspots [9]; Epirus cherry virus produces rasp-leaf symptoms in cherry and cassava virus C induces severe stunting and a yellow mosaic pattern in cassava. Members of the other genera infect fungi; their previously reported association with oomycetes [10] is unlikely since their presence has not been confirmed in isolates of vast collections of cultivable oomycetes.
Taxonomy
Current taxonomy: www.ictv.global/taxonomy. Ourmiaviruses are clearly separated from members of the other genera based on their host and the number of genomic segments. For other botourmiaviruses, members of different genera are <70% identical in their complete RdRP amino acid sequences. Binomial names for all species will be introduced next year.
Resources
Full ICTV Report on the family Botourmiaviridae: ictv.global/report/botourmiaviridae.
Acknowledgements
We thank Evelien Adriaenssens, Luisa Rubino, ICTV Report Editors and Donald B. Smith (Managing Editor, ICTV Report).
Abbreviations
- CP
coat protein
- ICTV
International Committee on Taxonomy of Viruses
- MP
movement protein
- RdRP
RNA-directed RNA polymerase
Footnotes
Funding: Production of this Profile, the ICTV Report, and associated resources was supported by the Microbiology Society.
Contributor Information
Livia Donaire, Email: ldonaire@cebas.csic.es.
Jiatao Xie, Email: jiataoxie@mail.hzau.edu.cn.
Luca Nerva, Email: luca.nerva@crea.gov.it.
Daohong Jiang, Email: daohongjiang@mail.hzau.edu.cn.
Shin-Yi Lee Marzano, Email: ShinYi.Marzano@usda.gov.
Sead Sabanadzovic, Email: SSabanadzovic@entomology.msstate.edu.
Massimo Turina, Email: massimo.turina@ipsp.cnr.it.
María A. Ayllón, Email: mariaangeles.ayllon@upm.es.
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