Family: Gammaflexiviridae

Chapter Version: ICTV Ninth Report; 2009 Taxonomy Release

Since only one genus is currently recognized, the family description corresponds to the genus description.

Genus Mycoflexivirus

Type species Botrytis virus F

Virion properties

Morphology

Virions are flexuous filaments of 720 nm modal length and about 13 nm in diameter.

Physicochemical and physical properties

Not known.

Nucleic acid

Virions contain a single molecule of linear ssRNA, 6827 nt in length, excluding the 3’-poly(A) tail.

Proteins

The only structural protein is the coat protein composed of 302 aa (32 kDa).

Lipids

None reported.

Carbohydrates

None reported.

Genome organization and replication

The genomic RNA comprises two major ORFs on the positive strand, a 5’-UTR of 63 nt and a 3’-UTR of 71 nt, followed by a poly(A) tail (Figure 1). ORF1 contains conserved methyltransferase and helicase motifs, terminating with an opal stop codon (UGA) and yielding a protein of 153 kDa. Readthrough of this codon is expected to extend the protein to 212 kDa that then also includes an RNA-dependent RNA polymerase (RdRp) domain. ORF2 encodes the 32 kDa coat protein.

Antigenic properties

Not known.

Biological properties

The virus was discovered infecting an isolate of the plant pathogenic fungus Botrytis cinerea. Its mode of transmission is unknown. The same fungal isolate was also infected with a virus now classified as Botrytis virus X (genus Botrexvirus, family Alphaflexiviridae).

Species demarcation criteria in the genus

Not applicable.

List of species in the genus Mycoflexivirus

Species names are in italic script; names of isolates are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.

List of other related viruses which may be members of the genus Mycoflexivirus but have not been approved as species

None reported.

List of unassigned species in the family Gammaflexiviridae

None.

Similarity with other taxa

There are clear phylogenetic relationships in both ORFs to other viruses in the family Tymovirales. Nearly all these are plant-infecting viruses and many of them also have flexuous virions (which is unusual for a mycovirus). This may suggest that the virus was originally acquired by a filamentous fungus from its plant host but has subsequently lost the cell-to-cell movement protein(s) characteristic of plant viruses. A separate family for this genus is justified by phylogenetic analyses of the order and also because of the readthrough translation strategy of the replication protein, a strategy that has not been found elsewhere in the order.

Derivation of names

Flexi: from flexus, Latin for “bent”.

Mycoflexi: from mycovirus with flexuous virions.

Further reading

Howitt et al., 2001 R.L.J. Howitt, R.E. Beever, M.N. Pearson, R.L.S. Forster, Genome characterization of Botrytis virus F, a flexuous rod-shaped mycovirus resembling plant “potex-like” viruses. J. Gen. Virol. 82 (2001) 67–78.

Martelli et al., 2007 G. Martelli, M.J. Adams, J.F. Kreuze, V.V. Dolja, Family Flexiviridae: a case study in virion and genome plasticity. Annu. Rev. Phytopathol. 45 (2007) 73–100.

Contributed by

Adams, M.J., Kreuze, J.F. and Pearson, M.N.