Notes on Family: Alphaflexiviridae

flexuous filaments
flexuous filaments


General Description

The family Flexiviridae was originally created to contain plant-infecting viruses with:
  1. Flexuous filamentous virions 12-13 nm in diameter (giving the family its name)
  2. Monopartite, positive sense, ssRNA genomes with a 3'-polyA tail
  3. Translation of at least some ORFs from subgenomic mRNAs
  4. Up to 6 open reading frames ordered from 5' to 3':
    • An alpha-like replication protein (150-250 kDa) containing conserved methyl transferase, helicase and RNA-dependent RNA polymerase (RdRp) motifs
    • One or more movement proteins
    • A single coat protein (CP) of 22-44 kDa
    • A sixth ORF in some viruses, which may partially overlap the 3'-end of the CP gene and is thought to have nucleotide-binding properties.

Recently, the family has been divided

  1. to reflect the very different lineages of replication protein (potex-like and carla-like)
  2. to include some related viruses of fungi
  3. to support the inclusion of these viruses with members of the family Tymoviridae in the order Tymovirales.

The family Alphaflexiviridae includes the plant viruses with a potex-like polymerase (all of which have a 'triple gene block' set of movement proteins) and some related mycoviruses while those viruses with a larger, carla-like, polymerase are now classified within the family Betaflexiviridae.


Virions filamentous, not enveloped, 470-800 nm long and 12-13 nm in diameter.


Monopartite, linear, polyadenylated ssRNA of 5.4-9.0 kb.

Genera in the Family

The genera are distinguished by the host, the number of ORFs and the sizes of the virion, the replication protein and the coat protein. These are also supported by phylogenetic analysis:
GenusHostVirion length
No of
Replication protein
Coat protein
Allexivirusplantsc. 800 6170-195 26-29
Botrexvirusfungi720 5158 43
Lolavirusplants640 6196 32
Mandarivirusplants650 6187 34
Potexvirusplants470-580 5150-195 22-27
Sclerodarnavirusfunginone 1193 none