Notes on Family: Alphaflexiviridae

flexuous filaments

General Description

The family Flexiviridae was originally created to contain plant-infecting viruses with:

Flexuous filamentous virions 12-13 nm in diameter (giving the family its name)
Monopartite, positive sense, ssRNA genomes with a 3'-polyA tail
Translation of at least some ORFs from subgenomic mRNAs
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

to reflect the very different lineages of replication protein (potex-like and carla-like)
to include some related viruses of fungi
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.

Morphology

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

Genomen

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:

Genus	Host	Virion length (nm)	No of ORFs	Replication protein (kDa)	Coat protein (kDa)
Allexivirus	plants	c. 800	6	170-195	26-29
Botrexvirus	fungi	720	5	158	43
Lolavirus	plants	640	6	196	32
Mandarivirus	plants	650	6	187	34
Potexvirus	plants	470-580	5	150-195	22-27
Sclerodarnavirus	fungi	none	1	193	none