Quadriviridae

Quadriviridae is a family of double-stranded RNA viruses with a single genus Quadrivirus.^[1] The fungi Rosellinia necatrix serves as a natural host. The name of the group derives from the quadripartite genome of its members where in Latin quad means four. The genus has three species.^[2][3]

Quadrivirus
(Left) Electron micrographs of the Rosellinia necatrix quadrivirus 1, bar = 50 nm. (Right) Three-dimensional cryo-electron microscopy reconstruction of RnQV1 virions at 8Å resolution.
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Duplornaviricota
Class:	Chrymotiviricetes
Order:	Ghabrivirales
Family:	Quadriviridae
Genus:	Quadrivirus

Structure

Schematic diagram of Quadriviridae virions. The four genomic segments may be separately encapsulated.^[3]

Mycoviruses in the family Quadriviridae have a non-enveloped isometric capsid which consists of 60 copies of heterodimers of the structural proteins P2 and P4. The diameter of the capsid is around 48 nm.^[2][3]

Genome

Genome of Rosellinia necatrix quadrivirus 1

Family member genomes are composed of double-stranded RNA. They are divided in to four segments which each code for a protein. The length of the different segments are between 3.5 and 5.0 kbp. The total genome is around 16.8 kbp. Inside the capsid with the genome there is also the RNA-dependent RNA polymerase.^[2][3]

Life cycle

Quadriviruses are transmitted internally. They are propagated during cell division and hyphal anastomosis. Viral replication occurs in the cytoplasm. It follows the double-stranded RNA virus replication model. Double-stranded RNA virus transcription is the method of transcription. The fungi Rosellinia necatrix serves as a natural host.^[2][3]

Taxonomy

Phylogenetic tree of quadriviruses, chrysoviruses and some totiviruses

The family Quadrivirdae has one genus Quadrivirus, which contains the following species:^[4]

• Quadrivirus ichi (Rosellinia necatrix quadrivirus 1)
• Quadrivirus ni
• Quadrivirus sani