| Hypovirus | |
|---|---|
Virus classification | |
| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phylum: | Pisuviricota |
| Class: | Duplopiviricetes |
| Order: | Durnavirales |
| Family: | Hypoviridae |
| Genus: | Hypovirus |
Hypovirus is a genus ofviruses, in the familyHypoviridae.[1]Fungi serve as natural hosts. There are four species in this genus.[2] Infection reduces thevirulence of its parasitic host, making it ahyperparasite useful forblight control.[1][3]
The following species are recognized by theInternational Committee on Taxonomy of Viruses (ICTV), all of which were found withCryphonectria parasitica:[1][2]
There are numerous family members affecting other plant-pathogenic fungi not yet accepted into the ICTV nomenclature. A proposal reorganizes the family into three genera.[4] The informal familyFusariviridae is the sister group.[5]
The diameter is around 50–80 nm. Genomes are linear, around 9–13kb in length. The genome has 1 or 2open reading frames, named OrfA (not always present) and OrfB.[1][3]
| Genus | Structure | Symmetry | Capsid | Genomic arrangement | Genomic segmentation |
|---|---|---|---|---|---|
| Hypovirus | No true capsid | Non-enveloped | Linear | Monopartite |
The genome contains no structural proteins. The virus accordingly does not bud out of the cell (see "life cycle" below). Bothopen reading frames of CHV1 contain apapain-likeprotease to theN-terminal that is autocatalyticly cleaved. OrfA (p69,P10941) cleaves into the p29 C7 protease and a nonessential p40 protein. OrfB (Q04350) cleaves into a p48 C8 protease and theRNA replicase–helicase.[3]
Viral replication iscytoplasmic. Replication follows thedouble-stranded RNA virus replication model. Double-stranded RNA virus transcription is the method of transcription. The virus exits the host cell by cell to cell movement. Fungi serve as the natural host.[1][3]
| Genus | Host details | Tissue tropism | Entry details | Release details | Replication site | Assembly site | Transmission |
|---|---|---|---|---|---|---|---|
| Hypovirus | Fungi | None | Cytoplasmic exchange;hyphalanastomosis | Cytoplasmic exchange; hyphal anastomosis | Cytoplasm | Cytoplasm | Cytoplasmic exchange; hyphal anastomosis |
Up to 2000, Hypovirus CHV1 was the only hypovirus found in Europe.[6] It is known for reducing the virulence of the fungus that causeschestnut blight (i.e. hypovirulence).[7]Cryphonectria parasitica, the ascomycete fungus, originated in Asia and causes the diseasechestnut blight in severalchestnut species (Castanea spp.). Although symptoms are mild in Asian chestnut species that have co-evolved with the fungus, they are very severe in the NorthAmerican chestnut speciesC. dentata and also in the European sweet chestnut,C. sativa.[8] Hypovirus has been used for protection against chestnut blight in Europe since the 1970s.[6]