Tombusviridae
| Tombusviridae | |
|---|---|
| Virus classification | |
| Group: | Group IV ((+)ssRNA) |
| Family: | Tombusviridae |
| Genera | |
Tombusviridae is a family of single-stranded positive sense RNA plant viruses. There are currently 71 species in this family, divided among 13 genera. The name is derived from the type species of the Tombusvirus genus, Tomato bushy stunt virus (TBSV).
All Tombusviridae have a non-segmented linear genome, with the exception of Dianthoviruses, whose genome is bipartite. The genome is approximately 4.6–4.8kb in length, lacks a 5' cap and a poly(A) tail, and it encodes 4–6 ORFs. The polymerase encodes an amber stop codon which is the site of a readthrough event within ORF1, producing two products necessary for replication. There is no helicase encoded by the virus.
The RNA is encapsulated in an icosahedral (T=3) capsid, composed of 180 units of a single coat protein 27–42K in size; the virion measures 28–35 nm in diameter, and it is not enveloped.
Viral replication is cytoplasmic, and is lysogenic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription, using the premature termination model of subgenomic RNA transcription is the method of transcription. Translation takes place by leaky scanning, −1 ribosomal frameshifting, viral initiation, and suppression of termination. The virus exits the host cell by tubule-guided viral movement. Plants serve as the natural host. Transmission routes are mechanical, seed borne, and contact.
Viruses in this family are primarily soil-borne, some transmitted by fungal species of the order Chytridiales, others by no known vector. Virions may spread by water, root growth into infected soil, contact between plants, pollen, or seed, depending on the virus species. These viruses may be successfully transmitted by grafting or mechanical inoculation, and both the virion and the genetic material alone are ineffective.
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