Ipomovirus


Ipomovirus is a genus of positive-strand RNA viruses in the family Potyviridae. Member viruses infect plants and are transmitted by whiteflies. The name of the genus is derived from Ipomoea – the generic name of sweet potato. There are seven species in this genus.

Structure

Viruses in genus Ipomovirus are non-enveloped, with flexuous and filamentous geometries. The diameter is around 12–15 nm, and may have a variety of lengths depending on the species. The capsid has helical symmetry with a pitch of 3.4 nm. They induce characteristic inclusion bodies within infected plant cells.

Genome

The genome is either monpartite or bipartite depending on the species. Member viruses have linear, single stranded RNA genome of positive polarity about 10-11 kilobases in length. The 3’ terminus has a poly tract and the 5’ terminus has a genome linked protein.
Member viruses encode a single polypeptide with a predicted molecular weight of 390 kilodaltons which is cleaved into ~10 proteins. In 5'–3' order these proteins are
  • P1 : 83 kDa
  • HC : 51 kDa
  • P3: 34 kDa
  • 6K1: 5 kDa
  • Cl : 71 kDa
  • 6K2: 6 kDa
  • VPg : 20 kDa
  • NIa-Pro : 27 kDa
  • NIb : 57 kDa
  • Capsid protein: 34 kDa
There may be some variation in the number of the proteins depending on the species, for instance some ipomoviruses lack HC and have a P1 tandem. Inosine triphosphate pyrophosphatase is an atypical protein domain identified in some ipomoviruses.

Life cycle

Viral replication is cytoplasmic. 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 is the method of transcription. The virus exits the host cell by tubule-guided viral movement. Plants serve as the natural host. The virus is transmitted via a vector. Transmission routes are vector and mechanical.

Taxonomy

The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species:Ipomovirus brunusmanihotis, Cassava brown streak virusIpomovirus cocciniae, Coccinia mottle virusIpomovirus cucumisvenaflavi, Cucumber vein yellowing virusIpomovirus cucurbitavenaflavi, Squash vein yellowing virusIpomovirus lenisbatatae, Sweet potato mild mottle virusIpomovirus lycopersici, Tomato mild mottle virusIpomovirus manihotis, Ugandan [cassava brown streak virus]
Ugandan cassava brown streak virus was the first ipomovirus to be cloned and rescued using a plasmid cDNA vector system.