Necrovirus

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Necrovirus
Systematics
Classification : Viruses
Area : Riboviria
Empire : Orthornavirae
Phylum : Kitrinoviricota
Class : Tolucaviricetes
Order : Tolivirales
Family : Tombusviridae
Genre : Alphanecrovirus , Betanecrovirus
Taxonomic characteristics
Genome : (+) ssRNA linear
Baltimore : Group 4
Symmetry : icosahedral
Cover : no
Scientific name
Necrovirus
Left
NCBI  Taxonomy: 12052
ViralZone ( ExPASy , SIB): 4859
ICTVdB Virus Code : 00.074.0.03

The former genus Necrovirus has now been divided into the genera Alphacarmovirus and Betanecrovirus , both in the virus family Tombusviridae . These include non-enveloped plant viruses with a double-stranded RNA as a genome . The type species of the genus Alphacarmovirus is the tobacco necrosis virus A (scientifically Tobacco necrosis virus A ), which was discovered in 1935 in diseased tobacco plants ( Nicotiana tabacum ) in greenhouses. The type species of the genus Betanecrovirus is the tobacco necrosis virus D (scientifically Tobacco necrosis virus D ). The members of the two genera do not cause diseases that affect the entire plant (systemic infection) and reduce plant growth, but typically only locally limited foci of infection on leaves, stems or roots, which lead to patchy necrosis of the plant tissue. The genera got their names from this typical necrosis.

Morphology and genome

The unenveloped capsid of the necroviruses from both families is between 28  nm in diameter. With icosahedral symmetry, the virions (virus particles) have a triangulation number T = 3. The capsid consists of 180 capsomeres . The necroviruses contain a molecule of single-stranded RNA as a genome, which is 3660 to 3760  nt long. The RNA has a positive polarity and a similar gene organization as the genus Carmovirus ; a poly (A) tail at the 3 'end is missing from the necroviruses. The genome comprises five or six partly overlapping open reading frames ( English open reading frames , ORFs). Two types of subgenomic RNA are synthesized from the original RNA, each representing two ORFs with different reading frames.

Transmission and Disease

Necroviruses were isolated from the roots of various plant species and characterized according to the symptoms that arise after mechanical transmission to plant leaves. The common bean ( Phaseolus vulgaris ) is used as a test organism . Latent infections have been detected in cultivated apples , pears ( Pyrus communis L.) and olive trees .

Necroviruses are also found in natural waters and in the soil, where they are specifically associated with the cell surface of zoospores of the fungus Olpidium brassicae . The fungus can penetrate the roots of plants and thus infect the plant with the viruses; this fungus is the only known carrier of the necrovirus species. Necrovirus diseases only play a subordinate role economically.

Satellites

Necroviruses are often associated with specific satellite viruses that require the presence of necroviruses for their own reproduction ( helper virus ). In the case of TNV, the satellite ( Tobacco Necrosis Virus Satellite 1 , STNV-1) is about 17 nm in size and its RNA only codes for one capsid protein. The multiplication of the satellites of the necroviruses serves as an example system for researching a helper satellite system and a cap-independent translation .

Systematics

The former genus Necrovirus was divided as follows (as of ICTV March 2019):

  • Genus Alphanecrovirus
  • Genus Betanecrovirus
  • Species Beet Black Scorch Virus (s. Beet black scorch virus , BBSV)
  • Species Leek white stripe virus (en. Leek white stripe virus , LWSV)
  • Species tobacco necrosis virus D ( Tobacco necrosis virus D , TNV-D)
  • Species Turnip crinkle virus (type species)
  • Gender indefinite
  • Species Chenopodium necrosis virus (en. Chenopodium necrosis virus , ChNV)
  • Species ' Carnation yellow stripe virus ' (en. Carnation yellow stripe virus , CYSV) - proposed but not yet confirmed by ICTV

The following species have been placed in a different family / genus:

  • Species Lisianthus necrosis virus ( en.Lisianthus enation leaf curl virus , LNV)

swell

  • SA Lommel et al. : Genus Necrovirus . In: CM Fauquet, MA Mayo et al. : Eighth Report of the International Committee on Taxonomy of Viruses . London, San Diego 2005. ISBN 0-12-249951-4 . Pp. 926-929.
  • F. Meulewaeter: Necroviruses . In: A. Granoff, RG Webster (Ed.): Encyclopedia of Virology , Volume 1. San Diego 1999. ISBN 0-12-227030-4 . Pp. 1003-1007.
  • H. Fraenkel-Conrat: Tobacco necrosis, satellite tobacco necrosis and related viruses . In: R. König (Ed.): The plant viruses , Volume 3. New York 1988. S. 147 ff.

Individual evidence

  1. ↑ ICTV Master Species List 2018b v1 MSL # 34, Feb. 2019
  2. ↑ a b c d ICTV: ICTV Taxonomy history: Carrot mottle mimic virus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
  3. ^ KM Smith, JG Bald (1935) Parasitol. 27: p. 231.

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