PROFILPELAJAR.COM

Potexvirus
	Color break symptoms caused by narcissus mosaic virus (NMV) in daffodils (A, B) and normal flower (C)
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Kitrinoviricota
Class:	Alsuviricetes
Order:	Tymovirales
Family:	Alphaflexiviridae
Genus:	Potexvirus

Potexvirus is a genus of pathogenic viruses in the order Tymovirales, in the family Alphaflexiviridae. Plants serve as natural hosts. There are 48 species in this genus, three of which are assigned to a subgenus. Diseases associated with this genus include: mosaic and ringspot symptoms.^[1]^[2] The genus name comes from POTato virus X).

Taxonomy

Potexvirus contains one subgenus that has three species and 45 additional species unassigned to a subgenus. The following 48 species are assigned to the genus:^[2]

Subgenus: Mandarivirus

The following species are unassigned to a subgenus:

Allium virus X
Alstroemeria virus X
Alternanthera mosaic virus
Ambrosia asymptomatic virus 1
Asparagus virus 3
Babaco mosaic virus
Bamboo mosaic virus
Cactus virus X
Cassava Colombian symptomless virus
Cassava common mosaic virus
Cassava virus X
Clover yellow mosaic virus
Cnidium virus X
Cymbidium mosaic virus
Euonymus yellow mottle associated virus
Euonymus yellow vein virus
Foxtail mosaic virus
Hosta virus X
Hydrangea ringspot virus
Lagenaria mild mosaic virus
Lettuce virus X
Lily virus X
Malva mosaic virus
Mint virus X
Narcissus mosaic virus
Nerine virus X
Opuntia virus X
Papaya mosaic virus
Pepino mosaic virus
Phaius virus X
Pitaya virus X
Plantago asiatica mosaic virus
Plantain virus X
Potato aucuba mosaic virus
Potato virus X
Schlumbergera virus X
Senna mosaic virus
Strawberry mild yellow edge virus
Tamus red mosaic virus
Tulip virus X
Turtle grass virus X
Vanilla virus X
White clover mosaic virus
Yam virus X
Zygocactus virus X

Virology

The virion length may vary considerably (between 470 and 1000 nanometers or more) and is 12-13 nm in diameter. The pitch of the helix is of the basic helix 3.3-3.7 nm (8-9 copies of the coat protein per turn). It is non-enveloped, flexuous and filamentous. The coat itself is composed of 1000-1500 copies of the coat protein.^[1]

The genome is linear, 5.9-7 kilobases in length with a capped 5' end and a polyadenylated 3' end. The genome encodes 5 proteins. From left to right these proteins are: the viral replication protein that consists of a capping enzyme domain, a helicase-like domain, the RNA dependent RNA polymerase, three proteins - the triple gene block (TGB) 1, 2 and 3 - and the coat protein.^[1]

Genus	Structure	Symmetry	Capsid	Genomic arrangement	Genomic segmentation
Potexvirus	Filamentous		Non-enveloped	Linear	Monopartite

The RNA is translated giving rise to the viral RNA polymerase. This in turn produces a negative stranded template from which a series of subgenomic RNAs are generated. These subgenomic RNAs are then translated into the viral proteins.

The 5' end is about 80 nucleotides in length and typically begins with the sequence GAAAA.^[3]

In addition to its RNA polymerase activity, the viral RNA polymerase (molecular weight ~150 kilodaltons) also has methyltransferase and RNA helicase activities.

The TGB proteins are conserved among the Allexivirus, Carlavirus, Foveavirus, Furovirus, Hordeivirus, Pecluvirus, Pomovirus and Potexvirus genera. Their functions are a matter of active research.

TGB 1 (molecular weight 23 kDa) is a multifunctional protein. It has RNA helicase activity and seems to be involved in cell to cell movement.

The TGB 2 (molecular weight 11 kDa) and TGB 3 (molecular weight 10 kDa) proteins associate with the endoplasmic reticulum.

The coat protein has a molecular weight of ~25kDa.

The 3' untranslated region is ~100 nucleotides in length.

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. Translation takes place by leaky scanning. The virus exits the host cell by tripartite non-tubule guided viral movement. The virus is transmitted via a vector (insects). Transmission routes are vector and mechanical.^[1]

Genus	Host details	Tissue tropism	Entry details	Release details	Replication site	Assembly site	Transmission
Potexvirus	Plants	None	Viral movement; mechanical inoculation	Viral movement	Cytoplasm	Cytoplasm	Insects

Hosts

Known hosts are various flowering plants.

Distribution

These viruses appear to occur worldwide.

References

^ ^a ^b ^c ^d "Viral Zone". ExPASy. Retrieved 15 June 2015.
^ ^a ^b "Virus Taxonomy: 2020 Release". International Committee on Taxonomy of Viruses (ICTV). March 2021. Retrieved 15 May 2021.
^ Côté, F.; Paré, C.; Majeau, N.; Bolduc, M. N.; Leblanc, É.; Bergeron, M. G.; Bernardy, M. G.; Leclerc, D. (2008). "Nucleotide sequence and phylogenetic analysis of a new potexvirus: Malva Mosaic Virus". Infection, Genetics and Evolution. 8 (1): 83–93. Bibcode:2008InfGE...8...83C. doi:10.1016/j.meegid.2007.10.006. PMID 18054524.