''Tobamovirus'' is a genus of

positive-strand RNA virus Positive-strand RNA viruses (+ssRNA viruses) are a group of related viruses that have positive-sense, single-stranded genomes made of ribonucleic acid. The positive-sense genome can act as messenger RNA (mRNA) and can be directly translated int ...

es in the family '' Virgaviridae.'' Many plants, including

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

potato The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern Unit ...

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

, and

squash Squash may refer to: Sports * Squash (sport), the high-speed racquet sport also known as squash racquets * Squash (professional wrestling), an extremely one-sided match in professional wrestling * Squash tennis, a game similar to squash but pla ...

, serve as natural hosts. Diseases associated with this genus include: necrotic lesions on leaves. The name ''Tobamovirus'' comes from the host and symptoms of the first virus discovered (''Tobacco mosaic virus''). There are four informal subgroups within this genus: these are the tobamoviruses that infect the

brassica ''Brassica'' () is a genus of plants in the cabbage and mustard family ( Brassicaceae). The members of the genus are informally known as cruciferous vegetables, cabbages, or mustard plants. Crops from this genus are sometimes called ''cole c ...

s, cucurbits, malvaceous, and

solanaceous The Solanaceae , or nightshades, are a family of flowering plants that ranges from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and trees, and includes a number of agricultural crops, medicinal plants, spices, weeds, and orna ...

plants. The main differences between these groups are genome sequences, and respective range of host plants. There are 37 species in this genus.

Structure

Tobamoviruses are non-enveloped, with helical rod geometries, and helical symmetry. The diameter is around 18 nm, with a length of 300–310 nm. Genomes are linear and non-segmented, around 6.3–6.5kb in length.

Genome

The RNA genome encodes at least four

polypeptides Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A p ...

: these are the non-structural protein and the read-through product which are involved in virus replication (RNA-dependent RNA polymerase, RdRp); the

movement protein In order for a virus to infect a plant, it must be able to move between cells so it can spread throughout the plant. Plant cell walls make this moving/spreading quite difficult and therefore, for this to occur, movement proteins must be present. A ...

(MP) which is necessary for the virus to move between cells and the coat protein (CP). The read-through portion of the RdRp may be expressed as a separate protein in TMV. The virus is able to replicate without the movement or coat proteins, but the other two are essential. The non-structural protein has domains suggesting it is involved in RNA capping and the read-through product has a motif for an RNA polymerase. The movement proteins are made very early in the infection cycle and localized to the

plasmodesmata Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages, and spec ...

, they are probably involved in host specificity as they are believed to interact with some host cell factors.

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 suppression of termination. The virus exits the host cell by monopartite non-tubule guided viral movement. Plants serve as the natural host. Transmission routes are mechanical.

Enzymes

Tobamovirus RNA-dependent RNA polymerases are homologous with bromoviruses, ilarviruses, tobraviruses, and the carnation mottle virus.

Routes of infection

The infection is localized to begin with but if the virus remains unchallenged it will spread via the vascular system into a systemic infection. The exact mechanism the virus uses to move throughout the plant is unknown but the interaction of pectin methylesterase, a cellular

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

important for cell wall metabolism and plant development, with the movement protein has been implicated.

Evolution

These viruses are thought to have codiverged with their hosts from a common ancestor. There are at least 3 distinct clades of tobamoviruses, which to some extent follow their host ranges: that is, there is one infecting

species; a second infecting cucurbits and legumes and a third infecting the crucifers.

Classification

Species

The genus contains the following species: * '' Bell pepper mottle virus'' (BPeMV) * '' Brugmansia mild mottle virus'' * '' Cactus mild mottle virus'' (CMMoV) * '' Clitoria yellow mottle virus'' * '' Cucumber fruit mottle mosaic virus'' * '' Cucumber green mottle mosaic virus'' (CGMMV) * '' Cucumber mottle virus'' * '' Frangipani mosaic virus'' (FrMV) * '' Hibiscus latent Fort Pierce virus'' (HLFPV) * '' Hibiscus latent Singapore virus'' (HLSV) * '' Kyuri green mottle mosaic virus'' * '' Maracuja mosaic virus'' (MarMV) * '' Obuda pepper virus'' (ObPV) * '' Odontoglossum ringspot virus'' (ORSV) * '' Opuntia chlorotic ringspot virus'' * '' Paprika mild mottle virus'' * '' Passion fruit mosaic virus'' * ''

Pepper mild mottle virus ''Pepper mild mottle virus'' (PMMoV) is a plant pathogenic virus that occurs worldwide on species of field grown bell, hot and ornamental pepper species. It is caused by members of the plant virus genus ''Tobamovirus''- otherwise known as the tob ...

'' (PMMoV) * '' Plumeria mosaic virus'' * '' Rattail cactus necrosis-associated virus'' (RCNaV) * '' Rehmannia mosaic virus'' * '' Ribgrass mosaic virus'' (HRV) * '' Sammons's Opuntia virus'' (SOV) * '' Streptocarpus flower break virus'' * '' Sunn-hemp mosaic virus'' (SHMV) * '' Tobacco latent virus'' * '' Tobacco mild green mosaic virus'' * ''

Tobacco mosaic virus ''Tobacco mosaic virus'' (TMV) is a positive-sense single-stranded RNA virus species in the genus ''Tobamovirus'' that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteri ...

'' (TMV) * '' Tomato brown rugose fruit virus'' (ToBRFV) * ''

Tomato mosaic virus ''Tomato mosaic virus'' (ToMV) is a plant pathogenic virus. It is found worldwide and affects tomatoes and many other plants. Symptoms The foliage of affected tomato plants shows mottling, with alternating yellowish and darker green areas, the ...

'' (ToMV) * '' Tomato mottle mosaic virus'' * '' Tropical soda apple mosaic virus'' * '' Turnip vein-clearing virus'' (TVCV) * '' Ullucus mild mottle virus'' * '' Wasabi mottle virus'' (WMoV) * '' Yellow tailflower mild mottle virus'' * '' Youcai mosaic virus'' (YoMV) aka oilseed rape mosaic virus (ORMV) * '' Zucchini green mottle mosaic virus''

Proposed members

Proposed, but currently unrecognised members of the genus include: * Chara corallina virus (CCV) * Nicotiana velutina mosaic virus (NVMV)

References

External links

ICTV Online (10th) Report: ''Virgaviridae''

{{Taxonbar, from=Q3530126 Viral plant pathogens and diseases Virus genera