Tobacco Mosaic Virus (TMV)
Tobacco mosaic virus is a single-stranded, positive-sense RNA virus that infects a wide range of host plants.
What are Viruses?
Viruses are non-living entities (outside of their hosts), need an insect vector to get entry into the plant’s cell. For multiplication, viruses depend on the host plant’s living cells and proteins. During multiplication, they utilize the host’s factors and reduces their vigor to combat harmful elements. The virus’s primary purpose is to infect their hosts by accessing the vasculature.
History of Plant Virology
The discovery of the tobacco mosaic virus (TMV) leads the foundations of plant virology. When German scientist Adolf Mayer (working in the Netherlands) in 1882 discovered the color variegation symptoms on tobacco plants and called them mosaic: Tobacco mosaic disease.
He further claimed that this disease is infectious and can be transmitted from diseased plants to healthy plants by inoculating the sap from diseased plants to healthy.
“About the same time, a Russian scientist Dimitri Ivanosky in 1892 was working on the same disease and studied that disease can be transmitted by sap inoculations from infected plants to healthy tobacco plants.” He studied that sap remains infective after filtering through porcelain filters that had fine pores.
Later, in 1898, the Martinus Beijerinck in Delft, Holland studied that the sap from infected tobacco plants remains infected after filtration through porcelain filters and concluded that the microbes are not the causal agent of this disease.
He called this infectious entity “contagium vivum fluidum (contagious living liquid)”. He also deducted that the causing agent is not a microbe nor a small particle. Beijernick stated that the disease-causing agent is an infectious, living, and nonparticular agent later called a “Virus” meaning poison.
However, further investigations in this subject lead to many contributions that are these infectious agents are minute entities that are only visible under an electron microscope and filterable pathogenic agents.
Tobacco mosaic virus belongs to:
Family: Virgaviridae
Genus: Tobamovirus
Type species: Tobacco mosaic virus
Tobamovirus is the only genus in this family that are not transmitted by insect vector and only transmit by mechanical injuries.
Tobacco Mosaic Virus
The tobacco mosaic virus was the first pathogenic agent discovered by Martinus Beijernick that infects and reproduces within host tissues. The symptoms associated with TMV infections are stunting, yellowing of veins, yellow spots on leaves, and mosaic patterns.
TMV causes interveinal chlorosis. Chlorosis is the loss of chlorophyll. Due to chlorophyll loss, plants are unable to produce enough food. Abnormal and retarded growth is called stunted growth.
Mode of transmission
For their transmission, the tobacco mosaic virus does not need insect vector-mediated transmission. Rather than, TMV can be transmitted by sap from infected cells to diseased or through contact of diseased plants to healthy ones. As wounds support the entry of the virus into the first cell.
Seeds from diseased plants also carry the virus on seed coats, when the seed germinates, the virus enters into the seedling. Once inside the seedling, the virus dissembles its RNA from the protein coat and starts using host factors. And plants confuse this RNA to its own and start producing virus proteins.
Infection Cycle of Tobacco mosaic virus
Being biotrophs, viruses require host factors for replication. The infection process of the tobacco mosaic virus consists of pre-establishment into the first cell, then movement through plasmodesmata (PD) into neighboring uninfected cells, and entrance into the vasculature for systemic infection.
Plant viruses encode multifunctional proteins to trick their hosts. TMV encodes four proteins: replication-associated protein, movement protein (MP), and structural or coat protein (CP).
Tobacco mosaic virus is a positive-sense single-stranded RNA (ss RNA) virus that transmits mechanically via wounding, or by contact.
After entry into plant cells, TMV disassembles from coat protein and release viral RNA (vRNA) into the host cell cytoplasm. After release into the host cell cytoplasm, viral RNA encodes tiny granules in association with coat protein (CP). These granules transfer the vRNA into the replication site.
At the replication site, the replication-associated protein assists the virus in replication by using host cytoplasm proteins. For successful infection, TMV requires movement protein for intercellular movement. The intercellular movement of TMV occurs through vRNA, endoplasmic reticulum, movement protein.
Once the TMV into the neighboring uninfected cells, it disassembles itself and follows the same process as in first infected cells. After establishing a successful infection, TMV enters into the vasculature to spread systemically.
Host Range
Their host range (TMV) is narrow and geographically have widespread properties.
Disease Management
Tobacco mosaic virus can be controlled by the following methods:
- Use of resistant crop varieties. Resistant genomes have the ability to ward off TMV.
- Use of virus-free seedling and strict hygiene practices
- Avoidance of mechanical injuries as they encourage the spread of the virus within the field.
- Removal of infected tobacco plants from the field.
- Proper disinfection of farm tools before use.
- Seedlings should be in a clean zone.
Keynotes:
Tobacco mosaic virus is the first pathogenic agent that is given the name of “virus meaning poison” by Martinus Beijernick.
The tobacco mosaic virus is only transmitted by mechanical injuries or by infected seeds.
TMV does not require an insect vector for its transmission.
Only resistant genomes or varieties are helpful to manage the disease.
Sources
https://www.frontiersin.org/articles/10.3389/fpls.2013.00012/full