Tobamovirus is a genus in the virus family Virgaviridae. Many plants, including tobacco, potato, tomato, and squash, serve as natural hosts. There are currently 37 species in this genus including the type speciesTobacco mosaic virus. Diseases associated with this genus include: necrotic lesions on leaves. The name Tobamovirus comes from the host and symptoms of the first virus discovered. There are four informal subgroups within this genus: these are the tobamoviruses that infect the brassicas, the cucurbits, and malvaceous and solanaceous plants. The main differences between these groups are genome sequences, and respective range of host plants.
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 solanaceous species; a second infecting cucurbits and legumes and a third infecting the crucifers.
Genome
The RNA genome encodes at least four polypeptides: these are the non-structural protein and the read-through product which are involved in virus replication ; the movement protein which is necessary for the virus to move between cells and the coat protein. 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, they are probably involved in host specificity as they are believed to interact with some host cell factors.
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.
Genus
Structure
Symmetry
Capsid
Genomic arrangement
Genomic segmentation
Tobamovirus
Rod-shaped
Helical
Non-enveloped
Linear
Non-Segmented
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.
Genus
Host details
Tissue tropism
Entry details
Release details
Replication site
Assembly site
Transmission
Tobamovirus
Plants
-
Unknown
Viral movement
Cytoplasm
Cytoplasm
Mechanical
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 pectinmethylesterase, a cellular enzyme important for cell wall metabolism and plant development, with the movement protein has been implicated.
