Tobamovirus

The genus Tobamovirus contains viruses with a positive sense RNA genome that infect plants. The most common tobamovirus is probably tobacco mosaic virus, which infects tobacco and other plants including potatoes, tomatoes, and squashes. The name "Tobamovirus" comes from the host and symptoms: Toba for Tobacco and mo for mosaic. There are four subgroups within this genus; the solanaceous, brassicas, cucurbits and malvaceous-infecting tobamoviruses. The main differences between these groups are genome sequence and range of host plants.

The RNA genome encodes four polypeptides; 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 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 a RNA polymerase. The movement proteins are made very early in the infection cycle and localised to the plasmodesmata, they are probably involved in host specificity as they are believed to interact with some host cell factors. The infection is localised 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 important for cell wall metabolism and plant development, with the movement protein has been implicated.