Tobamovirus

Tobamovirus is a genus of positive-strand RNA viruses in the family Virgaviridae, infecting plants such as tobacco, potato, tomato, and squash. The name originates from the Tobacco mosaic virus, the first discovered species. It causes diseases characterized by necrotic lesions on leaves.

The genus includes 37 recognized species and two proposed members: Chara corallina virus (CCV) and Nicotiana velutina mosaic virus (NVMV). Four informal subgroups are based on host plant families: brassicas, cucurbits, malvaceous, and solanaceous. These groups differ in genome sequences and host ranges.

Tobamoviruses are non-enveloped, helical rod-shaped particles with dimensions of 18 nm in diameter and 300–310 nm in length. Their linear, non-segmented genomes measure approximately 6.4 kb. The RNA genome encodes four polypeptides: a non-structural protein (RdRp) for replication, a read-through product, a movement protein (MP), and a coat protein (CP). RdRp is essential for replication, while MP facilitates intercellular movement, both playing roles in host specificity.

The life cycle involves cytoplasmic replication and mechanical transmission. Entry occurs via cell penetration, followed by positive-stranded RNA replication and transcription. Translation suppresses termination, and the virus exits through non-tubule-guided movement. Systemic spread can occur, involving vascular tissues and interactions with host enzymes like pectin methylesterase.

Enzymatically, tobamoviruses share homology with bromoviruses, ilarviruses, tobraviruses, and carnation mottle virus in their RNA-dependent RNA polymerases. Evolutionarily, three distinct clades exist, correlating with host plant families: solanaceous, cucurbits/legumes, and crucifers.

Classification includes 37 species, with proposed members currently unrecognised.