Nepovirus

Nepoviruses, also known as nematode transmitted polyhedral viruses, are plant viruses of the family Comoviridae. They are classified as type IV viruses under the Baltimore classification system. Nepoviruses are one of three genera in the family Comoviridae the other two genera are comovirus and fabavirus. Nepoviruses unlike the other two genera in the family are transmitted by nematodes.

There are many members of the genus Nepovirus including tobacco ringspot virus, cherry leaf roll virus, beet ringspot virus and raspberry ringspot virus. Nepoviruses have bipartite, liner, single stranded positive sense RNA genomes. The two genome segments are encapsulated separately into two different icosahedral particles. The first segment (RNA1) which is approximately 8000 nucleotides appears as a single copy in each B type virion. The second segment (RNA2) is approximately 4000-7000 nucleotides and usually appears as a single copy in each M type virion, two copies will be present however if RNA2 is smaller than 4kb. Each of the genome segments produces a different polypeptide, which under goes a series of steps in order to produce a functional protein. RNA1 encodes the proteins that are important in replication and RNA2 encodes the proteins that are important in cell-cell movement.