[Nanoviruses, small plant viruses: similarities and differences with geminiviruses]

Nanoviridae family comprises genus Nanovirus (viruses infecting legume plants) and Babuvirus (viruses infecting banana plants). Nanovirus genomes consist of multiple circular single-stranded DNAs of about 1 kb each. They are encapsidated individually in small icosahedral particles. Each DNA molecule encodes only one protein. Nanoviruses replicate in the nucleus of infected plants by a rolling-circle replication mechanism initiated by viral Rep protein. Multiple DNAs encoding similar but clearly distinct Rep proteins have been described for each nanovirus. All Rep proteins of a given nanovirus are functional and each initiates replication of the DNA by which it is encoded (auto-replication). Only the Master Rep protein is able to initiate replication of other genome components (trans-replication). Induction of nanovirus disease by cloned genome components was established only for Faba bean necrotic yellows virus.