Flexiviridae: A case study in virion and genome plasticity
Posted by ajcann on January 3, 2008
The plant virus family Flexiviridae includes the definitive genera Potexvirus, Mandarivirus, Allexivirus, Carlavirus, Foveavirus, Capillovirus, Vitivirus, Trichovirus, the putative genus Citrivirus, and some unassigned species. Its establishment was based on similarities in virion morphology, common features in genome type and organization, and strong phylogenetic relationships between replicational and structural proteins. In this review, the authors provide a brief account of the main biological and molecular properties of the members of the family, with special emphasis on the relationships within and among the genera. In phylogenetic analyses the Potexvirus-like replicases were more closely related to tymoviruses than to carlaviruses. The authors postulate a common evolutionary ancestor for the family Tymoviridae and the two distinct evolutionary clusters of the Flexiviridae, i.e. a plant virus with a polyadenylated genome, filamentous virions, and a triple gene block of movement proteins. Subsequent recombination and gene loss would then have generated a very diverse group of plant and fungal viruses.
The most prominent aspect of the Flexiviridae is the unusual fluidity of their genomes compared to those of the related rod-shaped or icosahedral RNA viruses of the alphavirus-like superfamily. This could be explained by the relative ease with which the filamentous virions can accommodate the increase or reduction in the size of the viral genome. There is no region of flexiviral genomes that is left untouched by genetic variation. Do flexiviruses benefit from their genetic plasticity? It seems that the answer is yes.
