Genetic diversity in RNA virus quasispecies is controlled by host-virus interactions

Abstract

Many RNA viruses have genetically diverse populations known as quasispecies. Important biological characteristics may be related to the levels of diversity in the quasispecies (quasispecies cloud size), including adaptability and host range. Previous work using Tobacco mosaic virus and Cucumber mosaic virus indicated that evolutionarily related viruses have very different levels of diversity in a common host. The quasispecies cloud size for these viruses remained constant throughout serial passages. Inoculation of these viruses on a number of hosts demonstrated that quasispecies cloud size is not constant for these viruses but appears to be dependent on the host. The quasispecies cloud size remained constant as long as the viruses were maintained on a given host. Shifting the virus between hosts resulted in a change in cloud size to levels associated with the new host. Quasispecies cloud size for these viruses is related to host-virus interactions, and understanding these interactions may facilitate the prediction and prevention of emerging viral diseases.

FIG. 1

Distribution of mutations in cloned regions of CMV and TMV. Maps of the cloned regions of CMV (A) and TMV (B) are shown, with nucleotide positions marked above. The locations of mutations from cloned populations are shown as lines directly below the maps. The mutations from whole-plant populations are directly underneath the maps, with mutations from protoplast (prot.) populations below them. Mutation-free regions from whole-plant populations are marked with a double-headed arrow. In instances where multiple mutations have occurred at the same site, the site is marked with a single line with the number of mutations indicated directly below. The proposed origin-of-assembly region in TMV is denoted by the shaded bar over the movement protein gene. None of the changes in the origin-of-assembly region dramatically affected the proposed structure.