Unravelling the evolutionary significance of the tripartite genome of Cucumber mosaic virus.

Cucumber mosaic virus (CMV) is a tripartite plant RNA virus, comprised of three single-stranded (ss)RNA genome segments which are individually encapsidated. Viruses consisting of multiple RNA or DNA genome segments which are individually packaged and transmitted are said to be multipartite, requiring complementation of segments for infection. Theoretical analyses of the infection kinetics has shown there exists a cost to this strategy, however multipartition abounds for plant-infecting viruses. A virus and host-specific setpoint genome formula (SGF), i.e. an equilibrium for genome segment frequencies, has been demonstrated in plant and animal viruses. In this PhD using the model CMV we will explore the virus genotype effect on the SGF in multi-host infection experiments and determine the genetic basis for the SGF.The variable SGFs of these viruses across host genotypes suggests that genome partitioning may provide an advantage in allowing the rapid regulation of viral gene expression, hypothesised as similar to copy number variation changes in other organisms. Using experimental evolution we will test the hypothesis that the SGF confers rapid adaptation to a novel host and determine the stability of the SGF at within and between host level in different host species. By conducting analysis of infected leaves and protoplast cells we will examine changes in the GF and associated viral protein expression and thus demonstrate that the SGF is part of a dynamic viral process in host cells and tissues, which plays a role in viral accumulation, replication rate and establishment of systemic infection.