[
International Worm Meeting,
2011]
We isolated the first natural viruses infecting Caenorhabditis nematodes: the Orsay virus in C. elegans isolate JU1580 and the Santeuil virus in C. briggsae JU1264 (Felix & al., 2011). We more recently found a third virus in C. briggsae JU1498 (Le Blanc virus). These viruses cause disorders in intestinal cells of their host and are horizontally transmitted.
Their genomes are composed of two single-stranded positive RNA segments carrying 3 ORFs. One of them, the ORF d, has no homology with any known ORF (Felix & al., 2011). We aim to identify its role during infection. We thus cloned it and are currently expressing it in a JU1580 background in order to know whether it affects the anti-viral response of the worm.
In order to evaluate natural variation in sensitivity to these viruses, we scored the susceptibility of natural isolates and standard laboratory strains of C. elegans and C. briggsae. The results reveal i) a species specificity of infection by each virus and ii) intraspecific variation in sensitivity within both species for their respective viruses.
First, we found a species specificity of each virus for a specific Caenorhabditis host species. Indeed, the Santeuil and Le Blanc viruses do not infect JU1580, while the Orsay virus does not infect JU1264 and JU1498
Second, we evaluated the geographic and genetic distribution of Orsay virus susceptibility in a worldwide set of 25 C. elegans isolates representing wild genetic diversity. We measured the viral load by RT-qPCR. Preliminary results suggest that only a subset of isolates from the Old world are sensitive to the virus and none of the "New World". This diversity seems to be partially linked with their ability to perform a small RNA response that acts in anti-viral defense (Felix & al., 2011; poster by Nuez & Felix).
We plan to determine the genetic architecture and identify the molecular basis for this intraspecific variation in Orsay virus susceptibility. One approach is to cross closely related sensitive and resistant strains to obtain Recombinant Inbred Lines. We will test the susceptibility to the virus in these lines in order to find loci involved in the last evolutionary event causing resistance/sensitivity to the virus.
By identifying these loci, we will be able to describe the last step in the "arms race" between C. elegans and its natural virus.