In a recent PLoS pathogens paper, Joël van Mierlo and Gijs Overheul in the group of Ronald van Rij (dept. Medical Microbiology) and collaborators analyzed the intricate interactions between viruses and the RNAi-based antiviral immune response. It is long been proposed that viruses and their hosts engage in an evolutionary arms race. Viruses may select for hosts with more effective immune responses, whereas the immune response of the host may select for viruses that evade the immune system. These viral counter-defenses may in turn drive rapid evolution of host immune genes. A potential outcome of this perpetual cycle is that the interaction between virus and host becomes highly specific. While this is an attractive hypothesis, direct supporting evidence is scarce. Using the fruit fly Drosophila as a model, Van Mierlo and colleagues now provide strong support for an arms race between virus and host. The RNA interference (RNAi) pathway is a critical mechanism for antiviral defense in many systems. As a counter-defense, viruses encode suppressors proteins that sabotage antiviral RNAi. The authors identified novel viruses that infect different fruit fly species and showed that the RNAi suppressor proteins of these viruses can be specific to their host. These results are in line with the hypothesis that virus-host co-evolution shapes the genomes of both virus and host. Moreover, these results suggest that RNAi suppressor proteins have the potential to determine host specificity of viruses. van Mierlo JT, Overheul GJ, Obadia B, van Cleef KW, Webster CL, Saleh MC, Obbard DJ, van Rij RP. 2014. Novel Drosophila viruses encode host-specific suppressors of RNAi. PLoS Pathogens, 10: e1004256.
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