The alg-1 Gene Is Necessary for Orsay Virus Replication in Caenorhabditis elegans

The establishment of the Orsay virus-Caenorhabditis elegans infection model has enabled the identification of host factors essential for virus infection. Argonautes are RNA interacting proteins evolutionary conserved in the three domains of life that are key components of small RNA pathways. C. elegans encodes 27 argonautes or argonaute-like proteins. Here, we determined that mutation of the argonaute-like gene 1, alg-1, results in a greater than 10,000-fold reduction in Orsay viral RNA levels, which could be rescued by ectopic expression of alg-1. Mutation in ain-1, a known interactor of ALG-1 and component of the RNA-induced silencing complex, also resulted in a significant reduction in Orsay virus levels. Viral RNA replication from an endogenous transgene replicon system was impaired by the lack of ALG-1, suggesting that ALG-1 plays a role during the replication stage of the virus life cycle. Orsay virus RNA levels were unaffected by mutations in the ALG-1 RNase H-like motif that ablate the slicer activity of ALG-1. These findings demonstrate a novel function of ALG-1 in promoting Orsay virus replication in C. elegans. IMPORTANCE All viruses are obligate intracellular parasites that recruit the cellular machinery of the host they infect to support their own proliferation. We used Caenorhabditis elegans and its only known infecting virus, Orsay virus, to identify host proteins relevant for virus infection. We determined that ALG-1, a protein previously known to be important in influencing worm life span and the expression levels of thousands of genes, is required for Orsay virus infection of C. elegans. This is a new function attributed to ALG-1 that was not recognized before. In humans, it has been shown that AGO2, a close relative protein to ALG-1, is essential for hepatitis C virus replication. This demonstrates that through evolution from worms to humans, some proteins have maintained similar functions, and consequently, this suggests that studying virus infection in a simple worm model has the potential to provide novel insights into strategies used by viruses to proliferate.