Identification and characterization of host genes involved in regulating replication of brome mosaic virus

Brome mosaic virus (BMV) belongs to a viral class called positive-strand RNA [(+)RNA] viruses. This is the largest class of viruses and includes numerous important pathogens. BMV infects monocotyledonous plants and its replication can be recapitulated in the baker's yeast (Saccharomyces cerevisiae) under laboratory conditions to use yeast as an experimental model system. BMV generally does not infect dicotyledonous plants including the model plant Arabidopsis thaliana. One important shared feature of (+)RNA viruses is that they all make use of host proteins to aid in their own viral replication. In particular, (+)RNA viruses use host intracellular membranes for their replication and lipid composition of these membranes is crucial for viral replication. I show here that BMV replication protein 1a causes redistribution of host Lam5 (Lipid transfer protein Anchored at a Membrane contact site 5) and that Lam5 is necessary for BMV replication in yeast. Furthermore, in the absence of Lam5, BMV 1a affects the distribution of lipid droplets throughout yeast cells. Host factors also play critical roles in defense against viruses. Although wild-type Arabidopsis is not a host for BMV, the Arabidopsis cpr5 (Constitutive expression of Pathogenesis-Related genes 5) mutant can support systemic infection of BMV. I performed screens in Arabidopsis and have identified four genes that contribute to defense against BMV. These include two RNA-binding proteins, a lectin superfamily protein, and an alternative oxidase. My results also contribute to the growing evidence that reactive oxygen species play a key role in BMV replication. In summary, my work provided new insights into BMV replication in hosts and plant defense against BMV infection. The information gained from these projects aids in our understanding of (+)RNA virus biology in general and may identify targets for developing broad-spectrum antiviral strategies.