Host factors are crucial determinants of viral pathogenicity. Identifying host factors and their contributions to virus infections may lead to the development of novel antiviral strategies. The recently developed virus-induced gene silencing (VIGS) approach offers a rapid means to knock down expression of a given gene in plants. VIGS can be used to determine biological function of candidate genes or to discover new genes that play a role in a given biological pathway. Here, we describe genome-wide Tobacco rattle virus (TRV)-based VIGS screening methods to identify host factors involved in viral pathogenicity.