Receptor-like proteins (RLPs) are receptors on the surface of plant cells that are important for the activation of disease resistance. Furthermore, some RLPs are important for plant development. The Arabidopsis genome contains 57 genes encoding RLPs. A genome wide collection of RLP gene knock-out mutants was assembled and functionally analyzed for defects in defense and development. This resulted in the identification of an RLP that plays a role in hormone perception, and two RLPs that play a role in non-host resistance, the phenomenon that a plant species is typically resistant to pathogens of other plant species. RNA silencing is a regulatory mechanism by which the expression of genes is downregulated or entirely suppressed. In this thesis, it is demonstrated for the first time that this mechanism is important for defense of Arabidopsis against a fungal pathogen; the vascular wilt fungus Verticillium. This is an extremely important pathogen of over 200 plant species including economically important crops.