Receptor like proteins (RLPs) build large protein families in all higher plants. Apart from RLPs with conserved roles in development, an increasing number of RLPs could be associated with functions as immunoreceptors detecting specific patterns from a variety of pathogens. Recent work showed that functionality of these RLPs, at least those with leucine rich repeats in their extracellular domain, depends on association with the common adaptor kinase SOBIR1. We propose that these RLP/adaptor complexes, formed in the absence of ligands, are bimolecular equivalents of genuine receptor kinases. Similar to receptor kinases, activation of these RLP/adaptor complexes seems to require a ligand-dependent interaction step with co-receptors like BAK1 or other SERKs.