Receptor kinase signalling in plants and animals: distinct molecular systems with mechanistic similarities

Plant genomes encode large numbers of receptor kinases that are structurally related to the tyrosine and serine/threonine families of receptor kinase found in animals. Here, we describe recent advances in the characterisation of several of these plant receptor kinases at the molecular level, including the identification of receptor complexes, small polypeptide ligands and cytosolic proteins involved in signal transduction and receptor downregulation. Phylogenetic analysis indicates that plant receptor kinases have evolved independently of the receptor kinase families found in animals. This hypothesis is supported by functional studies that have revealed differences between receptor kinase signalling in plants and animals, particularly concerning their interactions with cytosolic proteins. Despite these dissimilarities, however, plant and animal receptor kinases share many common features, such as their single membrane-pass structure, their inclusion in membrane-associated complexes, the involvement of dimerisation and trans autophosphorylation in receptor activation, and the existence of inhibitors and phosphatases that downregulate receptor activity. These points of convergence may represent features that are essential for a functional receptor-kinase signalling system.