Receptor Complex Mediated Regulation of Symplastic Traffic

Plant receptor kinases (RKs) and receptor proteins (RPs) are involved in a plethora of cellular processes, including developmental decisions and immune responses. There is increasing evidence that plasmodesmata (PD)-localized RKs and RPs act as nexuses that perceive extracellular signals and convey them into intra- and intercellular responses by regulating the exchange of molecules through PD. How RK/RP complexes regulate the specific and nonspecific traffic of molecules through PD, and how these receptors are specifically targeted to PD, have been elusive but underpin comprehensive understanding of the function and regulation of the symplast. In this review we gather the current knowledge of RK/RP complex function at PD and how they might regulate intercellular traffic. There are increasing identifications of plasmodesmata-located receptor kinases and receptor complexes. Receptor kinases CLV1 and ACR4 form a specific complex in the plasmodesmal plasma membrane. The receptor kinase FLS2 and the receptor protein LYM2 modify plasmodesmal function in response to the pathogen-associated ligands flg22 and chitin, respectively. Plasmodesmal membranes have many characteristics of membrane microdomains, that is, they are enriched in sphingolipids and sterols and contain proteins such as remorins and tetraspanins. Membrane microdomains are associated with receptor signaling in animal cells.