Plant immunity and symbiosis signaling mediated by LysM receptors

Plants have the ability to recognize microbe-associated molecular patterns (MAMPs) and initiate various defense responses. Lysin motif (LysM) receptors are only identified in plant defense signaling mediated by carbohydrate MAMPs such as chitin, peptidoglycan (PGN). LysM-receptor kinase CERK1 is known for chitin and PGN induced defense response in rice and Arabidopsis. Recently, we found that the rice OsCERK1 knockout mutants mostly lose the activities of the LPS-induced ROS generation and gene expression. Interestingly, we also indicated that the mechanisms of LPS perception system of rice and Arabidopsis are significantly different. OsCERK1 is a bifunctional receptor, serving not only for the chitin/LPS-triggered defense response but also for arbuscular mycorrhizal (AM) symbiosis in rice, although the regulatory mechanism of these contradictory system with the same receptor is still unknown. OsCERK1 has non or very poor binding affinity to carbohydrate-ligand, therefor OsCERK1 requires a partner molecule to form the receptor complex for those signalings. We will discuss the investigation of the partner proteins for AM symbiosis. On the other hand, autophosphorylation of AtCERK1 is known to be critical for the activation of downstream signaling in Arabidopsis, however, little is known about the function of phosphorylation events in the activation of AtCERK1 as well as the regulation of chitin-induced immune responses. We will also discuss the downstream of defense signaling mediated by LysM receptor.