Receptor Kinases and Signal Pathway in the Arbuscular Mycorrhizal Symbiosis

Abstract

Most terrestrial plants establish symbiotic interactions with arbuscular mycorrhizal fungi (AMF) to acquire phosphorus and nitrogen nutrients. The current understanding regarding how plants recognize symbiotic signals has now been updated. Plant Lysin-Motif receptor kinases, that is, rice OsCERK1 and OsMYR1 or orthologs from other plants, perceive Myc factor, a lipochitooligosaccharide from AMF, to initiate symbiotic signaling pathway. The Myc factor receptor model is quite similar to the known Nod factor receptors required for rhizobial symbiosis and chitin receptors for chitin-triggered immunity. Thus, the open question is how plants use similar receptor complexes to recognize structurally similar molecules to induce different signaling pathways. Upon recognition of Myc/Nod factors signaling, LysM receptors could activate the symbiosis receptor kinase (SymRK), which is an essential component of common symbiotic signaling pathway (CSSP) for both mycorrhizal symbiosis and rhizobial symbiosis. Downstream of SymRK, a clear module in the CSSP by CCaMK-CYCLOPS-DELLA was identified to promote both mycorrhizal symbiosis by activating the expression of RAM1, and rhizobial symbiosis by forming a complex with NSP1/NSP2 to regulate the expression of NIN. In this chapter, we discussed the roles of receptor kinases and CSSP in mycorrhizal symbiosis, as well as in rhizobial symbiosis.