CERK1, a LysM receptor kinase, is essential for chitin elicitor signaling in Arabidopsis

Abstract

Chitin is a major component of fungal cell walls and serves as a microbe-associated molecular pattern (MAMP) for the detection of various potential pathogens in innate immune systems of both plants and animals. We recently showed that chitin elicitor-binding protein (CEBiP), plasma membrane glycoprotein with LysM motifs, functions as a cell surface receptor for chitin elicitor in rice. The predicted structure of CEBiP does not contain any intracellular domains, suggesting that an additional component(s) is required for signaling through the plasma membrane into the cytoplasm. Here, we identified a receptor-like kinase, designated CERK1, which is essential for chitin elicitor signaling in Arabidopsis. The KO mutants for CERK1 completely lost the ability to respond to the chitin elicitor, including MAPK activation, reactive oxygen species generation, and gene expression. Disease resistance of the KO mutant against an incompatible fungus, Alternaria brassicicola, was partly impaired. Complementation with the WT CERK1 gene showed cerk1 mutations were responsible for the mutant phenotypes. CERK1 is a plasma membrane protein containing three LysM motifs in the extracellular domain and an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity, suggesting that CERK1 plays a critical role in fungal MAMP perception in plants.plant immunity ͉ host-pathogen interaction ͉ N-acetylchitooligosaccharide P lants trigger various defense reactions against invading pathogens upon perception of so-called microbe-associated molecular patterns [MAMPs; also known as pathogenassociated molecular patterns (PAMPs)]. MAMP recognition has been implicated to play a major role in the nonhost or basal resistance that makes most plants immune to most potential pathogens (1, 2). In the course of coevolution between hosts and parasites, it seems that pathogens developed various virulence factors to overcome MAMP-mediated defense responses, whereas plants evolved resistance-gene-mediated defense system to detect such factors (3-5). Recent studies also revealed the presence of a striking similarity in the MAMP-mediated immunity between plants and animals (2, 6).Despite the importance of MAMP-mediated immunity in plants, molecular machineries involved in the perception of MAMPs and their signal transduction have been poorly understood. So far, only the receptor molecules for two bacterial MAMPs, flg22 and EF-Tu, have been identified (7,8). Both of these receptors, FLS2 and EFR, are receptor kinases with a leucine-rich repeat in the extracellular domain. However, much less information is available for the perception of fungal MAMPs. Chitin and its fragments, chitin oligosaccharides or N-acetylchitooligosaccharides, are typical fungal MAMPs that trigger various defense responses in both monocots and dicots, indicating the presence of a conserved machinery to perceive these oligosaccharides in a wide range of plant species (9, 10). A recent finding that chitin also induces immune responses in mice (11) suggest...

Chitin and chitin-related compounds in plant–fungal interactions

“…In the Arabidopsis genome, five chitin elicitor LysM receptor-like kinase 1 (LysM RLKs) are encoded, of which only one was implicated in chitin detection and named AtCERK1 for chitin elicitor receptor kinase 1 or LysM RLK1 (Miya et al 2007; Wan et al 2008). Structurally, AtCERK1, an RLK, is composed of a transmembrane domain, three tandem LysMs in its ectodomain and an intracellular serine/threonine kinase domain (Miya et al 2007; Wan et al 2008) in Arabidopsis .…”

“…Structurally, AtCERK1, an RLK, is composed of a transmembrane domain, three tandem LysMs in its ectodomain and an intracellular serine/threonine kinase domain (Miya et al 2007; Wan et al 2008) in Arabidopsis . Chitin-induced AtCERK1 homodimerisation has been proved to be necessary for its activation (Liu et al 2012).…”

“…In the situation of defence responses to pathogenic fungi, LysM RLK1 (Wan et al 2008) or CERK1 (Miya et al 2007)/CERK1 (as in Arabidopsis ) or CERK1/CEBiP receptor dimers (as in rice, Shimizu et al 2010) needs longer chito-oligomers, like octamers to activate its response through heterodimerisation (Hayafune et al 2014; Liu et al 2015). The perception of shorter oligosaccharides such as chitotetraose could instead rely on monomeric receptors (Miyata et al 2014; Shinya et al 2015) as into each receptor’s LysM domain, half of this oligomer molecule (C4) fits (Liu et al 2012; Shinya et al 2015).…”

“…The LysM motif is known to exist in the putative Nod-factor receptor kinases involved in the symbiotic signalling between leguminous plants and rhizobia (Desaki et al 2017). Chitin-oligomers from fungal pathogens are structurally like lipo-chito-oligosaccharide Nod factors produced by rhizobia, and LysM RLK1 (Wan et al 2008) or CERK1 (Miya et al 2007) is homologous to legume Nod factor receptors (NFR) NFR1 and NFR5 (Kaku et al 2006). …”

CAST AWAY, a Membrane-Associated Receptor-Like Kinase, Inhibits Organ Abscission in Arabidopsis

“…A recent study has revealed that, like PBS1, BIK1 and several PBS1-like (PBL) RLCKs are also substrates of the bacterial AvrPphB protease effector . This discovery and other work suggests that a bacterial effector can suppress PAMP-triggered immunity in plants by cleaving RLCKs known (BIK1) or proposed (PBL1, PBL2) to positively interact with RLKs that bind PAMPs, including FLS2, CHITIN ELICITOR RECEPTOR KINASE1, and the EF-Tu RE-CEPTOR (Zipfel et al, 2006;Miya et al, 2007;Zhang et al, 2010). During effector-triggered immunity, another RLCK, RPM1-INDUCED PROTEIN KINASE (RIPK), is involved in activating the NB-LRR protein RPM1 (Liu et al, 2011).…”