The Lysin Motif Receptor-like Kinase (LysM-RLK) CERK1 Is a Major Chitin-binding Protein in Arabidopsis thaliana and Subject to Chitin-induced Phosphorylation

Abstract

Plants detect potential pathogens by sensing microbe-associated molecular patterns via pattern recognition receptors. In the dicot model plant Arabidopsis, the lysin motif (LysM)-containing chitin elicitor receptor kinase 1 (CERK1) has been shown to be essential for perception of the fungal cell wall component chitin and for resistance to fungal pathogens. Recent in vitro studies with CERK1 protein expressed heterologously in yeast suggested direct chitin binding activity. Here we show in an affinity purification approach that CERK1 is a major chitinbinding protein of Arabidopsis cells, along with several known and putative chitinases. The ectodomain of CERK1 harbors three distinct LysM domains with potential ligand binding capacity. We demonstrate that the CERK1 ectodomain binds chitin and partially deacetylated chitosan directly without any requirement for interacting proteins and that all three LysM domains are necessary for chitin binding. Ligand-induced phosphorylation events are a general feature of animal and plant signal transduction pathways. Our studies show that chitin, chitin oligomers, and chitosan rapidly induce in vivo phosphorylation of CERK1 at multiple residues in the juxtamembrane and kinase domain. Functional analyses with a kinase dead variant provide evidence that kinase activity of CERK1 is required for its chitindependent in vivo phosphorylation, as well as for early defense responses and downstream signaling. Collectively, our data suggest that in Arabidopsis, CERK1 is a major chitin, chitosan, and chito-oligomer binding component and that chitin signaling depends on CERK1 post-translational modification and kinase activity.

OsLYP4 and OsLYP6 play critical roles in rice defense signal transduction

“…5,6 On the other hand, rice chitin receptor complex components CEBiP and co-receptor OsCERK1 both contain LysMs, and intact LysM domain is necessary for chitin binding in Arabidopsis CERK1. 7,8 Interestingly, Arabidopsis LYM1/LYM3 was found to contribute to PGN sensing but not chitin. 9 Recently, we identified two rice LysM proteins, OsLYP4 and OsLYP6, play dual function in chitin and PGN perception.…”

Analysis of Two in Planta Expressed LysM Effector Homologs from the FungusMycosphaerella graminicolaReveals Novel Functional Properties and Varying Contributions to Virulence on Wheat

“…However, the considerable reduction in virulence of the Mg3LysM mutants coupled with the magnitude of the host defense gene activation triggered through loss of this effector suggests that chitin recognition and signaling play a major role in controlling STB disease of wheat and, conversely, that evading the activation of chitin-mediated signaling pathways by wheat leaves is of key importance to fungal pathogenesis. Whether cultivated hexaploid wheat possesses functional homologs of the Arabidopsis (Arabidopsis thaliana) and rice (Oryza sativa) LysM domain-containing chitin receptors (Miya et al, 2007;Petutschnig et al, 2010;Shimizu et al, 2010) and downstream signaling components, therefore, awaits determination. However, the recent identification of a putative chitin receptor that is homologous to rice CEBiP in barley (Hordeum vulgare) suggests that CEBiP chitin receptors are conserved in monocot plant species (Tanaka et al, 2010).…”

LYM2-dependent chitin perception limits molecular flux via plasmodesmata

“…Arabidopsis homologs for CEBiP and OsCERK1 are LYSIN MOTIF DOMAIN-CONTAINING GLYCOSYLPHOSPHAT-IDYLINOSITOL-ANCHORED PROTEIN 2 (LYM2, also known as AtCEBiP) and CERK1, respectively (4,5). CERK1 was identified as a component of the chitin perception machinery in Arabidopsis; its ectodomain is capable of binding chitin (6)(7)(8), and the intracellular kinase domain is required for the induction of chitintriggered defense responses such as oxidative burst and MAPK activation (4). The observation that CERK1 is a target for the bacterial effector AvrPtoB (9) and functions as part of a peptidoglycan receptor system (10) indicates that it also plays a role in responses triggered by pathogens that do not contain chitin.…”