Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0004672 protein kinase activity	IEA GO_REF:0000002	MARK AS OVER ANNOTATED	Summary: CERK1 has an intracellular serine/threonine protein kinase domain and displays autophosphorylation and substrate (PBL27) kinase activity. This InterPro-based protein kinase activity annotation is correct but is a broad parent of the more specific Ser/Thr kinase term. Reason: The annotation is biochemically correct but is subsumed by the more specific and experimentally supported protein serine/threonine kinase activity (GO:0004674). It is retained as a non-misleading parent term. Supporting Evidence: PMID:18042724 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
GO:0004674 protein serine/threonine kinase activity	IEA GO_REF:0000003	ACCEPT	Summary: CERK1 has an intracellular Ser/Thr kinase domain and EC 2.7.11.1 catalytic activity (serine and threonine phosphorylation), supported experimentally by autophosphorylation and phosphorylation of PBL27. This is a core molecular function. Reason: Directly supported by experimental characterization of the intracellular Ser/Thr kinase domain and catalytic activity, and by the duplicate IDA annotation from PMID:18042724. Supporting Evidence: PMID:18042724 an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity file:ARATH/CERK1/CERK1-deep-research-falcon.md CERK1 has intrinsic kinase activity with autophosphorylation and myelin basic protein phosphorylation in vitro
GO:0005524 ATP binding	IEA GO_REF:0000002	ACCEPT	Summary: As an active protein kinase, CERK1 binds ATP. UniProt annotates the canonical kinase ATP-binding region (residues 328-336) and ATP-binding residue 349. This is a standard, correct molecular function for a kinase. Reason: Consistent with the conserved kinase ATP-binding motif and experimentally demonstrated kinase/autophosphorylation activity requiring ATP. Supporting Evidence: PMID:18042724 an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity
GO:0005886 plasma membrane	IEA GO_REF:0000120	ACCEPT	Summary: CERK1 is a single-pass plasma membrane receptor kinase. Plasma membrane localization is well supported experimentally (duplicate IDA annotations below). Reason: Plasma membrane localization is the established site of CERK1 function and is supported by multiple experimental studies. Supporting Evidence: PMID:18042724 as well as the localization of CERK1 in the plasma membrane file:ARATH/CERK1/CERK1-deep-research-falcon.md CERK1 is localized to the plasma membrane.
GO:0009617 response to bacterium	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: CERK1 participates in bacterial perception (peptidoglycan sensing with LYM1/LYM3) and restricts bacterial growth, so a broad "response to bacterium" annotation is appropriate. More specific terms (defense response to bacterium, detection of peptidoglycan) are also present. Reason: Biologically correct but broad; the bacterial role is real but secondary to the core chitin/fungal immune function, and is better captured by the more specific terms also annotated. Supporting Evidence: PMID:19816132 CERK1 mediates perception of an unknown bacterial PAMP in Arabidopsis file:ARATH/CERK1/CERK1-deep-research-falcon.md including LYM1/LYM3 for peptidoglycan signaling and LYM2 for plasmodesmal chitin responses.
GO:0019199 transmembrane receptor protein kinase activity	IEA GO_REF:0000002	ACCEPT	Summary: CERK1 is a single-pass transmembrane receptor with an extracellular ligand (chitin)-binding ectodomain and an intracellular Ser/Thr kinase domain; chitin-induced dimerization activates signaling. This term accurately captures its receptor kinase nature. Reason: Supported by domain architecture and the experimental demonstration that ligand-induced receptor dimerization activates kinase signaling (duplicate IDA/IMP annotations below). Supporting Evidence: PMID:22654057 chitin-induced AtCERK1 dimerization is critical for its activation file:ARATH/CERK1/CERK1-deep-research-falcon.md CERK1 is a single-pass membrane receptor with
GO:0045087 innate immune response	IEA GO_REF:0000120	ACCEPT	Summary: CERK1 is essential for chitin-triggered innate immunity and contributes to bacterial PAMP-triggered immunity. This is a core biological process. Reason: Strongly supported across the literature; cerk1 mutants lose chitin-induced immune responses. Duplicate IMP annotation also present. Supporting Evidence: PMID:18263776 LysM RLK1 is essential for chitin signaling in plants (likely as part of the receptor complex) and is involved in chitin-mediated plant innate immunity file:ARATH/CERK1/CERK1-deep-research-falcon.md CERK1 is a key PRR component required for chitin-induced PTI outputs including MAPK activation, ROS burst, and defense gene induction.
GO:0106310 protein serine kinase activity	IEA GO_REF:0000116	ACCEPT	Summary: Rhea/EC mapping of the serine phosphorylation half-reaction (EC 2.7.11.1). CERK1 phosphorylates serine residues (e.g. autophosphorylation at Ser-266, Ser-268, Ser-274). Correct but redundant with the broader Ser/Thr kinase term. Reason: Biochemically accurate; CERK1 demonstrably phosphorylates serine residues. Consistent with the curated phosphoserine sites. Supporting Evidence: PMID:20610395 chitin, chitin oligomers, and chitosan rapidly induce in vivo phosphorylation of CERK1 at multiple residues in the juxtamembrane and kinase domain
GO:1901701 cellular response to oxygen-containing compound	IEA GO_REF:0000117	MARK AS OVER ANNOTATED	Summary: This very broad ARBA machine-learning term likely derives from chitin (an oxygen-containing carbohydrate) responsiveness, but it is too generic to be informative for CERK1, whose specific roles are captured by "cellular response to chitin" and "response to chitin". Reason: Uninformatively broad ARBA-derived annotation; the specific and accurate response terms (cellular response to chitin, GO:0071323) are already present. Not wrong but over-general. Supporting Evidence: PMID:18263776 The mutation in this gene blocked the induction of almost all chitooligosaccharide-responsive genes
GO:0042802 identical protein binding	IPI PMID:22654057 Chitin-induced dimerization activates a plant immune recepto...	ACCEPT	Summary: CERK1 forms ligand-induced homodimers; a chitin octamer acts as a bivalent ligand driving AtCERK1-ECD dimerization required for activation. "Identical protein binding" captures the self-association, but the more specific "protein homodimerization activity" (also annotated) is preferable. Reason: Self-interaction (homodimerization) is experimentally demonstrated by crystallography and biochemistry. Retained as accurate; complementary to the homodimerization activity annotation. Supporting Evidence: PMID:22654057 a chitin octamer induces AtCERK1-ECD dimerization that is inhibited by shorter chitin oligomers
GO:0004672 protein kinase activity	IMP PMID:24750441 Selective regulation of the chitin-induced defense response ...	MARK AS OVER ANNOTATED	Summary: Kinase activity of CERK1 (mediating chitin-induced phosphorylation of PBL27) is supported by mutant phenotype analysis. Correct but a broad parent of the specific Ser/Thr kinase term. Reason: Biochemically correct but subsumed by the more specific Ser/Thr kinase activity (GO:0004674). Retained as a non-misleading parent. Supporting Evidence: PMID:24750441 In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1 and contributes to the regulation of chitin-induced immunity in Arabidopsis.
GO:0050832 defense response to fungus	IMP PMID:18263776 A LysM receptor-like kinase plays a critical role in chitin ...	ACCEPT	Summary: cerk1/lysm RLK1 mutants are more susceptible to fungal pathogens and lose chitin-induced defense, establishing a role in defense response to fungus. This is a core biological process. Reason: Directly supported by loss-of-function phenotypes showing increased susceptibility to fungal pathogens. Supporting Evidence: PMID:18263776 The mutation in this gene blocked the induction of almost all chitooligosaccharide-responsive genes and led to more susceptibility to fungal pathogens file:ARATH/CERK1/CERK1-deep-research-falcon.md Disease phenotype against Alternaria brassicicola showed lesion size 1.37 ± 0.57 mm in cerk1-2 versus 1.14 ± 0.56 mm in Col-0
GO:0005576 extracellular region	ISM GO_REF:0000122	REMOVE	Summary: This sequence-based (AtSubP) prediction is misleading. CERK1 is a single-pass plasma membrane protein with an extracellular ectodomain (the LysM domains face the apoplast), but the protein is not located in the extracellular region; it is membrane-anchored at the plasma membrane. Reason: The protein localizes to the plasma membrane (experimental IDA), not the extracellular region. The ISM prediction conflates the extracellular ectodomain topology with whole-protein localization and is incorrect. Supporting Evidence: PMID:18042724 as well as the localization of CERK1 in the plasma membrane
GO:0005515 protein binding	IPI PMID:29182677 Arabidopsis ubiquitin ligase PUB12 interacts with and negati...	REMOVE	Summary: Captures the interaction between CERK1 and the U-box E3 ligase PUB12 (and PUB13), which negatively regulate CERK1 in a phosphorylation-dependent manner. The generic "protein binding" term is uninformative. Reason: Bare "protein binding" is not informative about molecular function. The specific CERK1-PUB12/PUB13 interaction is documented in the gene notes and better represented by the regulatory biology rather than a generic MF term. Supporting Evidence: PMID:29182677 the ARM domains of PUB12 and its paralog PUB13 interacted with the intracellular domain of CERK1 in a manner that was dependent on its autophosphorylation
GO:0005515 protein binding	IPI PMID:27317676 The Arabidopsis Malectin-Like/LRR-RLK IOS1 Is Critical for B...	REMOVE	Summary: Captures the CERK1-IOS1 (malectin-like/LRR-RLK) interaction relevant to pattern-triggered immunity. Generic "protein binding" is uninformative. Reason: Bare "protein binding" provides no molecular-function information; the specific CERK1-IOS1 interaction is recorded in the gene notes. Supporting Evidence: PMID:27317676 CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) recognize microbe-associated molecular patterns (MAMPs) to activate pattern-triggered immunity (PTI)
GO:0005515 protein binding	IPI PMID:24750441 Selective regulation of the chitin-induced defense response ...	REMOVE	Summary: Captures the CERK1-PBL27 interaction. CERK1 interacts with and phosphorylates the receptor-like cytoplasmic kinase PBL27. Generic "protein binding" is uninformative and is better represented by the kinase-substrate relationship. Reason: Bare "protein binding" is uninformative; the functionally meaningful CERK1-PBL27 kinase-substrate interaction is captured by the kinase activity and protein phosphorylation annotations. Supporting Evidence: PMID:24750441 In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1 and contributes to the regulation of chitin-induced immunity in Arabidopsis.
GO:0005515 protein binding	IPI PMID:27679653 The Arabidopsis CERK1-associated kinase PBL27 connects chiti...	REMOVE	Summary: Captures the CERK1-PBL27 association connecting chitin perception to MAPK activation. Generic "protein binding" is uninformative. Reason: Bare "protein binding" is uninformative; the CERK1-PBL27 functional relationship is captured elsewhere (kinase activity, protein phosphorylation, intracellular signal transduction). Supporting Evidence: PMID:27679653 The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation
GO:0005886 plasma membrane	IDA PMID:24750441 Selective regulation of the chitin-induced defense response ...	ACCEPT	Summary: Experimental localization of CERK1 (and its interaction with PBL27) at the plasma membrane. Core localization. Reason: Direct experimental evidence for plasma membrane localization, consistent with CERK1's role as a cell-surface receptor. Supporting Evidence: PMID:18042724 as well as the localization of CERK1 in the plasma membrane
GO:0005886 plasma membrane	IDA PMID:27679653 The Arabidopsis CERK1-associated kinase PBL27 connects chiti...	ACCEPT	Summary: Experimental localization of CERK1 at the plasma membrane. Core localization; duplicate of the IDA annotation above. Reason: Direct experimental evidence for plasma membrane localization. Supporting Evidence: PMID:27679653 The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation
GO:0071323 cellular response to chitin	IMP PMID:24750441 Selective regulation of the chitin-induced defense response ...	ACCEPT	Summary: CERK1 is required for cellular responses to chitin, including PBL27 phosphorylation, MPK3/6 activation and downstream defense. Core process. Reason: Supported by mutant phenotypes showing loss of chitin-induced defense responses. Supporting Evidence: PMID:24750441 Knockout of PBL27 resulted in the suppression of several chitin-induced defense responses, including the activation of MPK3/6
GO:0006468 protein phosphorylation	IDA PMID:25036661 LIK1, a CERK1-interacting kinase, regulates plant immune res...	ACCEPT	Summary: CERK1 directly phosphorylates substrates such as the LRR-RLK LIK1 (and PBL27). Protein phosphorylation is a core activity of the kinase domain. Reason: Direct experimental evidence that CERK1 phosphorylates downstream substrates (LIK1 in vitro and in vivo). Supporting Evidence: PMID:25036661 In vitro experiments showed that LIK1 was directly phosphorylated by CERK1
GO:0016301 kinase activity	IDA PMID:25036661 LIK1, a CERK1-interacting kinase, regulates plant immune res...	MARK AS OVER ANNOTATED	Summary: Broad "kinase activity" term. CERK1 is a protein Ser/Thr kinase; the specific Ser/Thr kinase activity terms are preferable. Reason: Correct but uninformatively broad; subsumed by the specific protein serine/threonine kinase activity (GO:0004674). Supporting Evidence: PMID:25036661 In vitro experiments showed that LIK1 was directly phosphorylated by CERK1
GO:0005515 protein binding	IPI PMID:25340959 The kinase LYK5 is a major chitin receptor in Arabidopsis an...	REMOVE	Summary: Captures the chitin-induced CERK1-LYK5 complex, in which the high-affinity chitin receptor LYK5 recruits CERK1. Generic "protein binding" is uninformative; the specific functional interaction is described in the gene notes. Reason: Bare "protein binding" is uninformative. The biologically important chitin-dependent LYK5-CERK1 complex is recorded in the gene notes and reflected in the receptor-complex biology. Supporting Evidence: PMID:25340959 AtLYK5 interacts with AtCERK1 in a chitin-dependent manner
GO:0008061 chitin binding	IDA PMID:22654057 Chitin-induced dimerization activates a plant immune recepto...	ACCEPT	Summary: The CERK1 ectodomain binds chitin directly; the crystal structure of AtCERK1-ECD with a chitin pentamer shows binding mediated by a LysM domain and three NAG residues. Core molecular function. Reason: Direct structural and biochemical evidence for chitin binding by the LysM ectodomain. Supporting Evidence: PMID:22654057 directly binds chitin through its lysine motif (LysM)-containing ectodomain (AtCERK1-ECD)
GO:0008061 chitin binding	IDA PMID:22740685 How plant lysin motif receptors get activated: lessons learn...	ACCEPT	Summary: Review of CERK1 structural biology confirming chitin binding via the LysM ectodomain. Core molecular function; duplicate of other IDA chitin-binding annotations. Reason: Consistent with structural data that CERK1 binds NAG oligomers derived from chitin via its LysM ectodomain. Supporting Evidence: PMID:22740685 CERK1 binds NAG oligomers derived from chitin-the major constituent of fungal cell walls-and mediates immunity to fungal infection
GO:0042803 protein homodimerization activity	IDA PMID:22654057 Chitin-induced dimerization activates a plant immune recepto...	ACCEPT	Summary: Chitin octamer acts as a bivalent ligand inducing CERK1 homodimerization, which is required for receptor activation. This is a core, activating molecular function. Reason: Directly demonstrated by crystallography and biochemistry; mutations attenuating dimerization compromise CERK1-mediated signaling. Supporting Evidence: PMID:22654057 a chitin octamer induces AtCERK1-ECD dimerization that is inhibited by shorter chitin oligomers file:ARATH/CERK1/CERK1-deep-research-falcon.md Early model: CERK1 can homodimerize upon chitin binding.
GO:0042803 protein homodimerization activity	IDA PMID:22740685 How plant lysin motif receptors get activated: lessons learn...	ACCEPT	Summary: Review/structural confirmation that ligand-induced CERK1 homodimerization is required for immune signaling. Duplicate homodimerization annotation. Reason: Consistent with the structural model that NAG octamers stabilize CERK1 dimers to enable signaling. Supporting Evidence: PMID:22740685 Receptor activation and immune signaling requires, however, ligand-induced CERK1 homodimerization
GO:0071219 cellular response to molecule of bacterial origin	IEP PMID:22744984 LYK4, a lysin motif receptor-like kinase, is important for c...	KEEP AS NON CORE	Summary: CERK1 is induced by and participates in responses to bacterial molecules/PAMPs (including peptidoglycan), and CERK1 expression is induced by flagellin. cerk1 mutants show enhanced susceptibility to bacteria. Reason: Real but secondary to the core fungal-chitin function. The bacterial role is genuine (peptidoglycan sensing with LYM1/LYM3; restricting bacterial growth) but peripheral relative to chitin perception. Supporting Evidence: PMID:22744984 enhanced susceptibility to both the bacterial pathogen Pseudomonas syringae pv tomato DC3000 and the fungal pathogen Alternaria brassicicola
GO:0071323 cellular response to chitin	IEP PMID:22744984 LYK4, a lysin motif receptor-like kinase, is important for c...	ACCEPT	Summary: CERK1 is essential for cellular responses to chitin (induction of chitin-responsive genes, cytosolic calcium elevation). Core process; duplicate of the IMP annotation. Reason: Well supported; cerk1 mutants lose chitin-induced cellular responses. Supporting Evidence: PMID:22744984 reduced induction of chitin-responsive genes and diminished chitin-induced cytosolic calcium elevation
GO:0004674 protein serine/threonine kinase activity	IDA PMID:19951949 Direct binding of a plant LysM receptor-like kinase, LysM RL...	ACCEPT	Summary: CERK1 is autophosphorylated in vitro, demonstrating Ser/Thr protein kinase activity of the intracellular kinase domain. Core molecular function. Reason: Direct in vitro evidence of autophosphorylation by recombinant CERK1. Supporting Evidence: PMID:19951949 LysM RLK1-yEGFP was autophosphorylated in vitro
GO:0008061 chitin binding	IDA PMID:19951949 Direct binding of a plant LysM receptor-like kinase, LysM RL...	ACCEPT	Summary: First demonstration of direct, specific, high-affinity (Kd ~82 nM) binding of CERK1 to chitin in vitro. Core molecular function. Reason: Direct biochemical evidence of specific chitin binding by recombinant CERK1. Supporting Evidence: PMID:19951949 we present the first evidence for direct binding of LysM RLK1 to chitin file:ARATH/CERK1/CERK1-deep-research-falcon.md evidence supports preferential recognition of longer chitin oligomers, especially chitin heptamers/octamers, and GlcNAc8-driven receptor activation/dimerization
GO:0008061 chitin binding	IDA PMID:20610395 The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a m...	ACCEPT	Summary: CERK1 is a major chitin-binding protein of Arabidopsis cells; its ectodomain binds chitin (and chitosan) directly, with all three LysM domains required. Core molecular function. Reason: Affinity-purification and direct-binding experiments confirm chitin binding by the CERK1 ectodomain. Supporting Evidence: PMID:20610395 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
GO:0046777 protein autophosphorylation	IDA PMID:19951949 Direct binding of a plant LysM receptor-like kinase, LysM RL...	ACCEPT	Summary: CERK1 autophosphorylates in vitro. Autophosphorylation is a core regulatory feature of the kinase. Reason: Direct experimental evidence of in vitro autophosphorylation. Supporting Evidence: PMID:19951949 LysM RLK1-yEGFP was autophosphorylated in vitro
GO:0046777 protein autophosphorylation	IDA PMID:20610395 The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a m...	ACCEPT	Summary: Chitin, chitin oligomers and chitosan rapidly induce in vivo phosphorylation of CERK1 at multiple residues; kinase activity is required for this chitin-dependent autophosphorylation. Core regulatory process. Reason: Direct evidence of chitin-induced in vivo (auto)phosphorylation requiring CERK1 kinase activity. Supporting Evidence: PMID:20610395 kinase activity of CERK1 is required for its chitin-dependent in vivo phosphorylation
GO:2001080 chitosan binding	IDA PMID:20610395 The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a m...	ACCEPT	Summary: The CERK1 ectodomain binds partially deacetylated chitosan directly in addition to chitin. A specific, experimentally supported molecular function. Reason: Direct binding experiments show the CERK1 ectodomain binds chitosan. Supporting Evidence: PMID:20610395 the CERK1 ectodomain binds chitin and partially deacetylated chitosan directly
GO:0002752 cell surface pattern recognition receptor signaling pathway	IDA PMID:19816132 The LysM receptor kinase CERK1 mediates bacterial perception...	ACCEPT	Summary: CERK1 is a cell-surface pattern recognition receptor that perceives MAMPs (chitin; also a bacterial PAMP) and initiates defense signaling. Core process. Reason: CERK1 functions as a plasma-membrane PRR initiating PAMP-triggered immunity signaling. Supporting Evidence: PMID:19816132 Plants use pattern recognition receptors (PRRs) to perceive pathogen-associated molecular pattern (PAMPs) and initiate defence responses file:ARATH/CERK1/CERK1-deep-research-falcon.md CERK1 activation triggers hallmark PTI responses:
GO:0005515 protein binding	IPI PMID:19249211 AvrPtoB targets the LysM receptor kinase CERK1 to promote ba...	REMOVE	Summary: Captures the interaction between CERK1 and the Pseudomonas syringae type III effector AvrPtoB, which ubiquitinates and degrades CERK1 to suppress immunity. Generic "protein binding" is uninformative. Reason: Bare "protein binding" is uninformative; the CERK1-AvrPtoB interaction (host-pathogen) is documented in the gene notes and is not a constitutive molecular function of CERK1. Supporting Evidence: PMID:19249211 AvrPtoB ubiquitinates the CERK1 kinase domain in vitro and targets CERK1 for degradation in vivo
GO:0042742 defense response to bacterium	IDA PMID:19816132 The LysM receptor kinase CERK1 mediates bacterial perception...	KEEP AS NON CORE	Summary: CERK1 restricts bacterial growth and mediates perception of a bacterial PAMP; cerk1 plants show reduced PAMP-induced defense to bacterial extracts and enhanced bacterial susceptibility. A genuine but secondary defense role. Reason: The bacterial defense role is real (peptidoglycan sensing; restricting bacterial growth) but peripheral to the core chitin/fungal immune function. Supporting Evidence: PMID:19816132 plays an essential role in restricting bacterial growth on plants
GO:0004674 protein serine/threonine kinase activity	IDA PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: Original identification of CERK1 as a receptor kinase with an intracellular Ser/Thr kinase domain displaying autophosphorylation and MBP kinase activity. Core molecular function. Reason: Direct experimental evidence of Ser/Thr kinase activity from the founding CERK1 paper. Supporting Evidence: PMID:18042724 an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity
GO:0046777 protein autophosphorylation	IDA PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: The CERK1 kinase domain shows autophosphorylation activity. Core regulatory process; duplicate annotation. Reason: Direct experimental evidence of autophosphorylation. Supporting Evidence: PMID:18042724 an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity
GO:0008061 chitin binding	IDA PMID:22744984 LYK4, a lysin motif receptor-like kinase, is important for c...	ACCEPT	Summary: Chitin binding annotation associated with the LYK4 study context. CERK1 chitin binding via its LysM ectodomain is well established by direct biochemical and structural evidence. Core molecular function. Reason: Consistent with the extensive direct evidence that CERK1 binds chitin through its LysM ectodomain. Supporting Evidence: PMID:20610395 the CERK1 ectodomain binds chitin and partially deacetylated chitosan directly
GO:0045087 innate immune response	IMP PMID:22461667 The LysM receptor-like kinase LysM RLK1 is required to activ...	ACCEPT	Summary: CERK1/LysM RLK1 is required to activate chitin-induced defense (and abiotic-stress) responses; loss-of-function abolishes these responses. Core biological process. Reason: Mutant phenotype analysis shows CERK1 is required for chitin-induced immune responses. Supporting Evidence: PMID:22461667 known to play a critical role in signaling defense responses induced by exogenous chitin
GO:0019199 transmembrane receptor protein kinase activity	IMP PMID:22106285 Arabidopsis lysin-motif proteins LYM1 LYM3 CERK1 mediate bac...	ACCEPT	Summary: CERK1 acts as a transmembrane receptor kinase required for bacterial peptidoglycan sensing (with LYM1/LYM3). Confirms receptor kinase function. Core molecular function. Reason: Supported by mutant phenotypes; CERK1 functions as a transmembrane receptor kinase in PAMP perception. Supporting Evidence: PMID:22106285 PGN sensing and immunity to bacterial infection in Arabidopsis thaliana requires three lysin-motif (LysM) domain proteins
GO:0032499 detection of peptidoglycan	IMP PMID:22106285 Arabidopsis lysin-motif proteins LYM1 LYM3 CERK1 mediate bac...	KEEP AS NON CORE	Summary: With LYM1 and LYM3, CERK1 mediates sensing of bacterial peptidoglycan and immunity to bacterial infection. A specific, genuine but secondary process. Reason: Real role in peptidoglycan-mediated bacterial sensing, but secondary to CERK1's core chitin/fungal perception function. Supporting Evidence: PMID:22106285 PGN sensing and immunity to bacterial infection in Arabidopsis thaliana requires three lysin-motif (LysM) domain proteins
GO:0035556 intracellular signal transduction	IDA PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: CERK1 transduces the perceived chitin signal across the plasma membrane into the cytoplasm via its intracellular kinase domain, acting upstream of MAPK activation and ROS. Core process, though a broad term. Reason: CERK1 is positioned upstream of intracellular signaling cascades (MAPK, ROS) and transduces the signal via its cytoplasmic kinase domain. Supporting Evidence: PMID:18042724 CERK1 is involved in the perception of the chitin oligosaccharide elicitor at the cell surface and the transduction of the signal into the cytoplasm via its intracellular serine/threonine kinase activity file:ARATH/CERK1/CERK1-deep-research-falcon.md Activated CERK1 signals through RLCK-VII kinases including PBL27, BIK1, and PBL19, linking receptor activation to ROS production, Ca2+ influx, MAPK cascades, defense gene expression, callose deposition, and stomatal immunity.
GO:0010200 response to chitin	IMP PMID:18263776 A LysM receptor-like kinase plays a critical role in chitin ...	ACCEPT	Summary: CERK1 is essential for the response to chitin; mutants block induction of almost all chitooligosaccharide-responsive genes. Core process. Reason: Mutant phenotype analysis shows CERK1 is required for the chitin response. Supporting Evidence: PMID:18263776 The mutation in this gene blocked the induction of almost all chitooligosaccharide-responsive genes
GO:0005886 plasma membrane	IDA PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: Experimental demonstration that CERK1 is a plasma membrane protein. Core localization; founding study. Reason: Direct experimental evidence for plasma membrane localization. Supporting Evidence: PMID:18042724 as well as the localization of CERK1 in the plasma membrane
GO:0019199 transmembrane receptor protein kinase activity	IDA PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: CERK1 is a plasma membrane receptor kinase with extracellular LysM domains and an intracellular Ser/Thr kinase domain. Core molecular function; duplicate of the IMP annotation. Reason: Founding study establishes CERK1 as a transmembrane receptor kinase. Supporting Evidence: PMID:18042724 CERK1 is a plasma membrane protein containing three LysM motifs in the extracellular domain and an intracellular Ser/Thr kinase domain
GO:0032491 detection of molecule of fungal origin	IEP PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: CERK1 detects the fungal cell wall MAMP chitin at the cell surface, functioning as a master switch of chitin signaling. Core process; duplicate (IEP) of the IMP annotation. Reason: CERK1 perceives chitin (a fungal-origin molecule) and is essential for chitin signaling. Supporting Evidence: PMID:18042724 CERK1 plays a critical role in fungal MAMP perception in plants
GO:0032491 detection of molecule of fungal origin	IMP PMID:18042724 CERK1, a LysM receptor kinase, is essential for chitin elici...	ACCEPT	Summary: cerk1 KO mutants completely lose the ability to respond to chitin elicitor, demonstrating CERK1 is required to detect the fungal MAMP. Core process. Reason: Loss-of-function abolishes chitin detection/response, establishing CERK1's role in detecting a fungal-origin molecule. Supporting Evidence: PMID:18042724 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 file:ARATH/CERK1/CERK1-deep-research-falcon.md Loss-of-function cerk1 mutants lose chitin-elicitor responses (MAPK activation, ROS production, defense gene expression), placing CERK1 at the top of the signaling cascade.

Core Functions

Binds the fungal cell wall polysaccharide chitin (and partially deacetylated chitosan) through its extracellular three-LysM-domain ectodomain at the plasma membrane, providing the ligand-recognition step of chitin perception.

Molecular Function:

chitin binding

Directly Involved In:

detection of molecule of fungal origin response to chitin

Cellular Locations:

plasma membrane

Supporting Evidence:

PMID:22654057
directly binds chitin through its lysine motif (LysM)-containing ectodomain (AtCERK1-ECD)
PMID:20610395
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
file:ARATH/CERK1/CERK1-deep-research-falcon.md
All three LysM domains are required for full chitin responsiveness.

Functions as a transmembrane receptor protein serine/threonine kinase: chitin-induced homodimerization activates the intracellular kinase domain, which autophosphorylates and phosphorylates downstream substrates (e.g. PBL27, LIK1) to transduce the signal into the cytoplasm.

Molecular Function:

protein serine/threonine kinase activity

Directly Involved In:

protein phosphorylation intracellular signal transduction

Cellular Locations:

plasma membrane

Supporting Evidence:

PMID:18042724
an intracellular Ser/Thr kinase domain with autophosphorylation/myelin basic protein kinase activity
PMID:24750441
In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1 and contributes to the regulation of chitin-induced immunity in Arabidopsis.
file:ARATH/CERK1/CERK1-deep-research-falcon.md
CERK1 has intrinsic kinase activity with autophosphorylation and myelin basic protein phosphorylation in vitro

Acts as a cell-surface pattern recognition receptor that initiates chitin- triggered innate immunity (MAPK activation, ROS, gene induction) and is essential for defense against fungal pathogens; ligand-induced homodimerization is the activating event.

Molecular Function:

transmembrane receptor protein kinase activity

Directly Involved In:

cell surface pattern recognition receptor signaling pathway innate immune response defense response to fungus

Cellular Locations:

plasma membrane

Supporting Evidence:

PMID:18042724
CERK1, a LysM receptor kinase, is essential for chitin elicitor signaling in Arabidopsis
PMID:22654057
chitin-induced AtCERK1 dimerization is critical for its activation
file:ARATH/CERK1/CERK1-deep-research-falcon.md
CERK1 is a key PRR component required for chitin-induced PTI outputs including MAPK activation, ROS burst, and defense gene induction.

References

file:ARATH/CERK1/CERK1-deep-research-falcon.md

Falcon (Edison Scientific) deep research report for CERK1

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000003

Gene Ontology annotation based on Enzyme Commission mapping

GO_REF:0000116

Automatic Gene Ontology annotation based on Rhea mapping

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

GO_REF:0000122

AtSubP analysis

PMID:18042724

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

"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."

PMID:18263776

A LysM receptor-like kinase plays a critical role in chitin signaling and fungal resistance in Arabidopsis.

"LysM RLK1 is essential for chitin signaling in plants (likely as part of the receptor complex) and is involved in chitin-mediated plant innate immunity."

PMID:19249211

AvrPtoB targets the LysM receptor kinase CERK1 to promote bacterial virulence on plants.

"AvrPtoB ubiquitinates the CERK1 kinase domain in vitro and targets CERK1 for degradation in vivo."

PMID:19816132

The LysM receptor kinase CERK1 mediates bacterial perception in Arabidopsis.

"the Arabidopsis LysM receptor kinase CERK1 is required not only for chitin signalling and fungal resistance, but plays an essential role in restricting bacterial growth on plants"

PMID:19951949

Direct binding of a plant LysM receptor-like kinase, LysM RLK1/CERK1, to chitin in vitro.

"we present the first evidence for direct binding of LysM RLK1 to chitin"

PMID:20610395

The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a major chitin-binding protein in Arabidopsis thaliana and subject to chitin-induced phosphorylation.

"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"

PMID:22106285

Arabidopsis lysin-motif proteins LYM1 LYM3 CERK1 mediate bacterial peptidoglycan sensing and immunity to bacterial infection.

"PGN sensing and immunity to bacterial infection in Arabidopsis thaliana requires three lysin-motif (LysM) domain proteins"

PMID:22461667

The LysM receptor-like kinase LysM RLK1 is required to activate defense and abiotic-stress responses induced by overexpression of fungal chitinases in Arabidopsis plants.

"chitin-induced signaling mediated by LysM RLK1 receptor is not limited to biotic stress response but also encompasses abiotic-stress signaling"

PMID:22654057

Chitin-induced dimerization activates a plant immune receptor.

"a chitin octamer induces AtCERK1-ECD dimerization that is inhibited by shorter chitin oligomers"

PMID:22740685

How plant lysin motif receptors get activated: lessons learned from structural biology.

"CERK1 binds NAG oligomers derived from chitin-the major constituent of fungal cell walls-and mediates immunity to fungal infection"

PMID:22744984

LYK4, a lysin motif receptor-like kinase, is important for chitin signaling and plant innate immunity in Arabidopsis.

"LYK1/CERK1 (for LysM-containing receptor-like kinase1/chitin elicitor receptor kinase1) was shown to be essential for chitin recognition"

PMID:24750441

Selective regulation of the chitin-induced defense response by the Arabidopsis receptor-like cytoplasmic kinase PBL27.

"PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream component of the chitin receptor CERK1"

PMID:25036661

LIK1, a CERK1-interacting kinase, regulates plant immune responses in Arabidopsis.

"In vitro experiments showed that LIK1 was directly phosphorylated by CERK1"

PMID:25340959

The kinase LYK5 is a major chitin receptor in Arabidopsis and forms a chitin-induced complex with related kinase CERK1.

"AtLYK5 interacts with AtCERK1 in a chitin-dependent manner. Chitin binding to AtLYK5 is indispensable for chitin-induced AtCERK1 phosphorylation."

PMID:27317676

The Arabidopsis Malectin-Like/LRR-RLK IOS1 Is Critical for BAK1-Dependent and BAK1-Independent Pattern-Triggered Immunity.

"CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) recognize microbe-associated molecular patterns (MAMPs) to activate pattern-triggered immunity (PTI)"

PMID:27679653

The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation.

"The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation"

PMID:29182677

Arabidopsis ubiquitin ligase PUB12 interacts with and negatively regulates Chitin Elicitor Receptor Kinase 1 (CERK1).

"the ARM domains of PUB12 and its paralog PUB13 interacted with the intracellular domain of CERK1 in a manner that was dependent on its autophosphorylation"

Suggested Experiments

Experiment: Quantitative phosphoproteomics of cerk1 versus wild type after chitin treatment to comprehensively define the direct CERK1 substrate set beyond PBL27 and LIK1, distinguishing direct phosphorylation targets from downstream cascade effects.

Experiment: Structure-guided separation-of-function mutants that uncouple chitin binding, homodimerization, and kinase activity, tested for their effects on fungal versus bacterial (peptidoglycan) immunity to dissect whether the same molecular activities serve both perception pathways.

Deep Research

Falcon

(CERK1-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 27 citations 2 artifacts 2026-06-06T21:50:30.380402

Edison artifact artifact-00 (text/markdown)

## Context ID: pqac-00000016 The requested visual information for CERK1 has been extracted. Figure 1A provides a schematic representation of the CERK1 domain st (image/png)

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Comprehensive research report: Arabidopsis thaliana CERK1/LYK1 (At3g21630; UniProt A8R7E6) — functional annotation

0) Target verification (mandatory)

The literature retrieved here consistently matches the UniProt-provided target: Arabidopsis thaliana Chitin elicitor receptor kinase 1 (CERK1), also called LYK1/RLK1, encoded by At3g21630, encoding a plasma-membrane LysM receptor-like kinase with three extracellular LysM domains and an intracellular Ser/Thr protein kinase domain. (vasquez2024celldeathsignaling pages 13-16, miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4, miya2007cerk1alysm media be53cc3e)

1) Key concepts and definitions (current understanding)

1.1 Pattern recognition receptor (PRR) and chitin-triggered immunity

Plants detect conserved microbe-associated molecular patterns (MAMPs/PAMPs) using pattern recognition receptors (PRRs) at the plasma membrane. Chitin (a polymer of N-acetylglucosamine in fungal cell walls) is a canonical fungal MAMP that induces pattern-triggered immunity (PTI). CERK1 is a key PRR component required for chitin-induced PTI outputs including MAPK activation, ROS burst, and defense gene induction. (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4)

1.2 CERK1 protein architecture (definition of functional parts)

CERK1 is a single-pass membrane receptor with: (i) an extracellular domain containing three LysM motifs, (ii) a transmembrane (TM) segment, (iii) a juxtamembrane (JM) region, and (iv) a cytosolic protein kinase domain. A schematic of these domains is shown in Miya et al. (2007) (Figure 1A). (miya2007cerk1alysm media be53cc3e)

2) Molecular function of CERK1: ligand specificity and receptor complex assembly

2.1 Primary molecular function

Primary function: CERK1 acts as an essential receptor(-kinase) component for chitin oligosaccharide perception and signal initiation at the plasma membrane. Loss-of-function cerk1 mutants lose chitin-elicitor responses (MAPK activation, ROS production, defense gene expression), placing CERK1 at the top of the signaling cascade. (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4)

2.2 Ligand specificity (what is recognized)

Evidence across retrieved sources supports preferential responsiveness to longer chitin oligomers; chitin heptamers/octamers and the chitin octamer (GlcNAc)8 are repeatedly referenced as potent elicitors in Arabidopsis CERK1-dependent signaling. (vasquez2024celldeathsignaling pages 13-16, miya2007cerk1alysm pages 3-4, awwanah2020characterizationofpopulus pages 27-30)

2.3 Receptor complex components: CERK1 with LYK5/LKY4 and other LysM proteins

Current models describe CERK1 as operating in a chitin receptor complex involving other LysM proteins, notably LYK5 and LYK4, where LYK5 is often described as a high-affinity chitin-binding partner that associates with CERK1 after chitin exposure and becomes phosphorylated by CERK1. (muhr2022characterizationofpopulus pages 37-41, hu2021lysinmotif(lysm) pages 4-5, awwanah2020characterizationofpopulus pages 27-30)

Beyond fungal chitin signaling, CERK1 functionally intersects with additional LysM proteins (e.g., LYM1/LYM3 in peptidoglycan-triggered responses and LYM2 in plasmodesmal chitin-associated processes), indicating CERK1 can act as a shared signaling kinase for multiple carbohydrate-related immune perceptions. (vasquez2024celldeathsignaling pages 13-16)

3) Enzymatic activity: CERK1 kinase function, key residues, and phosphorylation logic

3.1 CERK1 is an active Ser/Thr kinase (EC 2.7.11.1)

Miya et al. (2007) experimentally demonstrated intrinsic kinase activity of the CERK1 intracellular region, including autophosphorylation and phosphorylation of a model substrate (myelin basic protein, MBP) in vitro. Importantly, truncation removing the juxtamembrane region reduced kinase activity, supporting a regulatory role of JM for catalytic function. (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4)

3.2 Phosphorylation sites and signaling branch control (recent synthesis)

Recent synthesis sources emphasize that specific CERK1 phosphorylation sites tune downstream signaling branches. Reported CERK1 residues implicated in chitin signaling include T479, Y428, T573, and Y557; at least one synthesis notes that Y557F can selectively disrupt ROS production while leaving MAPK activation relatively intact, consistent with a model where CERK1 phosphocodes route signaling into distinct outputs. (moffat2024molecularinsightsinto pages 38-41, muhr2022characterizationofpopulus pages 136-139, meresa2024carbohydrateelicitorinducedplant pages 20-21)

4) Downstream signaling pathways and pathway placement

4.1 Canonical PTI outputs downstream of CERK1

CERK1 activation triggers hallmark PTI responses: MAPK activation, reactive oxygen species (ROS) burst, defense-related transcriptional reprogramming, and enhanced resistance to non-adapted pathogens. (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4)

4.2 RLCK relay: CERK1 to receptor-like cytoplasmic kinases (RLCKs)

CERK1 signals through receptor-like cytoplasmic kinases (RLCKs) including PBL27 and BIK1 (RLCK-VII family). One 2024 review contextualizes RLCKs as a large Arabidopsis kinase subfamily (~149 RLCKs) frequently acting downstream of RLKs in immunity. (moffat2024molecularinsightsinto pages 38-41, zamora2024signalingofplant pages 5-7)

4.3 A mechanistically resolved module: LYK5–CERK1–PBL27–SLAH3 in stomatal immunity

A well-resolved, experimentally supported signaling module links chitin perception to guard-cell ion fluxes and stomatal defense. Liu et al. (2019) showed that chitin-triggered stomatal closure requires LYK5 and CERK1, and requires PBL27. Mechanistically, PBL27 phosphorylates the anion channel SLAH3 at S127 and S189, and these sites are required for chitin-induced stomatal closure and leaf-level anti-fungal immunity. (liu2019anionchannelslah3 pages 2-3)

5) Subcellular localization and receptor trafficking

5.1 Localization

CERK1 is a plasma membrane protein. Miya et al. (2007) visualized CERK1–GFP at the plasma membrane (Figure 4A; onion epidermal cells). (miya2007cerk1alysm pages 3-4, miya2007cerk1alysm media 06385074)

5.2 Trafficking and negative regulation (current view)

Multiple sources support that receptor complex components are dynamically regulated after activation. A recurring model is that upon chitin perception LYK5 undergoes CERK1-dependent endocytosis, while CERK1 is often reported to remain at the plasma membrane; additional negative regulatory processes (e.g., ubiquitin ligases and phosphatases) are proposed to tune receptor abundance and/or phosphorylation state. (moffat2024molecularinsightsinto pages 38-41, hu2021lysinmotif(lysm) pages 9-10, awwanah2020characterizationofpopulus pages 27-30)

6) Recent developments and latest research emphasis (prioritize 2023–2024)

6.1 2024 reviews: expanded mechanistic framing and translational context

Meresa et al., 2024 (Heliyon, Aug 2024; https://doi.org/10.1016/j.heliyon.2024.e34871) synthesizes carbohydrate-elicitor immunity and emphasizes CERK1 phosphorylation requirements (including Y428) and conserved contributions of juxtamembrane regions to signaling. (meresa2024carbohydrateelicitorinducedplant pages 20-21)
Zamora et al., 2024 (Horticulturae, Apr 2024; https://doi.org/10.3390/horticulturae10040361) emphasizes CERK1-centered RLK–RLCK–MAPK logic as a template for horticultural crop defense, including roles for RLCKs such as BIK1 in fungal resistance contexts. (zamora2024signalingofplant pages 5-7)

6.2 2024 mechanistic synthesis of CERK1 phosphoregulation and network control

A 2024 dissertation-level synthesis describes CERK1 as a chitin co-receptor kinase in a complex with LYK5, highlights multiple chitin-induced phosphorylation sites (including Thr and Tyr residues), and articulates how specific sites may steer ROS vs MAPK branches. It also summarizes negative regulation via dephosphorylation and ubiquitination/trafficking modules. (moffat2024molecularinsightsinto pages 38-41)

6.3 2024 biological-context studies touching CERK1 signaling outputs

A 2024 preprint/dissertation centered on cerk1-4 emphasizes CERK1’s role as a primary chitin receptor kinase, details ectodomain features (disulfides/glycosylation), and reiterates preferential responsiveness to longer oligomers such as heptamers/octamers. (vasquez2024celldeathsignaling pages 13-16)

7) Current applications and real-world implementations

7.1 Elicitor-based crop protection (chitin/chitooligosaccharides)

Chitin and related carbohydrate elicitors are widely discussed as plant defense elicitors with potential to reduce reliance on chemical fungicides. Recent reviews explicitly frame CERK1-centered perception/signaling as foundational to these approaches and to identifying/engineering comparable modules in horticultural crops. (meresa2024carbohydrateelicitorinducedplant pages 20-21, zamora2024signalingofplant pages 5-7)

7.2 Translation of CERK1 pathway logic beyond Arabidopsis

The CERK1–LysM co-receptor–RLCK paradigm is used as a mechanistic reference for crop species, both for understanding endogenous chitin receptor systems and for guiding receptor/module manipulation to improve fungal resistance traits. (zamora2024signalingofplant pages 5-7)

8) Expert opinions and authoritative interpretations

Two 2024 reviews (Heliyon; Horticulturae) converge on an expert consensus framing CERK1 as a central receptor-kinase node that integrates carbohydrate perception into RLCK/MAPK signaling and defense outputs, while emphasizing that phosphorylation and receptor complex regulation are key control points and plausible engineering levers. (meresa2024carbohydrateelicitorinducedplant pages 20-21, zamora2024signalingofplant pages 5-7)

9) Quantitative statistics and data points from studies

9.1 Global transcriptional dependence on CERK1 (Miya et al., 2007)

Miya et al. (2007) reported that chitin elicitor induced extensive transcriptional changes in wild type (1,222 genes upregulated; 421 downregulated) but that this response was almost absent in the cerk1 mutant (3 upregulated; 2 downregulated), demonstrating strong CERK1 dependence of elicitor-driven transcription. (miya2007cerk1alysm pages 3-4)

9.2 Quantified disease phenotype (Miya et al., 2007)

Against the incompatible fungus Alternaria brassicicola, cerk1-2 showed significantly larger lesions (1.37 ± 0.57 mm) compared to Col-0 (1.14 ± 0.56 mm), with n=86 and n=102, respectively (P < 0.01). (miya2007cerk1alysm pages 3-4)

9.3 Quantified phosphosite requirement in stomatal immunity (Liu et al., 2019)

In the CERK1-dependent guard-cell pathway, SLAH3 residues S127 and S189 were identified as functionally required phosphorylation sites for chitin-triggered stomatal closure and antifungal immunity, establishing a quantitatively testable mechanistic link between perception and ion channel control. (liu2019anionchannelslah3 pages 2-3)

10) Evidence summary table

The following table compiles the major functional-annotation elements supported by the retrieved literature.

Topic	Key findings	Key sources with year + DOI/URL (no citation IDs)	Notes/limitations
identity/domains	Arabidopsis thaliana CERK1 corresponds to At3g21630 (syn. LYK1/RLK1), a plasma-membrane LysM receptor-like kinase with three extracellular LysM motifs, a transmembrane/juxtamembrane region, and an intracellular Ser/Thr kinase domain. The ectodomain is reported as globular with tightly packed LysMs, disulfide bridges, and glycosylation sites. (vasquez2024celldeathsignaling pages 13-16, miya2007cerk1alysm pages 4-5)	Miya et al., 2007, PNAS, doi:10.1073/pnas.0705147104, https://doi.org/10.1073/pnas.0705147104; Vasquez, 2024, https://doi.org/10.53846/goediss-10844	Structural fine detail is partly summarized from review/thesis-style sources rather than a primary Arabidopsis structure paper directly retrieved here.
ligand specificity	CERK1 is essential for perception/signaling of chitin elicitors; evidence supports preferential recognition of longer chitin oligomers, especially chitin heptamers/octamers, and GlcNAc8-driven receptor activation/dimerization. One source also notes binding to non-branched 1,3-β-D-(Glc) hexasaccharides. All three LysM domains are required for full chitin responsiveness. (awwanah2020characterizationofpopulus pages 27-30, hu2021lysinmotif(lysm) pages 2-4, vasquez2024celldeathsignaling pages 13-16)	Miya et al., 2007, PNAS, doi:10.1073/pnas.0705147104, https://doi.org/10.1073/pnas.0705147104; Hu et al., 2021, Int J Mol Sci, doi:10.3390/ijms22063114, https://doi.org/10.3390/ijms22063114	Miya et al. 2007 established signaling necessity but did not directly prove Arabidopsis CERK1 ligand binding in the same way as later structural/mechanistic work summarized in secondary sources.
receptor complex components	Early model: CERK1 can homodimerize upon chitin binding. Current model: CERK1 functions with LysM co-receptors, especially LYK5 and LYK4; LYK5 is often described as the higher-affinity chitin-binding partner, associates with CERK1 after chitin treatment, and is phosphorylated by CERK1. Other CERK1-associated LysM proteins contribute in different contexts, including LYM1/LYM3 for peptidoglycan signaling and LYM2 for plasmodesmal chitin responses. (awwanah2020characterizationofpopulus pages 27-30, muhr2022characterizationofpopulus pages 37-41, hu2021lysinmotif(lysm) pages 4-5, liu2019anionchannelslah3 pages 2-3)	Liu et al., 2019, eLife, doi:10.7554/eLife.44474, https://doi.org/10.7554/eLife.44474; Hu et al., 2021, Int J Mol Sci, doi:10.3390/ijms22063114, https://doi.org/10.3390/ijms22063114	Exact stoichiometry and sequence of assembly remain model-dependent across studies; some statements come from synthesized literature rather than one decisive experiment.
kinase activity/phosphosites	CERK1 has intrinsic kinase activity with autophosphorylation and myelin basic protein phosphorylation in vitro; the juxtamembrane region is required for kinase function. Reported signaling-relevant phosphosites include T479, Y428, T573, and Y557; Y557F reportedly impairs ROS more than MAPK activation, indicating branch-specific signaling. Chitin-induced phosphorylation is central to activation. (moffat2024molecularinsightsinto pages 38-41, muhr2022characterizationofpopulus pages 136-139, miya2007cerk1alysm pages 4-5, meresa2024carbohydrateelicitorinducedplant pages 20-21, miya2007cerk1alysm pages 3-4)	Miya et al., 2007, PNAS, doi:10.1073/pnas.0705147104, https://doi.org/10.1073/pnas.0705147104; Meresa et al., 2024, Heliyon, doi:10.1016/j.heliyon.2024.e34871, https://doi.org/10.1016/j.heliyon.2024.e34871	Several phosphosite assignments are summarized from later reviews/theses in the gathered evidence; not all underlying primary phosphosite papers were directly retrieved.
downstream signaling	Activated CERK1 signals through RLCK-VII kinases including PBL27, BIK1, and PBL19, linking receptor activation to ROS production, Ca2+ influx, MAPK cascades, defense gene expression, callose deposition, and stomatal immunity. In guard cells, the LYK5-CERK1-PBL27 pathway targets the anion channel SLAH3; PBL27 phosphorylates SLAH3 at S127 and S189, which are required for chitin-induced stomatal closure and antifungal defense. (moffat2024molecularinsightsinto pages 38-41, hu2021lysinmotif(lysm) pages 2-4, liu2019anionchannelslah3 pages 2-3, zamora2024signalingofplant pages 5-7)	Liu et al., 2019, eLife, doi:10.7554/eLife.44474, https://doi.org/10.7554/eLife.44474; Zamora et al., 2024, Horticulturae, doi:10.3390/horticulturae10040361, https://doi.org/10.3390/horticulturae10040361	Specific pathway branches vary by cell type and readout; some roles of BIK1 vs PBL27 are synthesized across studies/reviews.
localization/trafficking	CERK1 is localized to the plasma membrane. After chitin perception, LYK5 undergoes CERK1-dependent endocytosis, whereas CERK1 is often reported to remain at the plasma membrane. Regulatory trafficking modules summarized in recent literature include PUB12/13-mediated turnover, EXO70B2-associated recycling, and dephosphorylation by CIPP1 as negative feedback. (awwanah2020characterizationofpopulus pages 27-30, moffat2024molecularinsightsinto pages 38-41, hu2021lysinmotif(lysm) pages 9-10, miya2007cerk1alysm pages 3-4)	Miya et al., 2007, PNAS, doi:10.1073/pnas.0705147104, https://doi.org/10.1073/pnas.0705147104; Hu et al., 2021, Int J Mol Sci, doi:10.3390/ijms22063114, https://doi.org/10.3390/ijms22063114	The degradation route for CERK1-complex components is still described as debated in a 2024 synthesis source.
quantitative/statistics	In Miya et al. 2007, elicitor-responsive transcription was strongly CERK1-dependent: 1,222 genes were upregulated in WT versus only 3 in cerk1-1, and 421 downregulated in WT versus 2 in cerk1-1. Disease phenotype against Alternaria brassicicola showed lesion size 1.37 ± 0.57 mm in cerk1-2 versus 1.14 ± 0.56 mm in Col-0 (~20% larger), with n=86 and n=102 and P < 0.01. Experimental inoculum included 5 × 10^5 spores mL^-1. (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4)	Miya et al., 2007, PNAS, doi:10.1073/pnas.0705147104, https://doi.org/10.1073/pnas.0705147104	Quantitative kinetics/binding constants for Arabidopsis CERK1 were limited in the gathered evidence; many recent sources were more mechanistic than numerically detailed.
recent developments 2023-2024	Recent syntheses emphasize CERK1 as an active RD kinase coreceptor in a broader chitin receptor network, with phosphosite-specific signaling outputs, dynamic receptor regulation, and links to systemic resistance after root chitin perception. A 2024 Arabidopsis study found Trichoderma atroviride-induced ISR was compromised in a chitin-receptor mutant, yet soil-applied chitin-triggered systemic resistance was not, suggesting partial separation between beneficial-fungus ISR and canonical chitin-CERK1 signaling. Recent reviews also frame CERK1-centered modules as templates for understanding horticultural crop immunity. (moffat2024molecularinsightsinto pages 32-35, meresa2024carbohydrateelicitorinducedplant pages 20-21, zamora2024signalingofplant pages 5-7)	Meresa et al., 2024, Heliyon, doi:10.1016/j.heliyon.2024.e34871, https://doi.org/10.1016/j.heliyon.2024.e34871; Zamora et al., 2024, Horticulturae, doi:10.3390/horticulturae10040361, https://doi.org/10.3390/horticulturae10040361; Sakai et al., 2024, Microbes Environ, doi:10.1264/jsme2.me24038, https://doi.org/10.1264/jsme2.me24038	2023-2024 Arabidopsis CERK1 primary literature in the gathered evidence is limited; some recent insights come from reviews or from studies focused on adjacent pathways/contexts.
applications	CERK1 knowledge is being used conceptually for crop protection via carbohydrate elicitors (especially chitin/chitooligosaccharides), receptor engineering, and transfer of LysM receptor modules across species to improve fungal resistance. Reviews highlight use of chitin-based elicitors as alternatives to chemical control and translation of Arabidopsis CERK1-LYK5-PBL27-MAPK paradigms into horticultural crops. (meresa2024carbohydrateelicitorinducedplant pages 20-21, zamora2024signalingofplant pages 5-7)	Meresa et al., 2024, Heliyon, doi:10.1016/j.heliyon.2024.e34871, https://doi.org/10.1016/j.heliyon.2024.e34871; Zamora et al., 2024, Horticulturae, doi:10.3390/horticulturae10040361, https://doi.org/10.3390/horticulturae10040361	Application evidence here is mostly translational/review-based rather than field-deployed Arabidopsis CERK1 implementations with agronomic performance metrics.

Table: This table summarizes literature-supported functional annotation evidence for Arabidopsis thaliana CERK1/LYK1, including receptor identity, ligand recognition, signaling partners, phosphoregulation, localization, quantitative findings, and recent translational relevance.

11) Key limitations of the retrieved evidence set (transparency)

The evidence set includes high-quality foundational primary papers (notably PNAS 2007 and eLife 2019) but comparatively fewer 2023–2024 primary research articles directly centered on Arabidopsis CERK1; several 2024 insights here are from reviews or dissertation/preprint-style syntheses rather than peer-reviewed primary reports. (moffat2024molecularinsightsinto pages 38-41, meresa2024carbohydrateelicitorinducedplant pages 20-21, zamora2024signalingofplant pages 5-7)
Several specific CERK1 phosphosite claims are cited in recent syntheses; the underlying primary phosphosite-mapping papers were not all directly retrieved in full text in this run, so those sites should be treated as well-supported but secondarily sourced within this report. (moffat2024molecularinsightsinto pages 38-41, muhr2022characterizationofpopulus pages 136-139, meresa2024carbohydrateelicitorinducedplant pages 20-21)

12) Core references (with URLs and publication dates)

Miya A. et al. “CERK1, a LysM receptor kinase, is essential for chitin elicitor signaling in Arabidopsis.” PNAS (Dec 2007). https://doi.org/10.1073/pnas.0705147104 (miya2007cerk1alysm pages 4-5, miya2007cerk1alysm pages 3-4, miya2007cerk1alysm media be53cc3e, miya2007cerk1alysm media 06385074)
Liu Y. et al. “Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure.” eLife (Sep 2019). https://doi.org/10.7554/eLife.44474 (liu2019anionchannelslah3 pages 2-3)
Meresa B.K. et al. “Carbohydrate elicitor-induced plant immunity: Advances and prospects.” Heliyon (Aug 2024). https://doi.org/10.1016/j.heliyon.2024.e34871 (meresa2024carbohydrateelicitorinducedplant pages 20-21)
Zamora O.R. et al. “Signaling of Plant Defense…Triggered by Fungal Chitin in Horticultural Crops.” Horticulturae (Apr 2024). https://doi.org/10.3390/horticulturae10040361 (zamora2024signalingofplant pages 5-7)
Hu S.-P. et al. “Lysin Motif (LysM) Proteins: Interlinking Manipulation of Plant Immunity and Fungi.” Int. J. Mol. Sci. (Mar 2021). https://doi.org/10.3390/ijms22063114 (hu2021lysinmotif(lysm) pages 9-10, hu2021lysinmotif(lysm) pages 2-4, hu2021lysinmotif(lysm) pages 4-5)

References

(vasquez2024celldeathsignaling pages 13-16): Andrea Vasquez. Cell death signaling in the arabidopsis chitin receptor mutant cerk1-4. ArXiv, 2024. URL: https://doi.org/10.53846/goediss-10844, doi:10.53846/goediss-10844. This article has 1 citations.
(miya2007cerk1alysm pages 4-5): Ayako Miya, Premkumar Albert, Tomonori Shinya, Yoshitake Desaki, Kazuya Ichimura, Ken Shirasu, Yoshihiro Narusaka, Naoto Kawakami, Hanae Kaku, and Naoto Shibuya. Cerk1, a lysm receptor kinase, is essential for chitin elicitor signaling in arabidopsis. Proceedings of the National Academy of Sciences, 104:19613-19618, Dec 2007. URL: https://doi.org/10.1073/pnas.0705147104, doi:10.1073/pnas.0705147104. This article has 1886 citations and is from a highest quality peer-reviewed journal.
(miya2007cerk1alysm pages 3-4): Ayako Miya, Premkumar Albert, Tomonori Shinya, Yoshitake Desaki, Kazuya Ichimura, Ken Shirasu, Yoshihiro Narusaka, Naoto Kawakami, Hanae Kaku, and Naoto Shibuya. Cerk1, a lysm receptor kinase, is essential for chitin elicitor signaling in arabidopsis. Proceedings of the National Academy of Sciences, 104:19613-19618, Dec 2007. URL: https://doi.org/10.1073/pnas.0705147104, doi:10.1073/pnas.0705147104. This article has 1886 citations and is from a highest quality peer-reviewed journal.
(miya2007cerk1alysm media be53cc3e): Ayako Miya, Premkumar Albert, Tomonori Shinya, Yoshitake Desaki, Kazuya Ichimura, Ken Shirasu, Yoshihiro Narusaka, Naoto Kawakami, Hanae Kaku, and Naoto Shibuya. Cerk1, a lysm receptor kinase, is essential for chitin elicitor signaling in arabidopsis. Proceedings of the National Academy of Sciences, 104:19613-19618, Dec 2007. URL: https://doi.org/10.1073/pnas.0705147104, doi:10.1073/pnas.0705147104. This article has 1886 citations and is from a highest quality peer-reviewed journal.
(awwanah2020characterizationofpopulus pages 27-30): Mo Awwanah. Characterization of populus x canescens lysm-receptor like kinases lyk4/lyk5 and lysm-receptor like protein lym2 and their roles in chitin signaling. Unknown journal, 2020. URL: https://doi.org/10.53846/goediss-7913, doi:10.53846/goediss-7913.
(muhr2022characterizationofpopulus pages 37-41): Mascha Muhr. Characterization of populus x canescens lysm receptor-like kinases cerk1-1 and cerk1-2 and their role in chitin signaling. ArXiv, 2022. URL: https://doi.org/10.53846/goediss-9128, doi:10.53846/goediss-9128. This article has 2 citations.
(hu2021lysinmotif(lysm) pages 4-5): Shu-Ping Hu, Jun-Jiao Li, Nikhilesh Dhar, Jun-Peng Li, Jie-Yin Chen, Wei Jian, Xiao-Feng Dai, and Xing-Yong Yang. Lysin motif (lysm) proteins: interlinking manipulation of plant immunity and fungi. International Journal of Molecular Sciences, 22:3114, Mar 2021. URL: https://doi.org/10.3390/ijms22063114, doi:10.3390/ijms22063114. This article has 66 citations.
(moffat2024molecularinsightsinto pages 38-41): Molecular Insights Into the Perception of Fungal-Derived Molecular Patterns and Its Impact on Disease Resistance This article has 0 citations.
(muhr2022characterizationofpopulus pages 136-139): Mascha Muhr. Characterization of populus x canescens lysm receptor-like kinases cerk1-1 and cerk1-2 and their role in chitin signaling. ArXiv, 2022. URL: https://doi.org/10.53846/goediss-9128, doi:10.53846/goediss-9128. This article has 2 citations.
(meresa2024carbohydrateelicitorinducedplant pages 20-21): Birhanu Kahsay Meresa, Kiros-Meles Ayimut, Micheale Yifter Weldemichael, Kalayou Hiluf Geberemedhin, Hagos Hailu Kassegn, Bruh Asmelash Geberemikael, and Etsay Mesele Egigu. Carbohydrate elicitor-induced plant immunity: advances and prospects. Heliyon, 10:e34871, Aug 2024. URL: https://doi.org/10.1016/j.heliyon.2024.e34871, doi:10.1016/j.heliyon.2024.e34871. This article has 15 citations.
(zamora2024signalingofplant pages 5-7): Orlando Reyes Zamora, Rosalba Troncoso-Rojas, María Elena Báez-Flores, Martín Ernesto Tiznado-Hernández, and Agustín Rascón-Chu. Signaling of plant defense mediated by receptor-like kinases, receptor-like cytoplasmic protein kinases and mapks triggered by fungal chitin in horticultural crops. Horticulturae, 10:361, Apr 2024. URL: https://doi.org/10.3390/horticulturae10040361, doi:10.3390/horticulturae10040361. This article has 15 citations.
(liu2019anionchannelslah3 pages 2-3): Yi Liu, Tobias Maierhofer, Katarzyna Rybak, Jan Sklenar, Andy Breakspear, Matthew G Johnston, Judith Fliegmann, Shouguang Huang, M Rob G Roelfsema, Georg Felix, Christine Faulkner, Frank LH Menke, Dietmar Geiger, Rainer Hedrich, and Silke Robatzek. Anion channel slah3 is a regulatory target of chitin receptor-associated kinase pbl27 in microbial stomatal closure. eLife, Sep 2019. URL: https://doi.org/10.7554/elife.44474, doi:10.7554/elife.44474. This article has 76 citations and is from a domain leading peer-reviewed journal.
(miya2007cerk1alysm media 06385074): Ayako Miya, Premkumar Albert, Tomonori Shinya, Yoshitake Desaki, Kazuya Ichimura, Ken Shirasu, Yoshihiro Narusaka, Naoto Kawakami, Hanae Kaku, and Naoto Shibuya. Cerk1, a lysm receptor kinase, is essential for chitin elicitor signaling in arabidopsis. Proceedings of the National Academy of Sciences, 104:19613-19618, Dec 2007. URL: https://doi.org/10.1073/pnas.0705147104, doi:10.1073/pnas.0705147104. This article has 1886 citations and is from a highest quality peer-reviewed journal.
(hu2021lysinmotif(lysm) pages 9-10): Shu-Ping Hu, Jun-Jiao Li, Nikhilesh Dhar, Jun-Peng Li, Jie-Yin Chen, Wei Jian, Xiao-Feng Dai, and Xing-Yong Yang. Lysin motif (lysm) proteins: interlinking manipulation of plant immunity and fungi. International Journal of Molecular Sciences, 22:3114, Mar 2021. URL: https://doi.org/10.3390/ijms22063114, doi:10.3390/ijms22063114. This article has 66 citations.
(hu2021lysinmotif(lysm) pages 2-4): Shu-Ping Hu, Jun-Jiao Li, Nikhilesh Dhar, Jun-Peng Li, Jie-Yin Chen, Wei Jian, Xiao-Feng Dai, and Xing-Yong Yang. Lysin motif (lysm) proteins: interlinking manipulation of plant immunity and fungi. International Journal of Molecular Sciences, 22:3114, Mar 2021. URL: https://doi.org/10.3390/ijms22063114, doi:10.3390/ijms22063114. This article has 66 citations.
(moffat2024molecularinsightsinto pages 32-35): Molecular Insights Into the Perception of Fungal-Derived Molecular Patterns and Its Impact on Disease Resistance This article has 0 citations.

Artifacts

Edison artifact artifact-00

Citations

vasquez2024celldeathsignaling pages 13-16
meresa2024carbohydrateelicitorinducedplant pages 20-21
zamora2024signalingofplant pages 5-7
moffat2024molecularinsightsinto pages 38-41
awwanah2020characterizationofpopulus pages 27-30
muhr2022characterizationofpopulus pages 37-41
muhr2022characterizationofpopulus pages 136-139
moffat2024molecularinsightsinto pages 32-35
https://doi.org/10.1016/j.heliyon.2024.e34871
https://doi.org/10.3390/horticulturae10040361
https://doi.org/10.1073/pnas.0705147104;
https://doi.org/10.53846/goediss-10844
https://doi.org/10.3390/ijms22063114
https://doi.org/10.7554/eLife.44474;
https://doi.org/10.1073/pnas.0705147104
https://doi.org/10.1016/j.heliyon.2024.e34871;
https://doi.org/10.3390/horticulturae10040361;
https://doi.org/10.1264/jsme2.me24038
https://doi.org/10.7554/eLife.44474
https://doi.org/10.53846/goediss-10844,
https://doi.org/10.1073/pnas.0705147104,
https://doi.org/10.53846/goediss-7913,
https://doi.org/10.53846/goediss-9128,
https://doi.org/10.3390/ijms22063114,
https://doi.org/10.1016/j.heliyon.2024.e34871,
https://doi.org/10.3390/horticulturae10040361,
https://doi.org/10.7554/elife.44474,

📚 Additional Documentation

Notes

(CERK1-notes.md)

CERK1 (CHITIN ELICITOR RECEPTOR KINASE 1, LysM RLK1, LYK1) — review notes

UniProt: A8R7E6 (CERK1_ARATH); locus AT3G21630; 617 aa precursor; EC 2.7.11.1.

Protein architecture (from UniProt A8R7E6)

Signal peptide 1-23; extracellular topo domain 24-232; single transmembrane helix 233-253; cytoplasmic domain 254-617.
Three LysM domains in the ectodomain: LysM1 46-74 (degenerate), LysM2 108-140 (degenerate), LysM3 168-211.
Chitin-binding residues 109-115 and 137-143 (ChEBI:CHEBI:17029).
Protein kinase domain 322-594; ATP binding 328-336 and 349; active site (proton acceptor) Asp-441.
Phosphosites: Ser-266, Ser-268, Ser-274, Thr-519 (PMID:20610395). N-glycosylation at Asn-40/52/102/123/152; disulfides 25-93, 29-155, 91-153 (PMID:22654057).
Crystal structures 4EBY/4EBZ (ectodomain 25-230).

Core molecular functions

Chitin binding via LysM ectodomain. First direct in vitro binding shown with Kd ~82 nM PMID:19951949. Endogenous CERK1 is a major chitin-binding protein and all three LysM domains are needed PMID:20610395. Structure: binding mediated by one LysM and three NAG residues PMID:22654057.
Chitosan binding also direct PMID:20610395.
Protein Ser/Thr kinase activity of the intracellular domain; autophosphorylation + MBP kinase activity PMID:18042724; autophosphorylated in vitro PMID:19951949.
Transmembrane receptor kinase: extracellular LysM + intracellular kinase PMID:18042724.
Homodimerization activity: chitin octamer is a bivalent ligand driving dimerization required for activation [PMID:22654057 "a chitin octamer induces AtCERK1-ECD dimerization that is inhibited by shorter chitin oligomers"; "chitin-induced AtCERK1 dimerization is critical for its activation"]. Confirmed by structural review PMID:22740685.

Core biological process — chitin-triggered immunity

Essential for chitin signaling; KO loses MAPK activation, ROS, gene expression PMID:18042724. "Master switch" of the cascade.
Required for chitin response and fungal resistance PMID:18263776.
Signal transduction into cytoplasm via intracellular kinase PMID:18042724.
Downstream: phosphorylates RLCK PBL27 connecting to MPK3/6 [PMID:24750441 "PBL27...is an immediate downstream component of the chitin receptor CERK1"; PMID:27679653 title "connects chitin perception to MAPK activation"]. Also phosphorylates LIK1 PMID:25036661.

Receptor complex with LYK5 (important caveat)

LYK5 is the high-affinity primary chitin receptor; binds chitin much more tightly than CERK1 and recruits CERK1 in a chitin-dependent complex PMID:25340959. CERK1 still binds chitin directly (above) but contributes the kinase/signal-output activity in vivo. LYK4 also contributes PMID:22744984.

Secondary / pleiotropic roles (kept as non-core)

Bacterial perception: with LYM1/LYM3 senses peptidoglycan, restricts bacterial growth [PMID:22106285 "PGN sensing and immunity to bacterial infection in Arabidopsis thaliana requires three lysin-motif (LysM) domain proteins"; PMID:19816132 "plays an essential role in restricting bacterial growth on plants"].
Abiotic stress: chitin signaling via CERK1 also encompasses salinity/heavy-metal tolerance PMID:22461667.

Regulation / host-pathogen (basis for REMOVE on generic protein binding)

Negative regulation by U-box E3 ligases PUB12/PUB13 binding the autophosphorylated intracellular domain PMID:29182677.
Targeted for degradation by P. syringae effector AvrPtoB PMID:19249211.
Interacts with malectin-like/LRR-RLK IOS1 in PTI PMID:27317676.

Curation decisions summary

ACCEPT (core MF/BP/CC): chitin binding (x4), chitosan binding, Ser/Thr kinase activity (x2), protein serine kinase activity, ATP binding, transmembrane receptor kinase activity (x2), homodimerization activity (x2), identical protein binding, autophosphorylation (x3), protein phosphorylation, plasma membrane (x4), cell surface PRR signaling, intracellular signal transduction, innate immune response (x2), cellular response to chitin (x2), response to chitin, defense response to fungus, detection of molecule of fungal origin (x2).
MARK_AS_OVER_ANNOTATED: protein kinase activity (broad parent, IEA + IMP), kinase activity (broad), cellular response to oxygen-containing compound (uninformative ARBA).
KEEP_AS_NON_CORE: response to bacterium, cellular response to molecule of bacterial origin, defense response to bacterium, detection of peptidoglycan (genuine bacterial/PGN role, secondary to core fungal-chitin function).
REMOVE: all GO:0005515 "protein binding" (uninformative; PUB12, IOS1, PBL27 x2, LYK5, AvrPtoB); GO:0005576 extracellular region (ISM/AtSubP misprediction — protein is plasma-membrane-anchored, only the ectodomain faces apoplast).

No proposed_new_terms: existing terms (chitin binding, transmembrane receptor protein kinase activity, cell surface PRR signaling pathway, detection of molecule of fungal origin) already capture CERK1 biology well. OLS MCP was unavailable, so no unverified GO IDs were introduced.

Deep research synthesis (Falcon / Edison Scientific, 2026-06-06)

A Falcon deep-research report (CERK1-deep-research-falcon.md) was reviewed to augment the existing curation. Findings fully corroborated the prior decisions; no actions were weakened, no UNDECIDED items existed, and no NEW GO terms with verifiable IDs were warranted.

Key corroborating points (with verbatim support added as file: supported_by entries):
- Architecture/MF: "CERK1 is a single-pass membrane receptor with" three LysM motifs, TM/juxtamembrane, and intracellular Ser/Thr kinase; "CERK1 has intrinsic kinase activity with autophosphorylation and myelin basic protein phosphorylation in vitro." Reinforces GO:0004674, GO:0019199.
- Ligand specificity: "evidence supports preferential recognition of longer chitin oligomers, especially chitin heptamers/octamers, and GlcNAc8-driven receptor activation/dimerization"; "All three LysM domains are required for full chitin responsiveness." Reinforces GO:0008061 and homodimerization (GO:0042803; "Early model: CERK1 can homodimerize upon chitin binding.").
- Localization: "CERK1 is localized to the plasma membrane." Reinforces GO:0005886.
- Immunity/PRR/signaling: "CERK1 is a key PRR component required for chitin-induced PTI outputs including MAPK activation, ROS burst, and defense gene induction"; "Loss-of-function cerk1 mutants lose chitin-elicitor responses..."; downstream relay "Activated CERK1 signals through RLCK-VII kinases including PBL27, BIK1, and PBL19...". Reinforces GO:0045087, GO:0002752, GO:0032491, GO:0035556.
- Fungal defense quantification: "Disease phenotype against Alternaria brassicicola showed lesion size 1.37 ± 0.57 mm in cerk1-2 versus 1.14 ± 0.56 mm in Col-0." Reinforces GO:0050832.
- Bacterial (non-core): LysM partners "including LYM1/LYM3 for peptidoglycan signaling and LYM2 for plasmodesmal chitin responses." Reinforces non-core GO:0009617 etc.

Note: The report also surfaces additional biology not separately annotated in GOA (LYK5-CERK1-PBL27-SLAH3 stomatal-immunity module; phosphosite-specific ROS-vs-MAPK branching; PUB12/13 / EXO70B2 / CIPP1 receptor-turnover modules). Several phosphosite assignments are secondarily sourced (reviews/theses), so they were not used to introduce new annotations. These remain candidates for GO-CAM modeling rather than new term proposals.

📄 View Raw YAML

id: A8R7E6
gene_symbol: CERK1
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:3702
  label: Arabidopsis thaliana
description: >-
  CERK1 (Chitin Elicitor Receptor Kinase 1; also called LysM RLK1 / LYK1) is a
  plasma membrane-localized lysin-motif (LysM) receptor-like kinase of
  Arabidopsis thaliana that acts as a pattern recognition receptor in
  PAMP/MAMP-triggered immunity. The protein has a cleaved N-terminal signal
  peptide, an extracellular ectodomain containing three LysM domains, a single
  transmembrane helix, and a cytoplasmic serine/threonine protein kinase domain.
  The ectodomain binds the fungal cell wall polysaccharide chitin (and partially
  deacetylated chitosan), with all three LysM domains contributing to binding.
  Binding of a long-chain chitin oligomer (chitin octamer) acts as a bivalent
  ligand to drive CERK1 homodimerization, which activates the intracellular
  kinase. In Arabidopsis, the high-affinity primary chitin receptor LYK5 binds
  chitin and recruits CERK1 into a chitin-induced complex; CERK1 provides the
  kinase activity needed for downstream signaling. Activated CERK1
  autophosphorylates and phosphorylates the receptor-like cytoplasmic kinase
  PBL27, linking chitin perception to the MAP kinase (MPK3/MPK6) cascade, ROS
  production, callose deposition, and transcriptional reprogramming. CERK1 is
  essential for chitin-induced immunity and contributes to resistance to fungal
  pathogens such as Alternaria brassicicola and Erysiphe cichoracearum. Together
  with the LysM proteins LYM1 and LYM3, CERK1 also participates in perception of
  bacterial peptidoglycan and restriction of bacterial growth, and
  chitin-induced signaling through CERK1 additionally contributes to abiotic
  stress tolerance. CERK1 is itself a target of host and pathogen regulation: it
  is negatively regulated by the U-box E3 ubiquitin ligases PUB12/PUB13, and is
  ubiquitinated and degraded via the Pseudomonas syringae type III effector
  AvrPtoB, which suppresses immunity.
existing_annotations:
- term:
    id: GO:0004672
    label: protein kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      CERK1 has an intracellular serine/threonine protein kinase domain and
      displays autophosphorylation and substrate (PBL27) kinase activity. This
      InterPro-based protein kinase activity annotation is correct but is a
      broad parent of the more specific Ser/Thr kinase term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The annotation is biochemically correct but is subsumed by the more
      specific and experimentally supported protein serine/threonine kinase
      activity (GO:0004674). It is retained as a non-misleading parent term.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: 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
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000003
  qualifier: enables
  review:
    summary: >-
      CERK1 has an intracellular Ser/Thr kinase domain and EC 2.7.11.1 catalytic
      activity (serine and threonine phosphorylation), supported experimentally
      by autophosphorylation and phosphorylation of PBL27. This is a core
      molecular function.
    action: ACCEPT
    reason: >-
      Directly supported by experimental characterization of the intracellular
      Ser/Thr kinase domain and catalytic activity, and by the duplicate IDA
      annotation from PMID:18042724.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: an intracellular Ser/Thr kinase domain with autophosphorylation/myelin
        basic protein kinase activity
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: CERK1 has intrinsic kinase activity with autophosphorylation
        and myelin basic protein phosphorylation in vitro
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      As an active protein kinase, CERK1 binds ATP. UniProt annotates the
      canonical kinase ATP-binding region (residues 328-336) and ATP-binding
      residue 349. This is a standard, correct molecular function for a kinase.
    action: ACCEPT
    reason: >-
      Consistent with the conserved kinase ATP-binding motif and experimentally
      demonstrated kinase/autophosphorylation activity requiring ATP.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: an intracellular Ser/Thr kinase domain with autophosphorylation/myelin
        basic protein kinase activity
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: >-
      CERK1 is a single-pass plasma membrane receptor kinase. Plasma membrane
      localization is well supported experimentally (duplicate IDA annotations
      below).
    action: ACCEPT
    reason: >-
      Plasma membrane localization is the established site of CERK1 function and
      is supported by multiple experimental studies.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: as well as the localization of CERK1 in the plasma membrane
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: CERK1 is localized to the plasma membrane.
- term:
    id: GO:0009617
    label: response to bacterium
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      CERK1 participates in bacterial perception (peptidoglycan sensing with
      LYM1/LYM3) and restricts bacterial growth, so a broad "response to
      bacterium" annotation is appropriate. More specific terms (defense
      response to bacterium, detection of peptidoglycan) are also present.
    action: KEEP_AS_NON_CORE
    reason: >-
      Biologically correct but broad; the bacterial role is real but secondary
      to the core chitin/fungal immune function, and is better captured by the
      more specific terms also annotated.
    supported_by:
    - reference_id: PMID:19816132
      supporting_text: CERK1 mediates perception of an unknown bacterial PAMP in Arabidopsis
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: including LYM1/LYM3 for peptidoglycan signaling and LYM2 for
        plasmodesmal chitin responses.
- term:
    id: GO:0019199
    label: transmembrane receptor protein kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      CERK1 is a single-pass transmembrane receptor with an extracellular
      ligand (chitin)-binding ectodomain and an intracellular Ser/Thr kinase
      domain; chitin-induced dimerization activates signaling. This term
      accurately captures its receptor kinase nature.
    action: ACCEPT
    reason: >-
      Supported by domain architecture and the experimental demonstration that
      ligand-induced receptor dimerization activates kinase signaling
      (duplicate IDA/IMP annotations below).
    supported_by:
    - reference_id: PMID:22654057
      supporting_text: chitin-induced AtCERK1 dimerization is critical for its activation
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: CERK1 is a single-pass membrane receptor with
- term:
    id: GO:0045087
    label: innate immune response
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      CERK1 is essential for chitin-triggered innate immunity and contributes
      to bacterial PAMP-triggered immunity. This is a core biological process.
    action: ACCEPT
    reason: >-
      Strongly supported across the literature; cerk1 mutants lose chitin-induced
      immune responses. Duplicate IMP annotation also present.
    supported_by:
    - reference_id: PMID:18263776
      supporting_text: LysM RLK1 is essential for chitin signaling in plants (likely
        as part of the receptor complex) and is involved in chitin-mediated plant
        innate immunity
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: CERK1 is a key PRR component required for chitin-induced PTI
        outputs including MAPK activation, ROS burst, and defense gene induction.
- term:
    id: GO:0106310
    label: protein serine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000116
  qualifier: enables
  review:
    summary: >-
      Rhea/EC mapping of the serine phosphorylation half-reaction (EC 2.7.11.1).
      CERK1 phosphorylates serine residues (e.g. autophosphorylation at Ser-266,
      Ser-268, Ser-274). Correct but redundant with the broader Ser/Thr kinase
      term.
    action: ACCEPT
    reason: >-
      Biochemically accurate; CERK1 demonstrably phosphorylates serine residues.
      Consistent with the curated phosphoserine sites.
    supported_by:
    - reference_id: PMID:20610395
      supporting_text: chitin, chitin oligomers, and chitosan rapidly induce in vivo
        phosphorylation of CERK1 at multiple residues in the juxtamembrane and kinase
        domain
- term:
    id: GO:1901701
    label: cellular response to oxygen-containing compound
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: >-
      This very broad ARBA machine-learning term likely derives from chitin
      (an oxygen-containing carbohydrate) responsiveness, but it is too generic
      to be informative for CERK1, whose specific roles are captured by
      "cellular response to chitin" and "response to chitin".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Uninformatively broad ARBA-derived annotation; the specific and accurate
      response terms (cellular response to chitin, GO:0071323) are already
      present. Not wrong but over-general.
    supported_by:
    - reference_id: PMID:18263776
      supporting_text: The mutation in this gene blocked the induction of almost all
        chitooligosaccharide-responsive genes
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:22654057
  qualifier: enables
  review:
    summary: >-
      CERK1 forms ligand-induced homodimers; a chitin octamer acts as a bivalent
      ligand driving AtCERK1-ECD dimerization required for activation. "Identical
      protein binding" captures the self-association, but the more specific
      "protein homodimerization activity" (also annotated) is preferable.
    action: ACCEPT
    reason: >-
      Self-interaction (homodimerization) is experimentally demonstrated by
      crystallography and biochemistry. Retained as accurate; complementary to
      the homodimerization activity annotation.
    supported_by:
    - reference_id: PMID:22654057
      supporting_text: a chitin octamer induces AtCERK1-ECD dimerization that is inhibited
        by shorter chitin oligomers
- term:
    id: GO:0004672
    label: protein kinase activity
  evidence_type: IMP
  original_reference_id: PMID:24750441
  qualifier: enables
  review:
    summary: >-
      Kinase activity of CERK1 (mediating chitin-induced phosphorylation of
      PBL27) is supported by mutant phenotype analysis. Correct but a broad
      parent of the specific Ser/Thr kinase term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Biochemically correct but subsumed by the more specific Ser/Thr kinase
      activity (GO:0004674). Retained as a non-misleading parent.
    supported_by:
    - reference_id: PMID:24750441
      supporting_text: >-
        In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an
        immediate downstream component of the chitin receptor CERK1 and contributes to the
        regulation of chitin-induced immunity in Arabidopsis.
- term:
    id: GO:0050832
    label: defense response to fungus
  evidence_type: IMP
  original_reference_id: PMID:18263776
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      cerk1/lysm RLK1 mutants are more susceptible to fungal pathogens and lose
      chitin-induced defense, establishing a role in defense response to fungus.
      This is a core biological process.
    action: ACCEPT
    reason: >-
      Directly supported by loss-of-function phenotypes showing increased
      susceptibility to fungal pathogens.
    supported_by:
    - reference_id: PMID:18263776
      supporting_text: The mutation in this gene blocked the induction of almost all
        chitooligosaccharide-responsive genes and led to more susceptibility to fungal
        pathogens
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: Disease phenotype against Alternaria brassicicola showed lesion
        size 1.37 ± 0.57 mm in cerk1-2 versus 1.14 ± 0.56 mm in Col-0
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: ISM
  original_reference_id: GO_REF:0000122
  qualifier: located_in
  review:
    summary: >-
      This sequence-based (AtSubP) prediction is misleading. CERK1 is a
      single-pass plasma membrane protein with an extracellular ectodomain (the
      LysM domains face the apoplast), but the protein is not located in the
      extracellular region; it is membrane-anchored at the plasma membrane.
    action: REMOVE
    reason: >-
      The protein localizes to the plasma membrane (experimental IDA), not the
      extracellular region. The ISM prediction conflates the extracellular
      ectodomain topology with whole-protein localization and is incorrect.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: as well as the localization of CERK1 in the plasma membrane
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:29182677
  qualifier: enables
  review:
    summary: >-
      Captures the interaction between CERK1 and the U-box E3 ligase PUB12 (and
      PUB13), which negatively regulate CERK1 in a phosphorylation-dependent
      manner. The generic "protein binding" term is uninformative.
    action: REMOVE
    reason: >-
      Bare "protein binding" is not informative about molecular function. The
      specific CERK1-PUB12/PUB13 interaction is documented in the gene notes and
      better represented by the regulatory biology rather than a generic MF term.
    supported_by:
    - reference_id: PMID:29182677
      supporting_text: the ARM domains of PUB12 and its paralog PUB13 interacted with
        the intracellular domain of CERK1 in a manner that was dependent on its autophosphorylation
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27317676
  qualifier: enables
  review:
    summary: >-
      Captures the CERK1-IOS1 (malectin-like/LRR-RLK) interaction relevant to
      pattern-triggered immunity. Generic "protein binding" is uninformative.
    action: REMOVE
    reason: >-
      Bare "protein binding" provides no molecular-function information; the
      specific CERK1-IOS1 interaction is recorded in the gene notes.
    supported_by:
    - reference_id: PMID:27317676
      supporting_text: CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) recognize microbe-associated
        molecular patterns (MAMPs) to activate pattern-triggered immunity (PTI)
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24750441
  qualifier: enables
  review:
    summary: >-
      Captures the CERK1-PBL27 interaction. CERK1 interacts with and
      phosphorylates the receptor-like cytoplasmic kinase PBL27. Generic
      "protein binding" is uninformative and is better represented by the
      kinase-substrate relationship.
    action: REMOVE
    reason: >-
      Bare "protein binding" is uninformative; the functionally meaningful
      CERK1-PBL27 kinase-substrate interaction is captured by the kinase activity
      and protein phosphorylation annotations.
    supported_by:
    - reference_id: PMID:24750441
      supporting_text: >-
        In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an
        immediate downstream component of the chitin receptor CERK1 and contributes to the
        regulation of chitin-induced immunity in Arabidopsis.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27679653
  qualifier: enables
  review:
    summary: >-
      Captures the CERK1-PBL27 association connecting chitin perception to MAPK
      activation. Generic "protein binding" is uninformative.
    action: REMOVE
    reason: >-
      Bare "protein binding" is uninformative; the CERK1-PBL27 functional
      relationship is captured elsewhere (kinase activity, protein
      phosphorylation, intracellular signal transduction).
    supported_by:
    - reference_id: PMID:27679653
      supporting_text: The Arabidopsis CERK1-associated kinase PBL27 connects chitin
        perception to MAPK activation
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:24750441
  qualifier: located_in
  review:
    summary: >-
      Experimental localization of CERK1 (and its interaction with PBL27) at the
      plasma membrane. Core localization.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for plasma membrane localization, consistent
      with CERK1's role as a cell-surface receptor.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: as well as the localization of CERK1 in the plasma membrane
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:27679653
  qualifier: located_in
  review:
    summary: >-
      Experimental localization of CERK1 at the plasma membrane. Core
      localization; duplicate of the IDA annotation above.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for plasma membrane localization.
    supported_by:
    - reference_id: PMID:27679653
      supporting_text: The Arabidopsis CERK1-associated kinase PBL27 connects chitin
        perception to MAPK activation
- term:
    id: GO:0071323
    label: cellular response to chitin
  evidence_type: IMP
  original_reference_id: PMID:24750441
  qualifier: involved_in
  review:
    summary: >-
      CERK1 is required for cellular responses to chitin, including PBL27
      phosphorylation, MPK3/6 activation and downstream defense. Core process.
    action: ACCEPT
    reason: >-
      Supported by mutant phenotypes showing loss of chitin-induced defense
      responses.
    supported_by:
    - reference_id: PMID:24750441
      supporting_text: Knockout of PBL27 resulted in the suppression of several chitin-induced
        defense responses, including the activation of MPK3/6
- term:
    id: GO:0006468
    label: protein phosphorylation
  evidence_type: IDA
  original_reference_id: PMID:25036661
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CERK1 directly phosphorylates substrates such as the LRR-RLK LIK1 (and
      PBL27). Protein phosphorylation is a core activity of the kinase domain.
    action: ACCEPT
    reason: >-
      Direct experimental evidence that CERK1 phosphorylates downstream
      substrates (LIK1 in vitro and in vivo).
    supported_by:
    - reference_id: PMID:25036661
      supporting_text: In vitro experiments showed that LIK1 was directly phosphorylated
        by CERK1
- term:
    id: GO:0016301
    label: kinase activity
  evidence_type: IDA
  original_reference_id: PMID:25036661
  qualifier: enables
  review:
    summary: >-
      Broad "kinase activity" term. CERK1 is a protein Ser/Thr kinase; the
      specific Ser/Thr kinase activity terms are preferable.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Correct but uninformatively broad; subsumed by the specific protein
      serine/threonine kinase activity (GO:0004674).
    supported_by:
    - reference_id: PMID:25036661
      supporting_text: In vitro experiments showed that LIK1 was directly phosphorylated
        by CERK1
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25340959
  qualifier: enables
  review:
    summary: >-
      Captures the chitin-induced CERK1-LYK5 complex, in which the high-affinity
      chitin receptor LYK5 recruits CERK1. Generic "protein binding" is
      uninformative; the specific functional interaction is described in the
      gene notes.
    action: REMOVE
    reason: >-
      Bare "protein binding" is uninformative. The biologically important
      chitin-dependent LYK5-CERK1 complex is recorded in the gene notes and
      reflected in the receptor-complex biology.
    supported_by:
    - reference_id: PMID:25340959
      supporting_text: AtLYK5 interacts with AtCERK1 in a chitin-dependent manner
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: IDA
  original_reference_id: PMID:22654057
  qualifier: enables
  review:
    summary: >-
      The CERK1 ectodomain binds chitin directly; the crystal structure of
      AtCERK1-ECD with a chitin pentamer shows binding mediated by a LysM domain
      and three NAG residues. Core molecular function.
    action: ACCEPT
    reason: >-
      Direct structural and biochemical evidence for chitin binding by the LysM
      ectodomain.
    supported_by:
    - reference_id: PMID:22654057
      supporting_text: directly binds chitin through its lysine motif (LysM)-containing
        ectodomain (AtCERK1-ECD)
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: IDA
  original_reference_id: PMID:22740685
  qualifier: enables
  review:
    summary: >-
      Review of CERK1 structural biology confirming chitin binding via the LysM
      ectodomain. Core molecular function; duplicate of other IDA chitin-binding
      annotations.
    action: ACCEPT
    reason: >-
      Consistent with structural data that CERK1 binds NAG oligomers derived
      from chitin via its LysM ectodomain.
    supported_by:
    - reference_id: PMID:22740685
      supporting_text: CERK1 binds NAG oligomers derived from chitin-the major constituent
        of fungal cell walls-and mediates immunity to fungal infection
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IDA
  original_reference_id: PMID:22654057
  qualifier: enables
  review:
    summary: >-
      Chitin octamer acts as a bivalent ligand inducing CERK1 homodimerization,
      which is required for receptor activation. This is a core, activating
      molecular function.
    action: ACCEPT
    reason: >-
      Directly demonstrated by crystallography and biochemistry; mutations
      attenuating dimerization compromise CERK1-mediated signaling.
    supported_by:
    - reference_id: PMID:22654057
      supporting_text: a chitin octamer induces AtCERK1-ECD dimerization that is inhibited
        by shorter chitin oligomers
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: 'Early model: CERK1 can homodimerize upon chitin binding.'
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IDA
  original_reference_id: PMID:22740685
  qualifier: enables
  review:
    summary: >-
      Review/structural confirmation that ligand-induced CERK1 homodimerization
      is required for immune signaling. Duplicate homodimerization annotation.
    action: ACCEPT
    reason: >-
      Consistent with the structural model that NAG octamers stabilize CERK1
      dimers to enable signaling.
    supported_by:
    - reference_id: PMID:22740685
      supporting_text: Receptor activation and immune signaling requires, however, ligand-induced
        CERK1 homodimerization
- term:
    id: GO:0071219
    label: cellular response to molecule of bacterial origin
  evidence_type: IEP
  original_reference_id: PMID:22744984
  qualifier: involved_in
  review:
    summary: >-
      CERK1 is induced by and participates in responses to bacterial
      molecules/PAMPs (including peptidoglycan), and CERK1 expression is induced
      by flagellin. cerk1 mutants show enhanced susceptibility to bacteria.
    action: KEEP_AS_NON_CORE
    reason: >-
      Real but secondary to the core fungal-chitin function. The bacterial role
      is genuine (peptidoglycan sensing with LYM1/LYM3; restricting bacterial
      growth) but peripheral relative to chitin perception.
    supported_by:
    - reference_id: PMID:22744984
      supporting_text: enhanced susceptibility to both the bacterial pathogen Pseudomonas
        syringae pv tomato DC3000 and the fungal pathogen Alternaria brassicicola
- term:
    id: GO:0071323
    label: cellular response to chitin
  evidence_type: IEP
  original_reference_id: PMID:22744984
  qualifier: involved_in
  review:
    summary: >-
      CERK1 is essential for cellular responses to chitin (induction of
      chitin-responsive genes, cytosolic calcium elevation). Core process;
      duplicate of the IMP annotation.
    action: ACCEPT
    reason: >-
      Well supported; cerk1 mutants lose chitin-induced cellular responses.
    supported_by:
    - reference_id: PMID:22744984
      supporting_text: reduced induction of chitin-responsive genes and diminished chitin-induced
        cytosolic calcium elevation
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:19951949
  qualifier: enables
  review:
    summary: >-
      CERK1 is autophosphorylated in vitro, demonstrating Ser/Thr protein kinase
      activity of the intracellular kinase domain. Core molecular function.
    action: ACCEPT
    reason: >-
      Direct in vitro evidence of autophosphorylation by recombinant CERK1.
    supported_by:
    - reference_id: PMID:19951949
      supporting_text: LysM RLK1-yEGFP was autophosphorylated in vitro
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: IDA
  original_reference_id: PMID:19951949
  qualifier: enables
  review:
    summary: >-
      First demonstration of direct, specific, high-affinity (Kd ~82 nM) binding
      of CERK1 to chitin in vitro. Core molecular function.
    action: ACCEPT
    reason: >-
      Direct biochemical evidence of specific chitin binding by recombinant
      CERK1.
    supported_by:
    - reference_id: PMID:19951949
      supporting_text: we present the first evidence for direct binding of LysM RLK1
        to chitin
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: evidence supports preferential recognition of longer chitin
        oligomers, especially chitin heptamers/octamers, and GlcNAc8-driven receptor
        activation/dimerization
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: IDA
  original_reference_id: PMID:20610395
  qualifier: enables
  review:
    summary: >-
      CERK1 is a major chitin-binding protein of Arabidopsis cells; its
      ectodomain binds chitin (and chitosan) directly, with all three LysM
      domains required. Core molecular function.
    action: ACCEPT
    reason: >-
      Affinity-purification and direct-binding experiments confirm chitin
      binding by the CERK1 ectodomain.
    supported_by:
    - reference_id: PMID:20610395
      supporting_text: 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
- term:
    id: GO:0046777
    label: protein autophosphorylation
  evidence_type: IDA
  original_reference_id: PMID:19951949
  qualifier: involved_in
  review:
    summary: >-
      CERK1 autophosphorylates in vitro. Autophosphorylation is a core
      regulatory feature of the kinase.
    action: ACCEPT
    reason: >-
      Direct experimental evidence of in vitro autophosphorylation.
    supported_by:
    - reference_id: PMID:19951949
      supporting_text: LysM RLK1-yEGFP was autophosphorylated in vitro
- term:
    id: GO:0046777
    label: protein autophosphorylation
  evidence_type: IDA
  original_reference_id: PMID:20610395
  qualifier: involved_in
  review:
    summary: >-
      Chitin, chitin oligomers and chitosan rapidly induce in vivo
      phosphorylation of CERK1 at multiple residues; kinase activity is required
      for this chitin-dependent autophosphorylation. Core regulatory process.
    action: ACCEPT
    reason: >-
      Direct evidence of chitin-induced in vivo (auto)phosphorylation requiring
      CERK1 kinase activity.
    supported_by:
    - reference_id: PMID:20610395
      supporting_text: kinase activity of CERK1 is required for its chitin-dependent
        in vivo phosphorylation
- term:
    id: GO:2001080
    label: chitosan binding
  evidence_type: IDA
  original_reference_id: PMID:20610395
  qualifier: enables
  review:
    summary: >-
      The CERK1 ectodomain binds partially deacetylated chitosan directly in
      addition to chitin. A specific, experimentally supported molecular
      function.
    action: ACCEPT
    reason: >-
      Direct binding experiments show the CERK1 ectodomain binds chitosan.
    supported_by:
    - reference_id: PMID:20610395
      supporting_text: the CERK1 ectodomain binds chitin and partially deacetylated
        chitosan directly
- term:
    id: GO:0002752
    label: cell surface pattern recognition receptor signaling pathway
  evidence_type: IDA
  original_reference_id: PMID:19816132
  qualifier: involved_in
  review:
    summary: >-
      CERK1 is a cell-surface pattern recognition receptor that perceives MAMPs
      (chitin; also a bacterial PAMP) and initiates defense signaling. Core
      process.
    action: ACCEPT
    reason: >-
      CERK1 functions as a plasma-membrane PRR initiating PAMP-triggered
      immunity signaling.
    supported_by:
    - reference_id: PMID:19816132
      supporting_text: Plants use pattern recognition receptors (PRRs) to perceive pathogen-associated
        molecular pattern (PAMPs) and initiate defence responses
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: 'CERK1 activation triggers hallmark PTI responses:'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19249211
  qualifier: enables
  review:
    summary: >-
      Captures the interaction between CERK1 and the Pseudomonas syringae type
      III effector AvrPtoB, which ubiquitinates and degrades CERK1 to suppress
      immunity. Generic "protein binding" is uninformative.
    action: REMOVE
    reason: >-
      Bare "protein binding" is uninformative; the CERK1-AvrPtoB interaction
      (host-pathogen) is documented in the gene notes and is not a constitutive
      molecular function of CERK1.
    supported_by:
    - reference_id: PMID:19249211
      supporting_text: AvrPtoB ubiquitinates the CERK1 kinase domain in vitro and targets
        CERK1 for degradation in vivo
- term:
    id: GO:0042742
    label: defense response to bacterium
  evidence_type: IDA
  original_reference_id: PMID:19816132
  qualifier: involved_in
  review:
    summary: >-
      CERK1 restricts bacterial growth and mediates perception of a bacterial
      PAMP; cerk1 plants show reduced PAMP-induced defense to bacterial extracts
      and enhanced bacterial susceptibility. A genuine but secondary defense
      role.
    action: KEEP_AS_NON_CORE
    reason: >-
      The bacterial defense role is real (peptidoglycan sensing; restricting
      bacterial growth) but peripheral to the core chitin/fungal immune function.
    supported_by:
    - reference_id: PMID:19816132
      supporting_text: plays an essential role in restricting bacterial growth on plants
- term:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  evidence_type: IDA
  original_reference_id: PMID:18042724
  qualifier: enables
  review:
    summary: >-
      Original identification of CERK1 as a receptor kinase with an
      intracellular Ser/Thr kinase domain displaying autophosphorylation and
      MBP kinase activity. Core molecular function.
    action: ACCEPT
    reason: >-
      Direct experimental evidence of Ser/Thr kinase activity from the founding
      CERK1 paper.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: an intracellular Ser/Thr kinase domain with autophosphorylation/myelin
        basic protein kinase activity
- term:
    id: GO:0046777
    label: protein autophosphorylation
  evidence_type: IDA
  original_reference_id: PMID:18042724
  qualifier: involved_in
  review:
    summary: >-
      The CERK1 kinase domain shows autophosphorylation activity. Core
      regulatory process; duplicate annotation.
    action: ACCEPT
    reason: >-
      Direct experimental evidence of autophosphorylation.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: an intracellular Ser/Thr kinase domain with autophosphorylation/myelin
        basic protein kinase activity
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: IDA
  original_reference_id: PMID:22744984
  qualifier: enables
  review:
    summary: >-
      Chitin binding annotation associated with the LYK4 study context. CERK1
      chitin binding via its LysM ectodomain is well established by direct
      biochemical and structural evidence. Core molecular function.
    action: ACCEPT
    reason: >-
      Consistent with the extensive direct evidence that CERK1 binds chitin
      through its LysM ectodomain.
    supported_by:
    - reference_id: PMID:20610395
      supporting_text: the CERK1 ectodomain binds chitin and partially deacetylated
        chitosan directly
- term:
    id: GO:0045087
    label: innate immune response
  evidence_type: IMP
  original_reference_id: PMID:22461667
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CERK1/LysM RLK1 is required to activate chitin-induced defense (and
      abiotic-stress) responses; loss-of-function abolishes these responses.
      Core biological process.
    action: ACCEPT
    reason: >-
      Mutant phenotype analysis shows CERK1 is required for chitin-induced
      immune responses.
    supported_by:
    - reference_id: PMID:22461667
      supporting_text: known to play a critical role in signaling defense responses
        induced by exogenous chitin
- term:
    id: GO:0019199
    label: transmembrane receptor protein kinase activity
  evidence_type: IMP
  original_reference_id: PMID:22106285
  qualifier: enables
  review:
    summary: >-
      CERK1 acts as a transmembrane receptor kinase required for bacterial
      peptidoglycan sensing (with LYM1/LYM3). Confirms receptor kinase function.
      Core molecular function.
    action: ACCEPT
    reason: >-
      Supported by mutant phenotypes; CERK1 functions as a transmembrane
      receptor kinase in PAMP perception.
    supported_by:
    - reference_id: PMID:22106285
      supporting_text: PGN sensing and immunity to bacterial infection in Arabidopsis
        thaliana requires three lysin-motif (LysM) domain proteins
- term:
    id: GO:0032499
    label: detection of peptidoglycan
  evidence_type: IMP
  original_reference_id: PMID:22106285
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      With LYM1 and LYM3, CERK1 mediates sensing of bacterial peptidoglycan and
      immunity to bacterial infection. A specific, genuine but secondary
      process.
    action: KEEP_AS_NON_CORE
    reason: >-
      Real role in peptidoglycan-mediated bacterial sensing, but secondary to
      CERK1's core chitin/fungal perception function.
    supported_by:
    - reference_id: PMID:22106285
      supporting_text: PGN sensing and immunity to bacterial infection in Arabidopsis
        thaliana requires three lysin-motif (LysM) domain proteins
- term:
    id: GO:0035556
    label: intracellular signal transduction
  evidence_type: IDA
  original_reference_id: PMID:18042724
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CERK1 transduces the perceived chitin signal across the plasma membrane
      into the cytoplasm via its intracellular kinase domain, acting upstream of
      MAPK activation and ROS. Core process, though a broad term.
    action: ACCEPT
    reason: >-
      CERK1 is positioned upstream of intracellular signaling cascades (MAPK,
      ROS) and transduces the signal via its cytoplasmic kinase domain.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: CERK1 is involved in the perception of the chitin oligosaccharide
        elicitor at the cell surface and the transduction of the signal into the cytoplasm
        via its intracellular serine/threonine kinase activity
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: Activated CERK1 signals through RLCK-VII kinases including PBL27,
        BIK1, and PBL19, linking receptor activation to ROS production, Ca2+ influx,
        MAPK cascades, defense gene expression, callose deposition, and stomatal immunity.
- term:
    id: GO:0010200
    label: response to chitin
  evidence_type: IMP
  original_reference_id: PMID:18263776
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CERK1 is essential for the response to chitin; mutants block induction of
      almost all chitooligosaccharide-responsive genes. Core process.
    action: ACCEPT
    reason: >-
      Mutant phenotype analysis shows CERK1 is required for the chitin response.
    supported_by:
    - reference_id: PMID:18263776
      supporting_text: The mutation in this gene blocked the induction of almost all
        chitooligosaccharide-responsive genes
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:18042724
  qualifier: located_in
  review:
    summary: >-
      Experimental demonstration that CERK1 is a plasma membrane protein. Core
      localization; founding study.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for plasma membrane localization.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: as well as the localization of CERK1 in the plasma membrane
- term:
    id: GO:0019199
    label: transmembrane receptor protein kinase activity
  evidence_type: IDA
  original_reference_id: PMID:18042724
  qualifier: enables
  review:
    summary: >-
      CERK1 is a plasma membrane receptor kinase with extracellular LysM domains
      and an intracellular Ser/Thr kinase domain. Core molecular function;
      duplicate of the IMP annotation.
    action: ACCEPT
    reason: >-
      Founding study establishes CERK1 as a transmembrane receptor kinase.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: CERK1 is a plasma membrane protein containing three LysM motifs
        in the extracellular domain and an intracellular Ser/Thr kinase domain
- term:
    id: GO:0032491
    label: detection of molecule of fungal origin
  evidence_type: IEP
  original_reference_id: PMID:18042724
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      CERK1 detects the fungal cell wall MAMP chitin at the cell surface,
      functioning as a master switch of chitin signaling. Core process;
      duplicate (IEP) of the IMP annotation.
    action: ACCEPT
    reason: >-
      CERK1 perceives chitin (a fungal-origin molecule) and is essential for
      chitin signaling.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: CERK1 plays a critical role in fungal MAMP perception in plants
- term:
    id: GO:0032491
    label: detection of molecule of fungal origin
  evidence_type: IMP
  original_reference_id: PMID:18042724
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      cerk1 KO mutants completely lose the ability to respond to chitin elicitor,
      demonstrating CERK1 is required to detect the fungal MAMP. Core process.
    action: ACCEPT
    reason: >-
      Loss-of-function abolishes chitin detection/response, establishing CERK1's
      role in detecting a fungal-origin molecule.
    supported_by:
    - reference_id: PMID:18042724
      supporting_text: 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
    - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
      supporting_text: Loss-of-function cerk1 mutants lose chitin-elicitor responses
        (MAPK activation, ROS production, defense gene expression), placing CERK1 at
        the top of the signaling cascade.
core_functions:
- description: >-
    Binds the fungal cell wall polysaccharide chitin (and partially deacetylated
    chitosan) through its extracellular three-LysM-domain ectodomain at the
    plasma membrane, providing the ligand-recognition step of chitin perception.
  molecular_function:
    id: GO:0008061
    label: chitin binding
  directly_involved_in:
  - id: GO:0032491
    label: detection of molecule of fungal origin
  - id: GO:0010200
    label: response to chitin
  locations:
  - id: GO:0005886
    label: plasma membrane
  supported_by:
  - reference_id: PMID:22654057
    supporting_text: directly binds chitin through its lysine motif (LysM)-containing
      ectodomain (AtCERK1-ECD)
  - reference_id: PMID:20610395
    supporting_text: 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
  - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
    supporting_text: All three LysM domains are required for full chitin responsiveness.
- description: >-
    Functions as a transmembrane receptor protein serine/threonine kinase:
    chitin-induced homodimerization activates the intracellular kinase domain,
    which autophosphorylates and phosphorylates downstream substrates (e.g.
    PBL27, LIK1) to transduce the signal into the cytoplasm.
  molecular_function:
    id: GO:0004674
    label: protein serine/threonine kinase activity
  directly_involved_in:
  - id: GO:0006468
    label: protein phosphorylation
  - id: GO:0035556
    label: intracellular signal transduction
  locations:
  - id: GO:0005886
    label: plasma membrane
  supported_by:
  - reference_id: PMID:18042724
    supporting_text: an intracellular Ser/Thr kinase domain with autophosphorylation/myelin
      basic protein kinase activity
  - reference_id: PMID:24750441
    supporting_text: >-
      In this study we show that PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate
      downstream component of the chitin receptor CERK1 and contributes to the regulation of
      chitin-induced immunity in Arabidopsis.
  - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
    supporting_text: CERK1 has intrinsic kinase activity with autophosphorylation and
      myelin basic protein phosphorylation in vitro
- description: >-
    Acts as a cell-surface pattern recognition receptor that initiates chitin-
    triggered innate immunity (MAPK activation, ROS, gene induction) and is
    essential for defense against fungal pathogens; ligand-induced
    homodimerization is the activating event.
  molecular_function:
    id: GO:0019199
    label: transmembrane receptor protein kinase activity
  directly_involved_in:
  - id: GO:0002752
    label: cell surface pattern recognition receptor signaling pathway
  - id: GO:0045087
    label: innate immune response
  - id: GO:0050832
    label: defense response to fungus
  locations:
  - id: GO:0005886
    label: plasma membrane
  supported_by:
  - reference_id: PMID:18042724
    supporting_text: CERK1, a LysM receptor kinase, is essential for chitin elicitor
      signaling in Arabidopsis
  - reference_id: PMID:22654057
    supporting_text: chitin-induced AtCERK1 dimerization is critical for its activation
  - reference_id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
    supporting_text: CERK1 is a key PRR component required for chitin-induced PTI outputs
      including MAPK activation, ROS burst, and defense gene induction.
proposed_new_terms: []
suggested_questions:
- question: >-
    Given that LYK5 is the high-affinity primary chitin receptor and recruits
    CERK1 into a chitin-induced complex, how should the division of labor
    between LYK5 (chitin binding) and CERK1 (kinase/signal output) be captured in
    GO annotations and GO-CAM models for chitin perception?
- question: >-
    CERK1 contributes to bacterial peptidoglycan sensing with LYM1/LYM3 and to
    abiotic (salinity/heavy-metal) stress tolerance via chitin signaling. Are
    these best modeled as distinct biological processes downstream of the same
    receptor, or as pleiotropic consequences of a single perception event?
suggested_experiments:
- description: Quantitative phosphoproteomics of cerk1 versus wild type after
    chitin treatment to comprehensively define the direct CERK1 substrate set
    beyond PBL27 and LIK1, distinguishing direct phosphorylation targets from
    downstream cascade effects.
- description: Structure-guided separation-of-function mutants that uncouple
    chitin binding, homodimerization, and kinase activity, tested for their
    effects on fungal versus bacterial (peptidoglycan) immunity to dissect
    whether the same molecular activities serve both perception pathways.
references:
- id: file:ARATH/CERK1/CERK1-deep-research-falcon.md
  title: Falcon (Edison Scientific) deep research report for CERK1
  findings: []
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000003
  title: Gene Ontology annotation based on Enzyme Commission mapping
  findings: []
- id: GO_REF:0000116
  title: Automatic Gene Ontology annotation based on Rhea mapping
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: GO_REF:0000122
  title: AtSubP analysis
  findings: []
- id: PMID:18042724
  title: CERK1, a LysM receptor kinase, is essential for chitin elicitor signaling
    in Arabidopsis.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: 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.
- id: PMID:18263776
  title: A LysM receptor-like kinase plays a critical role in chitin signaling and
    fungal resistance in Arabidopsis.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: LysM RLK1 is essential for chitin signaling in plants (likely
      as part of the receptor complex) and is involved in chitin-mediated plant innate
      immunity.
- id: PMID:19249211
  title: AvrPtoB targets the LysM receptor kinase CERK1 to promote bacterial virulence
    on plants.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: AvrPtoB ubiquitinates the CERK1 kinase domain in vitro and targets
      CERK1 for degradation in vivo.
- id: PMID:19816132
  title: The LysM receptor kinase CERK1 mediates bacterial perception in Arabidopsis.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: the Arabidopsis LysM receptor kinase CERK1 is required not only
      for chitin signalling and fungal resistance, but plays an essential role in restricting
      bacterial growth on plants
- id: PMID:19951949
  title: Direct binding of a plant LysM receptor-like kinase, LysM RLK1/CERK1, to
    chitin in vitro.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: we present the first evidence for direct binding of LysM RLK1
      to chitin
- id: PMID:20610395
  title: The lysin motif receptor-like kinase (LysM-RLK) CERK1 is a major chitin-binding
    protein in Arabidopsis thaliana and subject to chitin-induced phosphorylation.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: 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
- id: PMID:22106285
  title: Arabidopsis lysin-motif proteins LYM1 LYM3 CERK1 mediate bacterial peptidoglycan
    sensing and immunity to bacterial infection.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: PGN sensing and immunity to bacterial infection in Arabidopsis
      thaliana requires three lysin-motif (LysM) domain proteins
- id: PMID:22461667
  title: The LysM receptor-like kinase LysM RLK1 is required to activate defense and
    abiotic-stress responses induced by overexpression of fungal chitinases in Arabidopsis
    plants.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: chitin-induced signaling mediated by LysM RLK1 receptor is not
      limited to biotic stress response but also encompasses abiotic-stress signaling
- id: PMID:22654057
  title: Chitin-induced dimerization activates a plant immune receptor.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: a chitin octamer induces AtCERK1-ECD dimerization that is inhibited
      by shorter chitin oligomers
- id: PMID:22740685
  title: 'How plant lysin motif receptors get activated: lessons learned from structural
    biology.'
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: CERK1 binds NAG oligomers derived from chitin-the major constituent
      of fungal cell walls-and mediates immunity to fungal infection
- id: PMID:22744984
  title: LYK4, a lysin motif receptor-like kinase, is important for chitin signaling
    and plant innate immunity in Arabidopsis.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: LYK1/CERK1 (for LysM-containing receptor-like kinase1/chitin elicitor
      receptor kinase1) was shown to be essential for chitin recognition
- id: PMID:24750441
  title: Selective regulation of the chitin-induced defense response by the Arabidopsis
    receptor-like cytoplasmic kinase PBL27.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: PBL27, an Arabidopsis ortholog of OsRLCK185, is an immediate downstream
      component of the chitin receptor CERK1
- id: PMID:25036661
  title: LIK1, a CERK1-interacting kinase, regulates plant immune responses in Arabidopsis.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: In vitro experiments showed that LIK1 was directly phosphorylated
      by CERK1
- id: PMID:25340959
  title: The kinase LYK5 is a major chitin receptor in Arabidopsis and forms a chitin-induced
    complex with related kinase CERK1.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: AtLYK5 interacts with AtCERK1 in a chitin-dependent manner. Chitin
      binding to AtLYK5 is indispensable for chitin-induced AtCERK1 phosphorylation.
- id: PMID:27317676
  title: The Arabidopsis Malectin-Like/LRR-RLK IOS1 Is Critical for BAK1-Dependent
    and BAK1-Independent Pattern-Triggered Immunity.
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: CHITIN ELICITOR RECEPTOR KINASE1 (CERK1) recognize microbe-associated
      molecular patterns (MAMPs) to activate pattern-triggered immunity (PTI)
- id: PMID:27679653
  title: The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception
    to MAPK activation.
  findings:
  - reference_section_type: TITLE
    supporting_text: The Arabidopsis CERK1-associated kinase PBL27 connects chitin
      perception to MAPK activation
- id: PMID:29182677
  title: Arabidopsis ubiquitin ligase PUB12 interacts with and negatively regulates
    Chitin Elicitor Receptor Kinase 1 (CERK1).
  findings:
  - reference_section_type: ABSTRACT
    supporting_text: the ARM domains of PUB12 and its paralog PUB13 interacted with
      the intracellular domain of CERK1 in a manner that was dependent on its autophosphorylation

CERK1

Gene Description

Existing Annotations Review

Core Functions

Binds the fungal cell wall polysaccharide chitin (and partially deacetylated chitosan) through its extracellular three-LysM-domain ectodomain at the plasma membrane, providing the ligand-recognition step of chitin perception.

Functions as a transmembrane receptor protein serine/threonine kinase: chitin-induced homodimerization activates the intracellular kinase domain, which autophosphorylates and phosphorylates downstream substrates (e.g. PBL27, LIK1) to transduce the signal into the cytoplasm.

Acts as a cell-surface pattern recognition receptor that initiates chitin- triggered innate immunity (MAPK activation, ROS, gene induction) and is essential for defense against fungal pathogens; ligand-induced homodimerization is the activating event.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Comprehensive research report: Arabidopsis thaliana CERK1/LYK1 (At3g21630; UniProt A8R7E6) — functional annotation

0) Target verification (mandatory)

1) Key concepts and definitions (current understanding)

1.1 Pattern recognition receptor (PRR) and chitin-triggered immunity

1.2 CERK1 protein architecture (definition of functional parts)

2) Molecular function of CERK1: ligand specificity and receptor complex assembly

2.1 Primary molecular function

2.2 Ligand specificity (what is recognized)

2.3 Receptor complex components: CERK1 with LYK5/LKY4 and other LysM proteins

3) Enzymatic activity: CERK1 kinase function, key residues, and phosphorylation logic

3.1 CERK1 is an active Ser/Thr kinase (EC 2.7.11.1)

3.2 Phosphorylation sites and signaling branch control (recent synthesis)

4) Downstream signaling pathways and pathway placement

4.1 Canonical PTI outputs downstream of CERK1

4.2 RLCK relay: CERK1 to receptor-like cytoplasmic kinases (RLCKs)

4.3 A mechanistically resolved module: LYK5–CERK1–PBL27–SLAH3 in stomatal immunity

5) Subcellular localization and receptor trafficking

5.1 Localization

5.2 Trafficking and negative regulation (current view)

6) Recent developments and latest research emphasis (prioritize 2023–2024)

6.1 2024 reviews: expanded mechanistic framing and translational context

6.2 2024 mechanistic synthesis of CERK1 phosphoregulation and network control

6.3 2024 biological-context studies touching CERK1 signaling outputs

7) Current applications and real-world implementations

7.1 Elicitor-based crop protection (chitin/chitooligosaccharides)

7.2 Translation of CERK1 pathway logic beyond Arabidopsis

8) Expert opinions and authoritative interpretations

9) Quantitative statistics and data points from studies

9.1 Global transcriptional dependence on CERK1 (Miya et al., 2007)

9.2 Quantified disease phenotype (Miya et al., 2007)

9.3 Quantified phosphosite requirement in stomatal immunity (Liu et al., 2019)

10) Evidence summary table

11) Key limitations of the retrieved evidence set (transparency)

12) Core references (with URLs and publication dates)

Artifacts

Citations

📚 Additional Documentation

Notes

CERK1 (CHITIN ELICITOR RECEPTOR KINASE 1, LysM RLK1, LYK1) — review notes

Protein architecture (from UniProt A8R7E6)

Core molecular functions

Core biological process — chitin-triggered immunity

Receptor complex with LYK5 (important caveat)

Secondary / pleiotropic roles (kept as non-core)

Regulation / host-pathogen (basis for REMOVE on generic protein binding)

Curation decisions summary

Deep research synthesis (Falcon / Edison Scientific, 2026-06-06)

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