OsCERK1 (chitin elicitor receptor kinase 1; OsLysM-RLK9) is a plasma membrane lysin-motif (LysM) receptor-like kinase of rice with an N-terminal signal peptide, an extracellular region carrying a single recognisable LysM motif, one transmembrane helix and a cytoplasmic serine/threonine protein kinase domain. It is the kinase-bearing signalling partner of LysM receptor proteins that bind microbial ligands, rather than the principal ligand-binding subunit. In chitin-triggered immunity, the GPI-anchored LysM protein OsCEBiP binds fungal chitin oligosaccharides and forms a ligand-induced complex with OsCERK1; OsCERK1 then phosphorylates downstream substrates including the receptor-like cytoplasmic kinase OsRLCK185 (which relays to a MAP kinase cascade) and the Rac GEF OsRacGEF1 (activating the small GTPase OsRac1), leading to ROS production, phytoalexin synthesis, defense gene expression and resistance to the rice blast fungus Magnaporthe oryzae. With the LysM proteins LYP4 and LYP6 it also mediates responses to bacterial peptidoglycan. Independently of OsCEBiP, OsCERK1 is required for arbuscular mycorrhizal symbiosis: the LysM receptor OsMYR1/OsLYK2 binds short-chain chitooligosaccharides (CO4) and recruits kinase-active OsCERK1 into a symbiotic receptor heteromer that activates nuclear calcium oscillations and fungal colonisation. OsMYR1 and OsCEBiP compete for OsCERK1, helping to discriminate symbiotic from immune signals. In the resting state the U-box E3 ligase OsCIE1 ubiquitinates OsCERK1 and restrains its kinase activity; chitin-activated OsCERK1 phosphorylates OsCIE1 to release this brake.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0002752 cell surface pattern recognition receptor signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference placing OsCERK1 in cell-surface PRR signalling, as for Arabidopsis CERK1. Strongly consistent with rice data: OsCERK1 is the kinase component of the OsCEBiP-OsCERK1 chitin receptor complex and of the LYP4/LYP6-OsCERK1 peptidoglycan receptor system, and directly phosphorylates the immediate downstream RLCK OsRLCK185. Reason: Chitin and peptidoglycan are PAMPs; OsCERK1 is the transmembrane kinase that transduces their perception across the plasma membrane. This is the appropriately specific immune signalling term and is a core immune role. It describes the immune role only; the symbiotic role is captured separately (GO:0036377). Supporting Evidence: PMID:21070404 Knockdown of OsCERK1 resulted in marked suppression of the defense responses induced by chitin oligosaccharides, indicating that OsCERK1 is essential for chitin signaling in rice. PMID:23498959 In response to chitin, OsRLCK185 associates with, and is directly phosphorylated by, OsCERK1 at the plasma membrane. PMID:25335639 OsCERK1 is essential for both PGN and chitin signaling initiated by OsLYP4 and OsLYP6 |
| GO:0002768 immune response-regulating cell surface receptor signaling pathway | EXP PMID:23498959 A receptor-like cytoplasmic kinase targeted by a plant patho... | MODIFY | Summary: PHI-base annotation from the OsRLCK185 study, in which chitin-activated OsCERK1 directly phosphorylates OsRLCK185 to engage MAP kinase activation and immune responses. Reason: Correct but less specific than warranted. The ligands (chitin, peptidoglycan) are PAMPs perceived at the cell surface, so the is_a child cell surface pattern recognition receptor signaling pathway (GO:0002752), already supported here by IBA, is the more informative term. Proposed replacements: cell surface pattern recognition receptor signaling pathway Supporting Evidence: PMID:23498959 Chitin recognition by OsCERK1 triggers rapid engagement of a rice MAP kinase cascade, which leads to defense response activation. |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based kinase annotation. OsCERK1 has an active cytoplasmic kinase domain that autophosphorylates and phosphorylates OsRLCK185, OsRacGEF1, OsMYR1 and OsCIE1. Reason: Correct; the more specific serine/threonine kinase terms are also present. Retained as a correct, non-misleading parent. Supporting Evidence: PMID:21070404 OsCERK1 is a plasma membrane protein containing one LysM motif in the extracellular domain and an intracellular Ser/Thr kinase domain. |
| GO:0004674 protein serine/threonine kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of Ser/Thr kinase activity, matching direct rice evidence: OsCERK1 phosphorylates OsRacGEF1 on Ser549 and phosphorylates OsRLCK185 and OsCIE1. Reason: Core molecular function, inherited across the CERK1/LYK clade and experimentally verified for the rice protein. Supporting Evidence: PMID:23601108 is activated when its C-terminal S549 is phosphorylated by the cytoplasmic domain of OsCERK1 in response to chitin file:ORYSJ/CERK1/CERK1-deep-research-falcon.md Purified OsCERK1 kinase domain autophosphorylated and phosphorylated OsMYR1 and the assay substrate myelin basic protein |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000003 | ACCEPT | Summary: EC 2.7.11.1 mapping; UniProt assigns this EC from experimental data (PMID:23498959). Reason: Correct and consistent with the experimental and IBA annotations. Supporting Evidence: PMID:23601108 is activated when its C-terminal S549 is phosphorylated by the cytoplasmic domain of OsCERK1 in response to chitin |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro-based ATP binding from the protein kinase ATP-binding site signature; OsCERK1 is a catalytically active kinase. Reason: Correct consequence of an active protein kinase domain; not informative beyond the kinase activity terms but not wrong. Supporting Evidence: file:ORYSJ/CERK1/CERK1-deep-research-falcon.md Purified OsCERK1 kinase domain autophosphorylated and phosphorylated OsMYR1 and the assay substrate myelin basic protein |
| GO:0005886 plasma membrane | EXP PMID:24964058 Targeted gene disruption of OsCERK1 reveals its indispensabl... | ACCEPT | Summary: UniProt annotation from the OsCERK1 gene-targeting study, which localised GFP-tagged OsCERK1 at the cell periphery around invading blast-fungus hyphae. Reason: OsCERK1 is a single-pass transmembrane receptor kinase acting at the plasma membrane; consistent with multiple independent studies. Supporting Evidence: PMID:24964058 Green fluorescent protein-tagged OsCERK1 was localized around the primary infection hyphae. |
| GO:0005886 plasma membrane | EXP PMID:25335639 OsCERK1 and OsRLCK176 play important roles in peptidoglycan ... | ACCEPT | Summary: UniProt annotation from the OsCERK1/OsRLCK176 study describing OsCERK1 as a plasma-membrane adaptor in PGN and chitin signalling with LYP4/LYP6. Reason: Consistent with the receptor topology and other localisation evidence. Supporting Evidence: PMID:25335639 as an adaptor involved in signal transduction at the plasma membrane in conjunction with OsLYP4 and OsLYP6 |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of plasma membrane localisation; OsCERK1 itself is among the experimental sources for this node. Reason: Correct; the target's own experimental localisation grounds the IBA. Supporting Evidence: PMID:23601108 OsCEBiP, a chitin-binding protein, and OsCERK1, a receptor-like kinase, are plasma membrane (PM) proteins |
| GO:0005886 plasma membrane | IDA PMID:23498959 A receptor-like cytoplasmic kinase targeted by a plant patho... | ACCEPT | Summary: PHI-base annotation; the study shows OsCERK1 associating with and phosphorylating OsRLCK185 at the plasma membrane. Reason: Consistent with topology and other localisation studies. Supporting Evidence: PMID:23498959 OsRLCK185 associates with, and is directly phosphorylated by, OsCERK1 at the plasma membrane. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (Cell membrane). Reason: Correct and redundant with the experimental annotations. Supporting Evidence: PMID:21070404 OsCERK1 is a plasma membrane protein containing one LysM motif in the extracellular domain |
| GO:0008061 chitin binding | IEA GO_REF:0000117 | REMOVE | Summary: ARBA machine-learning transfer of chitin binding, reflecting the Arabidopsis CERK1 paradigm (whose three-LysM ectodomain binds chitin). In rice the chitin-binding subunit is OsCEBiP; OsCERK1 has a single recognisable LysM, chitin binding to rice membranes is unaffected by OsCERK1 knockdown, and the OsCERK1 ectodomain did not bind chitin in direct assays. Reason: The rice receptor system divides ligand binding (OsCEBiP; OsMYR1 for CO4) from kinase signalling (OsCERK1). Transferring direct chitin binding from AtCERK1 to OsCERK1 is a paralog/ortholog-function leak not supported by rice biochemistry. Supporting Evidence: PMID:21070404 the observed binding of a biotinylated chitin oligosaccharide, GN8-Bio (Shinya et al., 2010), to the microsomal membrane was not affected by knockdown of OsCERK1, confirming the previous finding that CEBiP is the major molecule that binds chitin oligosaccharides on the cell surface PMID:21070404 it does appear that CEBiP plays a major role in chitin elicitor binding and that OsCERK1 functions as a signal transducer through its Ser/Thr kinase activity in rice file:ORYSJ/CERK1/CERK1-deep-research-falcon.md in the tested colloidal-chitin assay, the rice OsCERK1 ectodomain did not bind, whereas partner receptors provide directly demonstrated ligand binding |
| GO:0008061 chitin binding | TAS PMID:23498959 A receptor-like cytoplasmic kinase targeted by a plant patho... | REMOVE | Summary: PHI-base traceable author statement. The cited paper studies OsRLCK185 phosphorylation and does not test OsCERK1 chitin binding; its general statement that CERK1 is a LysM PRR for chitin derives from the Arabidopsis protein. Reason: Not an experimental annotation, and the rice data argue against OsCERK1 being the chitin-binding subunit (see the ARBA row). The chitin-binding function belongs to OsCEBiP. Supporting Evidence: PMID:21070404 Concerning the question of whether OsCERK1 directly binds chitin oligosaccharides or not, we have not been able to show binding of radioactive or biotinylated chitin oligosaccharide derivatives to the expected band for OsCERK1 PMID:22891159 Studies of the chitin binding properties of the ectodomains of At/OsCERK1 and the chimeric receptors consisting of ecto/cytosolic domains of these molecules indicated that AtCERK1 is sufficient for chitin perception by itself. |
| GO:0019199 transmembrane receptor protein kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of transmembrane receptor kinase activity. OsCERK1 is a single-pass LysM receptor kinase that transmits ligand-induced complex formation (with OsCEBiP, LYP4/LYP6 or OsMYR1) across the membrane by phosphorylating cytoplasmic substrates. Reason: Best general description of OsCERK1's molecular function as the signal-transducing (co-receptor) kinase in heteromeric LysM receptor complexes, in both immunity and symbiosis. Supporting Evidence: PMID:21070404 Immunoprecipitation using a membrane preparation from rice cells treated with chitin oligosaccharides suggested the ligand-induced formation of a receptor complex containing both CEBiP and OsCERK1. PMID:31706032 CO4 directly binds to OsMYR1, promoting the dimerization and phosphorylation of this receptor complex. |
| GO:0019199 transmembrane receptor protein kinase activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro (CERK1/LYK3-like) mapping to transmembrane receptor protein kinase activity. Reason: Correct; consistent with IBA and experimental data. Supporting Evidence: file:ORYSJ/CERK1/CERK1-deep-research-falcon.md its LysM-containing region faces the extracellular space and its catalytic domain faces the cytoplasm |
| GO:0038187 pattern recognition receptor activity | EXP PMID:23498959 A receptor-like cytoplasmic kinase targeted by a plant patho... | MODIFY | Summary: PHI-base annotation. The term definition requires combining with the PAMP. In rice the chitin-binding PRR is OsCEBiP and the PGN-binding PRRs are LYP4/LYP6; OsCERK1 is the co-receptor kinase that transduces the signal. The cited abstract does not report OsCERK1 binding chitin. Reason: The essence (OsCERK1 is a receptor-complex component in PAMP signalling) is sound, but the term implies direct PAMP recognition, which belongs to OsCEBiP/LYP4/LYP6. Transmembrane receptor protein kinase activity captures what OsCERK1 contributes; coreceptor activity (GO:0015026) would also be an accurate description. Proposed replacements: transmembrane receptor protein kinase activity Supporting Evidence: PMID:21070404 it does appear that CEBiP plays a major role in chitin elicitor binding and that OsCERK1 functions as a signal transducer through its Ser/Thr kinase activity in rice PMID:25335639 These membrane receptors, which lack intracellular kinase domains, likely contain another component for transmembrane immune signal transduction. |
| GO:0045087 innate immune response | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of innate immunity. OsCERK1 knockout abolishes chitin-induced H2O2 and gene expression and increases blast hyphal growth. Reason: Well supported in rice; broader than GO:0002752 but a legitimate immune process annotation. Supporting Evidence: PMID:24964058 These results demonstrate that OsCERK1 is indispensable for chitin perception and participates in innate immunity in rice, and also mediates the peptidoglycan response. |
| GO:0045087 innate immune response | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro (CERK1/LYK3-like) mapping to innate immune response. Reason: Correct for OsCERK1, although note that this InterPro family also includes symbiosis-specialised members (e.g. legume LYK3/NFR1), so the mapping is not universally safe across the family. Supporting Evidence: PMID:24964058 These results demonstrate that OsCERK1 is indispensable for chitin perception and participates in innate immunity in rice |
| GO:0106310 protein serine kinase activity | EXP PMID:23498959 A receptor-like cytoplasmic kinase targeted by a plant patho... | ACCEPT | Summary: UniProt/PHI-base annotation from in vitro phosphorylation of OsRLCK185 by OsCERK1 (UniProt EC 2.7.11.1 with Ser and Thr reactions). Reason: Direct experimental support for OsCERK1 phosphorylating protein substrates. Supporting Evidence: PMID:23498959 In response to chitin, OsRLCK185 associates with, and is directly phosphorylated by, OsCERK1 at the plasma membrane. |
| GO:0106310 protein serine kinase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Rhea-based mapping from the UniProt catalytic activity (L-seryl-[protein] phosphorylation). Reason: Correct; redundant with the experimental annotation. Supporting Evidence: PMID:23601108 is activated when its C-terminal S549 is phosphorylated by the cytoplasmic domain of OsCERK1 in response to chitin |
| GO:0036377 arbuscular mycorrhizal association | IMP PMID:25231970 The bifunctional plant receptor, OsCERK1, regulates both chi... | NEW | Summary: OsCERK1 knockout mutants are impaired in arbuscular mycorrhizal colonisation, independently of OsCEBiP and chitin immunity. OsCERK1 is the active kinase of the OsMYR1-OsCERK1 Myc-factor receptor heteromer: CO4 bound by OsMYR1 promotes complex formation and phosphorylation, and kinase-dead OsCERK1 fails to rescue colonisation. Reason: No existing annotation records the symbiotic role; all current process terms are immune. Participation test: OsCERK1 performs the catalytic (kinase) step of symbiotic receptor signalling, phosphorylating the kinase-inactive OsMYR1, rather than merely being required. Comparator check (QuickGO): other symbiosis signalling components carry GO:0036377 by IMP, including rice D14L (Q10J20) and rice CYCLOPS (A9XMT5), Medicago CNGC15a/b and CYCLOPS; rice CCaMK carries it in this repository. Kept distinct from the immune terms, which are supported by separate evidence. Supporting Evidence: PMID:25231970 OsCERK1 but not chitin-triggered immunity is required for AM symbiosis. PMID:25399831 this gene is also necessary for the establishment of the mycorrhizal interaction as well as for resistance to the rice blast fungus PMID:31706032 we identified a heteromer of LysM receptor-like kinases consisting of OsMYR1/OsLYK2 and OsCERK1 that mediates the perception of AM fungi in rice file:ORYSJ/CERK1/CERK1-deep-research-falcon.md CO4-bound OsMYR1 recruits kinase-active OsCERK1, promoting receptor phosphorylation |
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Download this section (compressed HTML)Q: Does the OsCERK1 ectodomain bind short chitooligosaccharides (CO4/CO5) or LCOs with measurable affinity in the OsMYR1 or OsCEBiP heteromer context, or is it purely a scaffold for the kinase?
Q: Should GO:0038187 pattern recognition receptor activity be restricted to the ligand-binding subunit of heteromeric PRR complexes, with co-receptor kinases such as OsCERK1 and BAK1 annotated to coreceptor activity (GO:0015026) or transmembrane receptor protein kinase activity instead?
Q: Is OsCERK1 phosphorylation of OsCIE1 relevant to symbiosis as well as immunity, given that Oscie1 mutants show reduced mycorrhizal colonisation?
Experiment: Quantitative binding (ITC/MST) of purified OsCERK1 ectodomain, alone and with OsCEBiP or OsMYR1 ectodomains, to CO4, CO8 and LCOs, to settle whether OsCERK1 contributes directly to ligand recognition.
Experiment: Phosphoproteomics of roots expressing wild-type vs kinase-dead (T484A) OsCERK1 after CO4 vs CO8 treatment, to identify branch-specific substrates linking OsCERK1 to symbiotic versus immune outputs.
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