NFP

UniProt ID: Q0GXS4
Organism: Medicago truncatula
Review Status: COMPLETE
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Gene Description

NFP (Nod Factor Perception) is a plasma-membrane LysM-domain receptor-like kinase (LysM-RLK) of the model legume Medicago truncatula. It is the essential, non-redundant receptor that perceives rhizobial lipo-chitooligosaccharide signals (Nod factors) secreted by Sinorhizobium meliloti, and triggers the earliest steps of the nitrogen-fixing root nodule symbiosis. The extracellular region carries three tandem, heavily N-glycosylated LysM domains that bind the chitin-based Nod factor ligand; a single transmembrane helix; and an intracellular protein-kinase-like domain. Critically, the NFP kinase domain is a catalytically dead PSEUDOKINASE: it deviates from conserved catalytic kinase residues and shows no autophosphorylation activity, so signal transduction requires association with an active co-receptor kinase, principally LYK3, with which NFP forms heteromeric receptor complexes at the cell periphery. NFP acts in both the root epidermis and cortex to drive Nod factor signalling (calcium spiking, early nodulin expression, root hair deformation), nodule organogenesis and rhizobial infection thread development/bacterial release. Beyond symbiosis, NFP also contributes to M. truncatula immunity against the oomycete Aphanomyces euteiches and the fungus Colletotrichum trifolii.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004713 protein tyrosine kinase activity
IEA
GO_REF:0000043
REMOVE
Summary: Retired SwissProt-keyword (SPKW) annotation derived from the "Tyrosine-protein kinase" keyword, which itself comes from the PROSITE PS00109 (PROTEIN_KINASE_TYR) signature match. This annotation is doubly incorrect. First, plant receptor-like kinases including NFP are serine/threonine kinases, not tyrosine kinases (UniProt itself names the protein "Serine/threonine receptor-like kinase NFP"). Second, and more fundamentally, the NFP intracellular kinase domain is a catalytically dead pseudokinase: it deviates from conserved catalytic residues and shows no detectable autophosphorylation activity.
Reason: GOA's removal of this annotation was JUSTIFIED. The term is wrong on two counts. (1) NFP is a pseudokinase with no demonstrated catalytic activity: "NFP did not show autophosphorylation activity, suggesting that NFP needs to associate with an active kinase or has unusual functional characteristics different from classical kinases" and NFP belongs to "one subfamily ... characterized by deviations from conserved kinase sequences" (PMID:16844829). (2) Even if it were an active kinase, plant RLKs are Ser/Thr kinases; the tyrosine specificity is a PROSITE motif artefact, not a biological observation. The keyword2GO pipeline propagated a generic sequence-motif keyword without accounting for the experimentally established pseudokinase status. REMOVE; do not replace with any catalytic MF term.
Supporting Evidence:
PMID:16844829
Consistent with deviations from conserved kinase domain sequences, NFP did not show autophosphorylation activity, suggesting that NFP needs to associate with an active kinase or has unusual functional characteristics different from classical kinases.
file:MEDTR/NFP/NFP-deep-research-falcon.md
lacking key conserved motifs (including P-loop/DFG-related features and an activation-loop segment), and ... was observed in vitro, supporting interpretation of NFP as a likely ... or signaling subunit that requires an active kinase partner
GO:0006952 defense response
IEA
GO_REF:0000043
REMOVE
Summary: Retired SwissProt-keyword (SPKW) annotation derived from the "Plant defense" keyword. NFP does have a documented role in pathogen resistance (resistance to the oomycete Aphanomyces euteiches and the fungus Colletotrichum trifolii; PMID:23432463), so the keyword is not factually wrong. However, the broad "defense response" term adds nothing beyond the current GOA annotations, which already capture this role with the more specific and properly evidenced terms "positive regulation of defense response to oomycetes" (GO:1902290) and "regulation of defense response to fungus" (GO:1900150), both IMP from PMID:23432463.
Reason: GOA's removal of this annotation was JUSTIFIED. The broad keyword-derived term is fully subsumed by the existing, more informative curated annotations GO:1902290 and GO:1900150 (both IMP, PMID:23432463), which are direct or indirect descendants of defense response and pinpoint the specific pathogen classes and regulatory nature of NFP's role. Retaining a generic IEA "defense response" alongside specific experimental terms is redundant over-annotation. NFP's primary, defining function is symbiotic Nod-factor perception; its defense role is real but secondary and already well represented. REMOVE.
Supporting Evidence:
PMID:23432463
nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance. ... nfp mutants also showed an increased susceptibility to the fungus Colletotrichum trifolii. These results demonstrate that NFP intervenes in M. truncatula immunity.
file:MEDTR/NFP/NFP-deep-research-falcon.md
NFP/NFR-type receptors lie at a ... symbiosis–immunity interface ... Reviews summarize that NFs can induce transient defense outputs
GO:0004672 protein kinase activity
IEA
GO_REF:0000002
REMOVE
Summary: InterPro2GO IEA annotation from protein-kinase-domain signatures (IPR000719 Prot_kinase_dom, IPR001245 Ser-Thr/Tyr kinase catalytic domain, IPR008266 Tyr kinase active site). NFP does contain a protein-kinase-like domain in its intracellular region, but it is a catalytically dead pseudokinase: it lacks conserved catalytic residues and shows no autophosphorylation activity (PMID:16844829). The InterPro signatures detect the kinase FOLD but cannot distinguish active kinases from pseudokinases.
Reason: Although less obviously wrong than the retired tyrosine-kinase keyword, "protein kinase activity" has the same underlying problem: it asserts a catalytic molecular function that NFP does not have. NFP is an experimentally established pseudokinase ("NFP did not show autophosphorylation activity ... deviations from conserved kinase sequences"; PMID:16844829), and signalling requires the active co-receptor kinase LYK3 (PMID:25351493). The kinase domain functions as a protein-interaction/scaffolding module (e.g. it binds the GTPase ROP10; PMID:25794934), not as an enzyme. An IEA term that contradicts direct experimental evidence should not be retained. REMOVE; the genuine molecular function (signalling receptor / Nod factor perception) is captured by the proposed NEW annotations below.
Supporting Evidence:
PMID:16844829
Consistent with deviations from conserved kinase domain sequences, NFP did not show autophosphorylation activity, suggesting that NFP needs to associate with an active kinase or has unusual functional characteristics different from classical kinases.
PMID:25351493
our Förster resonance energy transfer-fluorescence lifetime imaging microscopy analysis indicates that NFP and LYK3 form heteromeric complexes at the cell periphery in M. truncatula nodules.
file:MEDTR/NFP/NFP-deep-research-falcon.md
lacking key conserved motifs (including P-loop/DFG-related features and an activation-loop segment), and ... was observed in vitro, supporting interpretation of NFP as a likely ... or signaling subunit that requires an active kinase partner
GO:0005524 ATP binding
IEA
GO_REF:0000002
KEEP AS NON CORE
Summary: InterPro2GO IEA annotation from the protein kinase domain signature (IPR000719). UniProt annotates a Gly-rich P-loop (residues 290-298) and a second ATP-binding residue (339) by PROSITE ProRule. Whether the pseudokinase domain of NFP actually binds ATP/nucleotide in vivo has not been tested; many pseudokinases retain nucleotide binding while others do not.
Reason: The P-loop/VAIK motif elements predicted by sequence (UniProt BINDING 290-298 and 339) make residual ATP binding plausible even though NFP is catalytically inactive, and ATP binding by a pseudokinase does not imply catalysis. The annotation is not contradicted by experiment, but it is not a core function: NFP's defining role is ligand perception, not nucleotide chemistry, and no study has demonstrated functional ATP binding. Retain as a plausible domain-derived prediction, marked non-core.
Supporting Evidence:
PMID:16844829
one subfamily, which includes NFP, was characterized by deviations from conserved kinase sequences.
GO:0005775 vacuolar lumen
IEA
GO_REF:0000044
KEEP AS NON CORE
Summary: Subcellular-location IEA derived from the UniProt subcellular location "Vacuole lumen", which is itself based on the experimental observation that NFP relocalizes to the vacuolar lumen in nodule cells undergoing receptor breakdown (PMID:25351493). This IEA is the keyword/subcell-mapping counterpart of the curated IDA annotation below.
Reason: The annotation accurately reflects the experimental finding that NFP is observed in the vacuolar lumen in cells undergoing receptor breakdown (PMID:25351493). It is a genuine but non-core, degradation-associated localization rather than the site of NFP signalling function. Keep, marked non-core (consistent with the curated IDA annotation from PMID:25351493).
Supporting Evidence:
UniProt:Q0GXS4
SUBCELLULAR LOCATION: Cell membrane; Single-pass membrane protein. Vacuole lumen. Note=Removed from the plasma membrane upon the release of rhizobia into the host cytoplasm. Vacuolar localization is observed in cells undergoing breakdown of the receptors.
GO:0005886 plasma membrane
IEA
GO_REF:0000120
ACCEPT
Summary: Multi-method IEA (ARBA + UniProtKB-SubCell mapping) placing NFP at the plasma membrane. NFP is a single-pass type I transmembrane protein and is experimentally localized at the cell periphery / plasma membrane (PMID:25351493).
Reason: Correct and core: NFP is a plasma-membrane receptor. The localization is directly supported by experiment (curated IDA annotation from PMID:25351493) and by the protein's single-pass transmembrane topology. Accept as-is.
Supporting Evidence:
PMID:25351493
It was found that inside Medicago truncatula nodules, NFP and LYK3 localize at the cell periphery in a narrow zone of about two cell layers at the nodule apex.
GO:0051707 response to other organism
IEA
GO_REF:0000117
MODIFY
Summary: ARBA machine-learning IEA. NFP responds to and perceives signals from other organisms - both the symbiotic rhizobium Sinorhizobium meliloti (Nod factors) and pathogenic oomycetes/fungi. The term is correct but very broad.
Reason: "Response to other organism" is accurate but uninformatively general. The specific, experimentally documented responses are already, or should be, represented by more precise terms: response to molecule of bacterial origin (GO:0002237, existing IMP), nodulation (GO:0009877), and the defense-response regulation terms. The best single specific replacement that captures NFP's defining symbiotic role is "response to molecule of bacterial origin" (GO:0002237), already present from PMID:12753588.
Supporting Evidence:
PMID:12753588
The nfp mutant thus shows no rapid calcium flux, the earliest detectable Nod factor response of wild-type plants, and no root hair deformation.
GO:0005515 protein binding
IPI
PMID:25794934
The small GTPase ROP10 of Medicago truncatula is required fo...
MODIFY
Summary: IPI annotation with WITH/FROM UniProtKB:B2MVQ1 (ROP10, a type II Rho-of-plants small GTPase). The kinase domain of NFP interacts with ROP10 in a GTP-dependent manner, and this interaction is required for root hair deformation during rhizobial infection (PMID:25794934).
Reason: "Protein binding" (GO:0005515) is uninformative and discouraged. The interacting partner is a small GTPase and the interaction is well characterized (GTP-dependent, mediated by the NFP kinase domain), so a more specific molecular function term is warranted: "small GTPase binding" (GO:0031267). This also reframes the NFP kinase domain correctly - as a protein-interaction/scaffolding module rather than a catalytic kinase.
Proposed replacements: small GTPase binding
Supporting Evidence:
PMID:25794934
ROP10 interacted with the kinase domain of the NF receptor NFP in a GTP-dependent manner.
GO:0009877 nodulation
IEP
PMID:22874912
Epidermal and cortical roles of NFP and DMI3 in coordinating...
ACCEPT
Summary: IEP annotation: NFP expression is associated with nodulation. NFP is expressed in root epidermis and cortex and is required for nodule organogenesis; epidermal NFP alone is sufficient to induce cortical cell divisions leading to nodule primordia (PMID:22874912).
Reason: Nodulation is the core biological process of NFP and is strongly supported. PMID:22874912 demonstrates that epidermal NFP induces cortical cell divisions leading to nodule primordia formation. Accept as a core function annotation.
Supporting Evidence:
PMID:22874912
Epidermal NFP is sufficient to induce cortical cell divisions leading to nodule primordia formation.
GO:0009877 nodulation
IMP
PMID:22874912
Epidermal and cortical roles of NFP and DMI3 in coordinating...
ACCEPT
Summary: IMP annotation based on mutant/complementation analysis: tissue-specific complementation of nfp mutants shows epidermal NFP is sufficient to induce cortical cell divisions for nodule primordium formation (PMID:22874912).
Reason: Strong genetic (loss-of-function plus tissue-targeted complementation) evidence that NFP is required for nodulation. Core function. Accept.
Supporting Evidence:
PMID:22874912
By complementing mutant plants with corresponding genes expressed either in the epidermis or in the cortex, we have shown that ... Epidermal NFP is sufficient to induce cortical cell divisions leading to nodule primordia formation.
GO:1900150 regulation of defense response to fungus
IMP
PMID:23432463
NFP, a LysM protein controlling Nod factor perception, also ...
ACCEPT
Summary: IMP annotation: nfp mutants show increased susceptibility to the fungus Colletotrichum trifolii, demonstrating that NFP positively contributes to antifungal immunity (PMID:23432463).
Reason: Directly supported by mutant phenotype: "nfp mutants also showed an increased susceptibility to the fungus Colletotrichum trifolii" (PMID:23432463). This is a specific, well-evidenced secondary (non-core) function distinct from NFP's primary symbiotic role. Accept. (The data arguably support the more specific "positive regulation of defense response to fungus", but the parent regulatory term as annotated is correct and adequately specific.)
Supporting Evidence:
PMID:23432463
nfp mutants also showed an increased susceptibility to the fungus Colletotrichum trifolii. These results demonstrate that NFP intervenes in M. truncatula immunity.
GO:1902290 positive regulation of defense response to oomycetes
IMP
PMID:23432463
NFP, a LysM protein controlling Nod factor perception, also ...
ACCEPT
Summary: IMP annotation: nfp mutants are more susceptible to the oomycete Aphanomyces euteiches, and NFP overexpression increases resistance, establishing NFP as a positive regulator of anti-oomycete defense (PMID:23432463).
Reason: Well supported by reciprocal genetic evidence: loss of function increases susceptibility while overexpression increases resistance to A. euteiches (PMID:23432463). The "positive regulation" directionality is justified by the overexpression result. Specific, properly evidenced secondary function. Accept.
Supporting Evidence:
PMID:23432463
nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance.
GO:0002237 response to molecule of bacterial origin
IMP
PMID:12753588
The NFP locus of Medicago truncatula controls an early step ...
ACCEPT
Summary: IMP annotation: nfp mutants fail to respond to rhizobial Nod factors (lipo-chitooligosaccharides of bacterial origin) by any assayed response - no calcium flux, no calcium spiking, no early nodulin expression, no root hair deformation (PMID:12753588).
Reason: Core function. The nfp mutant is completely unresponsive to the rhizobial Nod factor, establishing NFP as essential for perception of and response to this bacterial-origin molecule (PMID:12753588). Accept; this term also serves as the specific replacement for the broad ARBA term "response to other organism".
Supporting Evidence:
PMID:12753588
The nfp mutant thus shows no rapid calcium flux, the earliest detectable Nod factor response of wild-type plants, and no root hair deformation. The nfp mutant is also deficient in Nod factor-induced calcium spiking and early nodulin gene expression.
GO:0009101 glycoprotein biosynthetic process
IDA
PMID:16723404
LysM domains of Medicago truncatula NFP protein involved in ...
MARK AS OVER ANNOTATED
Summary: IDA annotation based on PMID:16723404, which showed that NFP expressed in M. truncatula roots is highly N-glycosylated, probably with both high-mannose and complex glycans. This annotation describes NFP as a glycoprotein substrate, not as an enzyme of the glycosylation machinery.
Reason: NFP is the SUBSTRATE of N-glycosylation, not a component of the glycoprotein biosynthetic pathway. Being a glycoprotein does not mean the gene product is "involved in" the biosynthetic process in the causal sense that the GO BP term implies. The underlying observation (NFP is N-glycosylated) is better captured as a protein modification/feature (UniProt CARBOHYD features) than as a BP annotation. This is an over-annotation: NFP plays no role in synthesizing glycans. Mark as over-annotated.
Supporting Evidence:
PMID:16723404
Expression of NFP in a homologous system (M. truncatula roots) revealed that the protein is highly N-glycosylated, probably with both high-mannose and complex glycans.
GO:0009877 nodulation
IMP
PMID:12753588
The NFP locus of Medicago truncatula controls an early step ...
ACCEPT
Summary: IMP annotation: the nfp mutant has a Nod-negative phenotype, failing all Nod factor responses and unable to nodulate (PMID:12753588). NFP controls the earliest, nodulation-specific step of Nod factor signal transduction.
Reason: Core function with strong loss-of-function evidence. The nfp mutant is Nod-negative and NFP "controls an early step of Nod factor signal transduction ... specific to nodulation" (PMID:12753588). Accept.
Supporting Evidence:
PMID:12753588
These data indicate that the NFP locus controls an early step of Nod factor signal transduction, upstream of previously identified genes and specific to nodulation.
GO:0009877 nodulation
IEP
PMID:16844829
The Medicago truncatula lysin [corrected] motif-receptor-lik...
ACCEPT
Summary: IEP annotation: NFP is expressed in association with infection thread development and nodule formation, and is involved in the infection process (PMID:16844829).
Reason: Expression-based support for the core nodulation function; NFP is expressed in roots and nodules in association with infection thread development (PMID:16844829). Consistent with the IMP annotations. Accept.
Supporting Evidence:
PMID:16844829
NFP was shown both to be expressed in association with infection thread development and to be involved in the infection process.
GO:0009877 nodulation
IMP
PMID:16844829
The Medicago truncatula lysin [corrected] motif-receptor-lik...
ACCEPT
Summary: IMP annotation: nfp-1 mutant analysis shows impaired nodulation - no root hair curling, no infection thread formation, no Nod factor-induced root hair deformation (PMID:16844829).
Reason: Core function, strong mutant evidence. The nfp-1 mutant shows an impaired nodulation response to S. meliloti (PMID:16844829). Accept.
Supporting Evidence:
PMID:16844829
NFP was shown both to be expressed in association with infection thread development and to be involved in the infection process.
GO:0005515 protein binding
IPI
PMID:25351493
Nod factor receptors form heteromeric complexes and are esse...
MODIFY
Summary: IPI annotation with WITH/FROM UniProtKB:Q6UD73 (LYK3, an active LysM receptor-like kinase). FRET-FLIM analysis showed that NFP and LYK3 form heteromeric receptor complexes at the cell periphery in M. truncatula nodules (PMID:25351493).
Reason: "Protein binding" (GO:0005515) is uninformative and discouraged. The characterized interaction is a specific heteromeric receptor complex between two LysM-RLKs, so a more informative molecular function term is appropriate: "protein heterodimerization activity" (GO:0046982). This interaction is functionally central - because NFP is a pseudokinase, the heteromer with the active kinase LYK3 is the mechanism by which Nod factor perception is transduced.
Supporting Evidence:
PMID:25351493
our Förster resonance energy transfer-fluorescence lifetime imaging microscopy analysis indicates that NFP and LYK3 form heteromeric complexes at the cell periphery in M. truncatula nodules.
GO:0005775 vacuolar lumen
IDA
PMID:25351493
Nod factor receptors form heteromeric complexes and are esse...
KEEP AS NON CORE
Summary: IDA annotation: NFP is observed in the vacuolar lumen of nodule cells undergoing breakdown of the receptors (PMID:25351493).
Reason: Directly observed localization, but it represents a degradation/turnover route ("Vacuolar localization is observed in cells undergoing breakdown of the receptors") rather than the site of NFP's signalling function. Keep, but mark non-core; the functionally relevant localization is the plasma membrane.
Supporting Evidence:
PMID:25351493
the role of the Nod factor receptors NOD FACTOR PERCEPTION (NFP) and LYSIN MOTIF RECEPTOR-LIKE KINASE3 (LYK3) in establishing the symbiotic interface in root nodules was investigated.
GO:0005886 plasma membrane
IDA
PMID:25351493
Nod factor receptors form heteromeric complexes and are esse...
ACCEPT
Summary: IDA annotation: NFP localizes at the cell periphery / plasma membrane in a narrow zone of about two cell layers at the nodule apex, where it can perceive bacterial Nod factors (PMID:25351493).
Reason: Core localization, directly observed. NFP is a plasma-membrane receptor; the plasma membrane is where it perceives Nod factors and forms heteromeric complexes with LYK3 (PMID:25351493). Accept.
Supporting Evidence:
PMID:25351493
It was found that inside Medicago truncatula nodules, NFP and LYK3 localize at the cell periphery in a narrow zone of about two cell layers at the nodule apex.
GO:0009877 nodulation
IEP
PMID:25351493
Nod factor receptors form heteromeric complexes and are esse...
ACCEPT
Summary: IEP annotation: NFP expression/protein accumulation is associated with nodulation, specifically with the meristem and infection zone of developing nodules where it perceives Nod factors (PMID:25351493).
Reason: Expression-pattern support for the core nodulation function, consistent with the multiple IMP annotations. Accept.
Supporting Evidence:
PMID:25351493
In these layers, the receptors can most likely perceive the bacterial Nod factors to regulate the formation of symbiotic interface.
GO:0038023 signaling receptor activity
IMP
PMID:12753588
The NFP locus of Medicago truncatula controls an early step ...
NEW
Summary: NFP is a Nod factor receptor: its LysM ectodomain binds the rhizobial lipo-chitooligosaccharide signal and the receptor triggers intracellular signalling. The nfp mutant fails every Nod factor response, placing NFP at the most upstream, receptor-level step of the pathway.
Reason: The current GOA set lacks any molecular function term for NFP's true activity. With the catalytic kinase terms removed (NFP is a pseudokinase), a signalling receptor MF term is needed to represent the gene's defining function. "Signaling receptor activity" (GO:0038023) is well supported: the nfp mutant abolishes all Nod factor responses (PMID:12753588) and NFP is described as a Nod factor receptor that perceives the bacterial signal (PMID:25351493, PMID:16723404).
Supporting Evidence:
PMID:12753588
These data indicate that the NFP locus controls an early step of Nod factor signal transduction, upstream of previously identified genes and specific to nodulation.
PMID:25351493
In these layers, the receptors can most likely perceive the bacterial Nod factors to regulate the formation of symbiotic interface.
GO:0008061 chitin binding
ISS
PMID:16723404
LysM domains of Medicago truncatula NFP protein involved in ...
NEW
Summary: The NFP extracellular region contains three tandem LysM domains. LysM domains are carbohydrate-binding modules that bind N-acetylglucosamine polymers (chitin/chitooligosaccharides); the rhizobial Nod factor is a lipo-chitooligosaccharide. Homology modelling and docking predict that the Nod factor / chitooligosaccharide binds the three LysM domains, and LysM residues (e.g. Leu154) are functionally required for Nod factor recognition.
Reason: NFP's molecular recognition function - binding the chitin-based Nod factor ligand via its LysM domains - is central and currently unrepresented in GOA. "Chitin binding" (GO:0008061) is the closest available GO term for the chitooligosaccharide/LCO-binding activity of the LysM ectodomain. Supported by modelling/docking (PMID:16723404) and by mutagenesis showing LysM residues are required for Nod factor recognition (PMID:22087221). Evidence is structural-modelling/inference plus mutant data, hence ISS.
Supporting Evidence:
PMID:16723404
A convergent model can be proposed where the sulfated, O-acetylated lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar orientation to the three LysM domains of M. truncatula NFP.
PMID:22087221
we have demonstrated the importance of the NFP LysM2 domain for rhizobial infection and we have pinpointed the importance of a single leucine residue of LysM2 in that step of the symbiosis.

Core Functions

Perception of rhizobial Nod factors (lipo-chitooligosaccharides) by the extracellular LysM domains, acting as a plasma-membrane signalling receptor that initiates Nod factor signal transduction.

Molecular Function:
signaling receptor activity
Directly Involved In:
Cellular Locations:
Supporting Evidence:
  • PMID:12753588
    These data indicate that the NFP locus controls an early step of Nod factor signal transduction, upstream of previously identified genes and specific to nodulation.
  • PMID:16723404
    A convergent model can be proposed where the sulfated, O-acetylated lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar orientation to the three LysM domains of M. truncatula NFP.
  • file:MEDTR/NFP/NFP-deep-research-falcon.md
    acts at the ... earliest stages of Nod factor signaling ... and is genetically placed ... upstream of DMI1/DMI2/DMI3 and NSP1/NSP2 ... the extracellular region comprises three LysM domains specialized for carbohydrate-derived ligands

Initiation of the nitrogen-fixing root nodule symbiosis - nodule organogenesis (induction of cortical cell divisions) and rhizobial infection thread development and bacterial release - through Nod factor signalling.

Directly Involved In:
Supporting Evidence:
  • PMID:22874912
    Epidermal NFP is sufficient to induce cortical cell divisions leading to nodule primordia formation.
  • PMID:16844829
    NFP was shown both to be expressed in association with infection thread development and to be involved in the infection process.

Formation of a heteromeric Nod factor receptor complex with the active co-receptor kinase LYK3; because NFP is a catalytically dead pseudokinase, this heteromer is the mechanism by which extracellular Nod factor perception is transduced intracellularly.

Supporting Evidence:
  • PMID:25351493
    our Förster resonance energy transfer-fluorescence lifetime imaging microscopy analysis indicates that NFP and LYK3 form heteromeric complexes at the cell periphery in M. truncatula nodules.
  • PMID:16844829
    NFP did not show autophosphorylation activity, suggesting that NFP needs to associate with an active kinase or has unusual functional characteristics different from classical kinases.
  • file:MEDTR/NFP/NFP-deep-research-falcon.md
    lacking key conserved motifs (including P-loop/DFG-related features and an activation-loop segment), and ... was observed in vitro, supporting interpretation of NFP as a likely ... or signaling subunit that requires an active kinase partner

Contribution to plant immunity - positive regulation of defense responses against the root oomycete Aphanomyces euteiches and the fungus Colletotrichum trifolii. This is a secondary, non-core role distinct from the primary symbiotic function.

Supporting Evidence:
  • PMID:23432463
    nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance.

References

Gene Ontology annotation through association of InterPro records with GO terms
  • InterPro2GO maps protein-kinase-domain signatures to protein kinase activity and ATP binding. For NFP these mappings detect the kinase fold but do not account for its experimentally established pseudokinase status.
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  • SwissProt keyword-derived (SPKW) annotations present in the Sept 2025 goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA retired the keyword2GO pipeline for cellular organisms.
  • The retired SPKW annotations for NFP - protein tyrosine kinase activity (from the Tyrosine-protein kinase keyword) and defense response (from the Plant defense keyword) - were both correctly removed; the first is biologically wrong (pseudokinase; Ser/Thr not Tyr) and the second is redundant with more specific curated defense terms.
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
  • Maps the UniProt subcellular location "Vacuole lumen" to GO:0005775; this reflects the experimentally observed vacuolar localization of NFP in cells undergoing receptor breakdown.
Electronic Gene Ontology annotations created by ARBA machine learning models
  • ARBA assigned the broad term "response to other organism"; the specific experimentally supported response is to bacterial-origin Nod factors.
Combined Automated Annotation using Multiple IEA Methods
  • Combined IEA methods place NFP at the plasma membrane, consistent with its single-pass transmembrane topology and experimental localization.
The NFP locus of Medicago truncatula controls an early step of Nod factor signal transduction upstream of a rapid calcium flux and root hair deformation.
  • The nfp mutant fails every assayed Nod factor response (no calcium flux, no calcium spiking, no early nodulin expression, no root hair deformation), placing NFP at the most upstream, nodulation-specific step of Nod factor signal transduction.
    "The nfp mutant thus shows no rapid calcium flux, the earliest detectable Nod factor response of wild-type plants, and no root hair deformation. The nfp mutant is also deficient in Nod factor-induced calcium spiking and early nodulin gene expression."
LysM domains of Medicago truncatula NFP protein involved in Nod factor perception. Glycosylation state, molecular modeling and docking of chitooligosaccharides and Nod factors.
  • The three tandem LysM domains of the NFP ectodomain are predicted to bind the rhizobial lipo-chitooligosaccharide Nod factor; NFP is highly N-glycosylated.
    "A convergent model can be proposed where the sulfated, O-acetylated lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar orientation to the three LysM domains of M. truncatula NFP."
The Medicago truncatula lysin [corrected] motif-receptor-like kinase gene family includes NFP and new nodule-expressed genes.
  • NFP is a LysM-RLK whose intracellular kinase domain is a pseudokinase - it deviates from conserved catalytic kinase sequences and shows no autophosphorylation activity, implying it must associate with an active kinase.
    "Consistent with deviations from conserved kinase domain sequences, NFP did not show autophosphorylation activity, suggesting that NFP needs to associate with an active kinase or has unusual functional characteristics different from classical kinases."
Contribution of NFP LysM domains to the recognition of Nod factors during the Medicago truncatula/Sinorhizobium meliloti symbiosis.
  • The NFP LysM2 domain, and specifically a single leucine residue (Leu154), are important for rhizobial infection, demonstrating that LysM domain residues are functionally required for Nod factor recognition.
    "we have demonstrated the importance of the NFP LysM2 domain for rhizobial infection and we have pinpointed the importance of a single leucine residue of LysM2 in that step of the symbiosis."
Epidermal and cortical roles of NFP and DMI3 in coordinating early steps of nodulation in Medicago truncatula.
  • Epidermal NFP is sufficient to induce cortical cell divisions leading to nodule primordium formation, establishing NFP's role in nodule organogenesis.
    "Epidermal NFP is sufficient to induce cortical cell divisions leading to nodule primordia formation."
NFP, a LysM protein controlling Nod factor perception, also intervenes in Medicago truncatula resistance to pathogens.
  • NFP positively contributes to M. truncatula immunity: nfp mutants are more susceptible to the oomycete Aphanomyces euteiches and the fungus Colletotrichum trifolii, and NFP overexpression increases resistance.
    "nfp, but not lyk3, mutants were significantly more susceptible than wildtype plants to A. euteiches, whereas NFP overexpression increased resistance."
Nod factor receptors form heteromeric complexes and are essential for intracellular infection in medicago nodules.
  • NFP and the active LysM-RLK LYK3 form heteromeric receptor complexes at the cell periphery (plasma membrane) in M. truncatula nodules; NFP is also observed in the vacuolar lumen of cells undergoing receptor breakdown.
    "our Förster resonance energy transfer-fluorescence lifetime imaging microscopy analysis indicates that NFP and LYK3 form heteromeric complexes at the cell periphery in M. truncatula nodules."
The small GTPase ROP10 of Medicago truncatula is required for both tip growth of root hairs and nod factor-induced root hair deformation.
  • The intracellular kinase domain of NFP interacts with the small GTPase ROP10 in a GTP-dependent manner; this interaction is required for root hair deformation during rhizobial infection.
    "ROP10 interacted with the kinase domain of the NF receptor NFP in a GTP-dependent manner."
file:MEDTR/NFP/NFP-deep-research-falcon.md
Deep research report (falcon / Edison Scientific) on Medicago truncatula NFP (UniProt Q0GXS4)
  • Independently confirms that NFP has a nonclassical/aberrant intracellular kinase domain lacking key conserved kinase motifs (P-loop/DFG-related features and an activation-loop segment) and shows no detectable autophosphorylation in vitro, supporting interpretation of NFP as a pseudokinase / non-catalytic signalling subunit - corroborating the REMOVE decisions on the catalytic kinase-activity annotations.
    "lacking key conserved motifs (including P-loop/DFG-related features and an activation-loop segment), and ... was observed in vitro, supporting interpretation of NFP as a likely ... or signaling subunit that requires an active kinase partner"
  • Confirms NFP is a plasma-membrane LysM receptor-like kinase whose three tandem extracellular LysM domains mediate recognition of rhizobial Nod factors (lipo-chitooligosaccharides), and that NFP acts at the earliest step of Nod factor signalling, genetically upstream of DMI1/DMI2/DMI3 and NSP1/NSP2, controlling both rhizobial infection and nodule organogenesis.
    "acts at the ... earliest stages of Nod factor signaling ... and is genetically placed ... upstream of DMI1/DMI2/DMI3 and NSP1/NSP2 ... Arrighi et al. further argue that NFP functions throughout infection and may control partly distinct pathways for ... symbiotic infection ... and ... nodule organogenesis"
  • Confirms NFP's role at the symbiosis-immunity interface: NFP/NFR-type receptors can trigger defense-like outputs, and recent work links the NFP kinase domain to the immune co-receptor MtSOBIR1 - consistent with the review's treatment of NFP's defense role as a real but secondary, non-core function.
    "NFP/NFR-type receptors lie at a ... symbiosis–immunity interface ... Recent work connects NFP to ... a known immunity coreceptor"
  • Adds recent (2023-2024) mechanistic context not in the original review: NFP can functionally associate with multiple LysM-RLK partners (MtLYK2, MtLYK3, MtLYK2bis) whose kinase-active cytoplasmic domains can trans-phosphorylate the NFP cytoplasmic domain, extending the single-partner NFP-LYK3 heteromer model toward a multi-partner receptor-complex landscape.
    "cytoplasmic domains of MtLYK2/3/2bis display kinase activity, and kinase-active versions can induce mobility shifts/retardation consistent with ... trans-phosphorylation of the MtNFP cytoplasmic domain"
UniProt:Q0GXS4
UniProtKB entry Q0GXS4 (NFP_MEDTR), Serine/threonine receptor-like kinase NFP
  • The UniProt curated subcellular location places NFP at the cell membrane and, on the basis of PMID:25351493, in the vacuole lumen of nodule cells undergoing breakdown of the Nod factor receptors - the source of the GO_REF:0000044 subcellular-location IEA to vacuolar lumen.
    "SUBCELLULAR LOCATION: Cell membrane; Single-pass membrane protein. Vacuole lumen. Note=Removed from the plasma membrane upon the release of rhizobia into the host cytoplasm. Vacuolar localization is observed in cells undergoing breakdown of the receptors."

Suggested Questions for Experts

Q: Does the NFP pseudokinase domain retain ATP/nucleotide binding in vitro, or has it lost nucleotide binding as well as catalysis?

Q: What is the structural basis of Nod factor recognition by the NFP LysM ectodomain, and which LysM domain(s) directly contact the lipo-chitooligosaccharide acyl and sulphate substitutions?

Q: How is signal transferred from the NFP pseudokinase domain to LYK3 within the heteromeric complex - by allosteric activation, transphosphorylation of NFP by LYK3, or scaffolding of downstream effectors?

Q: Does NFP perception of pathogen-derived chitooligosaccharides use the same LysM binding surface as Nod factor perception, and how is the symbiotic versus immune signalling outcome discriminated?

Suggested Experiments

Experiment: Reconstitute the NFP/LYK3 complex in vitro and test whether the active LYK3 kinase transphosphorylates the NFP pseudokinase domain, and whether NFP allosterically modulates LYK3 activity.

Hypothesis: NFP is a catalytically dead pseudokinase that is transphosphorylated by and allosterically regulates its active co-receptor LYK3.

Experiment: Solve a co-crystal or cryo-EM structure of the NFP LysM ectodomain bound to a defined Sinorhizobium meliloti Nod factor to confirm the predicted three-LysM-domain binding mode.

Hypothesis: The rhizobial lipo-chitooligosaccharide Nod factor binds across the three tandem LysM domains of the NFP ectodomain.

Experiment: Quantitative binding assays (ITC/SPR) with purified NFP ectodomain against Nod factors, chitooligosaccharides of varying length, and pathogen-derived chitin fragments to define ligand specificity and affinity.

Hypothesis: The NFP LysM ectodomain binds chitin-based ligands and discriminates symbiotic Nod factors from pathogen-derived chitooligosaccharides by affinity or substitution recognition.

Experiment: Structure-guided mutagenesis of NFP pseudokinase-domain residues to test whether nucleotide binding or specific surface residues are required for ROP10 interaction and for signalling output.

Hypothesis: The NFP pseudokinase domain functions as a protein-interaction module whose surface, rather than catalytic activity, is required for ROP10 binding and signalling.

Deep Research

Falcon

(NFP-deep-research-falcon.md)
Research Report: Functional Annotation of **NFP** (UniProt **Q0GXS4**) in *Medicago truncatula* Falcon Edison Scientific Literature 29 citations 2 artifacts 2026-05-21T14:05:14.699661

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.

Research Report: Functional Annotation of NFP (UniProt Q0GXS4) in Medicago truncatula

0. Target verification (critical disambiguation)

The Medicago truncatula gene NFP (Nod Factor Perception) corresponds to a plasma-membrane LysM receptor-like kinase (LysM-RLK) with an N-terminal signal peptide, three extracellular LysM domains, a single transmembrane helix, and a C-terminal intracellular kinase-like region (UniProt Q0GXS4), and is closely related to pea SYM10 and Lotus japonicus NFR5. This identity is supported by cloning/genetic linkage to nfp mutant alleles, complementation, and protein/domain analyses in M. truncatula (Jemalong A17) (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 3-4). Visual evidence for domain architecture and kinase motif losses is shown in Arrighi et al. figures (arrighi2006themedicagotruncatula media 0385937d, arrighi2006themedicagotruncatula media eefcd0eb).

1. Key concepts and definitions (current understanding)

1.1 Nod factors (NFs) and Nod factor perception

Nod factors are rhizobial lipo-chitooligosaccharides (LCOs) that initiate legume–rhizobia symbiosis by triggering early root responses (e.g., root hair deformation/curling, infection thread initiation) and downstream developmental programs culminating in root nodule formation. In M. truncatula, NFP is essential for the earliest NF responses, consistent with its name and mutant phenotype (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 8-10).

1.2 LysM receptor-like kinases (LysM-RLKs)

Plant LysM-RLKs are cell-surface receptors with extracellular LysM domains (∼40 aa modules often associated with binding N-acetylglucosamine-containing ligands such as chitin-derived molecules) linked through a transmembrane segment to an intracellular kinase domain. A key conceptual point emerging from M. truncatula analyses is that many plant LysM-RLKs contain a conserved “LysM triplet” (three LysM domains), including NFP (arrighi2006themedicagotruncatula pages 10-11).

1.3 “Dead”/nonclassical kinase domains and receptor complexes

A central mechanistic concept for NFP (and NFR5-like receptors) is that the intracellular region resembles a kinase domain but lacks conserved motifs and can function as a pseudokinase (“dead kinase”) that participates in signaling through heteromerization with kinase-active partners (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 11-12). This resembles general receptor biology where one subunit can provide ligand-binding specificity and another provides catalytic output, or where signaling is mediated via trans-phosphorylation in receptor complexes (arrighi2006themedicagotruncatula pages 11-12).

2. Gene/protein function: what NFP does (primary function)

2.1 Primary functional role

Primary function (experimentally supported): NFP is an essential component of the Nod factor receptor system required for Nod factor perception and early symbiotic signaling that enables rhizobial infection and nodulation in M. truncatula (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 8-10).

Genetic evidence: nfp mutants fail to undergo hallmark early NF responses (root hair deformation/curling; infection thread formation) and are defective for nodulation; complementation with a genomic NFP fragment restores nodulation, confirming gene identity and essential function (arrighi2006themedicagotruncatula pages 2-3).

2.2 Ligand specificity and binding determinants (mechanistic inference + supporting evidence)

Direct biochemical binding measurements for NFP–NF are not established in the retrieved evidence; however, multiple lines support NFP’s role in NF recognition:

  • Domain logic: the extracellular region comprises three LysM domains specialized for carbohydrate-derived ligands (mulder2006lysmdomainsof pages 1-2).
  • Mutant structure–function: Arrighi et al. report a strong nfp-2 allele mutated in the first LysM domain, consistent with a crucial role for LysM1 in recognition (arrighi2006themedicagotruncatula pages 11-12).
  • Computational structural modeling/docking (mechanistic hypothesis): docking of Nod factors to modeled NFP LysM domains predicts binding modes in which the LCO tetrasaccharide backbone and substituents (sulfate, O-acetyl group, and lipid chain) interact with specific residues and surface features, supporting a plausible structural basis for NF recognition (mulder2006lysmdomainsof pages 4-5). Mulder et al. further propose each LysM domain could potentially bind one NF, and discuss how triplicated LysMs could broaden recognition or amplify signaling (mulder2006lysmdomainsof pages 5-6).

2.3 Kinase activity: enzymatic reaction and substrate specificity

NFP is annotated as a receptor-like kinase (EC 2.7.10.-), but the best-supported functional interpretation is non-catalytic signaling rather than active enzymatic phosphorylation:

  • Motif loss: NFP lacks key conserved kinase motifs (e.g., missing activation loop segment; absent P-loop/DFG-related motifs described in Arrighi et al.), indicating a nonclassical kinase domain (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 11-12, arrighi2006themedicagotruncatula media 0385937d).
  • Biochemical assay: NFP showed no detectable autophosphorylation activity under in vitro conditions where other receptor kinases (e.g., LYK3, BAK1) did autophosphorylate, supporting pseudokinase-like behavior (arrighi2006themedicagotruncatula pages 3-4, arrighi2006themedicagotruncatula media d64c86c9).

Thus, NFP’s “substrate specificity” is currently best described as not established as an active kinase; instead, NFP likely acts as a signaling/scaffolding subunit in receptor complexes that are phosphorylated by kinase-active partners (arrighi2006themedicagotruncatula pages 11-12).

3. Cellular localization and expression context (where NFP acts)

3.1 Subcellular localization

NFP is described as a plasma-membrane receptor-like protein (consistent with signal peptide + transmembrane topology and extracellular glycosylation) (mulder2006lysmdomainsof pages 6-7).

3.2 Cell- and tissue-level expression patterns

Arrighi et al. map NFP promoter activity and conclude NFP expression is tightly associated with infection:

  • Root hairs: expression in growing and recently matured root hairs (arrighi2006themedicagotruncatula pages 2-3).
  • Cortex and primordia: expression in inner/middle cortex at sites associated with curling and nodule primordium formation (arrighi2006themedicagotruncatula pages 3-4).
  • Nodule infection zone: expression restricted to the infection zone in mature nodules and coincident with infection thread formation and bacterial release (arrighi2006themedicagotruncatula pages 3-4, arrighi2006themedicagotruncatula pages 10-11).
  • Not nitrogen fixation: declining expression toward nitrogen-fixing zone and lack of expression in central tissue suggests NFP is unlikely to directly mediate nitrogen fixation/assimilation, but instead functions in NF signaling/infection processes (arrighi2006themedicagotruncatula pages 10-11).

3.3 Post-translational modification relevant to localization/function

Mulder et al. provide biochemical evidence that NFP is extensively N-glycosylated extracellularly (with multiple predicted N-glycosylation sites; glycosidase tests indicating multiple modified sites), supporting extracellular domain maturation consistent with surface receptor function (mulder2006lysmdomainsof pages 6-7).

4. Pathway placement: how NFP connects to symbiotic signaling

4.1 Upstream role in NF signaling cascade

Arrighi et al. place NFP genetically upstream of canonical downstream symbiotic signaling components such as DMI1/DMI2/DMI3 (and downstream transcriptional regulators), based on known mutant pathway relationships and the null phenotype of nfp in early NF responses (arrighi2006themedicagotruncatula pages 10-11).

They further argue that because NFP has not been shown to control processes beyond NF perception, its expression and knockdown phenotypes suggest that NF perception/signaling continues throughout infection, not solely at the epidermis (arrighi2006themedicagotruncatula pages 10-11).

4.2 Infection vs organogenesis programs

Arrighi et al. interpret expression patterns and infection phenotypes as consistent with NFP controlling (directly or indirectly) distinct NF signaling routes: one supporting symbiotic infection (infection thread development) and one supporting nodule organogenesis (arrighi2006themedicagotruncatula pages 10-11).

5. Receptor complexes and partners (current models + new evidence)

5.1 Classical model: NFP/NFR5-like pseudokinase + kinase-active LysM-RLK partner

Both the aberrant kinase domain of NFP and general receptor logic support a model in which NFP functions with a kinase-active LysM-RLK partner (e.g., LYK3) in a heteromeric complex to transmit NF signals (mulder2006lysmdomainsof pages 6-7, arrighi2006themedicagotruncatula pages 11-12).

5.2 2023–2024 developments (prioritized)

(i) Expanded partner set and biochemical trans-phosphorylation (2024)

A 2024 preprint reports that M. truncatula MtLYK2, MtLYK3, and MtLYK2bis can associate functionally with MtNFP:

  • Heterologous co-expression phenotype: co-overexpression of MtNFP with MtLYK2/3/2bis in Nicotiana triggers apparent cell death, consistent with strong receptor complex signaling and immune crosstalk (li2024nodulationtrioin pages 1-3).
  • Kinase activity + trans-phosphorylation: cytoplasmic domains of MtLYK2/3/2bis display kinase activity, and kinase-active versions can induce mobility shifts/retardation consistent with trans-phosphorylation of the MtNFP cytoplasmic domain in co-expression assays; kinase-dead controls do not (li2024nodulationtrioin pages 3-9).
  • Genetic redundancy: these receptors show overlapping contributions to nodulation, supporting a model where NFP can partner with multiple LysM-RLKs with partially redundant/specialized roles (li2024nodulationtrioin pages 3-9, li2024nodulationtrioin pages 1-3).

Interpretation: this expands the earlier “single partner” view (NFP–LYK3) toward a multi-partner receptor complex landscape in M. truncatula (li2024nodulationtrioin pages 3-9).

(ii) Connection to immune co-receptor modules via SOBIR1 (2023)

A 2023 preprint reports identification of MtSOBIR1 as an interactor of the MtNFP kinase domain:

  • Yeast-two-hybrid (Y2H): the MtNFP kinase domain (aa 273–595) was used as bait, and partial clones corresponding to a SOBIR1-like RLK were recovered as interactors (sarrette2023medicagotruncatulasobir1 pages 4-5).
  • Expert framing: SOBIR1 is described as a known positive regulator of immunity and a common coreceptor for receptor-like proteins lacking intracellular signaling domains; it has an active kinase domain and can participate in complexes including BAK1, suggesting plausible mechanistic routes by which NFP-containing complexes could interface with immune signaling modules (sarrette2023medicagotruncatulasobir1 pages 4-5).

Interpretation: NFP may not act only within “symbiosis-only” receptor assemblies but may recruit (or be regulated by) immunity-associated RLK modules, potentially contributing to host specificity and defense suppression/activation balance (sarrette2023medicagotruncatulasobir1 pages 4-5).

(iii) Symbiosis–immunity interface emphasized by recent review (2023)

A 2023 review highlights that Nod factors can induce transient defense outputs but generally weaker than chitin, and that NFRs (including MtNFP) can trigger defense-like outcomes when expressed ectopically or outside their native context (grundy2023legumesregulatesymbiosis pages 8-9). Specifically, ectopic expression of MtNFP in nodules is reported to increase uninfected cell density and trigger premature death of infected cells, consistent with a tight requirement for correct spatial/temporal regulation of NFP signaling to maintain mutualism rather than defense (grundy2023legumesregulatesymbiosis pages 8-9).

6. Quantitative findings and statistics from the retrieved studies

6.1 RNAi phenotype penetrance (Arrighi et al., 2006)

RNAi knockdown targeting either LysM-region or kinase-region sequences caused a strong Nod2 phenotype in 79% and 90% of transformed roots (two constructs), affecting 21/24 total roots examined; most roots were non-nodulated, and when infection structures occurred they frequently aborted with aberrant morphology (arrighi2006themedicagotruncatula pages 3-4).

6.2 Scale of MtNFP-partner discovery screen (Sarrette et al., 2023)

The Y2H screen using MtNFP kinase domain bait screened 62.5 million clones, selected 355 His+ colonies, and identified 53 genes meeting confidence criteria; three partial clones of the MtSOBIR1 locus were recovered as NFP-KD interactors (sarrette2023medicagotruncatulasobir1 pages 4-5).

6.3 Glycosylation site statistics (Mulder et al., 2006)

Mulder et al. report 10 predicted extracellular N-glycosylation sites on NFP and provide biochemical evidence consistent with multiple sites being modified (mulder2006lysmdomainsof pages 6-7).

7. Current applications and real-world implementations

While NFP itself is not a deployed agricultural product, understanding NFP is practically relevant because it sits at the decision point between symbiosis initiation and defense responses. A concrete example of real-world-oriented implementation discussed in recent literature is engineering immune perception into legumes without abolishing nodulation:

  • A 2023 review describes introduction of the Arabidopsis pattern-recognition receptor EFR into M. truncatula to enable elf18 perception and improve resistance to Ralstonia solanacearum, while still allowing nodulation with S. meliloti; this demonstrates that immune signaling can be added/modified while maintaining symbiosis, motivating careful engineering of receptor networks that include Nod-factor receptors and their crosstalk nodes (grundy2023legumesregulatesymbiosis pages 8-9).

More broadly, mechanistic knowledge of NFP partner selection, phosphorylation-dependent tuning, and immune crosstalk (e.g., via SOBIR1-like modules) provides conceptual entry points for:

  • breeding/engineering for rhizobial specificity and stable infection,
  • minimizing defense-triggered incompatibility,
  • optimizing symbiosis under pathogen pressure,

all of which align with the “symbiosis–immunity interface” emphasized in 2023–2024 work (grundy2023legumesregulatesymbiosis pages 8-9, sarrette2023medicagotruncatulasobir1 pages 4-5, li2024nodulationtrioin pages 3-9).

8. Visual evidence (figures)

Arrighi et al. include figures that (i) depict NFP’s domain architecture and kinase motif losses and (ii) show autophosphorylation assays supporting kinase inactivity (arrighi2006themedicagotruncatula media 0385937d, arrighi2006themedicagotruncatula media d64c86c9, arrighi2006themedicagotruncatula media eefcd0eb).

9. Evidence map (summary table)

Aspect Key findings Evidence type (genetics/biochemistry/modeling/review) Primary sources with year and URL/DOI
identity/domains UniProt Q0GXS4 matches Medicago truncatula NFP, a LysM receptor-like kinase of ~595 aa with an N-terminal signal peptide, three extracellular LysM domains, a transmembrane helix, and a C-terminal kinase-like domain; it is closely related to Lotus japonicus NFR5 and pea SYM10. Figures in Arrighi et al. show the domain architecture and motif losses in the kinase region. (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula media 0385937d) Genetics, sequence/domain analysis, comparative analysis Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657
ligand/recognition NFP is required for specific recognition of Sinorhizobium meliloti Nod factors (lipo-chitooligosaccharides). Structural modeling/docking suggested that each LysM domain can bind a Nod factor, with residues near LysM1/2/3 contributing to sulfate, O-acetyl, and acyl-chain recognition; N-glycosylation is not predicted to block binding. A strong nfp-2 allele affecting the first LysM domain supports a crucial role of LysM1 in recognition. (mulder2006lysmdomainsof pages 1-2, mulder2006lysmdomainsof pages 4-5, arrighi2006themedicagotruncatula pages 11-12, mulder2006lysmdomainsof pages 5-6) Genetics, structural modeling, glycoprotein biochemistry Mulder et al., 2006, Glycobiology — https://doi.org/10.1093/glycob/cwl006; Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657
kinase activity NFP has a nonclassical/aberrant kinase domain lacking key conserved motifs (including P-loop/DFG-related features and an activation-loop segment), and no detectable autophosphorylation was observed in vitro, supporting interpretation of NFP as a likely pseudokinase or signaling subunit that requires an active kinase partner. (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 3-4, arrighi2006themedicagotruncatula pages 11-12, arrighi2006themedicagotruncatula media 0385937d) Biochemistry, motif analysis, comparative analysis Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657
localization/expression NFP is described as a plasma-membrane LysM receptor-like protein. Expression is detected in growing/root hairs, inner and middle cortex at sites of curling and primordium formation, nodule primordia, and the infection zone of mature nodules; expression declines toward the nitrogen-fixing zone, arguing against a direct role in nitrogen fixation/assimilation. NFP protein is heavily N-glycosylated extracellularly. (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 3-4, mulder2006lysmdomainsof pages 6-7, arrighi2006themedicagotruncatula pages 10-11) Promoter-reporter expression, transcript localization, glycoprotein biochemistry Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657; Mulder et al., 2006, Glycobiology — https://doi.org/10.1093/glycob/cwl006
pathway position NFP acts at the earliest stages of Nod factor signaling and is genetically placed upstream of DMI1/DMI2/DMI3 and NSP1/NSP2. nfp mutants fail in Nod factor-induced root hair deformation/curling and infection thread formation, and NFP has been linked to early responses including calcium fluxes, calcium spiking, and inhibition of reactive oxygen efflux. Arrighi et al. further argue that NFP functions throughout infection and may control partly distinct pathways for symbiotic infection and nodule organogenesis. (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 8-10, arrighi2006themedicagotruncatula pages 10-11) Genetics, expression analysis, pathway review Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657; Shumilina et al., 2023, IJMS — https://doi.org/10.3390/ijms242417397
receptor partners Modeling and comparative genetics suggested NFP may function in a heteromeric receptor complex with active LysM-RLK partners such as LYK3. Recent Medicago work extends this: MtLYK2, MtLYK3, and MtLYK2bis can functionally associate with MtNFP, and their kinase-active cytoplasmic domains can trans-phosphorylate NFP in heterologous assays, supporting multi-receptor complex models with overlapping specificities. A 2023 screen also identified MtSOBIR1 as a new interactor of the NFP kinase domain, linking NFP to additional receptor-coreceptor modules. (mulder2006lysmdomainsof pages 6-7, li2024nodulationtrioin pages 3-9, li2024nodulationtrioin pages 1-3, sarrette2023medicagotruncatulasobir1 pages 4-5) Structural inference, biochemistry, genetics, protein-protein interaction Mulder et al., 2006, Glycobiology — https://doi.org/10.1093/glycob/cwl006; Li et al., 2024, bioRxiv — https://doi.org/10.1101/2024.02.19.577609; Sarrette et al., 2023, bioRxiv — https://doi.org/10.1101/2023.10.15.561875
immune crosstalk NFP/NFR-type receptors lie at a symbiosis–immunity interface. Reviews summarize that NFs can induce transient defense outputs, but also suppress MTI by other mechanisms. Ectopic expression of MtNFP in nodule tissue increased uninfected cell density and caused premature death of infected cells, and NFRs from Medicago/Lotus can trigger cell death in tobacco. Recent work connects NFP to SOBIR1, a known immunity coreceptor, and co-expression of MtNFP with MtLYK2/3/2bis in Nicotiana induced apparent cell death, consistent with immune-like crosstalk. (grundy2023legumesregulatesymbiosis pages 8-9, sarrette2023medicagotruncatulasobir1 pages 4-5, li2024nodulationtrioin pages 1-3) Review, ectopic-expression phenotyping, protein interaction, heterologous assays Grundy et al., 2023, IJMS — https://doi.org/10.3390/ijms24032800; Sarrette et al., 2023, bioRxiv — https://doi.org/10.1101/2023.10.15.561875; Li et al., 2024, bioRxiv — https://doi.org/10.1101/2024.02.19.577609
quantitative data RNAi knockdown of NFP caused a strong Nod2 phenotype in 79% and 90% of transformed roots for two independent constructs (21/24 total roots affected), with most roots non-nodulated and rare infection threads abortive/aberrant. The 2023 MtNFP kinase-domain Y2H screen tested 62.5 million clones, yielding 355 His+ colonies and 53 candidate genes with satisfactory confidence scores; three partial clones of the MtSOBIR1 gene were recovered as NFP-KD interactors. Mulder et al. reported 10 predicted extracellular N-glycosylation sites on NFP, with biochemical evidence that multiple sites are glycosylated. (arrighi2006themedicagotruncatula pages 3-4, sarrette2023medicagotruncatulasobir1 pages 4-5, mulder2006lysmdomainsof pages 6-7) Genetics, screening statistics, glycoprotein biochemistry Arrighi et al., 2006, Plant Physiology — https://doi.org/10.1104/pp.106.084657; Sarrette et al., 2023, bioRxiv — https://doi.org/10.1101/2023.10.15.561875; Mulder et al., 2006, Glycobiology — https://doi.org/10.1093/glycob/cwl006

Table: This table summarizes the experimentally supported functional annotation of Medicago truncatula NFP (UniProt Q0GXS4), including domain structure, ligand recognition, signaling role, receptor partnerships, immune crosstalk, and quantitative findings. It is useful as a compact evidence map for building the full research report.

10. Limitations and open questions

  • Direct ligand-binding biochemistry/structures: The retrieved evidence includes docking/modeling but not definitive binding constants or co-crystal structures for NFP–Nod factor interactions; such quantitative binding remains a key gap (mulder2006lysmdomainsof pages 4-5, mulder2006lysmdomainsof pages 5-6).
  • Catalytic mechanism: NFP appears kinase-inactive by motif and assay, but its exact signaling mechanism (e.g., scaffolding, conformational gating, regulated phosphorylation by partners) remains unresolved; recent work strengthens trans-phosphorylation models but does not fully define in planta complex composition/dynamics (arrighi2006themedicagotruncatula pages 11-12, li2024nodulationtrioin pages 3-9).
  • PubMed ID cross-checking: UniProt references specific PubMed IDs (12753588; 16723404). The tool-driven retrieval here captured the closely aligned 2006 primary literature that provides direct experimental evidence for NFP identity and function; however, the original PubMed-ID-matched papers were not individually retrieved through the current search results, so statements are anchored to the retrieved articles rather than those PubMed IDs.

References (retrieved sources; publication dates and URLs)

  • Arrighi J-F. et al. July 2006. Plant Physiology. “The Medicago truncatula Lysine Motif-Receptor-Like Kinase Gene Family Includes NFP and New Nodule-Expressed Genes.” https://doi.org/10.1104/pp.106.084657 (arrighi2006themedicagotruncatula pages 2-3, arrighi2006themedicagotruncatula pages 3-4)
  • Mulder L. et al. Sep 2006. Glycobiology. “LysM domains of Medicago truncatula NFP protein involved in Nod factor perception…” https://doi.org/10.1093/glycob/cwl006 (mulder2006lysmdomainsof pages 4-5, mulder2006lysmdomainsof pages 6-7)
  • Grundy E.B. et al. Feb 2023. International Journal of Molecular Sciences. “Legumes Regulate Symbiosis with Rhizobia via Their Innate Immune System.” https://doi.org/10.3390/ijms24032800 (grundy2023legumesregulatesymbiosis pages 8-9)
  • Shumilina J. et al. Dec 2023. International Journal of Molecular Sciences. “Signaling in Legume–Rhizobia Symbiosis.” https://doi.org/10.3390/ijms242417397 (arrighi2006themedicagotruncatula pages 10-11)
  • Sarrette B. et al. Oct 2023 (posted Oct 17, 2023). bioRxiv preprint. “Medicago truncatula SOBIR1 controls specificity in the Rhizobium-legume symbiosis.” https://doi.org/10.1101/2023.10.15.561875 (sarrette2023medicagotruncatulasobir1 pages 4-5)
  • Li Y. et al. Feb 2024. bioRxiv preprint. “Nodulation Trio in Medicago truncatula: Unveiling the Overlapping Roles of MtLYK2, MtLYK3, and MtLYK2bis.” https://doi.org/10.1101/2024.02.19.577609 (li2024nodulationtrioin pages 3-9, li2024nodulationtrioin pages 1-3)

References

  1. (arrighi2006themedicagotruncatula pages 2-3): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  2. (arrighi2006themedicagotruncatula pages 3-4): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  3. (arrighi2006themedicagotruncatula media 0385937d): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  4. (arrighi2006themedicagotruncatula media eefcd0eb): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  5. (arrighi2006themedicagotruncatula pages 8-10): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  6. (arrighi2006themedicagotruncatula pages 10-11): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  7. (arrighi2006themedicagotruncatula pages 11-12): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  8. (mulder2006lysmdomainsof pages 1-2): Lonneke Mulder, Benoit Lefebvre, Julie Cullimore, and Anne Imberty. Lysm domains of medicago truncatula nfp protein involved in nod factor perception. glycosylation state, molecular modeling and docking of chitooligosaccharides and nod factors. Glycobiology, 16 9:801-9, Sep 2006. URL: https://doi.org/10.1093/glycob/cwl006, doi:10.1093/glycob/cwl006. This article has 130 citations and is from a peer-reviewed journal.

  9. (mulder2006lysmdomainsof pages 4-5): Lonneke Mulder, Benoit Lefebvre, Julie Cullimore, and Anne Imberty. Lysm domains of medicago truncatula nfp protein involved in nod factor perception. glycosylation state, molecular modeling and docking of chitooligosaccharides and nod factors. Glycobiology, 16 9:801-9, Sep 2006. URL: https://doi.org/10.1093/glycob/cwl006, doi:10.1093/glycob/cwl006. This article has 130 citations and is from a peer-reviewed journal.

  10. (mulder2006lysmdomainsof pages 5-6): Lonneke Mulder, Benoit Lefebvre, Julie Cullimore, and Anne Imberty. Lysm domains of medicago truncatula nfp protein involved in nod factor perception. glycosylation state, molecular modeling and docking of chitooligosaccharides and nod factors. Glycobiology, 16 9:801-9, Sep 2006. URL: https://doi.org/10.1093/glycob/cwl006, doi:10.1093/glycob/cwl006. This article has 130 citations and is from a peer-reviewed journal.

  11. (arrighi2006themedicagotruncatula media d64c86c9): J. Arrighi, A. Barre, Besma Ben Amor, Anne Bersoult, Lidia Campos Soriano, R. Mirabella, Fernanda de Carvalho-Niebel, E. Journet, M. Ghérardi, T. Huguet, R. Geurts, J. Dénarié, P. Rougé, and C. Gough. The medicago truncatula lysine motif-receptor-like kinase gene family includes nfp and new nodule-expressed genes1[w]. Plant Physiology, 142:265-279, Jul 2006. URL: https://doi.org/10.1104/pp.106.084657, doi:10.1104/pp.106.084657. This article has 658 citations and is from a highest quality peer-reviewed journal.

  12. (mulder2006lysmdomainsof pages 6-7): Lonneke Mulder, Benoit Lefebvre, Julie Cullimore, and Anne Imberty. Lysm domains of medicago truncatula nfp protein involved in nod factor perception. glycosylation state, molecular modeling and docking of chitooligosaccharides and nod factors. Glycobiology, 16 9:801-9, Sep 2006. URL: https://doi.org/10.1093/glycob/cwl006, doi:10.1093/glycob/cwl006. This article has 130 citations and is from a peer-reviewed journal.

  13. (li2024nodulationtrioin pages 1-3): Yaohua Li, Yanwen Zhao, Ziang Yan, Ru Dong, Haixiang Yu, Hui Zhu, and Yangrong Cao. Nodulation trio in medicago truncatula: unveiling the overlapping roles of mtlyk2, mtlyk3, and mtlyk2bis. bioRxiv, Feb 2024. URL: https://doi.org/10.1101/2024.02.19.577609, doi:10.1101/2024.02.19.577609. This article has 0 citations.

  14. (li2024nodulationtrioin pages 3-9): Yaohua Li, Yanwen Zhao, Ziang Yan, Ru Dong, Haixiang Yu, Hui Zhu, and Yangrong Cao. Nodulation trio in medicago truncatula: unveiling the overlapping roles of mtlyk2, mtlyk3, and mtlyk2bis. bioRxiv, Feb 2024. URL: https://doi.org/10.1101/2024.02.19.577609, doi:10.1101/2024.02.19.577609. This article has 0 citations.

  15. (sarrette2023medicagotruncatulasobir1 pages 4-5): Baptiste Sarrette, Thi-Bich Luu, Alexander Johansson, Judith Fliegmann, Cécile Pouzet, Aurélie Le Ru, Carole Pichereaux, Céline Remblière, Laurent Sauviac, Noémie Carles, Emilie Amblard, Valentin Guyot, Maxime Bonhomme, Julie Cullimore, Clare Gough, Christophe Jacquet, and Nicolas Pauly. Medicago truncatula sobir1 controls specificity in the rhizobium-legume symbiosis. bioRxiv, Oct 2023. URL: https://doi.org/10.1101/2023.10.15.561875, doi:10.1101/2023.10.15.561875. This article has 0 citations.

  16. (grundy2023legumesregulatesymbiosis pages 8-9): Estelle B. Grundy, Peter M. Gresshoff, Huanan Su, and Brett J. Ferguson. Legumes regulate symbiosis with rhizobia via their innate immune system. International Journal of Molecular Sciences, 24:2800, Feb 2023. URL: https://doi.org/10.3390/ijms24032800, doi:10.3390/ijms24032800. This article has 41 citations.

Artifacts

Citations

  1. arrighi2006themedicagotruncatula pages 10-11
  2. arrighi2006themedicagotruncatula pages 11-12
  3. arrighi2006themedicagotruncatula pages 2-3
  4. mulder2006lysmdomainsof pages 1-2
  5. mulder2006lysmdomainsof pages 4-5
  6. mulder2006lysmdomainsof pages 5-6
  7. mulder2006lysmdomainsof pages 6-7
  8. arrighi2006themedicagotruncatula pages 3-4
  9. li2024nodulationtrioin pages 1-3
  10. li2024nodulationtrioin pages 3-9
  11. grundy2023legumesregulatesymbiosis pages 8-9
  12. arrighi2006themedicagotruncatula pages 8-10
  13. w
  14. https://doi.org/10.1104/pp.106.084657
  15. https://doi.org/10.1093/glycob/cwl006;
  16. https://doi.org/10.1104/pp.106.084657;
  17. https://doi.org/10.1093/glycob/cwl006
  18. https://doi.org/10.3390/ijms242417397
  19. https://doi.org/10.1101/2024.02.19.577609;
  20. https://doi.org/10.1101/2023.10.15.561875
  21. https://doi.org/10.3390/ijms24032800;
  22. https://doi.org/10.1101/2023.10.15.561875;
  23. https://doi.org/10.1101/2024.02.19.577609
  24. https://doi.org/10.3390/ijms24032800
  25. https://doi.org/10.1104/pp.106.084657,
  26. https://doi.org/10.1093/glycob/cwl006,
  27. https://doi.org/10.1101/2024.02.19.577609,
  28. https://doi.org/10.1101/2023.10.15.561875,
  29. https://doi.org/10.3390/ijms24032800,

📚 Additional Documentation

Notes

(NFP-notes.md)

NFP (Nod Factor Perception) — Medicago truncatula — research notes

UniProt: Q0GXS4 (NFP_MEDTR). Gene: MTR_5g019040. 595 aa precursor.
Also called Nod-factor receptor 5 (NFR5 orthologue of Lotus japonicus).

Summary of gene function

NFP is a plasma-membrane LysM-domain receptor-like kinase (LysM-RLK) of the model
legume Medicago truncatula. It is the Nod factor receptor that perceives
rhizobial lipo-chitooligosaccharide (LCO) signals ("Nod factors") secreted by
Sinorhizobium meliloti, and triggers the earliest steps of the nitrogen-fixing
root nodule symbiosis. NFP is essential and non-redundant for Nod factor
perception: nfp mutants are completely Nod-negative.

Architecture: signal peptide (1-27), extracellular region (28-246) with three
LysM domains (LysM1 ~51-98, LysM2 ~113-160, plus a third predicted LysM), a single
transmembrane helix (247-267), and an intracellular protein-kinase-like domain
(284-573). The LysM ectodomain is heavily N-glycosylated (9 sites).

Nod factor perception by the LysM ectodomain

The extracellular LysM domains bind chitooligosaccharide / Nod factor ligands.
PMID:16723404 and PMID:16723404.

LysM domain residues are functionally required for Nod factor recognition:
the L154P substitution (in LysM2) impairs nodulation [PMID:22087221 / UniProt
SITE 154 "Required for nodulation"].

NFP is the most upstream component of the Nod factor signalling pathway. The
nfp mutant fails every assayed Nod-factor response PMID:12753588 and PMID:12753588.

NFP is a pseudokinase (catalytically dead intracellular domain)

The intracellular "kinase" domain of NFP is a pseudokinase — it lacks
catalytic activity. PMID:16844829 and
PMID:16844829.

NFP therefore depends on an active co-receptor kinase to transduce the signal.
The InterPro/PROSITE-derived "Tyr protein kinase family" classification (UniProt
SIMILARITY line, PROSITE PS00109 PROTEIN_KINASE_TYR) is a sequence-motif
artefact: NFP is annotated by UniProt itself as a serine/threonine RLK, and
plant RLKs are Ser/Thr kinases — there is no evidence for tyrosine kinase
activity. The web literature confirms NFP/NFR5 "has no detectable
autophosphorylation activity and is considered a pseudokinase" and that "the
inactive kinase domain of MtNFP can be weakly transphosphorylated by the active
kinase of MtLYK3."

Implication for GO: "protein tyrosine kinase activity" (GO:0004713) is doubly
wrong (pseudokinase + Ser/Thr family, not Tyr). "protein kinase activity"
(GO:0004672, current InterPro IEA) is also unsupported — the domain is
catalytically dead.

The NFP/LYK3 receptor complex

NFP and the active LysM-RLK LYK3 form heteromeric receptor complexes at the cell
periphery. PMID:25351493. NFP and LYK3
co-localize "in a narrow zone of about two cell layers at the nodule apex"
PMID:25351493. LYK3 (UniProt Q6UD73) is the active-kinase co-receptor; NFP
contributes ligand-binding/scaffolding but not phosphotransfer.

NFP also interacts with the small GTPase ROP10: PMID:25794934 and
PMID:25794934.
ROP10 (UniProt B2MVQ1) is a type II Rho-of-plants small GTPase.

Nodulation: organogenesis and infection

NFP acts in both the epidermis and the cortex during nodulation.
PMID:22874912. NFP is required throughout the
infection process: PMID:16844829. NFP is needed for intracellular infection / rhizobial
release: in nfp mutants "Infection threads enter the cells, but the release
of the bacteria is hampered" (UniProt DISRUPTION PHENOTYPE, ECO from
PMID:25351493).

Disruption phenotype: complete Nod- phenotype, no calcium flux/spiking, no early
nodulin expression, no root hair deformation/curling, no infection threads
[PMID:12753588; PMID:16844829].

NFP in pathogen resistance (defense)

Beyond symbiosis, NFP contributes to M. truncatula immunity against
filamentous pathogens. PMID:23432463 and PMID:23432463. This
supports specific curated terms — positive regulation of defense response to
oomycetes (GO:1902290) and regulation of defense response to fungus
(GO:1900150) — both IMP from PMID:23432463. A broad keyword-derived "defense
response" (GO:0006952) adds nothing beyond these.

Subcellular localization

Plasma membrane (cell periphery); also vacuolar lumen in cells where receptors
are being broken down. PMID:25351493 — NFP-GFP localizes at the cell
periphery, and "Vacuolar localization is observed in cells undergoing breakdown
of the receptors" (UniProt SUBCELLULAR LOCATION). Single-pass type I membrane
protein.

Glycosylation

NFP is highly N-glycosylated PMID:16723404. UniProt lists 9 N-glyc
sites. The IDA "glycoprotein biosynthetic process" (GO:0009101) GO annotation
captures NFP being a glycoprotein substrate — NFP is not an enzyme of the
glycosylation machinery, so this is a marginal/over-annotation as a process the
gene is "involved in."

Core function synthesis

  1. Molecular function: Nod factor (lipo-chitooligosaccharide) receptor —
    transmembrane signalling receptor whose LysM ectodomain binds the rhizobial
    LCO ligand. Carbohydrate (chitin-type/LCO) binding via LysM domains.
    NOT a catalytically active kinase (pseudokinase).
  2. Biological process: nodulation / root nodule symbiosis — perception of Nod
    factors and initiation of nodule organogenesis and rhizobial infection.
  3. Secondary process: contribution to immunity against oomycete/fungal
    pathogens.
  4. Cellular component: plasma membrane (forms heteromeric complex with LYK3).

GO term ID verification (OLS)

  • GO:0009877 nodulation — verified, leaf term.
  • GO:0038023 signaling receptor activity — verified.
  • GO:0004888 transmembrane signaling receptor activity — verified.
  • GO:0008061 chitin binding — verified.
  • GO:0007166 cell surface receptor signaling pathway — verified.
  • GO:0050832 defense response to fungus — verified.
  • GO:1900150 regulation of defense response to fungus — verified.
  • GO:1902290 positive regulation of defense response to oomycetes — verified.
  • GO:0031267 small GTPase binding — verified.
  • GO:0004713 protein tyrosine kinase activity / GO:0004672 protein kinase
    activity — verified IDs; both rejected on pseudokinase grounds.

📄 View Raw YAML

id: Q0GXS4
gene_symbol: NFP
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:3880
  label: Medicago truncatula
description: >-
  NFP (Nod Factor Perception) is a plasma-membrane LysM-domain receptor-like
  kinase (LysM-RLK) of the model legume Medicago truncatula. It is the essential,
  non-redundant receptor that perceives rhizobial lipo-chitooligosaccharide
  signals (Nod factors) secreted by Sinorhizobium meliloti, and triggers the
  earliest steps of the nitrogen-fixing root nodule symbiosis. The extracellular
  region carries three tandem, heavily N-glycosylated LysM domains that bind the
  chitin-based Nod factor ligand; a single transmembrane helix; and an
  intracellular protein-kinase-like domain. Critically, the NFP kinase domain is
  a catalytically dead PSEUDOKINASE: it deviates from conserved catalytic kinase
  residues and shows no autophosphorylation activity, so signal transduction
  requires association with an active co-receptor kinase, principally LYK3, with
  which NFP forms heteromeric receptor complexes at the cell periphery. NFP acts
  in both the root epidermis and cortex to drive Nod factor signalling (calcium
  spiking, early nodulin expression, root hair deformation), nodule
  organogenesis and rhizobial infection thread development/bacterial release.
  Beyond symbiosis, NFP also contributes to M. truncatula immunity against the
  oomycete Aphanomyces euteiches and the fungus Colletotrichum trifolii.
existing_annotations:
# --- SPKW keyword-mapping annotations (GO_REF:0000043) ---
# Present in the Sept 2025 goa_uniprot_gcrp snapshot (go-db plant.ddb); REMOVED
# from the current (2026) GOA release. Reviewed retrospectively; retired: true.
- term:
    id: GO:0004713
    label: protein tyrosine kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  retired: true
  review:
    summary: >-
      Retired SwissProt-keyword (SPKW) annotation derived from the
      "Tyrosine-protein kinase" keyword, which itself comes from the PROSITE
      PS00109 (PROTEIN_KINASE_TYR) signature match. This annotation is doubly
      incorrect. First, plant receptor-like kinases including NFP are
      serine/threonine kinases, not tyrosine kinases (UniProt itself names the
      protein "Serine/threonine receptor-like kinase NFP"). Second, and more
      fundamentally, the NFP intracellular kinase domain is a catalytically dead
      pseudokinase: it deviates from conserved catalytic residues and shows no
      detectable autophosphorylation activity.
    action: REMOVE
    reason: >-
      GOA's removal of this annotation was JUSTIFIED. The term is wrong on two
      counts. (1) NFP is a pseudokinase with no demonstrated catalytic activity:
      "NFP did not show autophosphorylation activity, suggesting that NFP needs
      to associate with an active kinase or has unusual functional
      characteristics different from classical kinases" and NFP belongs to "one
      subfamily ... characterized by deviations from conserved kinase sequences"
      (PMID:16844829). (2) Even if it were an active kinase, plant RLKs are
      Ser/Thr kinases; the tyrosine specificity is a PROSITE motif artefact, not
      a biological observation. The keyword2GO pipeline propagated a generic
      sequence-motif keyword without accounting for the experimentally
      established pseudokinase status. REMOVE; do not replace with any catalytic
      MF term.
    supported_by:
    - reference_id: PMID:16844829
      supporting_text: >-
        Consistent with deviations from conserved kinase domain sequences, NFP
        did not show autophosphorylation activity, suggesting that NFP needs to
        associate with an active kinase or has unusual functional
        characteristics different from classical kinases.
    - reference_id: file:MEDTR/NFP/NFP-deep-research-falcon.md
      supporting_text: >-
        lacking key conserved motifs (including P-loop/DFG-related features and
        an activation-loop segment), and ... was observed in vitro, supporting
        interpretation of NFP as a likely ... or signaling subunit that requires
        an active kinase partner
- term:
    id: GO:0006952
    label: defense response
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  retired: true
  review:
    summary: >-
      Retired SwissProt-keyword (SPKW) annotation derived from the "Plant
      defense" keyword. NFP does have a documented role in pathogen resistance
      (resistance to the oomycete Aphanomyces euteiches and the fungus
      Colletotrichum trifolii; PMID:23432463), so the keyword is not factually
      wrong. However, the broad "defense response" term adds nothing beyond the
      current GOA annotations, which already capture this role with the more
      specific and properly evidenced terms "positive regulation of defense
      response to oomycetes" (GO:1902290) and "regulation of defense response to
      fungus" (GO:1900150), both IMP from PMID:23432463.
    action: REMOVE
    reason: >-
      GOA's removal of this annotation was JUSTIFIED. The broad keyword-derived
      term is fully subsumed by the existing, more informative curated
      annotations GO:1902290 and GO:1900150 (both IMP, PMID:23432463), which are
      direct or indirect descendants of defense response and pinpoint the
      specific pathogen classes and regulatory nature of NFP's role. Retaining a
      generic IEA "defense response" alongside specific experimental terms is
      redundant over-annotation. NFP's primary, defining function is symbiotic
      Nod-factor perception; its defense role is real but secondary and already
      well represented. REMOVE.
    supported_by:
    - reference_id: PMID:23432463
      supporting_text: >-
        nfp, but not lyk3, mutants were significantly more susceptible than
        wildtype plants to A. euteiches, whereas NFP overexpression increased
        resistance. ... nfp mutants also showed an increased susceptibility to
        the fungus Colletotrichum trifolii. These results demonstrate that NFP
        intervenes in M. truncatula immunity.
    - reference_id: file:MEDTR/NFP/NFP-deep-research-falcon.md
      supporting_text: >-
        NFP/NFR-type receptors lie at a ... symbiosis–immunity interface ...
        Reviews summarize that NFs can induce transient defense outputs
# --- Current GOA annotations (2026 release) ---
- term:
    id: GO:0004672
    label: protein kinase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      InterPro2GO IEA annotation from protein-kinase-domain signatures
      (IPR000719 Prot_kinase_dom, IPR001245 Ser-Thr/Tyr kinase catalytic domain,
      IPR008266 Tyr kinase active site). NFP does contain a protein-kinase-like
      domain in its intracellular region, but it is a catalytically dead
      pseudokinase: it lacks conserved catalytic residues and shows no
      autophosphorylation activity (PMID:16844829). The InterPro signatures
      detect the kinase FOLD but cannot distinguish active kinases from
      pseudokinases.
    action: REMOVE
    reason: >-
      Although less obviously wrong than the retired tyrosine-kinase keyword,
      "protein kinase activity" has the same underlying problem: it asserts a
      catalytic molecular function that NFP does not have. NFP is an
      experimentally established pseudokinase ("NFP did not show
      autophosphorylation activity ... deviations from conserved kinase
      sequences"; PMID:16844829), and signalling requires the active co-receptor
      kinase LYK3 (PMID:25351493). The kinase domain functions as a
      protein-interaction/scaffolding module (e.g. it binds the GTPase ROP10;
      PMID:25794934), not as an enzyme. An IEA term that contradicts direct
      experimental evidence should not be retained. REMOVE; the genuine
      molecular function (signalling receptor / Nod factor perception) is
      captured by the proposed NEW annotations below.
    supported_by:
    - reference_id: PMID:16844829
      supporting_text: >-
        Consistent with deviations from conserved kinase domain sequences, NFP
        did not show autophosphorylation activity, suggesting that NFP needs to
        associate with an active kinase or has unusual functional
        characteristics different from classical kinases.
    - reference_id: PMID:25351493
      supporting_text: >-
        our Förster resonance energy transfer-fluorescence lifetime imaging
        microscopy analysis indicates that NFP and LYK3 form heteromeric
        complexes at the cell periphery in M. truncatula nodules.
    - reference_id: file:MEDTR/NFP/NFP-deep-research-falcon.md
      supporting_text: >-
        lacking key conserved motifs (including P-loop/DFG-related features and
        an activation-loop segment), and ... was observed in vitro, supporting
        interpretation of NFP as a likely ... or signaling subunit that requires
        an active kinase partner
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      InterPro2GO IEA annotation from the protein kinase domain signature
      (IPR000719). UniProt annotates a Gly-rich P-loop (residues 290-298) and a
      second ATP-binding residue (339) by PROSITE ProRule. Whether the
      pseudokinase domain of NFP actually binds ATP/nucleotide in vivo has not
      been tested; many pseudokinases retain nucleotide binding while others do
      not.
    action: KEEP_AS_NON_CORE
    reason: >-
      The P-loop/VAIK motif elements predicted by sequence (UniProt BINDING
      290-298 and 339) make residual ATP binding plausible even though NFP is
      catalytically inactive, and ATP binding by a pseudokinase does not imply
      catalysis. The annotation is not contradicted by experiment, but it is not
      a core function: NFP's defining role is ligand perception, not nucleotide
      chemistry, and no study has demonstrated functional ATP binding. Retain as
      a plausible domain-derived prediction, marked non-core.
    supported_by:
    - reference_id: PMID:16844829
      supporting_text: >-
        one subfamily, which includes NFP, was characterized by deviations from
        conserved kinase sequences.
- term:
    id: GO:0005775
    label: vacuolar lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Subcellular-location IEA derived from the UniProt subcellular location
      "Vacuole lumen", which is itself based on the experimental observation
      that NFP relocalizes to the vacuolar lumen in nodule cells undergoing
      receptor breakdown (PMID:25351493). This IEA is the keyword/subcell-mapping
      counterpart of the curated IDA annotation below.
    action: KEEP_AS_NON_CORE
    reason: >-
      The annotation accurately reflects the experimental finding that NFP is
      observed in the vacuolar lumen in cells undergoing receptor breakdown
      (PMID:25351493). It is a genuine but non-core, degradation-associated
      localization rather than the site of NFP signalling function. Keep, marked
      non-core (consistent with the curated IDA annotation from PMID:25351493).
    supported_by:
    - reference_id: UniProt:Q0GXS4
      supporting_text: >-
        SUBCELLULAR LOCATION: Cell membrane; Single-pass membrane protein. Vacuole
        lumen. Note=Removed from the plasma membrane upon the release of rhizobia into
        the host cytoplasm. Vacuolar localization is observed in cells undergoing
        breakdown of the receptors.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      Multi-method IEA (ARBA + UniProtKB-SubCell mapping) placing NFP at the
      plasma membrane. NFP is a single-pass type I transmembrane protein and is
      experimentally localized at the cell periphery / plasma membrane
      (PMID:25351493).
    action: ACCEPT
    reason: >-
      Correct and core: NFP is a plasma-membrane receptor. The localization is
      directly supported by experiment (curated IDA annotation from
      PMID:25351493) and by the protein's single-pass transmembrane topology.
      Accept as-is.
    supported_by:
    - reference_id: PMID:25351493
      supporting_text: >-
        It was found that inside Medicago truncatula nodules, NFP and LYK3
        localize at the cell periphery in a narrow zone of about two cell layers
        at the nodule apex.
- term:
    id: GO:0051707
    label: response to other organism
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      ARBA machine-learning IEA. NFP responds to and perceives signals from
      other organisms - both the symbiotic rhizobium Sinorhizobium meliloti
      (Nod factors) and pathogenic oomycetes/fungi. The term is correct but very
      broad.
    action: MODIFY
    reason: >-
      "Response to other organism" is accurate but uninformatively general. The
      specific, experimentally documented responses are already, or should be,
      represented by more precise terms: response to molecule of bacterial
      origin (GO:0002237, existing IMP), nodulation (GO:0009877), and the
      defense-response regulation terms. The best single specific replacement
      that captures NFP's defining symbiotic role is "response to molecule of
      bacterial origin" (GO:0002237), already present from PMID:12753588.
    proposed_replacement_terms:
    - id: GO:0002237
      label: response to molecule of bacterial origin
    supported_by:
    - reference_id: PMID:12753588
      supporting_text: >-
        The nfp mutant thus shows no rapid calcium flux, the earliest detectable
        Nod factor response of wild-type plants, and no root hair deformation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25794934
  review:
    summary: >-
      IPI annotation with WITH/FROM UniProtKB:B2MVQ1 (ROP10, a type II
      Rho-of-plants small GTPase). The kinase domain of NFP interacts with ROP10
      in a GTP-dependent manner, and this interaction is required for root hair
      deformation during rhizobial infection (PMID:25794934).
    action: MODIFY
    reason: >-
      "Protein binding" (GO:0005515) is uninformative and discouraged. The
      interacting partner is a small GTPase and the interaction is well
      characterized (GTP-dependent, mediated by the NFP kinase domain), so a
      more specific molecular function term is warranted: "small GTPase binding"
      (GO:0031267). This also reframes the NFP kinase domain correctly - as a
      protein-interaction/scaffolding module rather than a catalytic kinase.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:25794934
      supporting_text: >-
        ROP10 interacted with the kinase domain of the NF receptor NFP in a
        GTP-dependent manner.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IEP
  original_reference_id: PMID:22874912
  review:
    summary: >-
      IEP annotation: NFP expression is associated with nodulation. NFP is
      expressed in root epidermis and cortex and is required for nodule
      organogenesis; epidermal NFP alone is sufficient to induce cortical cell
      divisions leading to nodule primordia (PMID:22874912).
    action: ACCEPT
    reason: >-
      Nodulation is the core biological process of NFP and is strongly
      supported. PMID:22874912 demonstrates that epidermal NFP induces cortical
      cell divisions leading to nodule primordia formation. Accept as a core
      function annotation.
    supported_by:
    - reference_id: PMID:22874912
      supporting_text: >-
        Epidermal NFP is sufficient to induce cortical cell divisions leading to
        nodule primordia formation.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IMP
  original_reference_id: PMID:22874912
  review:
    summary: >-
      IMP annotation based on mutant/complementation analysis: tissue-specific
      complementation of nfp mutants shows epidermal NFP is sufficient to induce
      cortical cell divisions for nodule primordium formation (PMID:22874912).
    action: ACCEPT
    reason: >-
      Strong genetic (loss-of-function plus tissue-targeted complementation)
      evidence that NFP is required for nodulation. Core function. Accept.
    supported_by:
    - reference_id: PMID:22874912
      supporting_text: >-
        By complementing mutant plants with corresponding genes expressed either
        in the epidermis or in the cortex, we have shown that ... Epidermal NFP
        is sufficient to induce cortical cell divisions leading to nodule
        primordia formation.
- term:
    id: GO:1900150
    label: regulation of defense response to fungus
  evidence_type: IMP
  original_reference_id: PMID:23432463
  review:
    summary: >-
      IMP annotation: nfp mutants show increased susceptibility to the fungus
      Colletotrichum trifolii, demonstrating that NFP positively contributes to
      antifungal immunity (PMID:23432463).
    action: ACCEPT
    reason: >-
      Directly supported by mutant phenotype: "nfp mutants also showed an
      increased susceptibility to the fungus Colletotrichum trifolii"
      (PMID:23432463). This is a specific, well-evidenced secondary (non-core)
      function distinct from NFP's primary symbiotic role. Accept. (The data
      arguably support the more specific "positive regulation of defense
      response to fungus", but the parent regulatory term as annotated is
      correct and adequately specific.)
    supported_by:
    - reference_id: PMID:23432463
      supporting_text: >-
        nfp mutants also showed an increased susceptibility to the fungus
        Colletotrichum trifolii. These results demonstrate that NFP intervenes
        in M. truncatula immunity.
- term:
    id: GO:1902290
    label: positive regulation of defense response to oomycetes
  evidence_type: IMP
  original_reference_id: PMID:23432463
  review:
    summary: >-
      IMP annotation: nfp mutants are more susceptible to the oomycete
      Aphanomyces euteiches, and NFP overexpression increases resistance,
      establishing NFP as a positive regulator of anti-oomycete defense
      (PMID:23432463).
    action: ACCEPT
    reason: >-
      Well supported by reciprocal genetic evidence: loss of function increases
      susceptibility while overexpression increases resistance to A. euteiches
      (PMID:23432463). The "positive regulation" directionality is justified by
      the overexpression result. Specific, properly evidenced secondary
      function. Accept.
    supported_by:
    - reference_id: PMID:23432463
      supporting_text: >-
        nfp, but not lyk3, mutants were significantly more susceptible than
        wildtype plants to A. euteiches, whereas NFP overexpression increased
        resistance.
- term:
    id: GO:0002237
    label: response to molecule of bacterial origin
  evidence_type: IMP
  original_reference_id: PMID:12753588
  review:
    summary: >-
      IMP annotation: nfp mutants fail to respond to rhizobial Nod factors
      (lipo-chitooligosaccharides of bacterial origin) by any assayed response -
      no calcium flux, no calcium spiking, no early nodulin expression, no root
      hair deformation (PMID:12753588).
    action: ACCEPT
    reason: >-
      Core function. The nfp mutant is completely unresponsive to the rhizobial
      Nod factor, establishing NFP as essential for perception of and response
      to this bacterial-origin molecule (PMID:12753588). Accept; this term also
      serves as the specific replacement for the broad ARBA term "response to
      other organism".
    supported_by:
    - reference_id: PMID:12753588
      supporting_text: >-
        The nfp mutant thus shows no rapid calcium flux, the earliest detectable
        Nod factor response of wild-type plants, and no root hair deformation.
        The nfp mutant is also deficient in Nod factor-induced calcium spiking
        and early nodulin gene expression.
- term:
    id: GO:0009101
    label: glycoprotein biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:16723404
  review:
    summary: >-
      IDA annotation based on PMID:16723404, which showed that NFP expressed in
      M. truncatula roots is highly N-glycosylated, probably with both
      high-mannose and complex glycans. This annotation describes NFP as a
      glycoprotein substrate, not as an enzyme of the glycosylation machinery.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      NFP is the SUBSTRATE of N-glycosylation, not a component of the
      glycoprotein biosynthetic pathway. Being a glycoprotein does not mean the
      gene product is "involved in" the biosynthetic process in the causal sense
      that the GO BP term implies. The underlying observation (NFP is
      N-glycosylated) is better captured as a protein modification/feature
      (UniProt CARBOHYD features) than as a BP annotation. This is an
      over-annotation: NFP plays no role in synthesizing glycans. Mark as
      over-annotated.
    supported_by:
    - reference_id: PMID:16723404
      supporting_text: >-
        Expression of NFP in a homologous system (M. truncatula roots) revealed
        that the protein is highly N-glycosylated, probably with both
        high-mannose and complex glycans.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IMP
  original_reference_id: PMID:12753588
  review:
    summary: >-
      IMP annotation: the nfp mutant has a Nod-negative phenotype, failing all
      Nod factor responses and unable to nodulate (PMID:12753588). NFP controls
      the earliest, nodulation-specific step of Nod factor signal transduction.
    action: ACCEPT
    reason: >-
      Core function with strong loss-of-function evidence. The nfp mutant is
      Nod-negative and NFP "controls an early step of Nod factor signal
      transduction ... specific to nodulation" (PMID:12753588). Accept.
    supported_by:
    - reference_id: PMID:12753588
      supporting_text: >-
        These data indicate that the NFP locus controls an early step of Nod
        factor signal transduction, upstream of previously identified genes and
        specific to nodulation.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IEP
  original_reference_id: PMID:16844829
  review:
    summary: >-
      IEP annotation: NFP is expressed in association with infection thread
      development and nodule formation, and is involved in the infection process
      (PMID:16844829).
    action: ACCEPT
    reason: >-
      Expression-based support for the core nodulation function; NFP is
      expressed in roots and nodules in association with infection thread
      development (PMID:16844829). Consistent with the IMP annotations. Accept.
    supported_by:
    - reference_id: PMID:16844829
      supporting_text: >-
        NFP was shown both to be expressed in association with infection thread
        development and to be involved in the infection process.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IMP
  original_reference_id: PMID:16844829
  review:
    summary: >-
      IMP annotation: nfp-1 mutant analysis shows impaired nodulation - no root
      hair curling, no infection thread formation, no Nod factor-induced root
      hair deformation (PMID:16844829).
    action: ACCEPT
    reason: >-
      Core function, strong mutant evidence. The nfp-1 mutant shows an impaired
      nodulation response to S. meliloti (PMID:16844829). Accept.
    supported_by:
    - reference_id: PMID:16844829
      supporting_text: >-
        NFP was shown both to be expressed in association with infection thread
        development and to be involved in the infection process.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25351493
  review:
    summary: >-
      IPI annotation with WITH/FROM UniProtKB:Q6UD73 (LYK3, an active LysM
      receptor-like kinase). FRET-FLIM analysis showed that NFP and LYK3 form
      heteromeric receptor complexes at the cell periphery in M. truncatula
      nodules (PMID:25351493).
    action: MODIFY
    reason: >-
      "Protein binding" (GO:0005515) is uninformative and discouraged. The
      characterized interaction is a specific heteromeric receptor complex
      between two LysM-RLKs, so a more informative molecular function term is
      appropriate: "protein heterodimerization activity" (GO:0046982). This
      interaction is functionally central - because NFP is a pseudokinase, the
      heteromer with the active kinase LYK3 is the mechanism by which Nod factor
      perception is transduced.
    proposed_replacement_terms:
    - id: GO:0046982
      label: protein heterodimerization activity
    supported_by:
    - reference_id: PMID:25351493
      supporting_text: >-
        our Förster resonance energy transfer-fluorescence lifetime imaging
        microscopy analysis indicates that NFP and LYK3 form heteromeric
        complexes at the cell periphery in M. truncatula nodules.
- term:
    id: GO:0005775
    label: vacuolar lumen
  evidence_type: IDA
  original_reference_id: PMID:25351493
  review:
    summary: >-
      IDA annotation: NFP is observed in the vacuolar lumen of nodule cells
      undergoing breakdown of the receptors (PMID:25351493).
    action: KEEP_AS_NON_CORE
    reason: >-
      Directly observed localization, but it represents a degradation/turnover
      route ("Vacuolar localization is observed in cells undergoing breakdown of
      the receptors") rather than the site of NFP's signalling function. Keep,
      but mark non-core; the functionally relevant localization is the plasma
      membrane.
    supported_by:
    - reference_id: PMID:25351493
      supporting_text: >-
        the role of the Nod factor receptors NOD FACTOR PERCEPTION (NFP) and
        LYSIN MOTIF RECEPTOR-LIKE KINASE3 (LYK3) in establishing the symbiotic
        interface in root nodules was investigated.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: PMID:25351493
  review:
    summary: >-
      IDA annotation: NFP localizes at the cell periphery / plasma membrane in a
      narrow zone of about two cell layers at the nodule apex, where it can
      perceive bacterial Nod factors (PMID:25351493).
    action: ACCEPT
    reason: >-
      Core localization, directly observed. NFP is a plasma-membrane receptor;
      the plasma membrane is where it perceives Nod factors and forms heteromeric
      complexes with LYK3 (PMID:25351493). Accept.
    supported_by:
    - reference_id: PMID:25351493
      supporting_text: >-
        It was found that inside Medicago truncatula nodules, NFP and LYK3
        localize at the cell periphery in a narrow zone of about two cell layers
        at the nodule apex.
- term:
    id: GO:0009877
    label: nodulation
  evidence_type: IEP
  original_reference_id: PMID:25351493
  review:
    summary: >-
      IEP annotation: NFP expression/protein accumulation is associated with
      nodulation, specifically with the meristem and infection zone of developing
      nodules where it perceives Nod factors (PMID:25351493).
    action: ACCEPT
    reason: >-
      Expression-pattern support for the core nodulation function, consistent
      with the multiple IMP annotations. Accept.
    supported_by:
    - reference_id: PMID:25351493
      supporting_text: >-
        In these layers, the receptors can most likely perceive the bacterial
        Nod factors to regulate the formation of symbiotic interface.
# --- Proposed NEW annotations ---
- term:
    id: GO:0038023
    label: signaling receptor activity
  evidence_type: IMP
  original_reference_id: PMID:12753588
  review:
    summary: >-
      NFP is a Nod factor receptor: its LysM ectodomain binds the rhizobial
      lipo-chitooligosaccharide signal and the receptor triggers intracellular
      signalling. The nfp mutant fails every Nod factor response, placing NFP at
      the most upstream, receptor-level step of the pathway.
    action: NEW
    reason: >-
      The current GOA set lacks any molecular function term for NFP's true
      activity. With the catalytic kinase terms removed (NFP is a pseudokinase),
      a signalling receptor MF term is needed to represent the gene's defining
      function. "Signaling receptor activity" (GO:0038023) is well supported:
      the nfp mutant abolishes all Nod factor responses (PMID:12753588) and NFP
      is described as a Nod factor receptor that perceives the bacterial signal
      (PMID:25351493, PMID:16723404).
    supported_by:
    - reference_id: PMID:12753588
      supporting_text: >-
        These data indicate that the NFP locus controls an early step of Nod
        factor signal transduction, upstream of previously identified genes and
        specific to nodulation.
    - reference_id: PMID:25351493
      supporting_text: >-
        In these layers, the receptors can most likely perceive the bacterial
        Nod factors to regulate the formation of symbiotic interface.
- term:
    id: GO:0008061
    label: chitin binding
  evidence_type: ISS
  original_reference_id: PMID:16723404
  review:
    summary: >-
      The NFP extracellular region contains three tandem LysM domains. LysM
      domains are carbohydrate-binding modules that bind N-acetylglucosamine
      polymers (chitin/chitooligosaccharides); the rhizobial Nod factor is a
      lipo-chitooligosaccharide. Homology modelling and docking predict that the
      Nod factor / chitooligosaccharide binds the three LysM domains, and LysM
      residues (e.g. Leu154) are functionally required for Nod factor
      recognition.
    action: NEW
    reason: >-
      NFP's molecular recognition function - binding the chitin-based Nod factor
      ligand via its LysM domains - is central and currently unrepresented in
      GOA. "Chitin binding" (GO:0008061) is the closest available GO term for
      the chitooligosaccharide/LCO-binding activity of the LysM ectodomain.
      Supported by modelling/docking (PMID:16723404) and by mutagenesis showing
      LysM residues are required for Nod factor recognition (PMID:22087221).
      Evidence is structural-modelling/inference plus mutant data, hence ISS.
    supported_by:
    - reference_id: PMID:16723404
      supporting_text: >-
        A convergent model can be proposed where the sulfated, O-acetylated
        lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar
        orientation to the three LysM domains of M. truncatula NFP.
    - reference_id: PMID:22087221
      supporting_text: >-
        we have demonstrated the importance of the NFP LysM2 domain for
        rhizobial infection and we have pinpointed the importance of a single
        leucine residue of LysM2 in that step of the symbiosis.
core_functions:
- description: >-
    Perception of rhizobial Nod factors (lipo-chitooligosaccharides) by the
    extracellular LysM domains, acting as a plasma-membrane signalling receptor
    that initiates Nod factor signal transduction.
  supported_by:
  - reference_id: PMID:12753588
    supporting_text: >-
      These data indicate that the NFP locus controls an early step of Nod
      factor signal transduction, upstream of previously identified genes and
      specific to nodulation.
  - reference_id: PMID:16723404
    supporting_text: >-
      A convergent model can be proposed where the sulfated, O-acetylated
      lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar
      orientation to the three LysM domains of M. truncatula NFP.
  - reference_id: file:MEDTR/NFP/NFP-deep-research-falcon.md
    supporting_text: >-
      acts at the ... earliest stages of Nod factor signaling ... and is
      genetically placed ... upstream of DMI1/DMI2/DMI3 and NSP1/NSP2 ... the
      extracellular region comprises three LysM domains specialized for
      carbohydrate-derived ligands
  molecular_function:
    id: GO:0038023
    label: signaling receptor activity
  directly_involved_in:
  - id: GO:0009877
    label: nodulation
  locations:
  - id: GO:0005886
    label: plasma membrane
- description: >-
    Initiation of the nitrogen-fixing root nodule symbiosis - nodule
    organogenesis (induction of cortical cell divisions) and rhizobial infection
    thread development and bacterial release - through Nod factor signalling.
  supported_by:
  - reference_id: PMID:22874912
    supporting_text: >-
      Epidermal NFP is sufficient to induce cortical cell divisions leading to
      nodule primordia formation.
  - reference_id: PMID:16844829
    supporting_text: >-
      NFP was shown both to be expressed in association with infection thread
      development and to be involved in the infection process.
  directly_involved_in:
  - id: GO:0009877
    label: nodulation
- description: >-
    Formation of a heteromeric Nod factor receptor complex with the active
    co-receptor kinase LYK3; because NFP is a catalytically dead pseudokinase,
    this heteromer is the mechanism by which extracellular Nod factor perception
    is transduced intracellularly.
  supported_by:
  - reference_id: PMID:25351493
    supporting_text: >-
      our Förster resonance energy transfer-fluorescence lifetime imaging
      microscopy analysis indicates that NFP and LYK3 form heteromeric complexes
      at the cell periphery in M. truncatula nodules.
  - reference_id: PMID:16844829
    supporting_text: >-
      NFP did not show autophosphorylation activity, suggesting that NFP needs to
      associate with an active kinase or has unusual functional characteristics
      different from classical kinases.
  - reference_id: file:MEDTR/NFP/NFP-deep-research-falcon.md
    supporting_text: >-
      lacking key conserved motifs (including P-loop/DFG-related features and an
      activation-loop segment), and ... was observed in vitro, supporting
      interpretation of NFP as a likely ... or signaling subunit that requires
      an active kinase partner
  molecular_function:
    id: GO:0046982
    label: protein heterodimerization activity
- description: >-
    Contribution to plant immunity - positive regulation of defense responses
    against the root oomycete Aphanomyces euteiches and the fungus Colletotrichum
    trifolii. This is a secondary, non-core role distinct from the primary
    symbiotic function.
  supported_by:
  - reference_id: PMID:23432463
    supporting_text: >-
      nfp, but not lyk3, mutants were significantly more susceptible than
      wildtype plants to A. euteiches, whereas NFP overexpression increased
      resistance.
  directly_involved_in:
  - id: GO:1902290
    label: positive regulation of defense response to oomycetes
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings:
  - statement: >-
      InterPro2GO maps protein-kinase-domain signatures to protein kinase
      activity and ATP binding. For NFP these mappings detect the kinase fold but
      do not account for its experimentally established pseudokinase status.
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  findings:
  - statement: >-
      SwissProt keyword-derived (SPKW) annotations present in the Sept 2025
      goa_uniprot_gcrp snapshot but removed from the current GOA release after GOA
      retired the keyword2GO pipeline for cellular organisms.
  - statement: >-
      The retired SPKW annotations for NFP - protein tyrosine kinase activity
      (from the Tyrosine-protein kinase keyword) and defense response (from the
      Plant defense keyword) - were both correctly removed; the first is
      biologically wrong (pseudokinase; Ser/Thr not Tyr) and the second is
      redundant with more specific curated defense terms.
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings:
  - statement: >-
      Maps the UniProt subcellular location "Vacuole lumen" to GO:0005775; this
      reflects the experimentally observed vacuolar localization of NFP in cells
      undergoing receptor breakdown.
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings:
  - statement: >-
      ARBA assigned the broad term "response to other organism"; the specific
      experimentally supported response is to bacterial-origin Nod factors.
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings:
  - statement: >-
      Combined IEA methods place NFP at the plasma membrane, consistent with its
      single-pass transmembrane topology and experimental localization.
- id: PMID:12753588
  title: The NFP locus of Medicago truncatula controls an early step of Nod factor
    signal transduction upstream of a rapid calcium flux and root hair deformation.
  findings:
  - statement: >-
      The nfp mutant fails every assayed Nod factor response (no calcium flux,
      no calcium spiking, no early nodulin expression, no root hair deformation),
      placing NFP at the most upstream, nodulation-specific step of Nod factor
      signal transduction.
    supporting_text: >-
      The nfp mutant thus shows no rapid calcium flux, the earliest detectable
      Nod factor response of wild-type plants, and no root hair deformation. The
      nfp mutant is also deficient in Nod factor-induced calcium spiking and
      early nodulin gene expression.
- id: PMID:16723404
  title: LysM domains of Medicago truncatula NFP protein involved in Nod factor perception.
    Glycosylation state, molecular modeling and docking of chitooligosaccharides and
    Nod factors.
  findings:
  - statement: >-
      The three tandem LysM domains of the NFP ectodomain are predicted to bind
      the rhizobial lipo-chitooligosaccharide Nod factor; NFP is highly
      N-glycosylated.
    supporting_text: >-
      A convergent model can be proposed where the sulfated, O-acetylated
      lipo-chitooligosaccharidic Nod factor of S. meliloti binds in similar
      orientation to the three LysM domains of M. truncatula NFP.
- id: PMID:16844829
  title: The Medicago truncatula lysin [corrected] motif-receptor-like kinase gene
    family includes NFP and new nodule-expressed genes.
  findings:
  - statement: >-
      NFP is a LysM-RLK whose intracellular kinase domain is a pseudokinase - it
      deviates from conserved catalytic kinase sequences and shows no
      autophosphorylation activity, implying it must associate with an active
      kinase.
    supporting_text: >-
      Consistent with deviations from conserved kinase domain sequences, NFP did
      not show autophosphorylation activity, suggesting that NFP needs to
      associate with an active kinase or has unusual functional characteristics
      different from classical kinases.
- id: PMID:22087221
  title: Contribution of NFP LysM domains to the recognition of Nod factors during
    the Medicago truncatula/Sinorhizobium meliloti symbiosis.
  findings:
  - statement: >-
      The NFP LysM2 domain, and specifically a single leucine residue (Leu154),
      are important for rhizobial infection, demonstrating that LysM domain
      residues are functionally required for Nod factor recognition.
    supporting_text: >-
      we have demonstrated the importance of the NFP LysM2 domain for rhizobial
      infection and we have pinpointed the importance of a single leucine residue
      of LysM2 in that step of the symbiosis.
- id: PMID:22874912
  title: Epidermal and cortical roles of NFP and DMI3 in coordinating early steps
    of nodulation in Medicago truncatula.
  findings:
  - statement: >-
      Epidermal NFP is sufficient to induce cortical cell divisions leading to
      nodule primordium formation, establishing NFP's role in nodule
      organogenesis.
    supporting_text: >-
      Epidermal NFP is sufficient to induce cortical cell divisions leading to
      nodule primordia formation.
- id: PMID:23432463
  title: NFP, a LysM protein controlling Nod factor perception, also intervenes in
    Medicago truncatula resistance to pathogens.
  findings:
  - statement: >-
      NFP positively contributes to M. truncatula immunity: nfp mutants are more
      susceptible to the oomycete Aphanomyces euteiches and the fungus
      Colletotrichum trifolii, and NFP overexpression increases resistance.
    supporting_text: >-
      nfp, but not lyk3, mutants were significantly more susceptible than
      wildtype plants to A. euteiches, whereas NFP overexpression increased
      resistance.
- id: PMID:25351493
  title: Nod factor receptors form heteromeric complexes and are essential for intracellular
    infection in medicago nodules.
  findings:
  - statement: >-
      NFP and the active LysM-RLK LYK3 form heteromeric receptor complexes at
      the cell periphery (plasma membrane) in M. truncatula nodules; NFP is also
      observed in the vacuolar lumen of cells undergoing receptor breakdown.
    supporting_text: >-
      our Förster resonance energy transfer-fluorescence lifetime imaging
      microscopy analysis indicates that NFP and LYK3 form heteromeric complexes
      at the cell periphery in M. truncatula nodules.
- id: PMID:25794934
  title: The small GTPase ROP10 of Medicago truncatula is required for both tip growth
    of root hairs and nod factor-induced root hair deformation.
  findings:
  - statement: >-
      The intracellular kinase domain of NFP interacts with the small GTPase
      ROP10 in a GTP-dependent manner; this interaction is required for root hair
      deformation during rhizobial infection.
    supporting_text: >-
      ROP10 interacted with the kinase domain of the NF receptor NFP in a
      GTP-dependent manner.
- id: file:MEDTR/NFP/NFP-deep-research-falcon.md
  title: Deep research report (falcon / Edison Scientific) on Medicago truncatula
    NFP (UniProt Q0GXS4)
  findings:
  - statement: >-
      Independently confirms that NFP has a nonclassical/aberrant intracellular
      kinase domain lacking key conserved kinase motifs (P-loop/DFG-related
      features and an activation-loop segment) and shows no detectable
      autophosphorylation in vitro, supporting interpretation of NFP as a
      pseudokinase / non-catalytic signalling subunit - corroborating the REMOVE
      decisions on the catalytic kinase-activity annotations.
    supporting_text: >-
      lacking key conserved motifs (including P-loop/DFG-related features and an
      activation-loop segment), and ... was observed in vitro, supporting
      interpretation of NFP as a likely ... or signaling subunit that requires
      an active kinase partner
  - statement: >-
      Confirms NFP is a plasma-membrane LysM receptor-like kinase whose three
      tandem extracellular LysM domains mediate recognition of rhizobial Nod
      factors (lipo-chitooligosaccharides), and that NFP acts at the earliest
      step of Nod factor signalling, genetically upstream of DMI1/DMI2/DMI3 and
      NSP1/NSP2, controlling both rhizobial infection and nodule organogenesis.
    supporting_text: >-
      acts at the ... earliest stages of Nod factor signaling ... and is
      genetically placed ... upstream of DMI1/DMI2/DMI3 and NSP1/NSP2 ...
      Arrighi et al. further argue that NFP functions throughout infection and
      may control partly distinct pathways for ... symbiotic infection ... and
      ... nodule organogenesis
  - statement: >-
      Confirms NFP's role at the symbiosis-immunity interface: NFP/NFR-type
      receptors can trigger defense-like outputs, and recent work links the NFP
      kinase domain to the immune co-receptor MtSOBIR1 - consistent with the
      review's treatment of NFP's defense role as a real but secondary,
      non-core function.
    supporting_text: >-
      NFP/NFR-type receptors lie at a ... symbiosis–immunity interface ...
      Recent work connects NFP to ... a known immunity coreceptor
  - statement: >-
      Adds recent (2023-2024) mechanistic context not in the original review:
      NFP can functionally associate with multiple LysM-RLK partners (MtLYK2,
      MtLYK3, MtLYK2bis) whose kinase-active cytoplasmic domains can
      trans-phosphorylate the NFP cytoplasmic domain, extending the single-partner
      NFP-LYK3 heteromer model toward a multi-partner receptor-complex landscape.
    supporting_text: >-
      cytoplasmic domains of MtLYK2/3/2bis display kinase activity, and
      kinase-active versions can induce mobility shifts/retardation consistent
      with ... trans-phosphorylation of the MtNFP cytoplasmic domain
- id: UniProt:Q0GXS4
  title: UniProtKB entry Q0GXS4 (NFP_MEDTR), Serine/threonine receptor-like kinase NFP
  findings:
  - statement: >-
      The UniProt curated subcellular location places NFP at the cell membrane and,
      on the basis of PMID:25351493, in the vacuole lumen of nodule cells undergoing
      breakdown of the Nod factor receptors - the source of the GO_REF:0000044
      subcellular-location IEA to vacuolar lumen.
    supporting_text: >-
      SUBCELLULAR LOCATION: Cell membrane; Single-pass membrane protein. Vacuole
      lumen. Note=Removed from the plasma membrane upon the release of rhizobia into
      the host cytoplasm. Vacuolar localization is observed in cells undergoing
      breakdown of the receptors.
suggested_questions:
- question: >-
    Does the NFP pseudokinase domain retain ATP/nucleotide binding in vitro, or
    has it lost nucleotide binding as well as catalysis?
- question: >-
    What is the structural basis of Nod factor recognition by the NFP LysM
    ectodomain, and which LysM domain(s) directly contact the
    lipo-chitooligosaccharide acyl and sulphate substitutions?
- question: >-
    How is signal transferred from the NFP pseudokinase domain to LYK3 within the
    heteromeric complex - by allosteric activation, transphosphorylation of NFP
    by LYK3, or scaffolding of downstream effectors?
- question: >-
    Does NFP perception of pathogen-derived chitooligosaccharides use the same
    LysM binding surface as Nod factor perception, and how is the symbiotic
    versus immune signalling outcome discriminated?
suggested_experiments:
- description: >-
    Reconstitute the NFP/LYK3 complex in vitro and test whether the active LYK3
    kinase transphosphorylates the NFP pseudokinase domain, and whether NFP
    allosterically modulates LYK3 activity.
  hypothesis: >-
    NFP is a catalytically dead pseudokinase that is transphosphorylated by and
    allosterically regulates its active co-receptor LYK3.
- description: >-
    Solve a co-crystal or cryo-EM structure of the NFP LysM ectodomain bound to a
    defined Sinorhizobium meliloti Nod factor to confirm the predicted
    three-LysM-domain binding mode.
  hypothesis: >-
    The rhizobial lipo-chitooligosaccharide Nod factor binds across the three
    tandem LysM domains of the NFP ectodomain.
- description: >-
    Quantitative binding assays (ITC/SPR) with purified NFP ectodomain against
    Nod factors, chitooligosaccharides of varying length, and pathogen-derived
    chitin fragments to define ligand specificity and affinity.
  hypothesis: >-
    The NFP LysM ectodomain binds chitin-based ligands and discriminates
    symbiotic Nod factors from pathogen-derived chitooligosaccharides by affinity
    or substitution recognition.
- description: >-
    Structure-guided mutagenesis of NFP pseudokinase-domain residues to test
    whether nucleotide binding or specific surface residues are required for
    ROP10 interaction and for signalling output.
  hypothesis: >-
    The NFP pseudokinase domain functions as a protein-interaction module whose
    surface, rather than catalytic activity, is required for ROP10 binding and
    signalling.