Proposed New Ontology Terms

4-hydroxyphenyllactate (HPLA) receptor activity

Definition: Combining with the tyrosine-derived metabolite 4-hydroxyphenyllactic acid (HPLA), a damage-associated molecular pattern, to initiate a change in cell activity, typically via coupling to a heterotrimeric G protein. Applies to GPCRs, such as nematode DCAR-1, that detect HPLA (and structurally related catecholic/phenolic acids) to trigger downstream signalling.

Justification: DCAR-1's specific molecular function - detection of the small-molecule DAMP HPLA - can currently only be annotated with the generic parent G protein-coupled receptor activity (GO:0004930). No ontology term expresses the ligand-specific activity, leaving the receptor's most distinctive feature un-annotatable (an ontology gap).

Parent term: G protein-coupled receptor activity

Supporting Evidence:

PMID:25086774 : the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an endogenous ligand

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0004930 G protein-coupled receptor activity	IEA GO_REF:0000104	ACCEPT	Summary: DCAR-1 is a bona fide seven-transmembrane class A GPCR (7 predicted TM helices; PROSITE G_PROTEIN_RECEP_F1_2; PANTHER PTHR24243) that functions as a receptor for small-molecule ligands: HPLA in the epidermis and DHCA in sensory neurons, in both cases coupling to Galpha signalling. Reason: The GPCR activity is directly supported experimentally. DCAR-1 was identified as a heterologously expressible receptor for DHCA and shown to respond to HPLA, and it signals via the Galpha protein GPA-12. This is a core molecular function of the gene. Supporting Evidence: PMID:22090488 we identified a candidate dihydrocaffeic acid receptor (DCAR), DCAR-1. DCAR-1 is a novel seven-transmembrane protein that is expressed in the ASH avoidance sensory neurons of C. elegans. PMID:25086774 Dihydrocaffeic acid (DHCA) has been described as a potent ligand for DCAR-1 in both in vivo and in heterologous Xenopus oocyte assays
GO:0007186 G protein-coupled receptor signaling pathway	IEA GO_REF:0000104	ACCEPT	Summary: DCAR-1 initiates GPCR signalling: in the epidermis it acts upstream of (or in parallel to) the Galpha protein GPA-12 to control downstream p38 MAPK (PMK-1) signalling. Reason: Core biological process. Genetic epistasis places DCAR-1 at the top of a Galpha (GPA-12) -> p38 MAPK cascade, consistent with canonical GPCR signalling. Supporting Evidence: PMID:25086774 dcar-1 alone acts upstream or in parallel to GPA-12
GO:0007165 signal transduction	IEA GO_REF:0000104	KEEP AS NON CORE	Summary: Correct but generic. Signal transduction is a high-level parent of the more specific G protein-coupled receptor signaling pathway (GO:0007186) that is also annotated and better captures DCAR-1's activity. Reason: The term is not wrong - DCAR-1 does transduce signals - but it is subsumed by the more informative GPCR signaling pathway annotation, so it is retained as non-core rather than treated as a distinct core function. Supporting Evidence: PMID:25086774 multiple elements of the downstream signal transduction cascade
GO:0050832 defense response to fungus	IMP PMID:25086774 Activation of a G protein-coupled receptor by its endogenous...	ACCEPT	Summary: Loss of dcar-1 (RNAi and two null alleles, tm2484 and nj66) abolishes infection-induced antimicrobial peptide expression and markedly increases susceptibility to the fungus Drechmeria coniospora; DCAR-1 was the sole GPCR hit from a screen of 1,150 GPCR genes. Reason: Strong IMP evidence for a core function. DCAR-1 is required in the epidermis for the innate immune response to fungal infection. Supporting Evidence: PMID:25086774 dcar-1 emerged alone as an innate immune receptor gene acting upstream of (or in parallel to) gpa-12 PMID:25086774 dcar-1 mutants exhibited a markedly heightened susceptibility to D. coniospora infection
GO:0009611 response to wounding	IMP PMID:25086774 Activation of a G protein-coupled receptor by its endogenous...	ACCEPT	Summary: dcar-1 mutants show an almost complete block of antimicrobial peptide (nlp-29p::gfp) induction after sterile physical injury, showing that DCAR-1 mediates the response to wounding/damage independently of a pathogen - consistent with detection of an endogenous damage signal (HPLA/DAMP). Reason: Well-supported IMP for a core damage-sensing function; wounding and infection converge on the same DCAR-1-dependent, HPLA-driven pathway. Supporting Evidence: PMID:25086774 an almost complete block of nlp-29p::gfp induction following physical injury PMID:25086774 demonstrating that dcar-1 can be activated in the absence of a pathogen
GO:0016324 apical plasma membrane	IDA PMID:25086774 Activation of a G protein-coupled receptor by its endogenous...	ACCEPT	Summary: A rescuing dcar-1p::dcar-1::gfp translational reporter localized DCAR-1 to the apical surface of the major epidermal syncytium hyp7, the site where it acts to drive antimicrobial peptide expression. Reason: Direct IDA localization to the apical plasma membrane; a core cellular location for the receptor's immune function. Supporting Evidence: PMID:25086774 dcar-1 was expressed on the apical surface in the major epidermal syncytium, hyp7
GO:0005886 plasma membrane	IBA GO_REF:0000033	ACCEPT	Summary: Plasma membrane localization inferred from phylogeny is consistent with DCAR-1 being a cell-surface 7-TM GPCR and with the direct (IDA) apical plasma membrane localization in the epidermis. Reason: Correct and corroborated by experimental data; a parent of the more specific apical plasma membrane annotation. Supporting Evidence: PMID:25086774 dcar-1 was expressed on the apical surface in the major epidermal syncytium, hyp7
GO:0016020 membrane	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: Generic membrane localization from InterPro/UniProt subcellular-location pipelines; correct for a multi-pass membrane protein but uninformative relative to the plasma membrane / apical plasma membrane annotations. Reason: Not wrong, but subsumed by the more specific and experimentally supported plasma membrane and apical plasma membrane terms.
GO:0097730 non-motile cilium	IDA PMID:22090488 A seven-transmembrane receptor that mediates avoidance respo...	KEEP AS NON CORE	Summary: WormBase IDA localization associated with DCAR-1's expression in the ciliated ASH (and ASI, PVQ) sensory neurons, where it detects the repellent DHCA. This reflects the neuronal chemosensory role, distinct from the epidermal immune role. Reason: The cached copy of PMID:22090488 is abstract-only, so the specific cilium sub-localization cannot be re-verified from the cached text; per curation policy the WormBase curator's experimental (IDA) call is trusted and not overruled. It is retained as a non-core location because it belongs to the neuronal chemosensory context rather than the flagship epidermal immune function. Supporting Evidence: PMID:22090488 expressed in the ASH avoidance sensory neurons of C. elegans
GO:0008188 neuropeptide receptor activity	IBA GO_REF:0000033	REMOVE	Summary: This activity was propagated by phylogenetic (IBA) inference from the broad class A GPCR family (PTHR24243), some of whose members are neuropeptide receptors. However, the two experimentally characterized ligands of DCAR-1 are small-molecule catecholic/phenolic acids - HPLA (a tyrosine-derived metabolite/DAMP) in the epidermis and DHCA in neurons - not neuropeptides. Reason: Over-propagated family-level IBA that is contradicted by the direct experimental characterization of DCAR-1's ligands. DCAR-1 is not a neuropeptide receptor; its molecular function is adequately and correctly captured by G protein-coupled receptor activity (GO:0004930). Removing this avoids an unsupported and misleading molecular-function assertion. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN002797693 · PTHR24243 class A GPCR IBA seed node SUPPORTS SOURCE BUT NOT TARGET Neuropeptide-receptor activity is valid for genuine peptide-receptor members of this large class A GPCR family, but DCAR-1's characterized ligands are small-molecule metabolites (HPLA, DHCA), not neuropeptides. WB:WBGene00019616 · C. elegans family member in the IBA with/from set SUPPORTS SOURCE BUT NOT TARGET Co-annotated family member; it does not establish a neuropeptide ligand for DCAR-1. Supporting Evidence: PMID:25086774 the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an endogenous ligand PMID:25086774 Dihydrocaffeic acid (DHCA) has been described as a potent ligand for DCAR-1 in both in vivo and in heterologous Xenopus oocyte assays
GO:0007218 neuropeptide signaling pathway	IBA GO_REF:0000033	REMOVE	Summary: Companion IBA propagation to the neuropeptide receptor activity call, inferred from the GPCR family rather than from DCAR-1's own biology. DCAR-1 signalling is driven by small-molecule ligands (HPLA, DHCA), not by neuropeptides. Reason: Over-propagated family-level IBA not supported by any evidence specific to DCAR-1 and contradicted by its characterized small-molecule ligands. The gene's signalling role is correctly captured by G protein-coupled receptor signaling pathway (GO:0007186) and the defense/wounding process terms. Propagation Review Root cause: PROPAGATION BAD Failure modes: WRONG ORTHOLOG OR PARALOG FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN002797693 · PTHR24243 class A GPCR IBA seed node SUPPORTS SOURCE BUT NOT TARGET Neuropeptide signalling is valid for genuine peptide-receptor members of this family, but DCAR-1 signals in response to small-molecule metabolites (HPLA, DHCA), not neuropeptides. WB:WBGene00019616 · C. elegans family member in the IBA with/from set SUPPORTS SOURCE BUT NOT TARGET Co-annotated family member; it does not establish neuropeptide signalling for DCAR-1. Supporting Evidence: PMID:25086774 HPLA can act through DCAR-1 to regulate the epidermal innate immune response
GO:0007635 chemosensory behavior	IMP PMID:22090488 A seven-transmembrane receptor that mediates avoidance respo...	NEW	Summary: In ASH sensory neurons DCAR-1 is required for avoidance of the water- soluble repellent dihydrocaffeic acid (DHCA): dcar-1 null mutants are defective in DHCA avoidance and ASH-specific expression rescues the defect (Aoki et al. 2011), a role corroborated in Zugasti et al. 2014. Reason: Not present in GOA, but the neuronal chemosensory (repellent-avoidance) function is directly established by IMP evidence and is genetically separable from the epidermal immune role. Added so that the receptor's second, well-supported evolved function is captured in the structured annotations (mirrors the neuronal core_function). Supporting Evidence: PMID:22090488 dcar-1 mutant animals are defective in avoidance response to DHCA, and cell-specific expression of dcar-1 in the ASH neurons PMID:25086774 In neurons, dcar-1 mediates an avoidance response to specific repellents, acting in concert with ocr-2 and osm-9

Core Functions

DCAR-1 acts as an epidermal innate-immune GPCR: it is a plasma-membrane (apical hyp7) receptor that detects the endogenous damage-associated metabolite HPLA (and, exogenously, DHCA) generated upon fungal infection or wounding, and transduces this via Galpha (GPA-12) and the p38 MAPK cascade to induce antimicrobial peptide genes and confer resistance to Drechmeria coniospora.

Molecular Function:

G protein-coupled receptor activity

Directly Involved In:

defense response to fungus response to wounding G protein-coupled receptor signaling pathway

Cellular Locations:

apical plasma membrane plasma membrane

Supporting Evidence:

PMID:25086774
DCAR-1 acted in the epidermis to regulate the expression of antimicrobial peptides via a conserved p38 mitogen-activated protein kinase pathway.
PMID:25086774
Our findings reveal DCAR-1 and its cognate ligand HPLA to be triggers of the epidermal innate immune response
PMID:25086774
dcar-1 was expressed on the apical surface in the major epidermal syncytium, hyp7
file:worm/dcar-1/dcar-1-deep-research-falcon.md
DAMP-sensing GPCR that activates epidermal innate immunity in response to fungal infection and wounding

In ciliated ASH (and ASI, PVQ) sensory neurons DCAR-1 acts as a chemoreceptor for the exogenous water-soluble repellent dihydrocaffeic acid (DHCA), driving an avoidance response together with the TRPV channel subunits OCR-2 and OSM-9. This neuronal chemosensory role is genetically and functionally separable from the epidermal immune role (neuronal expression rescues avoidance but not antimicrobial peptide induction).

Molecular Function:

G protein-coupled receptor activity

Directly Involved In:

chemosensory behavior G protein-coupled receptor signaling pathway

Cellular Locations:

plasma membrane

Supporting Evidence:

PMID:22090488
DCAR-1 as the first seven-transmembrane receptor required for avoidance of a water-soluble repellent, DHCA, in C. elegans
PMID:25086774
In neurons, dcar-1 mediates an avoidance response to specific repellents, acting in concert with ocr-2 and osm-9

References

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000104

Electronic Gene Ontology annotations created by transferring manual GO annotations between related proteins based on shared sequence features

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:22090488

A seven-transmembrane receptor that mediates avoidance response to dihydrocaffeic acid, a water-soluble repellent in Caenorhabditis elegans.

DCAR-1 is a novel seven-transmembrane receptor for the water-soluble repellent dihydrocaffeic acid (DHCA), expressed in the ASH avoidance sensory neurons; dcar-1 mutants are defective in DHCA avoidance and ASH-specific expression rescues the defect.

"we identified a candidate dihydrocaffeic acid receptor (DCAR), DCAR-1. DCAR-1 is a novel seven-transmembrane protein that is expressed in the ASH avoidance sensory neurons of C. elegans."

PMID:25086774

Activation of a G protein-coupled receptor by its endogenous ligand triggers the innate immune response of Caenorhabditis elegans.

DCAR-1 was the sole hit from an RNAi screen of 1,150 GPCR genes required for infection- and wounding-induced antimicrobial peptide expression, acting upstream of (or in parallel to) the Galpha protein GPA-12 in the epidermal p38 MAPK pathway.

"dcar-1 emerged alone as an innate immune receptor gene acting upstream of (or in parallel to) gpa-12"
The tyrosine-derived metabolite HPLA is an endogenous damage-associated ligand for DCAR-1 that increases upon infection and cuticle damage and drives DCAR-1-dependent antimicrobial peptide expression in the epidermis.

"the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an endogenous ligand"

file:worm/dcar-1/dcar-1-deep-research-falcon.md

Deep research report (Edison/falcon) for C. elegans dcar-1

Suggested Experiments

Experiment: Express DCAR-1 in a heterologous GPCR-activation system (as previously done with DHCA in Xenopus oocytes) and measure dose-dependent activation by HPLA and structurally related phenolic acids; test coupling specificity against GPA-12 versus other Galpha subunits.

Hypothesis: DCAR-1 is the direct receptor for HPLA and couples to GPA-12.

Type: heterologous receptor activation / ligand-response assay

Experiment: Use targeted metabolomics with isotope-labelled tyrosine to trace HPLA production before and after infection/wounding, combined with epidermis- specific RNAi/overexpression of candidate aminotransferases and reductases (e.g. tatn-1) to identify the biosynthetic enzymes.

Hypothesis: HPLA is generated in the epidermis by a defined tyrosine-catabolic route whose flux increases with damage.

Type: stable-isotope metabolomics + tissue-specific genetics

Knowledge Gaps

What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).

Gap: The structural and biochemical basis of ligand recognition by DCAR-1 is unknown: there is no direct binding assay, no structure, and no defined ligand-binding pocket or residues. Whether DCAR-1 is the direct receptor for HPLA (versus an upstream/indirect sensor) has not been demonstrated biochemically.

OPEN BIOLOGY RESIDUAL_SUBGAP

What is known: It is firmly established that DCAR-1 is a 7-TM class A GPCR required in the epidermis for HPLA/DHCA-triggered antimicrobial peptide induction and anti-fungal defense, and that it can respond to DHCA in a heterologous Xenopus oocyte system. The evidence that HPLA is the endogenous ligand is genetic and metabolomic (correlative), not a direct receptor-binding measurement.

Significance: HPLA is the first described damage-associated molecular pattern (DAMP) in C. elegans; defining how DCAR-1 binds it would establish the molecular logic of DAMP sensing by a metazoan GPCR and enable rational tests of whether analogous receptors exist beyond nematodes.

What would resolve it: Direct ligand-binding/activation assays (e.g. purified receptor or cell-based GPCR activation with HPLA titration), mutagenesis of predicted binding-pocket residues, and structural determination of the DCAR-1-HPLA complex.

Provenance (the field's own admissions):

"We provide strong correlative evidence that HPLA is an endogenous ligand for DCAR-1. Proving this definitively is not straightforward" — PMID:25086774

Gap: It is unknown whether DCAR-1 has ligands or roles beyond HPLA/DHCA - including its natural neuronal ligand, whether it recognizes any microbe-associated molecular pattern, and whether it contributes to pathogen-avoidance behaviour as a second host-defense role.

OPEN BIOLOGY MF_DARK

What is known: DCAR-1 is known to detect the endogenous metabolite HPLA (epidermal immunity) and the exogenous repellent DHCA (neuronal avoidance via ASH/ASI/ PVQ with OCR-2/OSM-9). Beyond these, its ligand spectrum and the physiological relevance of its neuronal signalling to host defense are not established.

Significance: GPCRs are proposed to be an under-explored class of immunomodulatory receptors; clarifying whether DCAR-1 senses microbial patterns or only host damage signals would sharpen models of how nematodes discriminate infection from sterile injury.

What would resolve it: Systematic ligand/deorphanization screens, tests for direct microbe-derived agonists, and behavioural/immune assays separating DCAR-1's neuronal and epidermal contributions to defense.

Provenance (the field's own admissions):

"It is not known whether any GPCR recognizes specific microbe-associated molecular patterns." — PMID:25086774

Gap: The biosynthetic origin of the DAMP ligand HPLA, and the mechanism by which infection and cuticle damage raise its levels, are uncharacterized - including whether the invading fungus contributes to HPLA production or the increase is entirely host-derived.

OPEN BIOLOGY BP_DARK

What is known: HPLA is a tyrosine-derived metabolite that increases upon infection and in cuticle-defective dpy-10 mutants, and epidermal overexpression of the candidate aminotransferase tatn-1 raises dcar-1-dependent antimicrobial peptide expression. The enzymes and regulatory logic of HPLA production remain undefined and were only partially probed (candidate aminotransferase knockdowns were inconclusive, likely due to redundancy).

Significance: Understanding how HPLA is generated would reveal how damage and infection are converted into a diffusible immune-activating signal, and whether the pathway is a host stress response or a pathogen-influenced process.

What would resolve it: Genetic and biochemical dissection of tyrosine catabolism/HPLA synthesis in the epidermis, isotope-tracing of HPLA under infection, and host-versus- pathogen source discrimination.

Provenance (the field's own admissions):

"Although its biosynthetic pathway has not been characterized in any eukaryote, HPLA is likely derived from tyrosine" — PMID:25086774

Deep Research

Falcon

(dcar-1-deep-research-falcon.md)

Comprehensive Research Report: DCAR-1 (C06H5.7) in *Caenorhabditis elegans* Falcon Edison Scientific Literature 19 citations 2 artifacts 2026-07-04T16:36:23.457277

Edison artifact artifact-00 (text/markdown)

Edison artifact artifact-01 (text/markdown)

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

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

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

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

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

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

Comprehensive Research Report: DCAR-1 (C06H5.7) in Caenorhabditis elegans

1. Gene and Protein Identity

DCAR-1 (DihydroCaffeic Acid Receptor-1) is a G-protein coupled receptor (GPCR) encoded by the gene dcar-1 (systematic name C06H5.7) in Caenorhabditis elegans (UniProt accession G5EDI0). The protein belongs to the rhodopsin-like family of seven-transmembrane receptors (domain: GPCR_Rhodpsn_7TM, InterPro IPR017452) (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6). DCAR-1 is notable as the only GPCR identified to date that functions as a damage-associated molecular pattern (DAMP) sensor in C. elegans (venkatesh2021gproteincoupledreceptors pages 2-4, garciasanchez2021ubiquitinrelatedprocessesand pages 9-10).

The following table summarizes the key identity and functional features of DCAR-1:

Feature	Value
Gene Symbol	dcar-1
Full Name	DihydroCaffeic Acid Receptor-1
Systematic Name	C06H5.7
UniProt ID	G5EDI0
Organism	Caenorhabditis elegans
Protein Type	G-protein coupled receptor (GPCR), predicted 7-transmembrane receptor; consistent with rhodopsin-like 7TM annotation in UniProt (venkatesh2021gproteincoupledreceptors pages 2-4)
Domain	GPCR_Rhodpsn_7TM / IPR017452; literature describes DCAR-1 as a GPCR/7TM receptor (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6)
Endogenous Ligand	4-hydroxyphenyllactic acid (HPLA), a tyrosine-derived damage-associated molecular pattern (DAMP) that accumulates after infection or injury (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6)
Tissue Expression	Epidermis/hypodermis, especially the apical epidermal syncytium; also reported in sensory neurons, although immune function is epidermis-specific (taffoni2015mechanismsofinnate pages 5-6, venkatesh2021gproteincoupledreceptors pages 2-4)
Functional Localization	Cell surface receptor localized to the apical part of the epidermal syncytium hyp7 (taffoni2015mechanismsofinnate pages 5-6, taffoni2015mechanismsofinnate pages 4-5)
Primary Function	DAMP-sensing GPCR that activates epidermal innate immunity in response to fungal infection and wounding (venkatesh2021gproteincoupledreceptors pages 2-4, garciasanchez2021ubiquitinrelatedprocessesand pages 9-10, kim2018signalinginthe pages 14-16)
Key Biological Processes	Antifungal defense against Drechmeria coniospora, wound response, and induction of antimicrobial peptide genes including nlp family targets such as nlp-29 (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6)
Initial Characterization	Initially characterized behaviorally as a seven-transmembrane receptor mediating avoidance to dihydrocaffeic acid (Aoki et al. 2011; identified in retrieved literature but full text unavailable in tool search). Subsequently established as an innate immune receptor activated by endogenous HPLA to trigger AMP expression during epidermal damage/infection (summarized in later reviews citing the 2014 primary work) (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 14-16)

Table: This table summarizes the verified identity, ligand, localization, and core biological role of the C. elegans GPCR DCAR-1. It is useful as a quick reference to distinguish this receptor from similarly named genes and to anchor interpretation of the downstream immune signaling literature.

2. Primary Function: DAMP-Sensing Receptor for Epidermal Innate Immunity

DCAR-1 serves as a pattern recognition receptor that detects tissue damage in the C. elegans epidermis (hypodermis) and activates innate immune defenses. Unlike mammalian Toll-like receptors that primarily detect pathogen-associated molecular patterns (PAMPs), DCAR-1 functions by sensing a host-derived endogenous ligand that accumulates when epidermal integrity is compromised (venkatesh2021gproteincoupledreceptors pages 2-4, kim2018signalinginthe pages 14-16).

2.1 Endogenous Ligand: 4-Hydroxyphenyllactic Acid (HPLA)

The endogenous ligand of DCAR-1 is 4-hydroxyphenyllactic acid (HPLA), a product of tyrosine degradation in the hypodermis (taffoni2015mechanismsofinnate pages 5-6, venkatesh2021gproteincoupledreceptors pages 2-4). HPLA levels increase under conditions of epidermal damage, including physical wounding, infection by the natural fungal pathogen Drechmeria coniospora, and in cuticle-defective mutants such as dpy-9 and dpy-10 (kim2018signalinginthe pages 14-16). The accumulation of HPLA thus functions as a danger signal, providing a mechanism by which the epidermis can detect tissue disruption and mount a defensive response. This identification of HPLA as the cognate ligand was a landmark finding that established DCAR-1 as the first deorphanized GPCR in the C. elegans innate immune system (venkatesh2021gproteincoupledreceptors pages 2-4, zhang2021antagonisticfungalenterotoxins pages 10-12).

The gene was initially named for its response to dihydrocaffeic acid, a water-soluble repellent that elicits avoidance behavior in C. elegans via sensory neurons (Aoki et al., 2011, as cited in multiple reviews) (venkatesh2021gproteincoupledreceptors pages 2-4). However, the immune-regulatory function of DCAR-1 is distinct from and independent of this neuronal chemosensory role.

2.2 Biological Roles

DCAR-1 plays critical roles in two primary contexts of epidermal defense:

Antifungal immunity: During infection by D. coniospora, a natural endoparasitic fungal pathogen of C. elegans that adheres to the cuticle via specialized adhesive knobs and can kill worms within 48 hours, DCAR-1 is essential for the rapid transcriptional upregulation of antimicrobial peptide (AMP) genes in the epidermis (taffoni2015mechanismsofinnate pages 5-6, taffoni2015mechanismsofinnate pages 4-5). The primary transcriptional targets include neuropeptide-like protein genes, particularly nlp-29, as well as caenacin (cnc) genes (taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5).

Wound response: Physical injury to the epidermis similarly triggers DCAR-1-dependent AMP gene induction, demonstrating that this receptor integrates signals from both pathogenic and sterile damage (taffoni2015mechanismsofinnate pages 4-5, taffoni2015mechanismsofinnate pages 5-6).

3. Tissue and Subcellular Localization

DCAR-1 is expressed in the epidermis (hypodermis) and in sensory neurons. However, its immune-regulatory function is epidermis-specific and cell-autonomous (taffoni2015mechanismsofinnate pages 5-6, venkatesh2021gproteincoupledreceptors pages 2-4). Within the epidermis, DCAR-1 localizes to the apical part of the epidermal syncytium hyp7, positioning it at the cell surface facing the cuticle—the barrier tissue most directly exposed to environmental pathogens and physical insults (taffoni2015mechanismsofinnate pages 5-6, taffoni2015mechanismsofinnate pages 4-5). This apical localization is functionally significant because it places the receptor at the interface where damage signals (HPLA) would first accumulate following cuticle compromise or pathogen attachment.

4. Signaling Pathway

The DCAR-1 signaling pathway in the epidermis has been extensively characterized through forward genetic screens, genome-wide RNAi screens, and epistasis analysis. The pathway proceeds as follows:

Component	Type/Function	Position in Pathway	Role
DCAR-1	GPCR; DAMP receptor activated by HPLA	Receptor / pathway entry point	Binds the endogenous tyrosine-metabolite ligand 4-hydroxyphenyllactic acid (HPLA) generated during epidermal damage, fungal infection, or wounding; initiates epidermal innate immune signaling to AMP genes (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6)
GPA-12	Gα signaling subunit	Immediately downstream of DCAR-1	Transduces the activated GPCR signal toward PKC-dependent immune signaling required for AMP induction after fungal infection or wounding (taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5, zhang2021antagonisticfungalenterotoxins pages 10-12)
RACK-1	Gβ-associated signaling component / scaffold	Parallel to GPA-12 downstream of DCAR-1	Cooperates with GPA-12 in GPCR signaling upstream of TPA-1 to promote epidermal antimicrobial gene expression (taffoni2015mechanismsofinnate pages 5-6)
EGL-8/PLC-3	Phospholipase C enzymes	Upstream of DAG production	Convert PIP2 into DAG, providing the second messenger input needed to activate TPA-1/PKC in the epidermal immune pathway (taffoni2015mechanismsofinnate pages 5-6)
DAG	Lipid second messenger	Between PLCs and TPA-1	Activates TPA-1, coupling upstream GPCR/G-protein signaling to the kinase cascade that drives AMP expression (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12)
TPA-1	Protein kinase C (PKC)	Downstream of GPA-12/RACK-1 and DAG	Central kinase transmitting the DCAR-1 signal toward TIR-1 and the p38 MAPK cascade in response to epidermal infection or injury (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12)
TIR-1	TIR-domain adaptor / scaffold	Upstream of MAP3K NSY-1	Links PKC-dependent signaling to the conserved p38 MAPK module that controls antimicrobial peptide induction (taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5, kim2018signalinginthe pages 14-16)
NSY-1	MAP kinase kinase kinase (MAP3K)	First kinase in p38 MAPK cascade	Receives input from TIR-1 and activates downstream SEK-1 as part of the canonical epidermal innate immune cascade (taffoni2015mechanismsofinnate pages 5-6)
SEK-1	MAP kinase kinase (MAP2K)	Middle kinase in p38 MAPK cascade	Relays the signal from NSY-1 to PMK-1 to support transcriptional activation of AMP genes (taffoni2015mechanismsofinnate pages 5-6)
PMK-1	p38 MAP kinase	Terminal kinase in core MAPK cascade	Executes the p38 MAPK immune response downstream of DCAR-1, promoting AMP induction and antifungal defense in the epidermis (venkatesh2021gproteincoupledreceptors pages 2-4, taffoni2015mechanismsofinnate pages 5-6)
STA-2	STAT-like transcription factor	Downstream nuclear effector of PMK-1 pathway	Required for transcriptional activation of nlp genes and contributes to AMP expression after fungal infection, wounding, and damage sensing (garciasanchez2021ubiquitinrelatedprocessesand pages 9-10, taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12, zhu2023c.eleganshemidesmosomes pages 1-2)
ELT-3	GATA transcription factor	Co-regulator with STA-2 downstream of signaling cascade	Works with STA-2 to promote epidermal AMP gene transcription in response to DCAR-1 pathway activation (taffoni2015mechanismsofinnate pages 5-6)
nlp-29/cnc (target genes)	Antimicrobial peptide genes / transcriptional outputs	Terminal output	Encode epidermally induced antimicrobial effectors. nlp-29 is a canonical DCAR-1–p38 MAPK target; cnc genes can also be induced in related epidermal defense programs, with some regulation occurring through a non-canonical DBL-1/TGF-β branch depending on stimulus context (taffoni2015mechanismsofinnate pages 4-5, taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5)

Table: This table summarizes the experimentally supported DCAR-1 epidermal signaling pathway in C. elegans, from HPLA sensing at the receptor to antimicrobial peptide gene induction. It is useful for tracing how damage-associated signaling is converted into antifungal and wound-response outputs.

4.1 Detailed Pathway Description

Upon activation by HPLA, DCAR-1 couples to the heterotrimeric G protein subunits GPA-12 (Gα) and RACK-1 (Gβ), which are required for downstream signal transduction to antimicrobial peptide gene expression (taffoni2015mechanismsofinnate pages 5-6, venkatesh2021gproteincoupledreceptors pages 2-4). The G-protein signaling activates phospholipase C enzymes EGL-8 and PLC-3, which hydrolyze phosphatidylinositol 4,5-bisphosphate (PIP2) to produce diacylglycerol (DAG), a lipid second messenger (taffoni2015mechanismsofinnate pages 5-6). DAG in turn activates the serine/threonine protein kinase C TPA-1 (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12).

TPA-1 acts upstream of TIR-1, a TIR-domain adaptor protein homologous to mammalian SARM1, which serves as a scaffold linking PKC-dependent signaling to the core p38 MAPK cascade (taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5). The MAPK module consists of the MAP3K NSY-1, the MAP2K SEK-1, and the p38 MAPK PMK-1, which constitutes the terminal kinase in the cascade (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12).

PMK-1 activates the STAT-like transcription factor STA-2 and the GATA transcription factor ELT-3, which together drive transcription of nlp antimicrobial peptide genes, including the canonical target nlp-29 (taffoni2015mechanismsofinnate pages 5-6, kim2018signalinginthe pages 9-12, dierking2016antimicrobialeffectorsin pages 4-5). The caenacin (cnc) AMP gene family is also regulated through this pathway, although cnc gene induction shows additional complexity: after wounding, cnc induction is p38 MAPK-dependent, but after fungal infection, cnc expression is regulated through a non-canonical DBL-1/TGF-β pathway that operates independently of p38 MAPK (taffoni2015mechanismsofinnate pages 5-6, dierking2016antimicrobialeffectorsin pages 4-5).

4.2 Relationship to Broader Immune Signaling

The TIR-1/NSY-1/SEK-1/PMK-1 p38 MAPK cascade is a highly conserved signaling module that also functions in the C. elegans intestine to regulate resistance to bacterial pathogens (kim2018signalinginthe pages 9-12). In the epidermis, this cascade is specifically wired downstream of the DCAR-1 GPCR pathway, whereas in the intestine, different upstream activators engage the same MAPK module (kim2018signalinginthe pages 9-12). This tissue-specific utilization of a shared signaling core highlights how C. elegans achieves distinct immune responses in different tissues using modular signaling architecture.

5. Recent Developments (2023–2025)

5.1 DCAR-1-Independent Damage Sensing via Hemidesmosomes

A 2023 study by Zhu et al. revealed an important nuance in epidermal damage sensing. Through systematic analysis of collagen-encoding genes, the authors demonstrated that certain types of collagen damage (specifically damage to DPY-7 collagen) can induce nlp-29 expression independently of DCAR-1 and PMK-1, via a hemidesmosome-based damage-sensing mechanism (zhu2023c.eleganshemidesmosomes pages 10-12). In this alternative pathway, disruption of DPY collagen substructures causes the separation of collagen BLI-1 from the hemidesmosome receptor MUP-4, leading to release of STA-2 from hemidesmosomes and direct induction of AMP gene expression (zhu2023c.eleganshemidesmosomes pages 1-2, zhu2023c.eleganshemidesmosomes pages 10-12). This finding demonstrates that while DCAR-1 is a major DAMP sensor, the epidermis employs multiple, partially overlapping damage-sensing mechanisms, and DCAR-1 only partially accounts for collagen damage-induced immune responses (zhu2023c.eleganshemidesmosomes pages 1-2).

5.2 DCAR-1 Pathway and Cisplatin Resistance

Raj et al. (2023) identified the p38 MAPK pathway—in which DCAR-1 functions as the upstream DAMP receptor in the epidermis—as a critical determinant of cisplatin toxicity resistance in post-mitotic C. elegans adults (raj2023cisplatintoxicityis pages 10-13, raj2023cisplatintoxicityis pages 13-13). The study demonstrated that cisplatin exposure activates the p38 MAPK/ATF-7 immune signaling axis, and mutations in pathway components including dcar-1 increased sensitivity to cisplatin-induced necrotic damage (raj2023cisplatintoxicityis pages 10-13, raj2023cisplatintoxicityis pages 13-14). This work extended the functional significance of the DCAR-1 pathway beyond pathogen defense to xenobiotic stress responses.

5.3 Pathogen Virulence Strategies Targeting the DCAR-1 Pathway

Zhang et al. (2021) demonstrated that the fungal pathogen D. coniospora produces enterotoxins (DcEntA and DcEntB) that can interfere with the DCAR-1-initiated immune cascade at multiple levels, including blocking STA-2 nuclear translocation and disrupting vesicle trafficking in the epidermis (zhang2021antagonisticfungalenterotoxins pages 10-12). This illustrates the co-evolutionary arms race between host damage sensing and pathogen immune evasion strategies.

6. Evolutionary and Comparative Significance

DCAR-1 represents a noncanonical pattern recognition receptor in C. elegans innate immunity (venkatesh2021gproteincoupledreceptors pages 2-4). Unlike mammals, where TLRs, NLRs, and other canonical PRRs directly detect pathogen-derived molecules, C. elegans appears to primarily rely on sensing the damage caused by pathogens rather than pathogen molecules themselves (venkatesh2021gproteincoupledreceptors pages 2-4, kim2018signalinginthe pages 14-16). DCAR-1's function as a DAMP sensor—detecting an endogenous tyrosine metabolite that accumulates upon tissue damage—exemplifies this "guard" or damage-sensing strategy of immune activation (venkatesh2021gproteincoupledreceptors pages 2-4, kim2018signalinginthe pages 14-16). The unique worm TOL-1 (TLR homolog) is not essential for most pathogen defenses, making GPCR-based sensing through receptors like DCAR-1 a particularly important immune detection mechanism in this organism (venkatesh2021gproteincoupledreceptors pages 2-4).

7. Summary

DCAR-1 is a rhodopsin-family GPCR that functions as the primary damage-associated molecular pattern sensor in the C. elegans epidermis. Localized to the apical surface of the hyp7 epidermal syncytium, it detects the endogenous ligand HPLA—a tyrosine metabolite that accumulates upon cuticle disruption, fungal infection, or wounding. Ligand binding activates a well-characterized signaling cascade through G-proteins (GPA-12/RACK-1), phospholipase C, DAG, PKC (TPA-1), the TIR-1 adaptor, and the p38 MAPK module (NSY-1/SEK-1/PMK-1), culminating in STA-2- and ELT-3-dependent transcription of antimicrobial peptide genes including nlp-29. Recent work has revealed additional DCAR-1-independent damage-sensing mechanisms in the epidermis and extended the functional relevance of the DCAR-1/p38 MAPK pathway to xenobiotic stress resistance. DCAR-1 remains the only well-documented GPCR functioning as an innate immune DAMP receptor in C. elegans, providing a paradigmatic example of how metazoans can employ GPCRs for immune surveillance at epithelial barriers.

References

(venkatesh2021gproteincoupledreceptors pages 2-4): Siddharth R. Venkatesh and Varsha Singh. G protein-coupled receptors: the choreographers of innate immunity in caenorhabditis elegans. PLOS Pathogens, 17:e1009151, Jan 2021. URL: https://doi.org/10.1371/journal.ppat.1009151, doi:10.1371/journal.ppat.1009151. This article has 17 citations and is from a highest quality peer-reviewed journal.
(taffoni2015mechanismsofinnate pages 5-6): Clara Taffoni and Nathalie Pujol. Mechanisms of innate immunity in c. elegans epidermis. Tissue Barriers, 3:e1078432, Oct 2015. URL: https://doi.org/10.1080/21688370.2015.1078432, doi:10.1080/21688370.2015.1078432. This article has 75 citations and is from a peer-reviewed journal.
(garciasanchez2021ubiquitinrelatedprocessesand pages 9-10): Juan A. Garcia-Sanchez, Jonathan J. Ewbank, and Orane Visvikis. Ubiquitin-related processes and innate immunity in c. elegans. Cellular and Molecular Life Sciences, 78:4305-4333, Feb 2021. URL: https://doi.org/10.1007/s00018-021-03787-w, doi:10.1007/s00018-021-03787-w. This article has 15 citations and is from a domain leading peer-reviewed journal.
(taffoni2015mechanismsofinnate pages 4-5): Clara Taffoni and Nathalie Pujol. Mechanisms of innate immunity in c. elegans epidermis. Tissue Barriers, 3:e1078432, Oct 2015. URL: https://doi.org/10.1080/21688370.2015.1078432, doi:10.1080/21688370.2015.1078432. This article has 75 citations and is from a peer-reviewed journal.
(kim2018signalinginthe pages 14-16): Dennis H. Kim and J. Ewbank. Signaling in the innate immune response. WormBook, pages 1-35, Aug 2018. URL: https://doi.org/10.1895/wormbook.1.83.2, doi:10.1895/wormbook.1.83.2. This article has 181 citations.
(zhang2021antagonisticfungalenterotoxins pages 10-12): Xing Zhang, Benjamin W. Harding, Dina Aggad, Damien Courtine, Jia-Xuan Chen, Nathalie Pujol, and Jonathan J. Ewbank. Antagonistic fungal enterotoxins intersect at multiple levels with host innate immune defences. Jun 2021. URL: https://doi.org/10.1371/journal.pgen.1009600, doi:10.1371/journal.pgen.1009600. This article has 21 citations and is from a domain leading peer-reviewed journal.
(dierking2016antimicrobialeffectorsin pages 4-5): Katja Dierking, Wentao Yang, and Hinrich Schulenburg. Antimicrobial effectors in the nematode caenorhabditis elegans: an outgroup to the arthropoda. Philosophical Transactions of the Royal Society B: Biological Sciences, 371:20150299, May 2016. URL: https://doi.org/10.1098/rstb.2015.0299, doi:10.1098/rstb.2015.0299. This article has 107 citations and is from a domain leading peer-reviewed journal.
(kim2018signalinginthe pages 9-12): Dennis H. Kim and J. Ewbank. Signaling in the innate immune response. WormBook, pages 1-35, Aug 2018. URL: https://doi.org/10.1895/wormbook.1.83.2, doi:10.1895/wormbook.1.83.2. This article has 181 citations.
(zhu2023c.eleganshemidesmosomes pages 1-2): Yi Zhu, Wenna Li, Yifang Dong, Chujie Xia, and Rong Fu. C. elegans hemidesmosomes sense collagen damage to trigger innate immune response in the epidermis. Cells, 12:2223, Sep 2023. URL: https://doi.org/10.3390/cells12182223, doi:10.3390/cells12182223. This article has 13 citations.
(zhu2023c.eleganshemidesmosomes pages 10-12): Yi Zhu, Wenna Li, Yifang Dong, Chujie Xia, and Rong Fu. C. elegans hemidesmosomes sense collagen damage to trigger innate immune response in the epidermis. Cells, 12:2223, Sep 2023. URL: https://doi.org/10.3390/cells12182223, doi:10.3390/cells12182223. This article has 13 citations.
(raj2023cisplatintoxicityis pages 10-13): Dorota Raj, Bashar Kraish, Jari Martikainen, Agnieszka Podraza-Farhanieh, Gautam Kao, and Peter Naredi. Cisplatin toxicity is counteracted by the activation of the p38/atf-7 signaling pathway in post-mitotic c. elegans. Nature Communications, May 2023. URL: https://doi.org/10.1038/s41467-023-38568-5, doi:10.1038/s41467-023-38568-5. This article has 13 citations and is from a highest quality peer-reviewed journal.
(raj2023cisplatintoxicityis pages 13-13): Dorota Raj, Bashar Kraish, Jari Martikainen, Agnieszka Podraza-Farhanieh, Gautam Kao, and Peter Naredi. Cisplatin toxicity is counteracted by the activation of the p38/atf-7 signaling pathway in post-mitotic c. elegans. Nature Communications, May 2023. URL: https://doi.org/10.1038/s41467-023-38568-5, doi:10.1038/s41467-023-38568-5. This article has 13 citations and is from a highest quality peer-reviewed journal.
(raj2023cisplatintoxicityis pages 13-14): Dorota Raj, Bashar Kraish, Jari Martikainen, Agnieszka Podraza-Farhanieh, Gautam Kao, and Peter Naredi. Cisplatin toxicity is counteracted by the activation of the p38/atf-7 signaling pathway in post-mitotic c. elegans. Nature Communications, May 2023. URL: https://doi.org/10.1038/s41467-023-38568-5, doi:10.1038/s41467-023-38568-5. This article has 13 citations and is from a highest quality peer-reviewed journal.

Artifacts

Citations

venkatesh2021gproteincoupledreceptors pages 2-4
kim2018signalinginthe pages 14-16
taffoni2015mechanismsofinnate pages 5-6
kim2018signalinginthe pages 9-12
zhang2021antagonisticfungalenterotoxins pages 10-12
garciasanchez2021ubiquitinrelatedprocessesand pages 9-10
taffoni2015mechanismsofinnate pages 4-5
dierking2016antimicrobialeffectorsin pages 4-5
raj2023cisplatintoxicityis pages 10-13
raj2023cisplatintoxicityis pages 13-13
raj2023cisplatintoxicityis pages 13-14
https://doi.org/10.1371/journal.ppat.1009151,
https://doi.org/10.1080/21688370.2015.1078432,
https://doi.org/10.1007/s00018-021-03787-w,
https://doi.org/10.1895/wormbook.1.83.2,
https://doi.org/10.1371/journal.pgen.1009600,
https://doi.org/10.1098/rstb.2015.0299,
https://doi.org/10.3390/cells12182223,
https://doi.org/10.1038/s41467-023-38568-5,

📚 Additional Documentation

Notes

(dcar-1-notes.md)

DCAR-1 (C. elegans) — research notes

UniProt: G5EDI0 (G5EDI0_CAEEL) · WormBase: WBGene00007395 · sequence name C06H5.7 ·
Reactome: R-CEL-416476 "G alpha (q) signalling events" · 396 aa, 7-TM class A (rhodopsin-like)
GPCR (PROSITE PS50262 G_PROTEIN_RECEP_F1_2; PANTHER PTHR24243). Chromosome V.

DCAR-1 = "DihydroCaffeic Acid Receptor 1". Two distinct, experimentally established
functional contexts, in two tissues:

Epidermal innate immunity (flagship function; Zugasti et al. 2014, Nat Immunol,
PMID:25086774). DCAR-1 is a plasma-membrane GPCR on the apical surface of the hyp7
epidermal syncytium that senses the endogenous tyrosine-derived metabolite HPLA
(4-hydroxyphenyllactic acid, a damage-associated molecular pattern, DAMP) produced upon
fungal infection/wounding, and triggers antimicrobial-peptide (nlp-29 cluster) gene
expression via the GPA-12 (Gα) → TIR-1 → NSY-1/SEK-1/PMK-1 (p38 MAPK) → STA-2 cascade in
the epidermis. Required for resistance to the fungus Drechmeria coniospora.
Neuronal chemosensory avoidance (Aoki et al. 2011, J Neurosci, PMID:22090488).
DCAR-1 was originally identified in a Xenopus oocyte expression screen as a receptor
for the water-soluble repellent dihydrocaffeic acid (DHCA); expressed in the ASH (and
ASI, PVQ) sensory neurons, where it mediates avoidance of DHCA acting with ocr-2/osm-9.

KNOWN (well supported)

7-TM class A GPCR. UniProt/InterPro: 7 predicted TM helices, GPCR family 1 profile
domain (PS50262), CDD 7tm_classA_rhodopsin-like, PANTHER PTHR24243. FunFam name
"DihydroCaffeic Acid Receptor". Reactome links it to "G alpha (q) signalling events".
Innate immune receptor. PMID:25086774 Sole
hit from an RNAi screen of 1,150 GPCR genes for reduced nlp-29p::gfp AMP induction; two
null alleles (tm2484, nj66) confirm. dcar-1 mutants are markedly more susceptible to
D. coniospora while having normal development/longevity and normal resistance to
P. aeruginosa.
Acts via p38 MAPK / GPA-12 in epidermis. PMID:25086774 PMID:25086774. Methods list gpa-12(pk322), tir-1(tm3036), pmk-1(km25),
tpa-1(fr1) epistasis strains — this is the GPA-12→TIR-1→p38/PMK-1 cassette. Links to the
already-reviewed gpa-12 (Gα12/13 ortholog).
Endogenous ligand = HPLA (a DAMP). PMID:25086774. Identified by comparative
metabolomics: HPLA present at low level in controls, increased upon infection and in
cuticle-defective dpy-10 mutants. PMID:25086774. PMID:25086774
Exogenous ligand = DHCA. PMID:25086774.
Original identification: PMID:22090488
Localization. Apical plasma membrane in hyp7 epidermis:
PMID:25086774 (IDA, GO:0016324). Neuronal expression in ASH/ASI/PVQ (ciliated sensory
neurons); WormBase IDA GO:0097730 non-motile cilium from PMID:22090488 (abstract-only in
cache; the cilium sub-localization is not stated in the abstract but was curated by
WormBase from the full text — trust the curator).
Response to wounding. PMID:25086774 dcar-1 mutants show "an almost complete block of
nlp-29p::gfp induction following physical injury", i.e. activation is damage/wound-dependent
even without a pathogen (GO:0009611 response to wounding, IMP).
Cell-autonomous, tissue-separable. Epidermal (col-12p) but not neuronal (sra-6p)
expression rescues AMP induction/immunity; conversely neuronal expression rescues the
avoidance phenotype. PMID:25086774.
Phylogenetically nematode-restricted. PMID:25086774.

NOT known / open (for knowledge_gaps)

Structural basis of HPLA/DHCA sensing is unknown. No direct binding data, no structure,
and the ligand-binding pocket / residues are undefined. HPLA binding is inferred from
correlative genetics + metabolomics, not a direct receptor-binding assay:
PMID:25086774. Whether DCAR-1 is even the
direct HPLA receptor (vs an upstream sensor) is not biochemically proven.
Whether DCAR-1 has other (neuropeptide or microbial) ligands / roles is unknown. Its
natural neuronal ligand and whether it detects any microbe-associated molecular pattern are
undetermined: PMID:25086774 A speculated second role in pathogen-avoidance
behavior is unproven.
HPLA biosynthesis / how infection raises HPLA is uncharacterized. PMID:25086774; whether the fungus contributes to HPLA or it is purely host
damage-derived is an open question.
Nematode-restricted receptor with a conserved-metabolite ligand — whether an
HPLA/DAMP-sensing receptor exists outside nematodes is unknown: PMID:25086774

Annotation review plan (existing_annotations)

term	ev	ref	action	rationale
GO:0004930 G protein-coupled receptor activity	IEA	GO_REF:0000104	ACCEPT (core MF)	7-TM class A GPCR; receptor for HPLA/DHCA
GO:0007186 GPCR signaling pathway	IEA	GO_REF:0000104	ACCEPT (core BP)	signals via GPA-12 Gα
GO:0007165 signal transduction	IEA	GO_REF:0000104	KEEP_AS_NON_CORE	correct but generic parent of GPCR signaling
GO:0050832 defense response to fungus	IMP	PMID:25086774	ACCEPT (core BP)	required for anti-D. coniospora defense
GO:0009611 response to wounding	IMP	PMID:25086774	ACCEPT (core BP)	wound/damage-activated AMP induction
GO:0016324 apical plasma membrane	IDA	PMID:25086774	ACCEPT (core CC)	apical hyp7 surface
GO:0005886 plasma membrane	IBA	GO_REF:0000033	ACCEPT	correct (parent of apical PM)
GO:0016020 membrane	IEA	GO_REF:0000120	KEEP_AS_NON_CORE	generic; subsumed by apical PM
GO:0097730 non-motile cilium	IDA	PMID:22090488	KEEP_AS_NON_CORE	neuronal (ASH) chemosensory localization; abstract-only cache, defer to WB curator
GO:0008188 neuropeptide receptor activity	IBA	GO_REF:0000033	REMOVE	over-propagated family IBA; DCAR-1 ligands are small-molecule metabolites (HPLA/DHCA), not neuropeptides
GO:0007218 neuropeptide signaling pathway	IBA	GO_REF:0000033	REMOVE	same; not a neuropeptide receptor

Proposed new term candidate: a specific MF for "dihydroxyphenyl/hydroxyphenyllactic acid
(DAMP) receptor activity" — currently only GO:0004930 available. Note as ontology gap.

Deep research provenance

The just deep-research-falcon recipe reported a 600s timeout on both the initial run and
the retry (and the perplexity-lite fallback returned HTTP 401, quota exhausted). However the
underlying Edison/falcon client kept running and, on the retry, DID write a genuine report
(dcar-1-deep-research-falcon.md, ~1005s runtime, 19 citations, 2 artifacts) after the
recipe's wrapper had already exited. That file was inspected and is authentic Edison output:
it correctly identifies DCAR-1, HPLA as the DAMP ligand, apical hyp7 epidermal localization,
and the full GPA-12 -> PLC/DAG -> TPA-1(PKC) -> TIR-1 -> NSY-1/SEK-1/PMK-1(p38) -> STA-2/ELT-3
-> nlp-29 pathway, plus the neuronal DHCA-avoidance origin. It is included in the commit and
referenced. No -deep-research-*.md file was fabricated.

All annotation/core-function supporting_text quotes are PMID-anchored (verified as verbatim
whitespace-normalized substrings of PMID:25086774 full text and PMID:22090488 abstract). The
single file: deep-research quote used was grep-verified against the falcon report (the
reference validator skips file: prefixes).

📄 View Raw YAML

id: G5EDI0
gene_symbol: dcar-1
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:6239
  label: Caenorhabditis elegans
description: >-
  DCAR-1 (DihydroCaffeic Acid Receptor 1) is a seven-transmembrane, class A
  (rhodopsin-like) G protein-coupled receptor of Caenorhabditis elegans that acts
  in two distinct tissues. In the epidermis it is a plasma-membrane receptor,
  localized to the apical surface of the hyp7 syncytium, that senses the
  endogenous tyrosine-derived metabolite 4-hydroxyphenyllactic acid (HPLA), a
  damage-associated molecular pattern produced upon fungal infection and
  wounding, and triggers antimicrobial peptide (nlp-29 cluster) gene expression
  through a Galpha (GPA-12) / p38 MAP kinase (TIR-1, NSY-1, SEK-1, PMK-1) /
  STA-2 signalling cassette, conferring resistance to the natural fungal pathogen
  Drechmeria coniospora. In sensory neurons (ASH, ASI, PVQ) the same receptor
  detects the exogenous water-soluble repellent dihydrocaffeic acid (DHCA) and
  mediates an avoidance response, acting with the TRPV channel subunits OCR-2 and
  OSM-9. DCAR-1 thus couples small-molecule (catecholic/phenolic acid) ligand
  detection to Galpha signalling, with clearly recognizable homologs restricted to
  nematode genomes.
existing_annotations:
  - term:
      id: GO:0004930
      label: G protein-coupled receptor activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000104
    qualifier: enables
    review:
      summary: >-
        DCAR-1 is a bona fide seven-transmembrane class A GPCR (7 predicted TM
        helices; PROSITE G_PROTEIN_RECEP_F1_2; PANTHER PTHR24243) that functions
        as a receptor for small-molecule ligands: HPLA in the epidermis and DHCA
        in sensory neurons, in both cases coupling to Galpha signalling.
      action: ACCEPT
      reason: >-
        The GPCR activity is directly supported experimentally. DCAR-1 was
        identified as a heterologously expressible receptor for DHCA and shown to
        respond to HPLA, and it signals via the Galpha protein GPA-12. This is a
        core molecular function of the gene.
      supported_by:
        - reference_id: PMID:22090488
          supporting_text: >-
            we identified a candidate dihydrocaffeic acid receptor (DCAR),
            DCAR-1. DCAR-1 is a novel seven-transmembrane protein that is
            expressed in the ASH avoidance sensory neurons of C. elegans.
        - reference_id: PMID:25086774
          supporting_text: >-
            Dihydrocaffeic acid (DHCA) has been described as a potent ligand for
            DCAR-1 in both in vivo and in heterologous Xenopus oocyte assays
  - term:
      id: GO:0007186
      label: G protein-coupled receptor signaling pathway
    evidence_type: IEA
    original_reference_id: GO_REF:0000104
    qualifier: involved_in
    review:
      summary: >-
        DCAR-1 initiates GPCR signalling: in the epidermis it acts upstream of
        (or in parallel to) the Galpha protein GPA-12 to control downstream p38
        MAPK (PMK-1) signalling.
      action: ACCEPT
      reason: >-
        Core biological process. Genetic epistasis places DCAR-1 at the top of a
        Galpha (GPA-12) -> p38 MAPK cascade, consistent with canonical GPCR
        signalling.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: dcar-1 alone acts upstream or in parallel to GPA-12
  - term:
      id: GO:0007165
      label: signal transduction
    evidence_type: IEA
    original_reference_id: GO_REF:0000104
    qualifier: involved_in
    review:
      summary: >-
        Correct but generic. Signal transduction is a high-level parent of the
        more specific G protein-coupled receptor signaling pathway (GO:0007186)
        that is also annotated and better captures DCAR-1's activity.
      action: KEEP_AS_NON_CORE
      reason: >-
        The term is not wrong - DCAR-1 does transduce signals - but it is
        subsumed by the more informative GPCR signaling pathway annotation, so it
        is retained as non-core rather than treated as a distinct core function.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: multiple elements of the downstream signal transduction cascade
  - term:
      id: GO:0050832
      label: defense response to fungus
    evidence_type: IMP
    original_reference_id: PMID:25086774
    qualifier: involved_in
    review:
      summary: >-
        Loss of dcar-1 (RNAi and two null alleles, tm2484 and nj66) abolishes
        infection-induced antimicrobial peptide expression and markedly increases
        susceptibility to the fungus Drechmeria coniospora; DCAR-1 was the sole
        GPCR hit from a screen of 1,150 GPCR genes.
      action: ACCEPT
      reason: >-
        Strong IMP evidence for a core function. DCAR-1 is required in the
        epidermis for the innate immune response to fungal infection.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            dcar-1 emerged alone as an innate immune receptor gene acting
            upstream of (or in parallel to) gpa-12
        - reference_id: PMID:25086774
          supporting_text: >-
            dcar-1 mutants exhibited a markedly heightened susceptibility to D.
            coniospora infection
  - term:
      id: GO:0009611
      label: response to wounding
    evidence_type: IMP
    original_reference_id: PMID:25086774
    qualifier: involved_in
    review:
      summary: >-
        dcar-1 mutants show an almost complete block of antimicrobial peptide
        (nlp-29p::gfp) induction after sterile physical injury, showing that
        DCAR-1 mediates the response to wounding/damage independently of a
        pathogen - consistent with detection of an endogenous damage signal
        (HPLA/DAMP).
      action: ACCEPT
      reason: >-
        Well-supported IMP for a core damage-sensing function; wounding and
        infection converge on the same DCAR-1-dependent, HPLA-driven pathway.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            an almost complete block of nlp-29p::gfp induction following physical
            injury
        - reference_id: PMID:25086774
          supporting_text: demonstrating that dcar-1 can be activated in the absence of a pathogen
  - term:
      id: GO:0016324
      label: apical plasma membrane
    evidence_type: IDA
    original_reference_id: PMID:25086774
    qualifier: located_in
    review:
      summary: >-
        A rescuing dcar-1p::dcar-1::gfp translational reporter localized DCAR-1
        to the apical surface of the major epidermal syncytium hyp7, the site
        where it acts to drive antimicrobial peptide expression.
      action: ACCEPT
      reason: >-
        Direct IDA localization to the apical plasma membrane; a core cellular
        location for the receptor's immune function.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            dcar-1 was expressed on the apical surface in the major epidermal
            syncytium, hyp7
  - term:
      id: GO:0005886
      label: plasma membrane
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: is_active_in
    review:
      summary: >-
        Plasma membrane localization inferred from phylogeny is consistent with
        DCAR-1 being a cell-surface 7-TM GPCR and with the direct (IDA) apical
        plasma membrane localization in the epidermis.
      action: ACCEPT
      reason: >-
        Correct and corroborated by experimental data; a parent of the more
        specific apical plasma membrane annotation.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            dcar-1 was expressed on the apical surface in the major epidermal
            syncytium, hyp7
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: IEA
    original_reference_id: GO_REF:0000120
    qualifier: located_in
    review:
      summary: >-
        Generic membrane localization from InterPro/UniProt subcellular-location
        pipelines; correct for a multi-pass membrane protein but uninformative
        relative to the plasma membrane / apical plasma membrane annotations.
      action: KEEP_AS_NON_CORE
      reason: >-
        Not wrong, but subsumed by the more specific and experimentally supported
        plasma membrane and apical plasma membrane terms.
  - term:
      id: GO:0097730
      label: non-motile cilium
    evidence_type: IDA
    original_reference_id: PMID:22090488
    qualifier: located_in
    review:
      summary: >-
        WormBase IDA localization associated with DCAR-1's expression in the
        ciliated ASH (and ASI, PVQ) sensory neurons, where it detects the
        repellent DHCA. This reflects the neuronal chemosensory role, distinct
        from the epidermal immune role.
      action: KEEP_AS_NON_CORE
      reason: >-
        The cached copy of PMID:22090488 is abstract-only, so the specific cilium
        sub-localization cannot be re-verified from the cached text; per curation
        policy the WormBase curator's experimental (IDA) call is trusted and not
        overruled. It is retained as a non-core location because it belongs to the
        neuronal chemosensory context rather than the flagship epidermal immune
        function.
      supported_by:
        - reference_id: PMID:22090488
          supporting_text: expressed in the ASH avoidance sensory neurons of C. elegans
  - term:
      id: GO:0008188
      label: neuropeptide receptor activity
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: enables
    review:
      summary: >-
        This activity was propagated by phylogenetic (IBA) inference from the
        broad class A GPCR family (PTHR24243), some of whose members are
        neuropeptide receptors. However, the two experimentally characterized
        ligands of DCAR-1 are small-molecule catecholic/phenolic acids - HPLA
        (a tyrosine-derived metabolite/DAMP) in the epidermis and DHCA in
        neurons - not neuropeptides.
      action: REMOVE
      reason: >-
        Over-propagated family-level IBA that is contradicted by the direct
        experimental characterization of DCAR-1's ligands. DCAR-1 is not a
        neuropeptide receptor; its molecular function is adequately and correctly
        captured by G protein-coupled receptor activity (GO:0004930). Removing
        this avoids an unsupported and misleading molecular-function assertion.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an
            endogenous ligand
        - reference_id: PMID:25086774
          supporting_text: >-
            Dihydrocaffeic acid (DHCA) has been described as a potent ligand for
            DCAR-1 in both in vivo and in heterologous Xenopus oocyte assays
      propagation_review:
        root_cause: PROPAGATION_BAD
        failure_modes:
          - WRONG_ORTHOLOG_OR_PARALOG
          - FUNCTIONAL_DIVERGENCE
        source_entities:
          - source_id: PANTHER:PTN002797693
            source_label: PTHR24243 class A GPCR IBA seed node
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              Neuropeptide-receptor activity is valid for genuine peptide-receptor
              members of this large class A GPCR family, but DCAR-1's characterized
              ligands are small-molecule metabolites (HPLA, DHCA), not neuropeptides.
          - source_id: WB:WBGene00019616
            source_label: C. elegans family member in the IBA with/from set
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              Co-annotated family member; it does not establish a neuropeptide ligand
              for DCAR-1.
  - term:
      id: GO:0007218
      label: neuropeptide signaling pathway
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: involved_in
    review:
      summary: >-
        Companion IBA propagation to the neuropeptide receptor activity call,
        inferred from the GPCR family rather than from DCAR-1's own biology.
        DCAR-1 signalling is driven by small-molecule ligands (HPLA, DHCA), not
        by neuropeptides.
      action: REMOVE
      reason: >-
        Over-propagated family-level IBA not supported by any evidence specific
        to DCAR-1 and contradicted by its characterized small-molecule ligands.
        The gene's signalling role is correctly captured by G protein-coupled
        receptor signaling pathway (GO:0007186) and the defense/wounding process
        terms.
      supported_by:
        - reference_id: PMID:25086774
          supporting_text: >-
            HPLA can act through DCAR-1 to regulate the epidermal innate immune
            response
      propagation_review:
        root_cause: PROPAGATION_BAD
        failure_modes:
          - WRONG_ORTHOLOG_OR_PARALOG
          - FUNCTIONAL_DIVERGENCE
        source_entities:
          - source_id: PANTHER:PTN002797693
            source_label: PTHR24243 class A GPCR IBA seed node
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              Neuropeptide signalling is valid for genuine peptide-receptor members
              of this family, but DCAR-1 signals in response to small-molecule
              metabolites (HPLA, DHCA), not neuropeptides.
          - source_id: WB:WBGene00019616
            source_label: C. elegans family member in the IBA with/from set
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              Co-annotated family member; it does not establish neuropeptide
              signalling for DCAR-1.
  - term:
      id: GO:0007635
      label: chemosensory behavior
    evidence_type: IMP
    original_reference_id: PMID:22090488
    qualifier: involved_in
    review:
      summary: >-
        In ASH sensory neurons DCAR-1 is required for avoidance of the water-
        soluble repellent dihydrocaffeic acid (DHCA): dcar-1 null mutants are
        defective in DHCA avoidance and ASH-specific expression rescues the
        defect (Aoki et al. 2011), a role corroborated in Zugasti et al. 2014.
      action: NEW
      reason: >-
        Not present in GOA, but the neuronal chemosensory (repellent-avoidance)
        function is directly established by IMP evidence and is genetically
        separable from the epidermal immune role. Added so that the receptor's
        second, well-supported evolved function is captured in the structured
        annotations (mirrors the neuronal core_function).
      supported_by:
        - reference_id: PMID:22090488
          supporting_text: >-
            dcar-1 mutant animals are defective in avoidance response to DHCA, and
            cell-specific expression of dcar-1 in the ASH neurons
        - reference_id: PMID:25086774
          supporting_text: >-
            In neurons, dcar-1 mediates an avoidance response to specific
            repellents, acting in concert with ocr-2 and osm-9
core_functions:
  - description: >-
      DCAR-1 acts as an epidermal innate-immune GPCR: it is a plasma-membrane
      (apical hyp7) receptor that detects the endogenous damage-associated
      metabolite HPLA (and, exogenously, DHCA) generated upon fungal infection or
      wounding, and transduces this via Galpha (GPA-12) and the p38 MAPK cascade
      to induce antimicrobial peptide genes and confer resistance to Drechmeria
      coniospora.
    molecular_function:
      id: GO:0004930
      label: G protein-coupled receptor activity
    directly_involved_in:
      - id: GO:0050832
        label: defense response to fungus
      - id: GO:0009611
        label: response to wounding
      - id: GO:0007186
        label: G protein-coupled receptor signaling pathway
    locations:
      - id: GO:0016324
        label: apical plasma membrane
      - id: GO:0005886
        label: plasma membrane
    supported_by:
      - reference_id: PMID:25086774
        supporting_text: >-
          DCAR-1 acted in the epidermis to regulate the expression of
          antimicrobial peptides via a conserved p38 mitogen-activated protein
          kinase pathway.
      - reference_id: PMID:25086774
        supporting_text: >-
          Our findings reveal DCAR-1 and its cognate ligand HPLA to be triggers
          of the epidermal innate immune response
      - reference_id: PMID:25086774
        supporting_text: >-
          dcar-1 was expressed on the apical surface in the major epidermal
          syncytium, hyp7
      - reference_id: file:worm/dcar-1/dcar-1-deep-research-falcon.md
        supporting_text: >-
          DAMP-sensing GPCR that activates epidermal innate immunity in response
          to fungal infection and wounding
  - description: >-
      In ciliated ASH (and ASI, PVQ) sensory neurons DCAR-1 acts as a
      chemoreceptor for the exogenous water-soluble repellent dihydrocaffeic acid
      (DHCA), driving an avoidance response together with the TRPV channel
      subunits OCR-2 and OSM-9. This neuronal chemosensory role is genetically and
      functionally separable from the epidermal immune role (neuronal expression
      rescues avoidance but not antimicrobial peptide induction).
    molecular_function:
      id: GO:0004930
      label: G protein-coupled receptor activity
    directly_involved_in:
      - id: GO:0007635
        label: chemosensory behavior
      - id: GO:0007186
        label: G protein-coupled receptor signaling pathway
    locations:
      - id: GO:0005886
        label: plasma membrane
    supported_by:
      - reference_id: PMID:22090488
        supporting_text: >-
          DCAR-1 as the first seven-transmembrane receptor required for avoidance
          of a water-soluble repellent, DHCA, in C. elegans
      - reference_id: PMID:25086774
        supporting_text: >-
          In neurons, dcar-1 mediates an avoidance response to specific
          repellents, acting in concert with ocr-2 and osm-9
proposed_new_terms:
  - proposed_name: 4-hydroxyphenyllactate (HPLA) receptor activity
    proposed_definition: >-
      Combining with the tyrosine-derived metabolite 4-hydroxyphenyllactic acid
      (HPLA), a damage-associated molecular pattern, to initiate a change in cell
      activity, typically via coupling to a heterotrimeric G protein. Applies to
      GPCRs, such as nematode DCAR-1, that detect HPLA (and structurally related
      catecholic/phenolic acids) to trigger downstream signalling.
    justification: >-
      DCAR-1's specific molecular function - detection of the small-molecule DAMP
      HPLA - can currently only be annotated with the generic parent
      G protein-coupled receptor activity (GO:0004930). No ontology term expresses
      the ligand-specific activity, leaving the receptor's most distinctive
      feature un-annotatable (an ontology gap).
    proposed_parent:
      id: GO:0004930
      label: G protein-coupled receptor activity
    supported_by:
      - reference_id: PMID:25086774
        supporting_text: >-
          the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an
          endogenous ligand
knowledge_gaps:
  - gap_statement: >-
      The structural and biochemical basis of ligand recognition by DCAR-1 is
      unknown: there is no direct binding assay, no structure, and no defined
      ligand-binding pocket or residues. Whether DCAR-1 is the direct receptor for
      HPLA (versus an upstream/indirect sensor) has not been demonstrated
      biochemically.
    boundary: >-
      It is firmly established that DCAR-1 is a 7-TM class A GPCR required in the
      epidermis for HPLA/DHCA-triggered antimicrobial peptide induction and
      anti-fungal defense, and that it can respond to DHCA in a heterologous
      Xenopus oocyte system. The evidence that HPLA is the endogenous ligand is
      genetic and metabolomic (correlative), not a direct receptor-binding
      measurement.
    gap_kind:
      - BIOLOGY
    dark_aspect: RESIDUAL_SUBGAP
    status: OPEN
    significance: >-
      HPLA is the first described damage-associated molecular pattern (DAMP) in
      C. elegans; defining how DCAR-1 binds it would establish the molecular logic
      of DAMP sensing by a metazoan GPCR and enable rational tests of whether
      analogous receptors exist beyond nematodes.
    resolution: >-
      Direct ligand-binding/activation assays (e.g. purified receptor or
      cell-based GPCR activation with HPLA titration), mutagenesis of predicted
      binding-pocket residues, and structural determination of the DCAR-1-HPLA
      complex.
    provenance:
      - reference_id: PMID:25086774
        supporting_text: >-
          We provide strong correlative evidence that HPLA is an endogenous
          ligand for DCAR-1. Proving this definitively is not straightforward
  - gap_statement: >-
      It is unknown whether DCAR-1 has ligands or roles beyond HPLA/DHCA -
      including its natural neuronal ligand, whether it recognizes any
      microbe-associated molecular pattern, and whether it contributes to
      pathogen-avoidance behaviour as a second host-defense role.
    boundary: >-
      DCAR-1 is known to detect the endogenous metabolite HPLA (epidermal
      immunity) and the exogenous repellent DHCA (neuronal avoidance via ASH/ASI/
      PVQ with OCR-2/OSM-9). Beyond these, its ligand spectrum and the physiological
      relevance of its neuronal signalling to host defense are not established.
    gap_kind:
      - BIOLOGY
    dark_aspect: MF_DARK
    status: OPEN
    significance: >-
      GPCRs are proposed to be an under-explored class of immunomodulatory
      receptors; clarifying whether DCAR-1 senses microbial patterns or only host
      damage signals would sharpen models of how nematodes discriminate infection
      from sterile injury.
    resolution: >-
      Systematic ligand/deorphanization screens, tests for direct microbe-derived
      agonists, and behavioural/immune assays separating DCAR-1's neuronal and
      epidermal contributions to defense.
    provenance:
      - reference_id: PMID:25086774
        supporting_text: >-
          It is not known whether any GPCR recognizes specific
          microbe-associated molecular patterns.
  - gap_statement: >-
      The biosynthetic origin of the DAMP ligand HPLA, and the mechanism by which
      infection and cuticle damage raise its levels, are uncharacterized -
      including whether the invading fungus contributes to HPLA production or the
      increase is entirely host-derived.
    boundary: >-
      HPLA is a tyrosine-derived metabolite that increases upon infection and in
      cuticle-defective dpy-10 mutants, and epidermal overexpression of the
      candidate aminotransferase tatn-1 raises dcar-1-dependent antimicrobial
      peptide expression. The enzymes and regulatory logic of HPLA production
      remain undefined and were only partially probed (candidate aminotransferase
      knockdowns were inconclusive, likely due to redundancy).
    gap_kind:
      - BIOLOGY
    dark_aspect: BP_DARK
    status: OPEN
    significance: >-
      Understanding how HPLA is generated would reveal how damage and infection
      are converted into a diffusible immune-activating signal, and whether the
      pathway is a host stress response or a pathogen-influenced process.
    resolution: >-
      Genetic and biochemical dissection of tyrosine catabolism/HPLA synthesis in
      the epidermis, isotope-tracing of HPLA under infection, and host-versus-
      pathogen source discrimination.
    provenance:
      - reference_id: PMID:25086774
        supporting_text: >-
          Although its biosynthetic pathway has not been characterized in any
          eukaryote, HPLA is likely derived from tyrosine
suggested_questions:
  - question: >-
      Does DCAR-1 bind HPLA directly, and which extracellular/transmembrane
      residues form the ligand-binding pocket?
    experts:
      - Jonathan J Ewbank
      - Nathalie Pujol
  - question: >-
      Do HPLA-sensing receptors functionally analogous to DCAR-1 exist outside
      the nematode phylum, given that HPLA is a conserved tyrosine metabolite?
    experts:
      - Jonathan J Ewbank
suggested_experiments:
  - hypothesis: >-
      DCAR-1 is the direct receptor for HPLA and couples to GPA-12.
    description: >-
      Express DCAR-1 in a heterologous GPCR-activation system (as previously done
      with DHCA in Xenopus oocytes) and measure dose-dependent activation by HPLA
      and structurally related phenolic acids; test coupling specificity against
      GPA-12 versus other Galpha subunits.
    experiment_type: heterologous receptor activation / ligand-response assay
  - hypothesis: >-
      HPLA is generated in the epidermis by a defined tyrosine-catabolic route
      whose flux increases with damage.
    description: >-
      Use targeted metabolomics with isotope-labelled tyrosine to trace HPLA
      production before and after infection/wounding, combined with epidermis-
      specific RNAi/overexpression of candidate aminotransferases and reductases
      (e.g. tatn-1) to identify the biosynthetic enzymes.
    experiment_type: stable-isotope metabolomics + tissue-specific genetics
references:
  - id: GO_REF:0000033
    title: Annotation inferences using phylogenetic trees
    findings: []
  - id: GO_REF:0000104
    title: >-
      Electronic Gene Ontology annotations created by transferring manual GO
      annotations between related proteins based on shared sequence features
    findings: []
  - id: GO_REF:0000120
    title: Combined Automated Annotation using Multiple IEA Methods
    findings: []
  - id: PMID:22090488
    title: >-
      A seven-transmembrane receptor that mediates avoidance response to
      dihydrocaffeic acid, a water-soluble repellent in Caenorhabditis elegans.
    findings:
      - statement: >-
          DCAR-1 is a novel seven-transmembrane receptor for the water-soluble
          repellent dihydrocaffeic acid (DHCA), expressed in the ASH avoidance
          sensory neurons; dcar-1 mutants are defective in DHCA avoidance and
          ASH-specific expression rescues the defect.
        supporting_text: >-
          we identified a candidate dihydrocaffeic acid receptor (DCAR), DCAR-1.
          DCAR-1 is a novel seven-transmembrane protein that is expressed in the
          ASH avoidance sensory neurons of C. elegans.
        reference_section_type: ABSTRACT
        full_text_unavailable: true
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        PubMed-verified (Aoki et al., J Neurosci 2011). Original identification of
        DCAR-1 as a 7-TM receptor for the repellent DHCA expressed in ASH sensory
        neurons; establishes the neuronal chemosensory role and the receptor's
        small-molecule ligand. Cached copy is abstract-only (full text
        unavailable), so the non-motile cilium localization it supports cannot be
        re-verified from the cache and is deferred to the WormBase curator.
  - id: PMID:25086774
    title: >-
      Activation of a G protein-coupled receptor by its endogenous ligand triggers
      the innate immune response of Caenorhabditis elegans.
    findings:
      - statement: >-
          DCAR-1 was the sole hit from an RNAi screen of 1,150 GPCR genes required
          for infection- and wounding-induced antimicrobial peptide expression,
          acting upstream of (or in parallel to) the Galpha protein GPA-12 in the
          epidermal p38 MAPK pathway.
        supporting_text: >-
          dcar-1 emerged alone as an innate immune receptor gene acting upstream
          of (or in parallel to) gpa-12
        reference_section_type: RESULTS
      - statement: >-
          The tyrosine-derived metabolite HPLA is an endogenous damage-associated
          ligand for DCAR-1 that increases upon infection and cuticle damage and
          drives DCAR-1-dependent antimicrobial peptide expression in the epidermis.
        supporting_text: >-
          the tyrosine derivative 4-hydroxyphenyllactic acid (HPLA) as an
          endogenous ligand
        reference_section_type: ABSTRACT
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        PubMed-verified (Zugasti et al., Nat Immunol 2014); full text available in
        cache. Flagship paper establishing DCAR-1 as the epidermal innate-immune
        GPCR, identifying HPLA as its endogenous DAMP ligand, the apical hyp7
        localization, and the GPA-12/p38-MAPK signalling context. Directly
        supports the defense-response, wounding, GPCR-signalling and apical
        plasma membrane annotations.
  - id: file:worm/dcar-1/dcar-1-deep-research-falcon.md
    title: Deep research report (Edison/falcon) for C. elegans dcar-1
    findings: []
    reference_review:
      relevance: MEDIUM
      correctness: VERIFIED
      review_notes: >-
        Automated Edison/falcon deep-research report (19 citations). Content was
        inspected and corroborates the primary literature: DCAR-1 as an apical
        epidermal HPLA/DAMP-sensing GPCR driving the GPA-12 -> PLC/DAG -> TPA-1 ->
        TIR-1 -> p38/PMK-1 -> STA-2 antimicrobial-peptide pathway, and the
        neuronal DHCA-avoidance origin. Used only for corroboration; all primary
        evidence in this review is PMID-anchored, and the single file quote used
        was grep-verified (the reference validator skips file: prefixes).

dcar-1

Gene Description

Proposed New Ontology Terms

4-hydroxyphenyllactate (HPLA) receptor activity

Existing Annotations Review

Core Functions

References

Suggested Questions for Experts

Suggested Experiments

Knowledge Gaps

Deep Research

Falcon

Comprehensive Research Report: DCAR-1 (C06H5.7) in Caenorhabditis elegans

1. Gene and Protein Identity

2. Primary Function: DAMP-Sensing Receptor for Epidermal Innate Immunity

2.1 Endogenous Ligand: 4-Hydroxyphenyllactic Acid (HPLA)

2.2 Biological Roles

3. Tissue and Subcellular Localization

4. Signaling Pathway

4.1 Detailed Pathway Description

4.2 Relationship to Broader Immune Signaling

5. Recent Developments (2023–2025)

5.1 DCAR-1-Independent Damage Sensing via Hemidesmosomes

5.2 DCAR-1 Pathway and Cisplatin Resistance

5.3 Pathogen Virulence Strategies Targeting the DCAR-1 Pathway

6. Evolutionary and Comparative Significance

7. Summary

Artifacts

Citations

📚 Additional Documentation

Notes

DCAR-1 (C. elegans) — research notes

KNOWN (well supported)

NOT known / open (for knowledge_gaps)

Annotation review plan (existing_annotations)

Deep research provenance

📄 View Raw YAML