ERS1 (ETHYLENE RESPONSE SENSOR 1, At2g40940) is one of the five Arabidopsis ethylene receptors and, with ETR1, makes up receptor subfamily 1. It is a multi-pass endoplasmic reticulum membrane protein with an N-terminal three-helix ethylene-binding sensor domain (copper-dependent by analogy with ETR1), a GAF domain and a histidine-kinase-like domain, but it lacks the C-terminal receiver domain found in ETR1. ERS1 forms disulfide-linked homodimers and heteromeric receptor complexes at the ER and binds ethylene with an affinity similar to ETR1. In the absence of ethylene the receptors keep the Raf-like kinase CTR1 active and thereby repress the pathway; ethylene binding inactivates this output, allowing EIN2-dependent signalling. ERS1 acts redundantly with ETR1 as a negative regulator of ethylene responses (etr1 ers1 double null mutants show a strong constitutive ethylene response), although genetic studies indicate it can also promote ethylene responses in some receptor-mutant backgrounds. ERS1 is transcriptionally induced by ethylene, providing negative feedback on signalling. In vitro it autophosphorylates on serine and, only with Mn2+, on histidine.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000155 phosphorelay sensor kinase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: InterPro-based transfer from the histidine-kinase dimerization/phosphoacceptor domain. ERS1 lacks a receiver domain and its histidine autophosphorylation is lost under physiological Mg2+/Mn2+ conditions; ethylene signalling does not appear to proceed through a phosphorelay. Reason: The domain-based inference describes the ancestral fold, not a demonstrated phosphorelay sensor function for ERS1. The autophosphorylation study concluded that ethylene signal transduction does not occur through a phosphorelay mechanism. Supporting Evidence: PMID:15358768 histidine autophosphorylation is lost when ERS1 is assayed in the presence of both Mg2+ and Mn2+, suggesting that this activity may not occur in vivo |
| GO:0000160 phosphorelay signal transduction system | IEA GO_REF:0000108 | MARK AS OVER ANNOTATED | Summary: Inferred logically from the phosphorelay sensor kinase IEA. There is no evidence that ERS1 output proceeds via His-Asp phosphotransfer; receptor output is mediated through CTR1. Reason: Derived from an over-annotated domain-based MF. Biochemical data argue against a phosphorelay mechanism for the ERS1 signal. Supporting Evidence: PMID:15358768 suggest that ethylene signal transduction does not occur through a phosphorelay mechanism |
| GO:0004673 protein histidine kinase activity | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: ERS1 retains the conserved histidine-kinase motifs of subfamily 1 and can autophosphorylate on histidine in vitro in the presence of Mn2+, but this activity is lost when Mg2+ is present and is not required for receptor output. Reason: The activity is biochemically demonstrable in vitro but is unlikely to be the physiological signalling output; it should not be treated as core. Supporting Evidence: PMID:15358768 ERS1, the only other subfamily 1 receptor, is able to phosphorylate on both histidine and serine residues in the presence of Mn2+ |
| GO:0004673 protein histidine kinase activity | TAS PMID:15703053 Ethylene-binding activity, gene expression levels, and recep... | KEEP AS NON CORE | Summary: Traceable author statement from a paper on ethylene binding and receptor output across the family. The paper itself measures ethylene binding, not kinase activity; direct biochemistry (PMID:15358768) shows Mn2+-dependent histidine autophosphorylation that may not occur in vivo. Reason: Consistent with the in vitro biochemistry, but the activity is not the core signalling mechanism of ERS1. Supporting Evidence: PMID:15358768 ERS1, the only other subfamily 1 receptor, is able to phosphorylate on both histidine and serine residues in the presence of Mn2+ |
| GO:0005515 protein binding | IPI PMID:19567478 AtTRP1 encodes a novel TPR protein that interacts with the e... | REMOVE | Summary: ERS1 interacts with the TPR protein AtTRP1 (TRP1, At5g59430) in yeast two-hybrid and co-immunoprecipitation assays. The interaction is real but "protein binding" conveys nothing about ERS1 function, and the role of AtTRP1 in receptor signalling is not resolved. Reason: Uninformative protein binding term and no more specific MF term describes an interaction of unknown functional consequence. Removal does not mean the interaction is false; it is recorded in the references section. Supporting Evidence: PMID:19567478 AtTRP1 interacts preferentially with the Arabidopsis ethylene receptor ERS1 in the yeast two-hybrid system. |
| GO:0005515 protein binding | IPI PMID:9560288 Association of the Arabidopsis CTR1 Raf-like kinase with the... | MODIFY | Summary: The CTR1 N-terminal domain interacts with the histidine-kinase domain of ETR1 and ERS in yeast two-hybrid and in vitro assays. This physical receptor-CTR1 association is the basis of receptor output, but it is better described by the receptor activity term than by protein binding. Later co-purification found only weak ERS1-CTR1 association. Reason: Replace uninformative protein binding with the informative signalling MF; the receptor-CTR1 association is how ERS1 transmits the ethylene receptor signal. GO:0038199 is already carried by ERS1 on a separate ACCEPTed row (IBA), so this MODIFY is a merge into that existing annotation, not a request to mint a new one. Proposed replacements: ethylene receptor activity Supporting Evidence: PMID:9560288 we detected a specific interaction between the CTR1 amino-terminal domain and the predicted histidine kinase domain of ETR1 and ERS PMID:25814663 we did not observe co-purification of ERS1 or ERS2 with CTR1 in our pull-down analysis |
| GO:0005634 nucleus | ISM GO_REF:0000122 | REMOVE | Summary: AtSubP sequence-based prediction of nuclear localization. ERS1 is a multi-pass ER membrane protein; all five ethylene receptors localize to the ER and not to the nucleus. Reason: Contradicted by direct localization of the receptor family to the ER and by the polytopic membrane topology of ERS1. Supporting Evidence: PMID:19825542 all ethylene receptors are targeted to the ER endomembrane network and do not localize to the plasmalemma |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference for the plant ethylene receptor clade, seeded in part by ERS1's own experimental ER localization. Consistent with direct evidence. Reason: The receptor family is ER-localized; ERS1 is inside the clade. Supporting Evidence: PMID:19825542 all ethylene receptors are targeted to the ER endomembrane network and do not localize to the plasmalemma |
| GO:0005783 endoplasmic reticulum | IDA PMID:19825542 Subcellular localization and in vivo interactions of the Ara... | ACCEPT | Summary: Fluorescent-protein-tagged ERS1, like the other receptors, localizes to the ER network in transient expression. Reason: Direct localization evidence for the site of ethylene perception. Supporting Evidence: PMID:19825542 the ethylene receptors form homomeric and heteromeric protein complexes at the ER in living plant cells |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA prediction consistent with the experimental ER localization. Reason: Matches IDA evidence. |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping. ERS1 is a membrane-associated, multi-pass protein localized to the ER; ER membrane is the most precise location. Reason: Consistent with membrane fractionation and ER localization data. Supporting Evidence: PMID:10938361 ERS1, like ETR1, forms a membrane-associated, disulfide-linked dimer. |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Correct but very general; ethylene-activated signaling pathway is the appropriate specific process. Reason: Uninformative parent of the ethylene-specific process annotations. |
| GO:0009873 ethylene-activated signaling pathway | IEA GO_REF:0000108 | ACCEPT | Summary: Logically inferred from ethylene receptor activity. ERS1 is a bona fide ethylene receptor acting upstream of CTR1 in the pathway. Reason: Receptor activity places ERS1 within the ethylene-activated pathway. Supporting Evidence: PMID:7569898 Double-mutant analysis indicates that ERS acts upstream of the CTR1 protein kinase gene in the ethylene-response pathway. |
| GO:0010105 negative regulation of ethylene-activated signaling pathway | IEA GO_REF:0000117 | ACCEPT | Summary: ERS1 acts redundantly with ETR1 as a negative regulator of ethylene signalling; etr1 ers1 null double mutants show a strong constitutive ethylene response. Reason: Supported by loss-of-function genetics. Supporting Evidence: PMID:17224067 Our results are consistent with the ethylene receptors acting as redundant negative regulators of ethylene signaling, but with subfamily 1 receptors playing the predominant role. |
| GO:0010105 negative regulation of ethylene-activated signaling pathway | TAS PMID:7569898 Ethylene insensitivity conferred by Arabidopsis ERS gene. | ACCEPT | Summary: The original ERS paper showed that an etr1-4-equivalent mutation in ERS confers dominant ethylene insensitivity and that ERS acts upstream of CTR1. Subsequent loss-of-function studies confirmed the negative regulatory role. Reason: Core biological role of the receptor, confirmed by later null alleles. Supporting Evidence: PMID:7569898 The altered ERS gene conferred dominant ethylene insensitivity to wild-type Arabidopsis. PMID:17224067 Double mutants of ers1-3 with etr1-9, as well as with the previously isolated etr1-7, display a constitutive ethylene-response phenotype |
| GO:0016772 transferase activity, transferring phosphorus-containing groups | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Very general parent of protein kinase activity, inferred from the histidine-kinase-like domain. Reason: Uninformative; the kinase activity itself is non-core for ERS1. |
| GO:0038199 ethylene receptor activity | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference at the plant ethylene receptor node, seeded by ETR1. ERS1 binds ethylene, acts upstream of CTR1 and negatively regulates the pathway, exactly as expected for a family member that inherited receptor function. Reason: Sound phylogenetic inference corroborated by ERS1-specific binding and genetic data. Supporting Evidence: PMID:10938361 This finding supports previous genetic evidence that isoforms of ETR1 also function in plants as ethylene receptors. |
| GO:0051740 ethylene binding | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference; ERS1 (AT2G40940) is itself among the experimental sources, consistent with direct binding data for all five receptors. Reason: Supported by direct binding assays on ERS1. |
| GO:0051740 ethylene binding | IDA PMID:15703053 Ethylene-binding activity, gene expression levels, and recep... | ACCEPT | Summary: Ethylene-binding domains of all five Arabidopsis receptors, including ERS1, expressed in yeast show high-affinity ethylene binding. Reason: Direct biochemical evidence for the core sensing activity. Supporting Evidence: PMID:15703053 Expression in yeast of ethylene-binding domains from the five receptor isoforms from Arabidopsis thaliana and five-receptor isoforms from tomato confirmed that all members of the family are capable of high-affinity ethylene-binding activity. |
| GO:0051740 ethylene binding | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA prediction consistent with direct binding data. Reason: Matches IDA evidence. |
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Download this section (compressed HTML)Q: Does ERS1 transmit its signal to CTR1 through direct stable association, or mainly through heteromeric complexes with receiver-domain receptors such as ETR1, given that ERS1 co-purifies weakly with CTR1?
Q: Under what conditions, and by what mechanism, does ERS1 promote rather than inhibit ethylene responses, as proposed from receptor-mutant genetics?
Experiment: Quantitative in planta proximity labelling or single-molecule pull-down of ERS1-CTR1 versus ETR1-CTR1 complexes in etr1 and wild-type backgrounds, with and without ethylene.
Experiment: Test whether serine autophosphorylation of ERS1 changes with ethylene in vivo by phosphoproteomics of ERS1 from ethylene-treated and untreated seedlings.
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