TIR1 is a predominantly nuclear Arabidopsis F-box/leucine-rich-repeat auxin receptor and the substrate-recognition subunit of SCF(TIR1). Auxin stabilizes association with Aux/IAA transcriptional repressors, allowing their ubiquitination and proteasomal degradation and changing ARF-dependent gene expression. Its receptor fold binds an inositol hexakisphosphate cofactor. TIR1 also catalyzes cAMP production: separation-of-function mutants retain Aux/IAA recruitment and degradation but impair transcriptional auxin responses. Receptor redundancy and tissue context shape its effects on lateral roots, reproductive development and phosphate-starvation responses.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0019005 SCF ubiquitin ligase complex | IDA PMID:10398681 Identification of an SCF ubiquitin-ligase complex required f... | ACCEPT | Summary: TIR1 is the F-box subunit of the ASK–CUL1 SCF complex. Reason: The original study identifies TIR1 together with ASK and AtCUL1; the complex is the setting for its substrate-recognition function. Supporting Evidence: PMID:10398681 The complex consists of proteins related to yeast Skp1p and Cdc53p called ASK and AtCUL1, respectively, as well as the F-box protein TIR1. |
| GO:0000151 ubiquitin ligase complex | IDA PMID:10398681 Identification of an SCF ubiquitin-ligase complex required f... | MODIFY | Summary: The TIR1-containing ubiquitin ligase is specifically an SCF complex. Reason: Refine the true broad complex term to the experimentally identified SCF complex, already independently annotated. Proposed replacements: SCF ubiquitin ligase complex Supporting Evidence: PMID:10398681 The complex consists of proteins related to yeast Skp1p and Cdc53p called ASK and AtCUL1, respectively, as well as the F-box protein TIR1. |
| GO:0010011 auxin binding | IDA PMID:17410169 Mechanism of auxin perception by the TIR1 ubiquitin ligase. | ACCEPT | Summary: TIR1 directly accommodates auxin in the crystallographically defined substrate-binding pocket. Reason: The TIR1–ASK1 structures contain auxin and an Aux/IAA peptide; ligand binding is an integral receptor property. The accessible primary abstract explicitly reports these structures. Supporting Evidence: PMID:17410169 recognizes auxin and the Aux/IAA polypeptide substrate through a single surface |
| GO:0010011 auxin binding | IDA PMID:18391211 Small-molecule agonists and antagonists of F-box protein-sub... | ACCEPT | Summary: Crystallographic agonist/antagonist analysis identifies ligand binding to TIR1. Reason: PMID18391211 directly corroborates the auxin pocket; antagonist occupancy can block Aux/IAA recruitment, separating binding from productive signaling. Supporting Evidence: PMID:18391211 their mode of action in binding to TIR1 is confirmed by x-ray crystallographic analysis |
| GO:0038198 auxin receptor activity | IDA PMID:15917797 The F-box protein TIR1 is an auxin receptor. | ACCEPT | Summary: TIR1 perceives auxin by forming an auxin-stabilized complex with Aux/IAA substrates. Reason: Direct ligand-binding and pull-down work establishes receptor activity on TIR1, independently of downstream growth phenotypes. Supporting Evidence: PMID:15917797 TIR1 is an auxin receptor that mediates Aux/IAA degradation PMID:17410169 recognizes auxin and the Aux/IAA polypeptide substrate through a single surface file:ARATH/TIR1/TIR1-deep-research-falcon.md |
| GO:0000822 inositol hexakisphosphate binding | IDA PMID:17410169 Mechanism of auxin perception by the TIR1 ubiquitin ligase. | ACCEPT | Summary: The TIR1 receptor fold binds an inositol hexakisphosphate cofactor. Reason: The structural cofactor is an integral biochemical property of this receptor; binding rather than catalysis is not a reason to classify it as peripheral. This is direct TIR1 structural evidence. Supporting Evidence: PMID:17410169 the leucine-rich repeat domain of TIR1 contains an unexpected inositol hexakisphosphate co-factor |
| GO:0004842 ubiquitin-protein transferase activity | IC PMID:10398681 Identification of an SCF ubiquitin-ligase complex required f... | MODIFY | Summary: TIR1 recognizes substrates within a ubiquitin ligase rather than independently transferring ubiquitin. Reason: The source establishes an SCF complex containing TIR1, not purified TIR1-catalyzed ubiquitin transfer. The seeded row has no contributes_to qualifier; preserve that original payload and refine its molecular-function claim to the directly supported substrate-adaptor activity. A contribution to complex-level ligase activity remains biologically valid. Proposed replacements: ubiquitin-like ligase-substrate adaptor activity Supporting Evidence: PMID:10398681 The complex consists of proteins related to yeast Skp1p and Cdc53p called ASK and AtCUL1, respectively, as well as the F-box protein TIR1. PMID:17410169 recognizes auxin and the Aux/IAA polypeptide substrate through a single surface |
| GO:0009734 auxin-activated signaling pathway | IMP PMID:18391211 Small-molecule agonists and antagonists of F-box protein-sub... | ACCEPT | Summary: Auxin-dependent TIR1–Aux/IAA assembly initiates auxin signaling. Reason: The primary agonist/antagonist study couples pocket occupancy and substrate recruitment to auxin responses; this is the receptor’s central process. Supporting Evidence: PMID:18391211 Auxin binding enhances the interaction between TIR1 and its substrates, the Aux/IAA repressors |
| GO:0016036 cellular response to phosphate starvation | IEP PMID:19106375 Phosphate availability alters lateral root development in Ar... | KEEP AS NON CORE | Summary: TIR1-mediated auxin sensitivity contributes to root adaptation to phosphate starvation. Reason: PMID19106375 links low-phosphate enhancement of TIR1 expression to Aux/IAA degradation and altered root sensitivity. This is a supported environmental response of the auxin receptor, not evidence that TIR1 directly binds phosphate. Supporting Evidence: |
| GO:0010311 lateral root formation | IMP PMID:9436980 The TIR1 protein of Arabidopsis functions in auxin response ... | KEEP AS NON CORE | Summary: tir1 mutants have deficient lateral-root formation. Reason: The original mutant study explicitly includes lateral-root formation among affected auxin-regulated growth processes. Retain this precise developmental role without making it the receptor’s defining biochemical function. Supporting Evidence: PMID:9436980 The tir1 mutants are deficient in a variety of auxin-regulated growth processes including hypocotyl elongation and lateral root formation. |
| GO:0010152 pollen maturation | IGI PMID:18628351 Auxin regulates Arabidopsis anther dehiscence, pollen matura... | KEEP AS NON CORE | Summary: TIR1/AFB-dependent auxin signaling regulates the timing of pollen maturation. Reason: The study reports earlier pollen maturation in tir1 afb triple/quadruple mutants. This supports a redundant receptor contribution to reproductive timing; it does not show that TIR1 alone is indispensable for pollen maturation. Supporting Evidence: PMID:18628351 We found that in tir1 afb triple and quadruple mutants, anther dehiscence and pollen maturation occur earlier than in the wild type |
| GO:0009733 response to auxin | IMP PMID:26236497 Untethering the TIR1 auxin receptor from the SCF complex inc... | MODIFY | Summary: Changing TIR1 SCF association alters auxin signaling. Reason: The source tests TIR1 assembly/stability and auxin-response defects. Refine broad response to auxin to the established auxin-activated signaling pathway, already retained for this receptor. Proposed replacements: auxin-activated signaling pathway Supporting Evidence: PMID:15917797 TIR1 is an auxin receptor that mediates Aux/IAA degradation |
| GO:0009733 response to auxin | IMP PMID:9436980 The TIR1 protein of Arabidopsis functions in auxin response ... | MODIFY | Summary: The original tir1 mutant phenotypes reveal impaired auxin response. Reason: Independent receptor and Aux/IAA-degradation evidence now identifies the mechanism as auxin-activated signaling. Refine the general response term consistently across both source rows. Proposed replacements: auxin-activated signaling pathway Supporting Evidence: PMID:15917797 TIR1 is an auxin receptor that mediates Aux/IAA degradation |
| GO:0048443 stamen development | IGI PMID:18628351 Auxin regulates Arabidopsis anther dehiscence, pollen matura... | KEEP AS NON CORE | Summary: TIR1/AFB signaling coordinates late stamen development. Reason: The primary study resolves anther dehiscence, pollen maturation and filament elongation in receptor-mutant combinations. Retain this reproductive role while preserving the shared/redundant genetic context. Supporting Evidence: PMID:18628351 auxin synthesized in anthers plays a major role in coordinating anther dehiscence and pollen maturation |
| GO:0006511 ubiquitin-dependent protein catabolic process | TAS PMID:11019805 Protein degradation in signaling. | MODIFY | Summary: TIR1 recruits Aux/IAA repressors for SCF-dependent proteasomal degradation. Reason: The cited review is broad; direct PMID11713520 establishes the specific SCF-dependent route. Refine to that retained process rather than treating generic protein degradation as false. Proposed replacements: SCF-dependent proteasomal ubiquitin-dependent protein catabolic process Supporting Evidence: PMID:11713520 SCF(TIR1) is required for AUX/IAA degradation |
| GO:0031146 SCF-dependent proteasomal ubiquitin-dependent protein catabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: TIR1 participates in SCF-dependent degradation of Aux/IAA repressors. Reason: The broad ancestral F-box SCF-catabolic assertion is present at PAINT PTN009029653 in PTHR16134; the seeded fallback row lacks WITH/FROM details, so no original node field is invented. Target-specific PMID11713520 independently establishes the process. Supporting Evidence: PMID:11713520 SCF(TIR1) is required for AUX/IAA degradation file:interpro/panther/PTHR16134/PTHR16134-paint.tsv |
| GO:0004016 adenylate cyclase activity | IDA PMID:36289340 Adenylate cyclase activity of TIR1/AFB auxin receptors in pl... | NEW | Summary: Purified TIR1 catalyzes conversion of ATP to cAMP. Reason: The 2022 study assays purified full-length His-GFP-FLAG-TIR1 from Sf9 cells by LC-MS/MS, and an independently expressed C-terminal TIR1 fragment retains activity that motif substitutions abolish. This is target-specific catalytic evidence, not transfer from AFB5 or moss receptors. The measured rate is low; the 2025 separation-of-function study independently supports a signaling role while preserving Aux/IAA degradation. No new process term is inferred solely from necessity. Supporting Evidence: file:publications/url_https___pure.coventry.ac.uk_ws_portalfiles_portal_60931587_Post_Print.pdf.md Vmax = 7.462 fmol/min/µg and KM = 0.644 mM for TIR1 PMID:40044868 TIR1ACm1 and TIR1ACm3 do not affect the TIR1 interaction with ASK1 PMID:40044868 comparable cvxIAA-induced degradation of all these Aux/IAAs in pTIR1::ccvTIR1, pTIR1::ccvTIR1ACm1 and pTIR1::ccvTIR1ACm3 PMID:40044868 cvxIAA-induced DR5::Luc activation was strongly reduced in pTIR1::ccvTIR1ACm1 and completely lost in the pTIR1::ccvTIR1ACm3 line |
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Download this section (compressed HTML)Q: Which native cAMP-binding effector couples TIR1-generated cAMP to ARF-dependent transcription?
Q: How do local TIR1 cAMP fluxes and Aux/IAA degradation combine across tissues without imposing a requirement for cAMP in substrate degradation?
Experiment: Quantify native TIR1-dependent Aux/IAA degradation kinetics across auxin analogs and SCF assembly mutants.
Experiment: Compare TIR1 versus related AFB subfamily members for substrate specificity and developmental-output specificity.
Experiment: Measure localized cAMP and matched Aux/IAA degradation/transcription reporters in TIR1 ACm1/ACm3 separation-of-function lines; test candidate cAMP effectors without assuming direct cAMP binding by ARFs.
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