Gene Ontology annotation through association of InterPro records with GO terms
Electronic Gene Ontology annotations created by ARBA machine learning models
Combined Automated Annotation using Multiple IEA Methods
Cloning of the Arabidopsis clock gene TOC1, an autoregulatory response regulator homolog.
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Original positional cloning of TOC1 from the short-period toc1 mutant; TOC1 encodes a nuclear protein containing an atypical (pseudo) receiver domain and a C-terminal CCT motif (CONSTANS-like) suggesting a role in transcriptional regulation.
"The TOC1 gene was isolated and found to encode a nuclear protein containing an atypical response regulator receiver domain and two motifs that suggest a role in transcriptional regulation: a basic motif conserved within the CONSTANS family of transcription factors and an acidic domain."
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TOC1 controls photoperiodic flowering through clock function and is itself circadianly regulated, participating in a feedback loop to control its own expression.
"TOC1 controls photoperiodic flowering response through clock function. The TOC1 gene was isolated and found to encode a nuclear protein... TOC1 is itself circadianly regulated and participates in a feedback loop to control its own expression."
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The toc1 short-period phenotype persists in the absence of light input, demonstrating that TOC1 contributes to the central oscillator independently of light entrainment.
"we report the same toc1 effect in the absence of light input to the clock."
Circadian waves of expression of the APRR1/TOC1 family of pseudo-response regulators in Arabidopsis thaliana: insight into the plant circadian clock.
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TOC1/APRR1 and the four other family members (APRR3, APRR5, APRR7, APRR9) form a quintet of pseudo-response regulators whose transcripts accumulate sequentially after dawn at ~2-3 h intervals (APRR9 -> APRR7 -> APRR5 -> APRR3 -> APRR1/TOC1), defining a circadian wave of PRR expression.
"It was found that all these members of the APRR1/TOC1 family (APRR1, APRR3, APRR5, APRR7, and APRR9) are subjected to a circadian rhythm at the level of transcription. ... the APRR-mRNAs started accumulating sequentially after dawn with 2-3 h intervals in the order of APRR9-->APRR7-->APRR5-->APRR3-->APRR1."
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TOC1/APRR1 has a pseudo-receiver domain and a C-terminal CONSTANS (CCT) motif, originally characterized as a presumed component of His-to-Asp phosphorelay systems; the receiver domain lacks the catalytic Asp.
"APRR1, has a unique structural design containing a pseudo-receiver domain and a C-terminal CONSTANS motif."
The APRR1/TOC1 quintet implicated in circadian rhythms of Arabidopsis thaliana: II. Characterization with CCA1-overexpressing plants.
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Characterization of the APRR1/TOC1 quintet in CCA1-overexpressing plants further establishes the sequential, coordinately phased expression (APRR9 -> APRR7 -> APRR5 -> APRR3 -> APRR1/TOC1) and that overexpression of CCA1 disrupts these circadian waves, supporting interlocked PRR-CCA1 feedback.
"each APRR-transcript starts accumulating sequentially after dawn with 2 to 3 h intervals in the order: APRR9-->APRR7-->APRR5-->APRR3-->APRR1/TOC1."
Two-component signal transduction pathways in Arabidopsis.
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Review of Arabidopsis two-component / phosphorelay signaling components (His protein kinases, response regulators, and PRRs); provides the family-level context in which TOC1 is classified as a pseudo-response regulator without a functional receiver Asp.
"The identification of 54 His protein kinases, His-containing phosphotransfer proteins, response regulators, and related proteins in Arabidopsis suggests an important role of two-component phosphorelay in plant signal transduction."
Targeted degradation of TOC1 by ZTL modulates circadian function in Arabidopsis thaliana.
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ZEITLUPE (ZTL) targets TOC1 for proteasomal degradation; the physical interaction of TOC1 with the F-box ZTL provides genetic and molecular evidence that proteasome-mediated TOC1 turnover modulates the clock.
"Here we provide genetic and molecular evidence for a role of ZEITLUPE (ZTL) in the targeted degradation of TIMING OF CAB EXPRESSION 1 (TOC1) in Arabidopsis thaliana"
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Circadian changes in protein stability, phosphorylation, and subcellular localization (including ZTL-mediated proteolysis of TOC1) contribute to clock generation in addition to transcriptional feedback, supporting the SCF(ZTL)-TOC1 axis.
"Circadian changes in protein stability, phosphorylation and subcellular localization also contribute to the generation and maintenance of this clock."
Identification of ASK and clock-associated proteins as molecular partners of LKP2 (LOV kelch protein 2) in Arabidopsis.
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LKP2 interacts with the clock component TOC1 via the LOV domain (necessary and sufficient for TOC1 binding); together with the equivalent ZTL-TOC1 interaction, this places TOC1 as a substrate of the ADO/FKF/LKP/ZTL LOV-F-box family.
"The LOV domain of LKP2 was shown to be necessary and sufficient for the interaction with TOC1."
Circadian rhythm of circumnutation in inflorescence stems of Arabidopsis.
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toc1 shortens the period of circumnutation in inflorescence stems while elf3 abolishes the rhythm, demonstrating that the circadian clock regulates circumnutation - a clock-output role for TOC1 in plant movement.
"toc1 appears to shorten the period and elf3 causes an arrhythmic phenotype in circumnutation speed in LL, suggesting that a common circadian clock may control both circumnutation speed and other circadian outputs."
ZEITLUPE is a circadian photoreceptor stabilized by GIGANTEA in blue light.
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ZTL functions as a circadian photoreceptor whose blue-light-enhanced LOV-mediated interaction with GIGANTEA stabilizes ZTL itself - the family paradigm directly underpinning the SCF(ZTL)-mediated turnover of TOC1, since ZTL stability gates TOC1 degradation.
"Rhythmic expression of the Arabidopsis thaliana F-box protein ZEITLUPE (ZTL) is necessary to sustain a normal circadian period by controlling the proteasome-dependent degradation of a central clock protein, TIMING OF CAB EXPRESSION 1 (TOC1)."
PRR3 Is a vascular regulator of TOC1 stability in the Arabidopsis circadian clock.
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PRR3 binds TOC1 in the vasculature and stabilizes TOC1 protein by competing with the F-box ZTL for TOC1 binding, hindering SCF(ZTL)-mediated degradation; the pseudo-receiver domain of TOC1 lacks the catalytic Asp.
"we present evidence for the involvement of PRR3 in the regulation of TOC1 protein stability."
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PRR3 is temporally coexpressed with TOC1 under different photoperiods, providing a vascular-specific stabilization mechanism that contributes to TOC1's circadian function.
"PRR3 was temporally coexpressed with TOC1 under different photoperiods, yet its tissue expression"
Post-translational regulation of the Arabidopsis circadian clock through selective proteolysis and phosphorylation of pseudo-response regulator proteins.
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TOC1 and PRR5 are the principal SCF(ZTL) E3 ubiquitin ligase substrates within the PRR family; selective proteolysis of these PRRs contributes to circadian clock period and phasing.
"we show that, together with TOC1, PRR5 is the only other likely proteolytic substrate of the E3 ubiquitin ligase SCF(ZTL) within this PRR family."
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TOC1 and the PRR family undergo circadian phosphorylation and are nuclear-localized, establishing nuclear localization plus phospho-modification as core regulatory layers of the central oscillator.
"Peak expression of TOC1 (timing of cab expression 1)/PRR1, PRR3, PRR5, PRR7, and PRR9 are each phased differently over the course of the day and loss of any PRR protein alters period."
A functional genomics approach reveals CHE as a component of the Arabidopsis circadian clock.
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CHE is identified as a TCP transcription factor that binds the CCA1 promoter and partners with TOC1; the TOC1-CHE interaction recruits TOC1 to the CCA1 promoter to repress CCA1, providing a key mechanism by which TOC1 reaches clock-gene promoters.
"We established a functional genomic strategy that led to the identification of CHE, a TCP transcription factor that binds specifically to the CCA1 promoter."
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Because CHE and TOC1 interact and CHE binds CCA1, a molecular linkage between TOC1 and CCA1 gene regulation is established without requiring direct DNA binding by TOC1 at the CHE-bound site.
"Because CHE and TOC1 interact, and CHE binds to the CCA1 promoter, a molecular linkage between TOC1 and CCA1 gene regulation is established."
PRR5 regulates phosphorylation, nuclear import and subnuclear localization of TOC1 in the Arabidopsis circadian clock.
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PRR5 interacts with TOC1 through their N-terminal pseudo-receiver domains to promote TOC1 nuclear import, phosphorylation, and subnuclear foci formation, defining PRR5 as a positive regulator of TOC1 nuclear function.
"Both TOC1 and a closely related protein, PRR5, are nuclear localized, expressed in the same phase, and shorten period when deficient"
Evidence for network evolution in an Arabidopsis interactome map.
Arabidopsis circadian clock protein, TOC1, is a DNA-binding transcription factor.
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Purified TOC1 binds DNA directly through its CCT domain and acts as a general transcriptional repressor of CCA1 and LHY; TOC1 occupies specific genomic regions in the CCA1 and LHY promoters in vivo.
"Here we show that TOC1 occupies specific genomic regions in the CCA1 and LHY promoters. Purified TOC1 binds directly to DNA through its CCT domain"
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DNA binding through the CCT domain is required for TOC1's transcriptional repression of CCA1/LHY, providing the molecular basis for TOC1 acting as a DNA-binding TF (revising the earlier view that TOC1 lacked DNA-binding activity).
"Arabidopsis circadian clock protein, TOC1, is a DNA-binding transcription factor."
Accurate timekeeping is controlled by a cycling activator in Arabidopsis.
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TOC1 is one of several evening-phase Myb-like/PRR repressors that act at the EE; REVEILLE8 (RVE8) is a counter-balancing direct transcriptional activator at the same EE motifs, revising the prior view of an exclusively repressor-based oscillator.
"Current models of the Arabidopsis circadian network consist of several coupled feedback loops composed almost exclusively of transcriptional repressors."
CrY2H-seq: a massively multiplexed assay for deep-coverage interactome mapping.
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Massively multiplexed yeast two-hybrid (CrY2H-seq) interactome mapping technology used to assemble high-coverage Arabidopsis protein-protein interaction networks, providing screening-level TOC1 interactor data.
"CrY2H-seq: a massively multiplexed assay for deep-coverage interactome mapping."
Pseudo Response Regulators Regulate Photoperiodic Hypocotyl Growth by Repressing PIF4/5 Transcription.
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Pseudo-response regulators including TOC1 directly bind the PIF4 and PIF5 promoters and repress their transcription, controlling photoperiodic hypocotyl growth; TOC1 DNA-binding-domain mutants disrupt this photoperiodic hypocotyl response.
"The circadian clock measures and conveys daylength information to control"
Extensive signal integration by the phytohormone protein network.
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Large-scale Arabidopsis phytohormone-related protein-protein interactome integrates signals across hormone pathways; TOC1 appears as a node in this network, supporting protein-binding (IPI) annotations across hormone-pathway partners.
"Extensive signal integration by the phytohormone protein network."
Falcon/Edison deep research report: TOC1
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TOC1/APRR1 is a nuclear, evening-phase pseudo-response regulator containing an atypical (pseudo) receiver domain (lacking the catalytic Asp) and a C-terminal CCT motif; it acts as a sequence-specific DNA-binding transcriptional repressor of CCA1/LHY in the central oscillator.
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TOC1 protein levels and activity are post-translationally regulated by SCF(ZTL)-mediated proteasomal degradation, PRR3-dependent stabilization, and PRR5-promoted nuclear import and phosphorylation.
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Beyond core oscillator function, TOC1 contributes to clock outputs including photoperiodic flowering (via clock control), hypocotyl elongation (via direct PIF4/PIF5 promoter repression), and circumnutation; some outputs may use partner-TF recruitment (e.g. CHE) rather than direct DNA binding by TOC1.
TOC1 (APRR1/PRR1) reviewer research notes
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Curated reviewer notes synthesizing TOC1 / APRR1 biology - domain architecture (pseudo-receiver + CCT), nuclear localization, sequential PRR9-7-5-3-1 expression wave, SCF(ZTL)-mediated turnover, PRR3/PRR5 partner regulation, and CCT-domain-mediated direct DNA binding.
UniProt entry Q9LKL2 (APRR1_ARATH)
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UniProt entry Q9LKL2 (APRR1_ARATH) - documents TOC1/APRR1 as a nuclear two-component response regulator-like protein with pseudo-receiver and CCT domains, circadian regulation, role in photoperiodic flowering, and interactions with ZTL, PRR3, PRR5, and CHE.