ABI1

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0006470 protein dephosphorylation	TAS PMID:9869399 Protein phosphatase 2C (PP2C) function in higher plants.	ACCEPT	Summary: ABI1/ABI2 are central PP2Cs in ABA signaling. Reason: ABI1/ABI2 are central PP2Cs in ABA signaling. protein dephosphorylation is a core molecular/process annotation for ABI1 phosphatase function. Supporting Evidence: PMID:9869399 the ABI1/ABI2 PP2Cs are central components in abscisic acid (ABA) signal transduction.
GO:0009408 response to heat	IMP PMID:15923322 Heat stress phenotypes of Arabidopsis mutants implicate mult...	KEEP AS NON CORE	Summary: abi1 has impaired acquired thermotolerance. Reason: abi1 has impaired acquired thermotolerance. This is a supported physiological output, but the core role is PP2C-mediated negative regulation of ABA signaling. Supporting Evidence: PMID:15923322 Abscisic acid (ABA) signaling mutants (abi1 and abi2) and the UV-sensitive mutant, uvh6, showed the strongest defects in acquired thermotolerance of root growth and seedling survival.
GO:0009409 response to cold	IMP PMID:12228349 Role of Abscisic Acid in Drought-Induced Freezing Tolerance,...	KEEP AS NON CORE	Summary: The abi1 and aba-1 mutants have impaired induced freezing tolerance in this study. Reason: The abi1 and aba-1 mutants have impaired induced freezing tolerance in this study. This is a supported physiological output, but the core role is PP2C-mediated negative regulation of ABA signaling. Supporting Evidence: PMID:12228349 ABA appears to be involved in both LT- and drought-induced freezing tolerance, since both ABA mutants were impaired in their responses to these stimuli.
GO:0009409 response to cold	IMP PMID:1834244 Cold acclimation and cold-regulated gene expression in ABA m...	KEEP AS NON CORE	Summary: Gilmour and Thomashow (1991) found that abi1 impaired ABA-induced, but not cold-induced, expression of three cor genes, and that abi mutations had no apparent effect on freezing tolerance. Response to cold remains a supported peripheral claim for ABI1 from other work (row from PMID:12228349, and cold induction of ABI1 transcripts recorded in UniProt). Reason: This row shares its term with the PMID:12228349 IMP row, which is kept as non-core, and the review judges the claim rather than the individual paper. The 1991 abstract mainly separates the ABA-dependent and cold-dependent control of cor genes, with abi1 affecting the ABA branch only, so on its own it is weak support for a cold-response role. It does not contradict the later freezing-tolerance phenotype or the cold induction of ABI1. The curators had the full text, which may include data not summarized in the abstract, so the row is not removed. Response to cold is an output of ABA signaling rather than the core PP2C function, so it is kept as non-core. Supporting Evidence: PMID:1834244 Our data indicate that the ABA-induced expression of three ABA-regulated Arabidopsis cor genes was unaffected in the abi2, abi3, and aba-1 mutants, but was dramatically impaired in the abi1 mutant. PMID:1834244 Cold-regulated expression of all three cor genes, however, was nearly the same in wild-type and abi1 mutant plants. PMID:12228349 ABA appears to be involved in both LT- and drought-induced freezing tolerance, since both ABA mutants were impaired in their responses to these stimuli. file:ARATH/ABI1/ABI1-uniprot.txt Induced by low temperature, drought,
GO:0009737 response to abscisic acid	IMP PMID:8492808 Abscisic acid-insensitive mutations provide evidence for sta...	ACCEPT	Summary: ABI1 affects ABA inducibility in a developmental-stage-dependent manner. Reason: ABA-dependent control of ABI1 phosphatase activity and its downstream signaling effects are central to ABI1 function. The specific negative regulation of ABA signaling is represented separately; the ABA response claim is not a peripheral function simply because it is broad. Supporting Evidence: PMID:8492808 the abi1 and abi2 mutants showed a very slight reduction of ABA inducibility in 8-day-old plants
GO:0009787 regulation of abscisic acid-activated signaling pathway	IMP PMID:18298671 Nuclear localization of the mutant protein phosphatase abi1 ...	MODIFY	Summary: Nuclear ABI1 accumulation is associated with enhanced inhibition of ABA responses. Reason: Nuclear ABI1 accumulation is associated with enhanced inhibition of ABA responses. The evidence supports the more specific negative-regulation term for ABI1's PP2C role in ABA signaling. Proposed replacements: negative regulation of abscisic acid-activated signaling pathway Supporting Evidence: PMID:18298671 Application of a proteosomal inhibitor led to both a preferential nuclear accumulation of ABI1 and an enhancement of PP2C-dependent inhibitory action on the ABA response. PMID:19407143 RCAR1 was shown to bind ABA, to mediate ABA-dependent inactivation of ABI1 or ABI2 in vitro, and to antagonize PP2C action in planta.
GO:0009788 negative regulation of abscisic acid-activated signaling pathway	IMP PMID:16614222 A bifurcating pathway directs abscisic acid effects on stoma...	ACCEPT	Summary: PA binding to ABI1 links ABA signaling to stomatal closure. Reason: PA binding to ABI1 links ABA signaling to stomatal closure. Regulation, especially negative regulation, of ABA signaling is the central biological process for ABI1. Supporting Evidence: PMID:16614222 PLDalpha1-produced phosphatidic acid (PA) binds to the ABI1 PP2C to signal ABA-promoted stomatal closure PMID:19407143 RCAR1 was shown to bind ABA, to mediate ABA-dependent inactivation of ABI1 or ABI2 in vitro, and to antagonize PP2C action in planta.
GO:0010119 regulation of stomatal movement	IMP PMID:16614222 A bifurcating pathway directs abscisic acid effects on stoma...	KEEP AS NON CORE	Summary: PA binding to ABI1 links ABA signaling to stomatal closure. Reason: PA binding to ABI1 links ABA signaling to stomatal closure. This is a supported physiological output, but the core role is PP2C-mediated negative regulation of ABA signaling. Supporting Evidence: PMID:16614222 PLDalpha1-produced phosphatidic acid (PA) binds to the ABI1 PP2C to signal ABA-promoted stomatal closure
GO:0004721 phosphoprotein phosphatase activity	IDA PMID:22090030 Molecular mechanism for inhibition of a critical component i...	MODIFY	Summary: ABI1 recognizes the SnRK2.6 activation loop for dephosphorylation. Reason: ABI1 recognizes the SnRK2.6 activation loop for dephosphorylation. The PP2C family and experimental ABI1 studies support the more specific Ser/Thr protein phosphatase term. Proposed replacements: protein serine/threonine phosphatase activity Supporting Evidence: PMID:22090030 Structural modeling suggested that the two interfaces lock SnRK2.6 and ABI1 in an orientation such that the activation loop of SnRK2.6 is posited to the catalytic site of ABI1 for dephosphorylation. PMID:8898906 recombinant proteins that contained the ABI1 C-terminal domain displayed in vitro phosphatase activity towards 32P-labelled casein, and this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C.
GO:0004722 protein serine/threonine phosphatase activity	IEA GO_REF:0000002	ACCEPT	Summary: ABI1 is a PP2C protein serine/threonine phosphatase that dephosphorylates ABA signaling substrates. Reason: This electronic catalytic-function mapping agrees with direct ABI1 PP2C assays in PMID:8898906 and PMID:9537523; the precise Ser/Thr phosphatase function is supported independently of the mapping.
GO:0004722 protein serine/threonine phosphatase activity	IEA GO_REF:0000003	ACCEPT	Summary: ABI1 is a PP2C protein serine/threonine phosphatase that dephosphorylates ABA signaling substrates. Reason: This electronic catalytic-function mapping agrees with direct ABI1 PP2C assays in PMID:8898906 and PMID:9537523; the precise Ser/Thr phosphatase function is supported independently of the mapping.
GO:0004722 protein serine/threonine phosphatase activity	IEA GO_REF:0000116	ACCEPT	Summary: ABI1 is a PP2C protein serine/threonine phosphatase that dephosphorylates ABA signaling substrates. Reason: This electronic catalytic-function mapping agrees with direct ABI1 PP2C assays in PMID:8898906 and PMID:9537523; the precise Ser/Thr phosphatase function is supported independently of the mapping.
GO:0004722 protein serine/threonine phosphatase activity	IEA GO_REF:0000117	ACCEPT	Summary: ABI1 is a PP2C protein serine/threonine phosphatase that dephosphorylates ABA signaling substrates. Reason: This electronic catalytic-function mapping agrees with direct ABI1 PP2C assays in PMID:8898906 and PMID:9537523; the precise Ser/Thr phosphatase function is supported independently of the mapping.
GO:0004722 protein serine/threonine phosphatase activity	EXP PMID:10645425 The role of ABI1 in abscisic acid signal transduction: from ...	ACCEPT	Summary: Biochemistry and complementation establish PP2C activity. Reason: Biochemistry and complementation establish PP2C activity. protein serine/threonine phosphatase activity is a core molecular/process annotation for ABI1 phosphatase function. Supporting Evidence: PMID:10645425 A combination of in vitro assays and yeast mutant complementation studies confirmed that ABI1 is a functional protein phosphatase 2C.
GO:0004722 protein serine/threonine phosphatase activity	IDA PMID:8898906 Protein phosphatase activity of abscisic acid insensitive 1 ...	ACCEPT	Summary: ABI1 has Mg/Mn-dependent PP2C catalytic activity. Reason: ABI1 has Mg/Mn-dependent PP2C catalytic activity. protein serine/threonine phosphatase activity is a core molecular/process annotation for ABI1 phosphatase function. Supporting Evidence: PMID:8898906 recombinant proteins that contained the ABI1 C-terminal domain displayed in vitro phosphatase activity towards 32P-labelled casein, and this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C.
GO:0004722 protein serine/threonine phosphatase activity	IDA PMID:9537523 ABI1 of Arabidopsis is a protein serine/threonine phosphatas...	ACCEPT	Summary: ABI1 is a magnesium-sensitive protein serine/threonine phosphatase. Reason: ABI1 is a magnesium-sensitive protein serine/threonine phosphatase. protein serine/threonine phosphatase activity is a core molecular/process annotation for ABI1 phosphatase function. Supporting Evidence: PMID:9537523 The ABI1 protein (ABI1p) has been characterized as a protein serine/threonine phosphatase of type 2C that is highly affected in its activity by changes in the proton and magnesium ion concentrations.
GO:0005509 calcium ion binding	TAS PMID:7910981 Arabidopsis ABA response gene ABI1: features of a calcium-mo...	MARK AS OVER ANNOTATED	Summary: An early sequence analysis proposed an EF-hand calcium-binding site; this was not a direct calcium-binding assay. Reason: The original paper proposes a calcium-binding motif from sequence, while PMID:8898906 reports that the putative EF-hand is unlikely to mediate phosphatase regulation at physiological calcium concentrations. Retain MARK_AS_OVER_ANNOTATED for an unestablished calcium-binding activity; this is not justified merely by the greater informativeness of phosphatase activity. Supporting Evidence: PMID:7910981 the ABI1 protein has a unique amino-terminal extension containing an EF hand calcium-binding site. PMID:8898906 the putative EF-hand motif is unlikely to mediate Ca2+ regulation of the ABI1 phosphatase activity at physiological Ca2+ concentrations
GO:0005509 calcium ion binding	TAS PMID:8197457 A protein phosphatase 2C involved in ABA signal transduction...	MARK AS OVER ANNOTATED	Summary: The original cloning paper proposed a putative calcium-binding site from sequence. Reason: The original paper proposes a calcium-binding motif from sequence, while PMID:8898906 reports that the putative EF-hand is unlikely to mediate phosphatase regulation at physiological calcium concentrations. Retain MARK_AS_OVER_ANNOTATED for an unestablished calcium-binding activity; this is not justified merely by the greater informativeness of phosphatase activity. Supporting Evidence: PMID:8197457 The ABI1 gene encodes a protein with high similarity to protein serine or threonine phosphatases of type 2C with the novel feature of a putative Ca2+ binding site. PMID:8898906 the putative EF-hand motif is unlikely to mediate Ca2+ regulation of the ABI1 phosphatase activity at physiological Ca2+ concentrations
GO:0005515 protein binding	IPI PMID:16365038 The regulatory domain of SRK2E/OST1/SnRK2.6 interacts with A...	REMOVE	Summary: ABI1 physically interacts with the ABA-responsive regulatory domain of OST1/SnRK2.6. Reason: ABI1 physically interacts with the ABA-responsive regulatory domain of OST1/SnRK2.6. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:16365038 Domain II interacted with the ABI1 protein in a yeast two-hybrid assay.
GO:0005515 protein binding	IPI PMID:17267444 The role of Arabidopsis SCAR genes in ARP2-ARP3-dependent ce...	REMOVE	Summary: The SCAR/WAVE study used yeast two-hybrid and BiFC to map interactions among ARP2/3 regulators. UniProt records ABI1 (P49597) interactions with SCAR1, SCAR2, SCAR3 and SCARL, consistent with this curated row. Reason: Following the convention for the other protein-binding rows in this review, the generic protein-binding term is removed because it is uninformative. This does not reject the interaction. UniProt lists SCAR interactions for P49597, so the earlier worry that the curator confused ABI1 with an Abl-interactor (ABI/ABIL) subunit of the SCAR/WAVE complex is not supported. The functional significance of an ABI1-SCAR interaction is not established, and no more informative molecular function follows from it. Supporting Evidence: PMID:17267444 Systematic application of the yeast two-hybrid system and Bimolecular Fluorescence Complementation (BiFC) revealed a complex protein-interaction network between the ARP2-ARP3 complex and its genetically defined regulators. file:ARATH/ABI1/ABI1-uniprot.txt SRK2D, SRK2I, SCAR1, SCAR2, SCAR3 and SCARL
GO:0005515 protein binding	IPI PMID:19407142 Abscisic acid inhibits type 2C protein phosphatases via the ...	REMOVE	Summary: ABA-regulated PYR1-PP2C interaction was confirmed in plants. Reason: ABA-regulated PYR1-PP2C interaction was confirmed in plants. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19407142 Co-immunoprecipitation experiments performed on ABA or mock-treated plants recapitulate the PYR1-PP2C interactions observed in yeast
GO:0005515 protein binding	IPI PMID:19407143 Regulators of PP2C phosphatase activity function as abscisic...	REMOVE	Summary: ABA receptor RCAR1 inhibits ABI1 and ABI2. Reason: ABA receptor RCAR1 inhibits ABI1 and ABI2. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19407143 RCAR1 was shown to bind ABA, to mediate ABA-dependent inactivation of ABI1 or ABI2 in vitro, and to antagonize PP2C action in planta.
GO:0005515 protein binding	IPI PMID:19769575 Closely related receptor complexes differ in their ABA selec...	REMOVE	Summary: RCAR3 physically interacts with ABI1/ABI2. Reason: RCAR3 physically interacts with ABI1/ABI2. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19769575 RCAR3 was identified in a screen for interactors of the PP2Cs ABI1 and ABI2
GO:0005515 protein binding	IPI PMID:19805022 Type 2C protein phosphatases directly regulate abscisic acid...	MODIFY	Summary: Group A PP2Cs inhibit SnRK2 kinases by activation-loop dephosphorylation. Reason: The cited functional experiments establish that ABI1 dephosphorylates and inactivates SnRK2 protein kinases. Replace generic protein binding with the demonstrated serine/threonine phosphatase activity, rather than treating substrate association as a separate uninformative function. Proposed replacements: protein serine/threonine phosphatase activity Supporting Evidence: PMID:19805022 Group A PP2Cs interacted physically with SnRK2s in various combinations, and efficiently inactivated ABA-activated SnRK2s via dephosphorylation of multiple Ser/Thr residues in the activation loop.
GO:0005515 protein binding	IPI PMID:19855379 Structural basis of abscisic acid signalling.	REMOVE	Summary: The ABA-PYL1-ABI1 complex structurally explains phosphatase inhibition. Reason: The ABA-PYL1-ABI1 complex structurally explains phosphatase inhibition. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19855379 (+)-ABA-bound PYL1 tightly interacts with a PP2C domain of ABI1 by using the hydrophobic pocket to cover the active site of ABI1 like a plug.
GO:0005515 protein binding	IPI PMID:19874541 PYR/PYL/RCAR family members are major in-vivo ABI1 protein p...	REMOVE	Summary: ABI1 associates with three ABA-responsive SnRK2 kinases in planta. Reason: ABI1 associates with three ABA-responsive SnRK2 kinases in planta. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19874541 We confirm previous studies in yeast and now show that ABI1 interacts with the ABA-signalling kinases OST1, SnRK2.2 and SnRK2.3 in plants.
GO:0005515 protein binding	IPI PMID:19893533 Structural insights into the mechanism of abscisic acid sign...	REMOVE	Summary: ABA-bound PYL1 occludes the ABI1 active site. Reason: ABA-bound PYL1 occludes the ABI1 active site. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19893533 In the ternary complex, the CL2 loop is located near the active site of ABI1, blocking the entry of substrate proteins.
GO:0005515 protein binding	IPI PMID:19898420 A gate-latch-lock mechanism for hormone signalling by abscis...	REMOVE	Summary: PYR1 and PYL1-6 were tested for interaction with ABI1 as well as other PP2Cs. Reason: PYR1 and PYL1-6 were tested for interaction with ABI1 as well as other PP2Cs. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:19898420 Each of these family members was capable of interacting with the ABA-signaling PP2Cs HAB1, ABI1, and ABI2
GO:0005515 protein binding	IPI PMID:19924127 In vitro reconstitution of an abscisic acid signalling pathw...	MODIFY	Summary: Reconstitution establishes direct phosphatase control of SnRK2 activity. Reason: The cited functional experiments establish that ABI1 dephosphorylates and inactivates SnRK2 protein kinases. Replace generic protein binding with the demonstrated serine/threonine phosphatase activity, rather than treating substrate association as a separate uninformative function. Proposed replacements: protein serine/threonine phosphatase activity Supporting Evidence: PMID:19924127 the SnRK2 kinases are kept inactive by the PP2Cs through physical interaction and dephosphorylation.
GO:0005515 protein binding	IPI PMID:19955405 Activity of guard cell anion channel SLAC1 is controlled by ...	REMOVE	Summary: Geiger et al. (2009) showed by BiFC that ABI1 interacts directly with OST1 and that ABI1 stops OST1 from activating SLAC1. In vitro, ABI1 did not dephosphorylate the SLAC1 N terminus, which places it as a negative regulator of OST1. Reason: The ABI1-OST1 interaction is well supported. As with the other OST1 and PYL interaction rows in this review (e.g. PMID:16365038), the generic protein-binding term is removed as uninformative while the interaction evidence is retained. The informative functions are already captured by protein serine/threonine phosphatase activity and negative regulation of ABA-activated signaling. Supporting Evidence: PMID:19955405 indicating that OST1 directly interacts with ABI1 PMID:19955405 This indicates that ABI1 acts as a negative regulator of OST1 rather than of the SLAC1 channel.
GO:0005515 protein binding	IPI PMID:19955427 A protein kinase-phosphatase pair interacts with an ion chan...	REMOVE	Summary: Lee et al. (2009) describe a physical interaction chain between a PP2C, OST1 and SLAC1 in guard cells. The abstract foregrounds PP2CA, but the curated row records an ABI1 interaction from the same paper, which is plausible given that clade A PP2Cs share OST1 binding. Reason: The full text was not available in the cache, and the abstract does not name the ABI1 interaction partner. Following CLAUDE.md, the PP2CA focus of the abstract is not taken as evidence of mis-attribution, and the interaction is not rejected. Whatever the partner (OST1 or SLAC1), generic protein binding is uninformative, so it is removed as for the other protein-binding rows in this review. ABI1's informative activities are captured elsewhere. Supporting Evidence: PMID:19955427 The results suggest that ABA signaling is mediated by a physical interaction chain consisting of several components, including a PP2C member, SnRK2-type kinase (OST1), and an ion channel, SLAC1, to regulate stomatal movements.
GO:0005515 protein binding	IPI PMID:20729862 Identification and mechanism of ABA receptor antagonism.	REMOVE	Summary: The PYL1-pyrabactin-ABI1 complex supports receptor interaction. Reason: The PYL1-pyrabactin-ABI1 complex supports receptor interaction. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:20729862 Crystal structures of the PYL2-pyrabactin and PYL1-pyrabactin-ABI1 complexes reveal the mechanism responsible for receptor-selective activation and inhibition
GO:0005515 protein binding	IPI PMID:21436041 Jasmonate signaling involves the abscisic acid receptor PYL4...	REMOVE	Summary: Lackman et al. (2011) show that the PYR/PYL/RCAR receptor NtPYL4 inhibits clade A PP2Cs in an ABA-dependent manner. The curated row records a receptor-PP2C interaction involving ABI1. Reason: This is a PYL-PP2C receptor interaction like those in the other PYL rows of this review, which are removed as generic protein binding while the interaction evidence is retained. The cached abstract does not name ABI1, but the abstract's focus is not taken as evidence against the curator, and the interaction is not rejected. The functional consequence (phosphatase inhibition by ABA receptors) is captured by negative regulation of ABA signaling and by the receptor side. Supporting Evidence: PMID:21436041 NtPYL4 inhibited the type-2C protein phosphatases known to be key negative regulators of ABA signaling in an ABA-dependent manner.
GO:0005515 protein binding	IPI PMID:21658606 The molecular basis of ABA-independent inhibition of PP2Cs b...	REMOVE	Summary: Hao et al. (2011) characterized the Arabidopsis PYLs biochemically and showed that a subclass, represented by PYL10, inhibits PP2Cs without ABA. UniProt records free-PYL interactions with ABI1 (PYL2, PYL3, PYL4, PYL13) and ABA-bound PYL10 binding. Reason: This is a PYL-PP2C receptor interaction row. For consistency with the other PYL interaction rows, the generic protein-binding term is removed as uninformative, without rejecting the interaction. The abstract emphasizes PYL10-HAB1 structures, but the systematic biochemical characterization covers PP2C inhibition, and that focus is not evidence that ABI1 was not assayed. Supporting Evidence: PMID:21658606 PYR1/PYL/RCAR proteins (PYLs) are confirmed abscisic acid (ABA) receptors, which inhibit protein phosphatase 2C (PP2C) upon binding to ABA. file:ARATH/ABI1/ABI1-uniprot.txt PYL2, PYL3, PYL4 and PYL13
GO:0005515 protein binding	IPI PMID:21798944 Evidence for network evolution in an Arabidopsis interactome...	REMOVE	Summary: Arabidopsis Interactome-1 (AI-1) is a high-throughput yeast two-hybrid map of 5,664 binary interactions. The specific ABI1 (At4g26080) partner is in the supplementary interaction table, not the main text. Reason: This is a high-throughput Y2H binary interaction. The cached main text does not name the ABI1 pair, but that is a feature of a supplementary-table dataset, not evidence against the curator. A single systematic Y2H edge does not support a more informative molecular function, so the generic protein-binding term is removed, as for the other protein-binding rows in this review. This does not reject the interaction. Supporting Evidence: PMID:21798944 Confirmed pairs were assembled into a dataset of 5,664 binary interactions between 2,661 proteins, called Arabidopsis Interactome version 1 “main screen” (AI-1MAIN) (table S4).
GO:0005515 protein binding	IPI PMID:24165892 Molecular basis for the selective and ABA-independent inhibi...	REMOVE	Summary: Li et al. (2013) characterize PYL13, the ABA-insensitive PYL, and its ABA-independent inhibition of clade A PP2Cs. UniProt records an interaction between free PYL13 and ABI1. Reason: This is a PYL-PP2C interaction row. The extracted text concentrates on PYL13-PP2CA selectivity, and the ABI1 assay may be in figures or supplements not captured in the extraction. UniProt independently lists free PYL13 as an ABI1 partner. As with the other PYL rows, the generic protein-binding term is removed as uninformative without rejecting the interaction. Supporting Evidence: PMID:24165892 These two PYLs antagonize each other in their respective ABA-independent inhibitions of PP2Cs. file:ARATH/ABI1/ABI1-uniprot.txt PYL2, PYL3, PYL4 and PYL13
GO:0005515 protein binding	IPI PMID:26443375 Arabidopsis ABA-Activated Kinase MAPKKK18 is Regulated by Pr...	MODIFY	Summary: ABI1 interacts with and inhibits MKKK18. Reason: The cited work directly identifies ABI1 as a MKKK18-interacting protein and demonstrates inhibition of kinase activity. Protein kinase inhibitor activity captures this measured regulatory function more informatively than generic binding; this assignment does not require inferring a phosphatase-independent inhibition mechanism. Proposed replacements: protein kinase inhibitor activity Supporting Evidence: PMID:26443375 Notably, we identified abscisic acid insensitive 1 (ABI1) PP2C as a MKKK18-interacting protein, and demonstrated that ABI1 inhibited its activity.
GO:0005515 protein binding	IPI PMID:27192441 Release of GTP Exchange Factor Mediated Down-Regulation of A...	REMOVE	Summary: ABI1 directly interacts with RopGEF1. Reason: ABI1 directly interacts with RopGEF1. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:27192441 RopGEF1 directly interacts with several clade A PP2C protein phosphatases, including ABI1.
GO:0005515 protein binding	IPI PMID:27923613 Arabidopsis thaliana RECEPTOR DEAD KINASE1 Functions as a Po...	REMOVE	Summary: RDK1 recruits ABI1 to the plasma membrane. Reason: RDK1 recruits ABI1 to the plasma membrane. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:27923613 RDK1 interacted in the plasma membrane with type 2C protein phosphatase ABSCISIC ACID INSENSITIVE1 (ABI1)
GO:0005515 protein binding	IPI PMID:29928509 CARK1 mediates ABA signaling by phosphorylation of ABA recep...	REMOVE	Summary: RCAR3 phosphorylation strengthens binding to ABI1. Reason: RCAR3 phosphorylation strengthens binding to ABI1. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:29928509 Surface plasmon resonance (SPR) assay further demonstrated the phosphorylation of RCAR3 by CARK1 could distinctly enhance its interaction with ABI1 in vitro.
GO:0005515 protein binding	IPI PMID:32490347 A point-to-point protein-protein interaction assay reveals t...	REMOVE	Summary: JAZ1-ABI1 interaction contributes to hormone signaling cross-talk. Reason: JAZ1-ABI1 interaction contributes to hormone signaling cross-talk. Remove the uninformative generic protein-binding annotation while retaining this interaction evidence. This does not reject the interaction, and interaction alone does not establish a distinct molecular activity beyond the supported functions reviewed elsewhere. Supporting Evidence: PMID:32490347 we next revealed the signaling cross talk between jasmonate and abscisic acid by characterizing the JAZ1-PYL4 and JAZ1-ABI1 interactions.
GO:0005515 protein binding	IPI PMID:32612234 Extensive signal integration by the phytohormone protein net...	REMOVE	Summary: Altmann et al. (2020) generated a systems-level binary interaction map of the Arabidopsis phytohormone signaling network (>2,000 interactions). The ABI1 partner is in the supplementary dataset. Reason: This is a systematic binary interaction screen. The abstract does not enumerate the ABI1 pair, and that is not evidence against the curator. A single network edge does not support a more informative molecular function than ABI1's established PP2C activity, so the generic protein-binding term is removed, consistent with the other protein-binding rows in this review. This does not reject the interaction. Supporting Evidence: PMID:32612234 Here, we experimentally generated a systems-level map of the Arabidopsis phytohormone signalling network, consisting of more than 2,000 binary protein-protein interactions.
GO:0016791 phosphatase activity	IDA PMID:24179127 ABI1 and PP2CA phosphatases are negative regulators of Snf1-...	MODIFY	Summary: ABI1 and PP2CA couple ABA and energy signaling by inhibiting SnRK1. Reason: The recovered full text demonstrates ABI1-dependent SnRK1.1 dephosphorylation, corroborating the specific protein serine/threonine phosphatase term together with established PP2C enzymology. Proposed replacements: protein serine/threonine phosphatase activity Supporting Evidence: PMID:24179127 two clade A type 2C protein phosphatases (PP2Cs), established repressors of the abscisic acid (ABA) hormonal pathway, interact with the SnRK1 catalytic subunit causing its dephosphorylation and inactivation. PMID:8898906 recombinant proteins that contained the ABI1 C-terminal domain displayed in vitro phosphatase activity towards 32P-labelled casein, and this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C.
GO:0019900 kinase binding	IPI PMID:24179127 ABI1 and PP2CA phosphatases are negative regulators of Snf1-...	MODIFY	Summary: ABI1 and PP2CA couple ABA and energy signaling by inhibiting SnRK1. Reason: The recovered full text shows ABI1-SnRK1.1 interaction by yeast two-hybrid and co-immunoprecipitation. SnRK1 is a Ser/Thr kinase, supporting refinement to protein serine/threonine kinase binding. Proposed replacements: protein serine/threonine kinase binding Supporting Evidence: PMID:24179127 SnRK1.1 interacted with ABI1 and PP2CA in yeast cells, and deletion of its regulatory domain (RD) abolished this interaction
GO:0019901 protein kinase binding	IPI PMID:20385816 Guard cell anion channel SLAC1 is regulated by CDPK protein ...	MODIFY	Summary: Geiger et al. (2010) showed that ABI1 suppresses activation of the anion channel SLAC1 by the calcium-dependent kinases CPK21 and CPK23. UniProt records direct ABI1 binding to CPK21 and CPK23 from this study. Reason: The cached abstract states that ABI1 suppresses CPK-dependent SLAC1 activation. UniProt records ABI1 binding to CPK21 and CPK23, and the PMC full text (consulted online, not cached) reports BiFC complementation in oocytes between ABI1 and CPK21 or CPK23, interpreted as a direct kinase-phosphatase interaction. The binding claim is therefore accepted. CPK21 and CPK23 are serine/threonine kinases, so the term is refined to protein serine/threonine kinase binding. This matches the replacement proposed for the kinase binding row from PMID:24179127. Proposed replacements: protein serine/threonine kinase binding Supporting Evidence: PMID:20385816 In line with activation by OST1, CPK activation of the guard cell anion channel was suppressed by ABI1. file:ARATH/ABI1/ABI1-uniprot.txt Binds to RPL12B, CPK21 and CPK23.
GO:0043169 cation binding	IEA GO_REF:0000002	MODIFY	Summary: The Mg2+/Mn2+-dependent PP2C catalytic site supports binding these divalent metal cofactors. Refine the true but broad cation-binding term to both experimentally supported ions; broadness is not a reason to designate the claim non-core. Reason: The Mg2+/Mn2+-dependent PP2C catalytic site supports binding these divalent metal cofactors. Refine the true but broad cation-binding term to both experimentally supported ions; broadness is not a reason to designate the claim non-core. Proposed replacements: magnesium ion binding manganese ion binding Supporting Evidence: PMID:8898906 this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C.
GO:0009737 response to abscisic acid	IEP PMID:25680457 An abscisic acid inducible Arabidopsis MAPKKK, MAPKKK18 regu...	ACCEPT	Summary: ABI1 transcripts are induced by ABA, which UniProt records from several independent studies. The IEP row from the MAPKKK18 study most likely reflects ABI1 being monitored as an ABA-responsive marker, but that measurement is not visible in the cached abstract. Reason: ABA-dependent control of ABI1 phosphatase activity and its downstream signaling effects are central to ABI1 function. The specific negative regulation of ABA signaling is represented separately; the ABA response claim is not a peripheral function simply because it is broad. Supporting Evidence: file:ARATH/ABI1/ABI1-uniprot.txt high salt, abscisic acid (ABA) and ethylene.
GO:0009788 negative regulation of abscisic acid-activated signaling pathway	IGI PMID:18835996 F-box protein DOR functions as a novel inhibitory factor for...	ACCEPT	Summary: Genetic epistasis places abi1-1 downstream of DOR in the ABA response. Reason: Genetic epistasis places abi1-1 downstream of DOR in the ABA response. Regulation, especially negative regulation, of ABA signaling is the central biological process for ABI1. Supporting Evidence: PMID:18835996 Double-mutant analyses of dor with ABA-insensitive mutant abi1-1 showed that abi1-1 is epistatic to dor PMID:19407143 RCAR1 was shown to bind ABA, to mediate ABA-dependent inactivation of ABI1 or ABI2 in vitro, and to antagonize PP2C action in planta.
GO:0009788 negative regulation of abscisic acid-activated signaling pathway	IMP PMID:26443375 Arabidopsis ABA-Activated Kinase MAPKKK18 is Regulated by Pr...	ACCEPT	Summary: ABI1 interacts with and inhibits MKKK18. Reason: ABI1 interacts with and inhibits MKKK18. Regulation, especially negative regulation, of ABA signaling is the central biological process for ABI1. Supporting Evidence: PMID:26443375 Notably, we identified abscisic acid insensitive 1 (ABI1) PP2C as a MKKK18-interacting protein, and demonstrated that ABI1 inhibited its activity.
GO:1902531 regulation of intracellular signal transduction	IBA GO_REF:0000033	ACCEPT	Summary: Inherited intracellular signaling regulation is consistent with ABI1 phosphatase function. Reason: The PAINT IBA asserts inherited participation in intracellular signaling regulation, consistent with ABI1 PP2C function. The target-specific ABA mechanism provides additional specificity but does not invalidate the broader ancestral inference.
GO:0005634 nucleus	IEA GO_REF:0000044	ACCEPT	Summary: ABI1 has documented nucleus localization compatible with ABA signaling outputs. Reason: Nuclear and cytoplasmic localization are compatible with ABI1 regulation of SnRK2s and ABA-responsive transcription.
GO:0005634 nucleus	IDA PMID:18298671 Nuclear localization of the mutant protein phosphatase abi1 ...	ACCEPT	Summary: Nuclear ABI1 accumulation is associated with enhanced inhibition of ABA responses. Reason: Nuclear ABI1 accumulation is associated with enhanced inhibition of ABA responses. Nuclear and cytoplasmic localization are compatible with ABI1 regulation of SnRK2s and ABA-responsive transcription. Supporting Evidence: PMID:18298671 Application of a proteosomal inhibitor led to both a preferential nuclear accumulation of ABI1 and an enhancement of PP2C-dependent inhibitory action on the ABA response.
GO:0005737 cytoplasm	IEA GO_REF:0000044	ACCEPT	Summary: ABI1 has documented cytoplasm localization compatible with ABA signaling outputs. Reason: Nuclear and cytoplasmic localization are compatible with ABI1 regulation of SnRK2s and ABA-responsive transcription.
GO:0005737 cytoplasm	ISM GO_REF:0000122	ACCEPT	Summary: ABI1 has documented cytoplasm localization compatible with ABA signaling outputs. Reason: Nuclear and cytoplasmic localization are compatible with ABI1 regulation of SnRK2s and ABA-responsive transcription.
GO:0005886 plasma membrane	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: ABI1 can be recruited to the plasma membrane by RDK1. Reason: PMID:27923613 reports RDK1-ABI1 interaction at the plasma membrane, supporting the electronic location mapping. This is a context-dependent site in addition to nucleocytoplasmic action.
GO:0008287 protein serine/threonine phosphatase complex	TAS PMID:9869399 Protein phosphatase 2C (PP2C) function in higher plants.	UNDECIDED	Summary: ABI1 catalytic activity and signaling complexes are established, but the intended phosphatase-complex assertion in the cited review is unresolved. Reason: QuickGO defines this as a complex, normally with catalytic and regulatory subunits, that catalyzes protein Ser/Thr dephosphorylation; it does not categorically exclude PP2Cs. The cached PMID:9869399 abstract establishes ABI1/ABI2 signaling roles but does not identify the asserted phosphatase complex, and its full text was unavailable. Receptor-bound inhibited complexes do not by themselves establish an active phosphatase complex. Retain uncertainty rather than infer absence of every such complex from PP2C family identity. Supporting Evidence: PMID:9869399 the ABI1/ABI2 PP2Cs are central components in abscisic acid (ABA) signal transduction.

Gene Description

Existing Annotations Review

Core Functions

Clade A PP2C protein serine/threonine phosphatase activity that negatively regulates abscisic acid signaling by dephosphorylating and inhibiting ABA-activated SnRK kinases until ABA-bound PYR/PYL/RCAR receptors inhibit ABI1.

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