Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.3.16 (calcineurin)
17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The plant hormone abscisic acid (ABA) orchestrates plant adaptive responses to a variety of stresses, including drought. This signaling pathway is regulated by reversible protein phosphorylation, and genetic evidence demonstrated that several related protein phosphatases 2C (PP2Cs) are negative regulators of this pathway in Arabidopsis thaliana. Here, we developed a protein phosphatase profiling strategy to define the substrate preferences of the HAB1 PP2C implicated in ABA signaling and used these data to screen for putative substrates. Interestingly, this analysis designated the activation loop of the ABA activated kinase OST1, related to Snf1 and AMPK kinases, as a putative HAB1 substrate. We experimentally demonstrated that HAB1 dephosphorylates and deactivates OST1 in vitro. Furthermore, HAB1 and the related PP2Cs ABI1 and ABI2 interact with OST1 in vivo, and mutations in the corresponding genes strongly affect OST1 activation by ABA. Our results provide evidence that PP2Cs are directly implicated in the ABA-dependent activation of OST1 and further suggest that the activation mechanism of AMPK/Snf1-related kinases through the inhibition of regulating PP2Cs is conserved from plants to human.
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PMID:Protein phosphatases 2C regulate the activation of the Snf1-related kinase OST1 by abscisic acid in Arabidopsis. 1985 47

The phytohormone abscisic acid (ABA) regulates the expression of many genes in plants; it has critical functions in stress resistance and in growth and development. Several proteins have been reported to function as ABA receptors, and many more are known to be involved in ABA signalling. However, the identities of ABA receptors remain controversial and the mechanism of signalling from perception to downstream gene expression is unclear. Here we show that by combining the recently identified ABA receptor PYR1 with the type 2C protein phosphatase (PP2C) ABI1, the serine/threonine protein kinase SnRK2.6/OST1 and the transcription factor ABF2/AREB1, we can reconstitute ABA-triggered phosphorylation of the transcription factor in vitro. Introduction of these four components into plant protoplasts results in ABA-responsive gene expression. Protoplast and test-tube reconstitution assays were used to test the function of various members of the receptor, protein phosphatase and kinase families. Our results suggest that the default state of the SnRK2 kinases is an autophosphorylated, active state and that the SnRK2 kinases are kept inactive by the PP2Cs through physical interaction and dephosphorylation. We found that in the presence of ABA, the PYR/PYL (pyrabactin resistance 1/PYR1-like) receptor proteins can disrupt the interaction between the SnRK2s and PP2Cs, thus preventing the PP2C-mediated dephosphorylation of the SnRK2s and resulting in the activation of the SnRK2 kinases. Our results reveal new insights into ABA signalling mechanisms and define a minimal set of core components of a complete major ABA signalling pathway.
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PMID:In vitro reconstitution of an abscisic acid signalling pathway. 1995 45

In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently identified guard cell anion channel SLAC1 appeared to be the key ion channel in this signaling pathway but remained electrically silent when expressed heterologously. Using split YFP assays, we identified OST1 as an interaction partner of SLAC1 and ABI1. Upon coexpression of SLAC1 with OST1 in Xenopus oocytes, SLAC1-related anion currents appeared similar to those observed in guard cells. Integration of ABI1 into the SLAC1/OST1 complex, however, prevented SLAC1 activation. Our studies demonstrate that SLAC1 represents the slow, deactivating, weak voltage-dependent anion channel of guard cells controlled by phosphorylation/dephosphorylation.
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PMID:Activity of guard cell anion channel SLAC1 is controlled by drought-stress signaling kinase-phosphatase pair. 1995 5

The soluble receptors of abscisic acid (ABA) have been identified in Arabidopsis thaliana. The 14 proteins in this family, bearing the double name of PYRABACTIN RESISTANCE/PYRABACTIN-LIKE (PYR/PYL) or REGULATORY COMPONENTS OF ABA RECEPTOR (RCAR) (collectively referred to as PYR/PYL/RCAR), contain between 150 and 200 amino acids with homology to the steroidogenic acute regulatory-related lipid transfer (START) protein. Structural studies of these receptors have provided rich insights into the early mechanisms of ABA signaling. The binding of ABA to PYR/PYL/RCAR triggers the pathway by inducing structural changes in the receptors that allows them to sequester members of the clade A negative regulating protein phosphatase 2Cs (PP2Cs). This liberates the class III ABA-activated Snf1-related kinases (SnRK2s) to phosphorylate various targets. In guard cells, a specific SnRK2, OPEN STOMATA 1 (OST), stimulates H(2)O(2) production by NADPH oxidase respiratory burst oxidase protein F and inhibits potassium ion influx by the inward-rectifying channel KAT1. OST1, the kinase CPK23, the calcium-dependent kinase CPK21, and the counteracting PP2Cs modulate the slow anion channel SLAC1, a pathway that contributes to stomatal responses to diverse stimuli, including ABA and carbon dioxide. A minimal ABA response pathway that leads to activation of the SLAC1 homolog, SLAH3, and presumably stomatal closure has been reconstituted in vitro. The identification of the soluble receptors and core components of the ABA signaling pathway provides promising targets for crop design with higher resilience to water deficit while maintaining biomass.
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PMID:A brand new START: abscisic acid perception and transduction in the guard cell. 2212 65

Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S-type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata' phenotype. Given the fact that guard cells express both SLAC- and R-/QUAC-type anion channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 channel. In other words, are ABI1/OST1 defects preventing both of the guard cell anion channel types from operating properly in terms of stomatal closure? The activation of the R-/QUAC-type anion channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes. Patch-clamp studies on guard cells show that ABA activates R-/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi1-1 and ost1-2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R-type anion channel. These studies indicate that OST1 is addressing both S-/SLAC- and R-/QUAC-type guard cell anion channels, and explain why the ost1-2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.
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PMID:Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells. 2345 38

ABI1 (ABA Insensitive 1) is an important component of the core regulatory network in early ABA (Abscisic acid) signaling. Here, we investigated the functions of an ABI1 ortholog in Brassica oleracea (BolABI1). The expression of BolABI1 was dramatically induced by drought, and constitutive expression of BolABI1 confers ABA insensitivity upon the wild-type. Subcellular localization and phosphatase assays reveal that BolABI1 is predominantly localized in the nucleus and harbors phosphatase activity. Furthermore, BolABI1 interacts with a homolog of OST1 (OPEN STOMATA 1) in B. oleracea (BolOST1) and can dephosphorylate ABI5 (ABA Insensitive 5) in vitro. Overall, these results suggest that BolABI1 is a functional PP2C-type protein phosphatase that is involved in the negative modulation of the ABA signaling pathway.
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PMID:Negative regulation of abscisic acid signaling by the Brassica oleracea ABI1 ortholog. 2426 21

Due to its ability to be rapidly generated and propagated over long distances, H2O2 is an important second messenger for biotic and abiotic stress signaling in plants. In response to low water potential and high salt concentrations sensed in the roots of plants, the stress hormone abscisic acid (ABA) activates NADPH oxidase to generate H2O2, which is propagated in guard cells in leaves to induce stomatal closure and prevent water loss from transpiration. Using a reconstituted system, we demonstrate that H2O2 reversibly prevents the protein phosphatase HAB1, a key component of the core ABA-signaling pathway, from inhibiting its main target in guard cells, SnRK2.6/OST1 kinase. We have identified HAB1 C186 and C274 as H2O2-sensitive thiols and demonstrate that their oxidation inhibits both HAB1 catalytic activity and its ability to physically associate with SnRK2.6 by formation of intermolecular dimers.
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PMID:H2O2 inhibits ABA-signaling protein phosphatase HAB1. 2546 Sep 14

During infection plants recognize microbe-associated molecular patterns (MAMPs), and this leads to stomatal closure. This study analyzes the molecular mechanisms underlying this MAMP response and its interrelation with ABA signaling. Stomata in intact Arabidopsis thaliana plants were stimulated with the bacterial MAMP flg22, or the stress hormone ABA, by using the noninvasive nanoinfusion technique. Intracellular double-barreled microelectrodes were applied to measure the activity of plasma membrane ion channels. Flg22 induced rapid stomatal closure and stimulated the SLAC1 and SLAH3 anion channels in guard cells. Loss of both channels resulted in cells that lacked flg22-induced anion channel activity and stomata that did not close in response to flg22 or ABA. Rapid flg22-dependent stomatal closure was impaired in plants that were flagellin receptor (FLS2)-deficient, as well as in the ost1-2 (Open Stomata 1) mutant, which lacks a key ABA-signaling protein kinase. By contrast, stomata of the ABA protein phosphatase mutant abi1-1 (ABscisic acid Insensitive 1) remained flg22-responsive. These data suggest that the initial steps in flg22 and ABA signaling are different, but that the pathways merge at the level of OST1 and lead to activation of SLAC1 and SLAH3 anion channels.
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PMID:Guard cell SLAC1-type anion channels mediate flagellin-induced stomatal closure. 2593 9

The plant hormone abscisic acid (ABA) confers drought tolerance in plants through stomatal closure and regulation of gene expression. The complex consisting of the ABA receptor PYRABACTIN RESISTANCE/REGULATORY COMPONENTS OF ABA RECEPTOR (PYR/RCAR), type 2C protein phosphatase (PP2C), and SNF1-related protein kinase 2 (SnRK2) has a key role in ABA signaling. Basic helix-loop-helix (bHLH) transcriptional activator ABA-RESPONSIVE KINASE SUBSTRATE1 (AKS1, also known as FBH3) is released from DNA by phosphorylation-induced monomerization in response to ABA in guard cells. Here we reconstituted the release of AKS1 from DNA via the ABA signaling core complex in vitro. We first obtained evidence to confirm that AKS1 is an endogenous substrate for SnRK2s. Phosphorylation of AKS1 and activation of SnRK2 showed the same time course in response to ABA in guard cells. AKS1 was bound to SnRK2.6 in vivo. Three ABA-responsive SnRK2s (SnRK2.2/SRK2D, SnRK2.3/SRK2I, and SnRK2.6/SRK2E/OST1) phosphorylated AKS1 in vitro, and the phosphorylation was eliminated by the triple mutation of SnRK2s in plants. We reconstituted the AKS1 phosphorylation in vitro via the signaling complex containing the ABA receptor PYR1, a PP2C, HYPERSENSITIVE TO ABA1 (HAB1), and a protein kinase, SnRK2.6 in response to ABA We further reconstituted the release of AKS1 from the target gene of POTASSIUM CHANNEL IN ARABIDOPSIS THALIANA 1 (KAT1) via the complex in response to ABA These results demonstrate that AKS1 provides a link between the signaling complex and ABA-responsive genes and furnish evidence for a minimal signaling mechanism from ABA perception to DNA.
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PMID:Reconstitution of Abscisic Acid Signaling from the Receptor to DNA via bHLH Transcription Factors. 2843 92

Phytohormone abscisic acid (ABA) is the canonical trigger for stomatal closure upon abiotic stresses like drought. Soil-drying is known to facilitate root-to-shoot transport of sulfate. Remarkably, sulfate and sulfide-a downstream product of sulfate assimilation-have been independently shown to promote stomatal closure. For induction of stomatal closure, sulfate must be incorporated into cysteine, which triggers ABA biosynthesis by transcriptional activation of NCED3. Here, we apply reverse genetics to unravel if the canonical ABA signal transduction machinery is required for sulfate-induced stomata closure, and if cysteine biosynthesis is also mandatory for the induction of stomatal closure by the gasotransmitter sulfide. We provide genetic evidence for the importance of reactive oxygen species (ROS) production by the plasma membrane-localized NADPH oxidases, RBOHD, and RBOHF, during the sulfate-induced stomatal closure. In agreement with the established role of ROS as the second messenger of ABA-signaling, the SnRK2-type kinase OST1 and the protein phosphatase ABI1 are essential for sulfate-induced stomata closure. Finally, we show that sulfide fails to close stomata in a cysteine-biosynthesis depleted mutant. Our data support the hypothesis that the two mobile signals, sulfate and sulfide, induce stomatal closure by stimulating cysteine synthesis to trigger ABA production.
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PMID:Sulfate-Induced Stomata Closure Requires the Canonical ABA Signal Transduction Machinery. 3065 85


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