The Experts below are selected from a list of 14505 Experts worldwide ranked by ideXlab platform
Yasunobu Okada - One of the best experts on this subject based on the ideXlab platform.
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Biophysics and Physiology of the Volume-Regulated Anion Channel (VRAC)/Volume-Sensitive Outwardly Rectifying Anion Channel (VSOR)
Pflügers Archiv - European Journal of Physiology, 2016Co-Authors: Stine F. Pedersen, Yasunobu Okada, Bernd NiliusAbstract:The volume-regulated Anion Channel (VRAC), also known as the volume-sensitive outwardly rectifying (VSOR) Anion Channel or the volume-sensitive organic osmolyte/Anion Channel (VSOAC), is essential for cell volume regulation after swelling in most vertebrate cell types studied to date. In addition to its role in cell volume homeostasis, VRAC has been implicated in numerous other physiological and pathophysiological processes, including cancer, ischemic brain edema, cell motility, proliferation, angiogenesis, programmed cell death, and excitotoxic glutamate release. Although VRAC has been extensively biophysically, pharmacologically, and functionally characterized, its molecular identity was highly controversial until the recent identification of the leucine-rich repeats containing 8A (LRRC8A) protein as essential for the VRAC current in multiple cell types and a likely pore-forming subunit of VRAC. Members of this distantly pannexin-1-related protein family form heteromers, and in addition to LRRC8A, at least another LRRC8 family member is required for the formation of a functional VRAC. This review summarizes the biophysical and pharmacological properties of VRAC, highlights its main physiological functions and pathophysiological implications, and outlines the search for its molecular identity.
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Distinct pharmacological and molecular properties of the acid-sensitive outwardly rectifying (ASOR) Anion Channel from those of the volume-sensitive outwardly rectifying (VSOR) Anion Channel
Pflugers Archiv : European journal of physiology, 2016Co-Authors: Kaori Sato-numata, Tomohiro Numata, Ryuji Inoue, Yasunobu OkadaAbstract:Expressed by many cell types, acid-sensitive outwardly rectifying (ASOR) Anion Channels are known to be activated by extracellular acidification and involved in acidotoxic necrotic cell death. In contrast, ubiquitously expressed volume-sensitive outwardly rectifying (VSOR) Anion Channels are activated by osmotic cell swelling and involved in cell volume regulation and apoptotic cell death. Distinct inhibitors to distinguish ASOR from VSOR Anion Channels have not been identified. Although leucine-rich repeats containing 8A (LRRC8A) was recently found to be an essential component of VSOR Anion Channels, the possibility of an LRRC8 family member serving as a component of ASOR Anion Channels has not been examined. In this study, we explored the effects of 12 known VSOR Channel inhibitors and small interfering RNA (siRNA)-mediated knockdown of LRRC8 family members on ASOR and VSOR currents in HeLa cells. Among these inhibitors, eight putative VSOR blockers, including 4-(2-butyl-6,7-dichlor-2-cyclopentylindan-1-on-5-yl) oxobutyric acid (DCPIB) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), were totally ineffective at blocking ASOR Channel activity, whereas suramin, R-(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy] acetic acid (DIOA), arachidonic acid, and niflumic acid were found to be effective ASOR Anion Channel antagonists. In addition, gene-silencing studies showed that no LRRC8 family members are essentially involved in ASOR Anion Channel activity, whereas LRRC8A is involved in VSOR Anion Channel activity in HeLa cells.
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Characteristics and roles of the volume-sensitive outwardly rectifying (VSOR) Anion Channel in the central nervous system
Neuroscience, 2014Co-Authors: Tenpei Akita, Yasunobu OkadaAbstract:Cell volume regulation (CVR) is essential for all types of cells in the central nervous system (CNS) to counteract cell volume changes that may be associated with neuronal activities or diseases and with osmosensing in the hypothalamus, to facilitate morphological changes during cell proliferation, differentiation and migration, and to execute apoptosis of cells. The regulation is attained by regulating the net influx or efflux of solutes and water across the plasma membrane. The volume-sensitive outwardly rectifying (VSOR) Anion Channel plays a major role in providing a pathway for Anion flux during the regulation. The VSOR Anion Channel is permeable not only to Cl(-) ions but also to amino acids like glutamate and taurine. This property confers a means of intercellular communications through the opening of the Channel in the CNS. Thus exploring the roles of VSOR Anion Channels is crucial to understand the basic principles of cellular functions in the CNS. Here we review biophysical and pharmacological characteristics of the VSOR Anion Channel in the CNS, discuss its activation mechanisms and roles in the CNS reported so far, and give some perspectives on the next issues to be examined in the near future.
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Activation of maxi-Anion Channel by protein tyrosine dephosphorylation
American journal of physiology. Cell physiology, 2009Co-Authors: Abduqodir H. Toychiev, Ravshan Z Sabirov, Nobuyaki Takahashi, Yuhko Ando-akatsuka, Hongtao Liu, Takafumi Shintani, Masaharu Noda, Yasunobu OkadaAbstract:The maxi-Anion Channel with a large single-Channel conductance of >300 pS, and unknown molecular identity, is functionally expressed in a large variety of cell types. The Channel is activated by a ...
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The maxi-Anion Channel: a classical Channel playing novel roles through an unidentified molecular entity
The Journal of Physiological Sciences, 2009Co-Authors: Ravshan Z Sabirov, Yasunobu OkadaAbstract:The maxi-Anion Channel is widely expressed and found in almost every part of the body. The Channel is activated in response to osmotic cell swelling, to excision of the membrane patch, and also to some other physiologically and pathophysiologically relevant stimuli, such as salt stress in kidney macula densa as well as ischemia/hypoxia in heart and brain. Biophysically, the maxi-Anion Channel is characterized by a large single-Channel conductance of 300–400 pS, which saturates at 580–640 pS with increasing the Cl^− concentration. The Channel discriminates well between Na^+ and Cl^−, but is poorly selective to other halides exhibiting weak electric-field selectivity with an Eisenman’s selectivity sequence I. The maxi-Anion Channel has a wide pore with an effective radius of ~1.3 nm and permits passage not only of Cl^− but also of some intracellular large organic Anions, thereby releasing major extracellular signals and gliotransmitters such as glutamate^− and ATP^4−. The Channel-mediated efflux of these signaling molecules is associated with kidney tubuloglomerular feedback, cardiac ischemia/hypoxia, as well as brain ischemia/hypoxia and excitotoxic neurodegeneration. Despite the ubiquitous expression, well-defined properties and physiological/pathophysiological significance of this classical Channel, the molecular entity has not been identified. Molecular identification of the maxi-Anion Channel is an urgent task that would greatly promote investigation in the fields not only of Anion Channel but also of physiological/pathophysiological signaling in the brain, heart and kidney.
Triin Vahisalu - One of the best experts on this subject based on the ideXlab platform.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Hannes Kollist, Noriyuki Nishimura, Yongfei Wang, Mikael BroscheAbstract:The stomata on the undersides of leaves control the exchange of carbon dioxide and water between plants and the atmosphere. Stomatal pore aperture is regulated by transport of ions and metabolites across guard-cell membranes. Perhaps surprisingly, until now no plant plasma membrane Anion Channel subunits have been cloned — and the homologues of animal Anion Channels have been shown not to encode functional ion Channels in plants. Now two groups working independently have identified a protein that is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli. Termed SLAC1, it is a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. One of two related studies that describe the identification of a protein which is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli including carbon dioxide and ozone. Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone — an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation1 and climate change2. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes3,4. Despite the vital role of guard cells in controlling plant water loss3,4, ozone sensitivity1,2 and CO2 supply2,5,6,7, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli3,4,8. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate9 suggest a vital role for SLAC1 in the function of S-type Anion Channels.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Mikael Brosche, Hannes Kollist, Noriyuki Nishimura, Yongfei Wang, Heino MoldauAbstract:Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone--an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation and climate change. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes. Despite the vital role of guard cells in controlling plant water loss, ozone sensitivity and CO2 supply, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate suggest a vital role for SLAC1 in the function of S-type Anion Channels.
Dietmar Geiger - One of the best experts on this subject based on the ideXlab platform.
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the desert plant phoenix dactylifera closes stomata via nitrate regulated slac1 Anion Channel
New Phytologist, 2017Co-Authors: Heike M Muller, Dietmar Geiger, Hubert Bauer, Nadine Schafer, Silke Lautner, Jorg Fromm, Markus Riederer, Amauri Bueno, Thomas Nussbaumer, Klaus F X MayerAbstract:Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss? Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera. To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid (ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The PhoenixSLAC1-type Anion Channel is regulated by ABA kinase PdOST1. Energy-dispersive X-ray analysis (EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl- medium, PdOST1 did not activate the desert plant Anion Channel PdSLAC1 per se. Only when nitrate was present at the extracellular face of the Anion Channel did the OST1-gated PdSLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure. Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major Anion Channel SLAC1. This initiates guard cell depolarization and the release of Anions together with potassium.
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Arabidopsis nanodomain-delimited ABA signaling pathway regulates the Anion Channel SLAH3
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Fatih Demir, Claudia Horntrich, Jörg O. Blachutzik, Sönke Scherzer, Yvonne Reinders, Sylwia Kierszniowska, Waltraud X. Schulze, Gregory S. Harms, Rainer Hedrich, Dietmar GeigerAbstract:The phytohormone abscisic acid (ABA) plays a key role in the plant response to drought stress. Hence, ABA-dependent gene transcription and ion transport is regulated by a variety of protein kinases and phosphatases. However, the nature of the membrane-delimited ABA signal transduction steps remains largely unknown. To gain insight into plasma membrane-bound ABA signaling, we identified sterol-dependent proteins associated with detergent resistant membranes from Arabidopsis thaliana mesophyll cells. Among those, we detected the central ABA signaling phosphatase ABI1 (abscisic-acid insensitive 1) and the calcium-dependent protein kinase 21 (CPK21). Using fluorescence microscopy, we found these proteins to localize in membrane nanodomains, as observed by colocalization with the nanodomain marker remorin Arabidopsis thaliana remorin 1.3 (AtRem 1.3). After transient coexpression, CPK21 interacted with SLAH3 [slow Anion Channel 1 (SLAC1) homolog 3] and activated this Anion Channel. Upon CPK21 stimulation, SLAH3 exhibited the hallmark properties of S-type Anion Channels. Coexpression of SLAH3/CPK21 with ABI1, however, prevented proper nanodomain localization of the SLAH3/CPK21 protein complex, and as a result Anion Channel activation failed. FRET studies revealed enhanced interaction of SLAH3 and CPK21 within the plasma membrane in response to ABA and thus confirmed our initial observations. Interestingly, the ABA-induced SLAH3/CPK21 interaction was modulated by ABI1 and the ABA receptor RCAR1/PYL9 [regulatory components of ABA receptor 1/PYR1 (pyrabactin resistance 1)-like protein 9]. We therefore propose that ABA signaling via inhibition of ABI1 modulates the apparent association of a signaling and transport complex within membrane domains that is necessary for phosphorylation and activation of the S-type Anion Channel SLAH3 by CPK21.
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Open stomata 1 (OST1) kinase controls R-type Anion Channel QUAC1 in Arabidopsis guard cells.
The Plant journal : for cell and molecular biology, 2013Co-Authors: Dennis Imes, Dietmar Geiger, Patrick Mumm, Irene Marten, Jennifer Böhm, Khaled A. S. Al-rasheid, Rainer HedrichAbstract: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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atalmt12 represents an r type Anion Channel required for stomatal movement in arabidopsis guard cells
Plant Journal, 2010Co-Authors: Stefan Meyer, Dietmar Geiger, Patrick Mumm, Khaled A S Alrasheid, Irene Marten, Dennis Imes, Anne Endler, Barbara Weder, Enrico Martinoia, Rainer HedrichAbstract:Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and Anions from guard cells. Anion efflux from guard cells involves slow (S-type) and rapid (R-type) Anion Channels. Recently the SLAC1 gene has been shown to encode the slow, voltage-independent Anion Channel component in guard cells. In contrast, the R-type Channel still awaits identification. Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R-type Anion Channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane. Plants lacking AtALMT12 are impaired in dark- and CO₂ -induced stomatal closure, as well as in response to the drought-stress hormone abscisic acid. Patch-clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R-type currents compared with wild-type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage-dependent Anion currents reminiscent to R-type Channels could be activated. In line with the features of the R-type Channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials. R-Type Channels, like voltage-dependent cation Channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long-term Anion and K(+) efflux via SLAC1 and GORK, respectively.
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guard cell Anion Channel slac1 is regulated by cdpk protein kinases with distinct ca2 affinities
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Dietmar Geiger, Patrick Mumm, Anja Liese, Susanne Matschi, Khaled A S Alrasheid, Peter Ache, Christian Wellmann, Sonke Scherzer, Irene Marten, Erwin GrillAbstract:Abstract In response to drought stress, the phytohormone abscisic acid (ABA) induces stomatal closure. Thereby the stress hormone activates guard cell Anion Channels in a calcium-dependent, as well as –independent, manner. Open stomata 1 protein kinase (OST1) and ABI1 protein phosphatase (ABA insensitive 1) represent key components of calcium-independent ABA signaling. Recently, the guard cell Anion Channel SLAC1 was identified. When expressed heterologously SLAC1 remained electrically silent. Upon coexpression with Ca2+-independent OST1, however, SLAC1 Anion Channels appear activated in an ABI1-dependent manner. Mutants lacking distinct calcium-dependent protein kinases (CPKs) appeared impaired in ABA stimulation of guard cell ion Channels, too. To study SLAC1 activation via the calcium-dependent ABA pathway, we studied the SLAC1 response to CPKs in the Xenopus laevis oocyte system. Split YFP-based protein–protein interaction assays, using SLAC1 as the bait, identified guard cell expressed CPK21 and 23 as major interacting partners. Upon coexpression of SLAC1 with CPK21 and 23, Anion currents document SLAC1 stimulation by these guard cell protein kinases. Ca2+-sensitive activation of SLAC1, however, could be assigned to the CPK21 pathway only because CPK23 turned out to be rather Ca2+-insensitive. In line with activation by OST1, CPK activation of the guard cell Anion Channel was suppressed by ABI1. Thus the CPK and OST1 branch of ABA signal transduction in guard cells seem to converge on the level of SLAC1 under the control of the ABI1/ABA-receptor complex.
Hannes Kollist - One of the best experts on this subject based on the ideXlab platform.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Hannes Kollist, Noriyuki Nishimura, Yongfei Wang, Mikael BroscheAbstract:The stomata on the undersides of leaves control the exchange of carbon dioxide and water between plants and the atmosphere. Stomatal pore aperture is regulated by transport of ions and metabolites across guard-cell membranes. Perhaps surprisingly, until now no plant plasma membrane Anion Channel subunits have been cloned — and the homologues of animal Anion Channels have been shown not to encode functional ion Channels in plants. Now two groups working independently have identified a protein that is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli. Termed SLAC1, it is a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. One of two related studies that describe the identification of a protein which is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli including carbon dioxide and ozone. Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone — an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation1 and climate change2. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes3,4. Despite the vital role of guard cells in controlling plant water loss3,4, ozone sensitivity1,2 and CO2 supply2,5,6,7, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli3,4,8. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate9 suggest a vital role for SLAC1 in the function of S-type Anion Channels.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Mikael Brosche, Hannes Kollist, Noriyuki Nishimura, Yongfei Wang, Heino MoldauAbstract:Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone--an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation and climate change. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes. Despite the vital role of guard cells in controlling plant water loss, ozone sensitivity and CO2 supply, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate suggest a vital role for SLAC1 in the function of S-type Anion Channels.
Julian I Schroeder - One of the best experts on this subject based on the ideXlab platform.
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identification of slac1 Anion Channel residues required for co2 bicarbonate sensing and regulation of stomatal movements
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jingbo Zhang, Nuo Wang, Yinglong Miao, Felix Hauser, Andrew J Mccammon, Wouterjan Rappel, Julian I SchroederAbstract:Increases in CO2 concentration in plant leaves due to respiration in the dark and the continuing atmospheric [CO2] rise cause closing of stomatal pores, thus affecting plant–water relations globally. However, the underlying CO2/bicarbonate (CO2/HCO3−) sensing mechanisms remain unknown. [CO2] elevation in leaves triggers stomatal closure by Anion efflux mediated via the SLAC1 Anion Channel localized in the plasma membrane of guard cells. Previous reconstitution analysis has suggested that intracellular bicarbonate ions might directly up-regulate SLAC1 Channel activity. However, whether such a CO2/HCO3− regulation of SLAC1 is relevant for CO2 control of stomatal movements in planta remains unknown. Here, we computationally probe for candidate bicarbonate-interacting sites within the SLAC1 Anion Channel via long-timescale Gaussian accelerated molecular dynamics (GaMD) simulations. Mutations of two putative bicarbonate-interacting residues, R256 and R321, impaired the enhancement of the SLAC1 Anion Channel activity by CO2/HCO3− in Xenopus oocytes. Mutations of the neighboring charged amino acid K255 and residue R432 and the predicted gate residue F450 did not affect HCO3− regulation of SLAC1. Notably, gas-exchange experiments with slac1-transformed plants expressing mutated SLAC1 proteins revealed that the SLAC1 residue R256 is required for CO2 regulation of stomatal movements in planta, but not for abscisic acid (ABA)-induced stomatal closing. Patch clamp analyses of guard cells show that activation of S-type Anion Channels by CO2/HCO3−, but not by ABA, was impaired, indicating the relevance of R256 for CO2 signal transduction. Together, these analyses suggest that the SLAC1 Anion Channel is one of the physiologically relevant CO2/HCO3− sensors in guard cells.
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Abscisic acid maintains S-type Anion Channel activity in ATP-depleted Vicia faba guard cells
FEBS letters, 1998Co-Authors: Martin Schwarz, Julian I SchroederAbstract:The plant hormone abscisic acid (ABA) regulates important developmental and stress responses. Recent data show that ABA activates phosphorylation events, but whether dephosphorylation events are post-translationally regulated by ABA or whether these are constitutive remains unknown. Slow Anion Channels in the plasma membrane of guard cells have been proposed to play an important role during ABA-induced stomatal closing. Anion Channels are deactivated by removal of cytosolic ATP. However, when guard cells were treated with ABA and depleted of ATP, Anion currents remained active. Subsequent removal of extracellular ABA caused deactivation of currents. Deactivation of currents was reversed by reintroduction of cytosolic MgATP. These data show that Anion Channels are regulated by ABA even in the absence of cytosolic ATP required for kinase-induced phosphorylation events and that Anion Channel activity is maintained by ABA under conditions that favor dephosphorylation-induced deactivation. Furthermore, Channel activation proceeded at high ATP concentrations with nanomolar cytosolic Ca2+ showing a Ca2+-independent final step in Anion Channel activation.
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Two types of Anion Channel currents in guard cells with distinct voltage regulation.
Proceedings of the National Academy of Sciences of the United States of America, 1992Co-Authors: Julian I Schroeder, Bernhard U. KellerAbstract:Abstract Transpirational water loss by plants is reduced by closing of stomatal pores in the leaf epidermis. Anion Channels in the plasma membrane of guard cells may provide a key molecular mechanism for control of stomatal closing in leaves. However, central questions regarding the regulation, diversity, and function of Anion Channels in guard cells and other higher plant cells remain unanswered. We show here that two highly distinct types of depolarization-activated Anion currents operate in the plasma membrane of Vicia faba guard cells. One described type of Anion Channel was activated rapidly within 50 ms by depolarization, inactivated during prolonged stimulation, and deactivated rapidly at hyperpolarized potentials (R-type Anion current). The other depolarization-activated Anion current showed extremely slow voltage-dependent activation and deactivation (S-type Anion current) and lacked inactivation. The distinct voltage and time dependencies of R-type and S-type Anion Channels suggest that they may play a role during depolarization-associated signal transduction in higher plant cells and that these Anion Channels may contribute to different processes in the regulation of stomatal movements. In particular, the slow and sustained nature of S-type Anion Channel activation revealed here leads us to hypothesize that S-type Anion Channels may provide a central molecular mechanism for control of stomatal closing, which is accompanied by long-term Anion efflux and depolarization.