Mutations in the SLAC1 anion channel slow stomatal opening and severely reduce K + uptake channel activity via enhanced cytosolic [Ca 2+ ] and increased Ca 2+ sensitivity of K + uptake channels (original) (raw)
Related papers
SLAC1 is required for plant guard cell S-type anion channel function in stomatal signalling
Nature, 2008
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 1 and climate change 2 . The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes 3,4 . Despite the vital role of guard cells in controlling plant water loss 3,4 , ozone sensitivity 1,2 and CO 2 supply 2,5-7 , 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 stimuli 3,4,8 . 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 CO 2 , 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 Ca 21 and abscisic acid, but do not affect rapid (R-type) anion channel currents or Ca 21 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 9 suggest a vital role for SLAC1 in the function of S-type anion channels.
New Phytologist
Guard cells control the opening of stomatal pores in the leaf surface, with the use of a network of protein kinases and phosphatases. Loss-of-function of the CBLinteracting protein kinase 23 (CIPK23) was previously shown to decrease the stomatal conductance, but the molecular mechanisms underlying this response still need to be clarified. CIPK23 was specifically expressed in Arabidopsis guard cells, using an estrogeninducible system. Stomatal movements were linked to changes in ion channel activity, determined with double-barreled intracellular electrodes in guard cells and with the two-electrode voltage clamp technique in Xenopus oocytes. Expression of the phosphomimetic variant CIPK23 T190D enhanced stomatal opening, while the natural CIPK23 and a kinase inactive CIPK23 K60N variant did not affect stomatal movements. Overexpression of CIPK23 T190D repressed the activity of S-type anion channels, while their steady state activity was unchanged by CIPK23 and CIPK23 K60N. We suggest that CIPK23 enhances the stomatal conductance at favorable growth conditions, via the regulation of several ion transport proteins in guard cells. The inhibition of SLAC1-type anion channels is an important facet of this response.
Homologue structure of the SLAC1 anion channel for closing stomata in leaves
2010
The plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. Here we determine the crystal structure of a bacterial homologue (Haemophilus influenzae) of SLAC1 at 1.20 Å resolution, and use structure-inspired mutagenesis to analyse the conductance properties of SLAC1 channels. SLAC1 is a symmetrical trimer composed from quasi-symmetrical subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features indicate a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics indicate that selectivity among different anions is largely a function of the energetic cost of ion dehydration.
Roles of AtTPC1, vacuolar two pore channel 1, in Arabidopsis stomatal closure
Plant & cell physiology, 2010
Abscisic acid (ABA) induces production of reactive oxygen species (ROS) and nitric oxide (NO), elevation of the cytosolic free calcium ion concentration ([Ca 2 + ] cyt ) and cytosolic pH (pH cyt ), and activation of S-type anion channels in guard cells, causing stomatal closure. To investigate whether Arabidopsis Two pore channel 1 ( AtTPC1 ) that encodes the slow vacuolar (SV) channel is involved in stomatal closure, we examined stomatal movements and mobilization of second messengers in the attpc1-2 loss-of-function mutant in response to ABA, methyl jasmonate (MeJA) and Ca 2 + . Both ABA and MeJA elicited production of ROS and NO, [Ca 2 + ] cyt oscillations, cytosolic alkalization and activation of S-type anion channel currents to lead to stomatal closure in the attpc1-2 mutant as well as the wild type. Unlike the wild type, in the attpc1-2 mutant exogenous Ca 2 + neither induced stomatal closure nor activated plasma membrane S-type anion channel currents despite [Ca 2 + ] cyt elevation. These results indicate that AtTPC1 functions in response to external Ca 2 + but not to ABA and MeJA in Arabidopsis guard cells and suggest that AtTPC1 could be involved in priming of plasma membrane S-type anion channels by external Ca 2 + in Arabidopsis guard cells.
F1000 - Post-publication peer review of the biomedical literature, 2000
The plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating exchange of water vapor and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. We determined the crystal structure of a bacterial homolog of SLAC1 at 1.20Å resolution, and we have used structureinspired mutagenesis to analyze the conductance properties of SLAC1 channels. SLAC1 is a symmetric trimer composed from quasi-symmetric subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features suggest a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics suggest that selectivity among different anions is largely a function of the energetic cost of ion dehydration. Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
PLANT PHYSIOLOGY, 2001
Inward-rectifying potassium (K ϩ in) channels in guard cells have been suggested to provide a pathway for K ϩ uptake into guard cells during stomatal opening. To test the proposed role of guard cell K ϩ in channels in light-induced stomatal opening, transgenic Arabidopsis plants were generated that expressed dominant negative point mutations in the K ϩ in channel subunit KAT1. Patch-clamp analyses with transgenic guard cells from independent lines showed that K ϩ in current magnitudes were reduced by approximately 75% compared with vector-transformed controls at Ϫ180 mV, which resulted in reduction in light-induced stomatal opening by 38% to 45% compared with vector-transformed controls. Analyses of intracellular K ϩ content using both sodium hexanitrocobaltate (III) and elemental x-ray microanalyses showed that light-induced K ϩ uptake was also significantly reduced in guard cells of K ϩ in channel depressor lines. These findings support the model that K ϩ in channels contribute to K ϩ uptake during light-induced stomatal opening. Furthermore, transpirational water loss from leaves was reduced in the K ϩ in channel depressor lines. Comparisons of guard cell K ϩ in current magnitudes among four different transgenic lines with different K ϩ in current magnitudes show the range of activities of K ϩ in channels required for guard cell K ϩ uptake during light-induced stomatal opening.
The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity
Nature, 2020
Perception of biotic and abiotic stresses often leads to stomatal closure in plants. Rapid influx of calcium ions (Ca 2+) across the plasma membrane plays an important role in this response, but the identity of Ca 2+ channels involved has remained elusive. Here, we report that the Arabidopsis thaliana Ca 2+-permeable channel OSCA1.3 controls stomatal closure during immunity. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phospho-proteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22 derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca 2+ , and that BIK1-mediated phosphorylation on its N-terminus increases this channel activity. Importantly, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immunity. Notably, OSCA1.3 does not regulate stomatal closure upon perception of abscisic acida plant hormone associated with abiotic stresses. Our study thus identifies a long sought-after plant Ca 2+ channel and its activation mechanisms underlying stomatal closure during immune signaling, and suggests specificity in Ca 2+ influx mechanisms in response to different stresses. Main text Diverse environmental stimuli induce rapid increases in cytosolic Ca 2+ concentrations ([Ca 2+ ]cyt) to activate signaling 1. In plants, rapid and transient [Ca 2+ ]cyt increases are for example, triggered upon perception of pathogen-associated molecular patterns (PAMPs), or abiotic stresses, such as hyper-osmolarity, drought or high ozone exposure 2,3. Leaf stomata, composed of two guard-cells, mediate water and gas exchanges and show dynamic Ca 2+ responses to such stimuli. Stomata provide natural entry points for plant pathogens 4 , and thus their closure must be tightly controlled to ensure optimal photosynthesis, while appropriately restricting evaporation and pathogen entry 5. Despite the central role of [Ca 2+ ]cyt for stomatal closure in response to multiple stimuli 6,7 , the identity of the corresponding Ca 2+ channel(s) is still unknown. In the model plant Arabidopsis thaliana (hereafter Arabidopsis), the plasma membraneassociated cytosolic kinase BIK1 and related PBL proteins act as central immune regulators acting downstream of multiple cell surface immune receptors. BIK1 orchestrates multiple
THE PLANT CELL ONLINE, 1997
Inward-rectifying K+ (K+in) channels in the guard cell plasma membrane have been suggested to function as a major pathway for K+ influx into guard cells during stomatal opening. When K+, channels were blocked with external Cs+ in wild-type Arabidopsis guard cells, light-induced stomatal opening was reduced. Transgenic Arabidopsis plants were generated that expressed a mutant of the guard cell K+, channel, KATl, which shows enhanced resistance to the Cs+ block. Stomata in these transgenic lines opened in the presence of external Cs+. Patch-clamp experiments with transgenic guard cells showed that inward K+i, currents were blocked less by Cs+ than were K+ currents in controls. These data provide direct evidence that KATl functions as a plasma membrane K+ channel in vivo and that K+, channels constitute an important mechanism for light-induced stomatal opening. In addition, biophysical properties of K+, channels in guard cells indicate that components in addition to KATl may contribute to the formation of K+in channels in vivo.
The Plant Journal, 2010
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 CO 2 -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 voltagedependent 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.