RESUMEN
In 1916, Ricca hypothesized that plant defense mediators are transported by xylem vessels. While it was discovered that electrical waves generated at plant wounds also transmit information over great distances, the molecular nature of the so-called Ricca factor remained unclear. In this issue of Cell, Gao et al. identify thioglucoside glucohydrolases as a Ricca factor in Arabidopsis.
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Proteínas de Arabidopsis , Arabidopsis , Herbivoria , Plantas , Proteínas de Arabidopsis/genética , XilemaRESUMEN
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMEN
Perception of biotic and abiotic stresses often leads to stomatal closure in plants1,2. Rapid influx of calcium ions (Ca2+) across the plasma membrane has an important role in this response, but the identity of the Ca2+ channels involved has remained elusive3,4. Here we report that the Arabidopsis thaliana Ca2+-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics 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, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid-a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca2+ channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca2+ influx mechanisms in response to different stresses.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/inmunología , Arabidopsis/metabolismo , Canales de Calcio/metabolismo , Calcio/metabolismo , Inmunidad de la Planta , Estomas de Plantas/inmunología , Estomas de Plantas/metabolismo , Ácido Abscísico/metabolismo , Moléculas de Patrón Molecular Asociado a Patógenos/inmunología , Moléculas de Patrón Molecular Asociado a Patógenos/metabolismo , Fosforilación , Unión Proteica , Proteínas Serina-Treonina Quinasas/metabolismo , Transducción de SeñalRESUMEN
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 CBL-interacting 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 estrogen-inducible 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 CIPK23T190D enhanced stomatal opening, while the natural CIPK23 and a kinase-inactive CIPK23K60N variant did not affect stomatal movements. Overexpression of CIPK23T190D repressed the activity of S-type anion channels, while their steady-state activity was unchanged by CIPK23 and CIPK23K60N . 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.
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Proteínas de Arabidopsis , Arabidopsis , Ácido Abscísico/metabolismo , Aniones/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de la Membrana/metabolismo , Estomas de Plantas/fisiología , Proteínas Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismoRESUMEN
Green plants are equipped with photoreceptors that are capable of sensing radiation in the ultraviolet-to-blue and the red-to-far-red parts of the light spectrum. However, plant cells are not particularly sensitive to green light (GL), and light which lies within this part of the spectrum does not efficiently trigger the opening of stomatal pores. Here, we discuss the current knowledge of stomatal responses to light, which are either provoked via photosynthetically active radiation or by specific blue light (BL) signaling pathways. The limited impact of GL on stomatal movements provides a unique option to use this light quality to control optogenetic tools. Recently, several of these tools have been optimized for use in plant biological research, either to control gene expression, or to provoke ion fluxes. Initial studies with the BL-activated potassium channel BLINK1 showed that this tool can speed up stomatal movements. Moreover, the GL-sensitive anion channel GtACR1 can induce stomatal closure, even at conditions that provoke stomatal opening in wild-type plants. Given that crop plants in controlled-environment agriculture and horticulture are often cultivated with artificial light sources (i.e. a combination of blue and red light from light-emitting diodes), GL signals can be used as a remote-control signal that controls stomatal transpiration and water consumption.
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Arabidopsis , Estomas de Plantas , Estomas de Plantas/fisiología , Arabidopsis/genética , Optogenética , Canales de Potasio/metabolismo , Aniones/metabolismoRESUMEN
Cytosolic calcium signals are evoked by a large variety of biotic and abiotic stimuli and play an important role in cellular and long distance signalling in plants. While the function of the plasma membrane in cytosolic Ca2+ signalling has been intensively studied, the role of the vacuolar membrane remains elusive. A newly developed vacuolar voltage clamp technique was used in combination with live-cell imaging, to study the role of the vacuolar membrane in Ca2+ and pH homeostasis of bulging root hair cells of Arabidopsis. Depolarisation of the vacuolar membrane caused a rapid increase in the Ca2+ concentration and alkalised the cytosol, while hyperpolarisation led to the opposite responses. The relationship between the vacuolar membrane potential, the cytosolic pH and Ca2+ concentration suggests that a vacuolar H+ /Ca2+ exchange mechanism plays a central role in cytosolic Ca2+ homeostasis. Mathematical modelling further suggests that the voltage-dependent vacuolar Ca2+ homeostat could contribute to calcium signalling when coupled to a recently discovered K+ channel-dependent module for electrical excitability of the vacuolar membrane.
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Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Calcio/metabolismo , Canales de Calcio/metabolismo , Señalización del Calcio , Citosol/metabolismo , Vacuolas/metabolismoRESUMEN
Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown. We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1. We show that within 1 min, prior to stomatal closure, O3 triggered a drop in whole-plant CO2 uptake. Within this early phase, O3 pulses (200-1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O3 induced cell death, systemic Ca2+ signals and an irreversible drop in stomatal conductance and photosynthetic capacity. We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca2+ ) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.
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Ozono , Calcio , Células del Mesófilo , Ozono/farmacología , Fotosíntesis , Hojas de la Planta , Estomas de PlantasRESUMEN
Plasma membrane (PM) depolarization functions as an initial step in plant defense signaling pathways. However, only a few ion channels/transporters have been characterized in the context of plant immunity. Here, we show that the Arabidopsis (Arabidopsis thaliana) Na+:K+:2Cl- (NKCC) cotransporter CCC1 has a dual function in plant immunity. CCC1 functions independently of PM depolarization and negatively regulates pathogen-associated molecular pattern-triggered immunity. However, CCC1 positively regulates plant basal and effector-triggered resistance to Pseudomonas syringae pv. tomato (Pst) DC3000. In line with the compromised immunity to Pst DC3000, ccc1 mutants show reduced expression of genes encoding enzymes involved in the biosynthesis of antimicrobial peptides, camalexin, and 4-OH-ICN, as well as pathogenesis-related proteins. Moreover, genes involved in cell wall and cuticle biosynthesis are constitutively down-regulated in ccc1 mutants, and the cell walls of these mutants exhibit major changes in monosaccharide composition. The role of CCC1 ion transporter activity in the regulation of plant immunity is corroborated by experiments using the specific NKCC inhibitor bumetanide. These results reveal a function for ion transporters in immunity-related cell wall fortification and antimicrobial biosynthesis.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/inmunología , Resistencia a la Enfermedad/genética , Pseudomonas syringae/inmunología , Miembro 2 de la Familia de Transportadores de Soluto 12/genética , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Arabidopsis/microbiología , Proteínas de Arabidopsis/genética , Bumetanida/farmacología , Membrana Celular/genética , Membrana Celular/metabolismo , Membrana Celular/fisiología , Pared Celular/química , Pared Celular/genética , Pared Celular/metabolismo , Resistencia a la Enfermedad/inmunología , Perfilación de la Expresión Génica , Indoles/metabolismo , Monosacáridos/química , Monosacáridos/metabolismo , Mutación , Moléculas de Patrón Molecular Asociado a Patógenos/metabolismo , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/inmunología , Enfermedades de las Plantas/microbiología , Inmunidad de la Planta/efectos de los fármacos , Inmunidad de la Planta/genética , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/genética , Hojas de la Planta/inmunología , Hojas de la Planta/microbiología , Plantas Modificadas Genéticamente/metabolismo , Pseudomonas syringae/efectos de los fármacos , Pseudomonas syringae/patogenicidad , RNA-Seq , Inhibidores del Simportador de Cloruro Sódico y Cloruro Potásico/farmacología , Simportadores de Cloruro de Sodio-Potasio/metabolismo , Miembro 2 de la Familia de Transportadores de Soluto 12/inmunología , Miembro 2 de la Familia de Transportadores de Soluto 12/metabolismo , Tiazoles/metabolismoRESUMEN
Contents Summary 84 I. Introduction 84 II. Stomatal form and biomechanics 85 III. Stomatal function 86 IV. Evolution of guard cell ion channels 87 V. Conclusions 88 Acknowledgements 88 Author contributions 88 References 88 SUMMARY: Stomatal pores with apertures that can be adjusted by changes in guard cell turgor have facilitated plant success in dry environments. We explore their evolutionary origins, considering recent findings from bryophytes. Unlike vascular plant stomata, which close to prevent water loss, bryophyte stomata become locked open to promote spore desiccation. We find that the families of ion channels, known to control stomatal movements in angiosperms, are ancient and represented across extant land plants. However, although angiosperm guard cells express specific ion channel genes, none appear specifically expressed in stomata-bearing moss tissues. Given the evolutionary shift in stomatal function from promotion to prevention of water loss, we postulate that ion channels adopted guard cell-specific functions after the divergence of bryophytes.
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Movimiento , Ósmosis , Estomas de Plantas/fisiología , Fenómenos Biomecánicos , Canales Iónicos/metabolismo , Modelos Biológicos , Estomas de Plantas/citología , Estomas de Plantas/genéticaRESUMEN
During drought, abscisic acid (ABA) induces closure of stomata via a signaling pathway that involves the calcium (Ca2+ )-independent protein kinase OST1, as well as Ca2+ -dependent protein kinases. However, the interconnection between OST1 and Ca2+ signaling in ABA-induced stomatal closure has not been fully resolved. ABA-induced Ca2+ signals were monitored in intact Arabidopsis leaves, which express the ratiometric Ca2+ reporter R-GECO1-mTurquoise and the Ca2+ -dependent activation of S-type anion channels was recorded with intracellular double-barreled microelectrodes. ABA triggered Ca2+ signals that occurred during the initiation period, as well as in the acceleration phase of stomatal closure. However, a subset of stomata closed in the absence of Ca2+ signals. On average, stomata closed faster if Ca2+ signals were elicited during the ABA response. Loss of OST1 prevented ABA-induced stomatal closure and repressed Ca2+ signals, whereas elevation of the cytosolic Ca2+ concentration caused a rapid activation of SLAC1 and SLAH3 anion channels. Our data show that the majority of Ca2+ signals are evoked during the acceleration phase of stomatal closure, which is initiated by OST1. These Ca2+ signals are likely to activate Ca2+ -dependent protein kinases, which enhance the activity of S-type anion channels and boost stomatal closure.
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Ácido Abscísico/farmacología , Señalización del Calcio , Calcio/metabolismo , Estomas de Plantas/citología , Estomas de Plantas/fisiología , Arabidopsis/efectos de los fármacos , Arabidopsis/fisiología , Proteínas de Arabidopsis/metabolismo , Canales de Calcio/metabolismo , Señalización del Calcio/efectos de los fármacos , Citosol/metabolismo , Estomas de Plantas/efectos de los fármacosRESUMEN
Plant gas exchange is regulated by guard cells that form stomatal pores. Stomatal adjustments are crucial for plant survival; they regulate uptake of CO2 for photosynthesis, loss of water, and entrance of air pollutants such as ozone. We mapped ozone hypersensitivity, more open stomata, and stomatal CO2-insensitivity phenotypes of the Arabidopsis thaliana accession Cvi-0 to a single amino acid substitution in MITOGEN-ACTIVATED PROTEIN (MAP) KINASE 12 (MPK12). In parallel, we showed that stomatal CO2-insensitivity phenotypes of a mutant cis (CO2-insensitive) were caused by a deletion of MPK12. Lack of MPK12 impaired bicarbonate-induced activation of S-type anion channels. We demonstrated that MPK12 interacted with the protein kinase HIGH LEAF TEMPERATURE 1 (HT1)-a central node in guard cell CO2 signaling-and that MPK12 functions as an inhibitor of HT1. These data provide a new function for plant MPKs as protein kinase inhibitors and suggest a mechanism through which guard cell CO2 signaling controls plant water management.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Dióxido de Carbono/metabolismo , Variación Genética , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Transducción de Señal , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Mapeo Cromosómico , Ozono/metabolismo , Fotosíntesis , Sitios de Carácter Cuantitativo , AguaRESUMEN
Recent studies have revealed that some responses of fern stomata to environmental signals differ from those of their relatives in seed plants. However, it is unknown whether the biophysical properties of guard cells differ fundamentally between species of both clades. Intracellular micro-electrodes and the fluorescent Ca2+ reporter FURA2 were used to study voltage-dependent cation channels and Ca2+ signals in guard cells of the ferns Polypodium vulgare and Asplenium scolopendrium. Voltage clamp experiments with fern guard cells revealed similar properties of voltage-dependent K+ channels as found in seed plants. However, fluorescent dyes moved within the fern stomata, from one guard cell to the other, which does not occur in most seed plants. Despite the presence of plasmodesmata, which interconnect fern guard cells, Ca2+ signals could be elicited in each of the cells individually. Based on the common properties of voltage-dependent channels in ferns and seed plants, it is likely that these key transport proteins are conserved in vascular plants. However, the symplastic connections between fern guard cells in mature stomata indicate that the biophysical mechanisms that control stomatal movements differ between ferns and seed plants.
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Calcio/metabolismo , Helechos/citología , Células Vegetales/metabolismo , Plasmodesmos/metabolismo , Transporte Biológico , Citosol/metabolismo , Helechos/metabolismo , Estomas de Plantas/citología , Estomas de Plantas/metabolismo , Polypodium/citología , Polypodium/metabolismo , Canales de Potasio con Entrada de Voltaje/metabolismoRESUMEN
The membrane-bound proton-pumping pyrophosphatase (V-PPase), together with the V-type H+ -ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V-PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton-pumping functions has yet to be dissected. For a better understanding of the molecular processes underlying V-PPase-dependent salt tolerance, we transiently overexpressed the pyrophosphate-driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch-clamp, impalement electrodes and pH imaging. NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3 d in salt-untreated conditions, V-PPase-overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP-hyperactive cells from cell death. Furthermore, a salt-induced rise in V-PPase but not of V-ATPase pump currents was detected in nontransformed plants. The results indicate that under normal growth conditions, plants need to regulate the V-PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V-PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton-coupled Na+ sequestration.
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Pirofosfatasa Inorgánica/metabolismo , Nicotiana/enzimología , Salinidad , Cloruro de Sodio/farmacología , Vacuolas/enzimología , Muerte Celular/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Difosfatos/metabolismo , Concentración de Iones de Hidrógeno , Isoenzimas/metabolismo , Potenciales de la Membrana/efectos de los fármacos , Células del Mesófilo/efectos de los fármacos , Células del Mesófilo/enzimología , Epidermis de la Planta/citología , Epidermis de la Planta/efectos de los fármacos , Bombas de Protones/metabolismo , Protones , Estrés Fisiológico/efectos de los fármacos , Nicotiana/efectos de los fármacos , ATPasas de Translocación de Protón Vacuolares/metabolismoRESUMEN
The roles of potassium channels from the Shaker family in stomatal movements have been investigated by reverse genetics analyses in Arabidopsis (Arabidopsis thaliana), but corresponding information is lacking outside this model species. Rice (Oryza sativa) and other cereals possess stomata that are more complex than those of Arabidopsis. We examined the role of the outward Shaker K+ channel gene OsK5.2. Expression of the OsK5.2 gene (GUS reporter strategy) was observed in the whole stomatal complex (guard cells and subsidiary cells), root vasculature, and root cortex. In stomata, loss of OsK5.2 functional expression resulted in lack of time-dependent outward potassium currents in guard cells, higher rates of water loss through transpiration, and severe slowdown of stomatal closure. In line with the expression of OsK5.2 in the plant vasculature, mutant plants displayed a reduced K+ translocation from the root system toward the leaves via the xylem. The comparison between rice and Arabidopsis show that despite the strong conservation of Shaker family in plants, substantial differences can exist between the physiological roles of seemingly orthologous genes, as xylem loading depends on SKOR and stomatal closure on GORK in Arabidopsis, whereas both functions are executed by the single OsK5.2 Shaker in rice.
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Canales Iónicos/metabolismo , Oryza/metabolismo , Exudados de Plantas/metabolismo , Proteínas de Plantas/metabolismo , Estomas de Plantas/metabolismo , Potasio/metabolismo , Xilema/metabolismo , Arabidopsis , Transporte Biológico , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Canales Iónicos/genética , Cinética , Mutación/genética , Técnicas de Placa-Clamp , Filogenia , Proteínas de Plantas/genética , Brotes de la Planta/metabolismo , Estomas de Plantas/citología , Transpiración de Plantas/fisiología , AguaRESUMEN
Phototropic hypocotyl bending in response to blue light excitation is an important adaptive process that helps plants to optimize their exposure to light. In Arabidopsis thaliana, phototropic hypocotyl bending is initiated by the blue light receptors and protein kinases phototropin1 (phot1) and phot2. Phototropic responses also require auxin transport and were shown to be partially compromised in mutants of the PIN-FORMED (PIN) auxin efflux facilitators. We previously described the D6 PROTEIN KINASE (D6PK) subfamily of AGCVIII kinases, which we proposed to directly regulate PIN-mediated auxin transport. Here, we show that phototropic hypocotyl bending is strongly dependent on the activity of D6PKs and the PIN proteins PIN3, PIN4, and PIN7. While early blue light and phot-dependent signaling events are not affected by the loss of D6PKs, we detect a gradual loss of PIN3 phosphorylation in d6pk mutants of increasing complexity that is most severe in the d6pk d6pkl1 d6pkl2 d6pkl3 quadruple mutant. This is accompanied by a reduction of basipetal auxin transport in the hypocotyls of d6pk as well as in pin mutants. Based on our data, we propose that D6PK-dependent PIN regulation promotes auxin transport and that auxin transport in the hypocotyl is a prerequisite for phot1-dependent hypocotyl bending.
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Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Hipocótilo/metabolismo , Ácidos Indolacéticos/metabolismo , Proteínas Quinasas/metabolismo , Arabidopsis/genética , Arabidopsis/fisiología , Proteínas de Arabidopsis/genética , Transporte Biológico/genética , Transporte Biológico/efectos de la radiación , Hipocótilo/genética , Hipocótilo/fisiología , Immunoblotting , Luz , Proteínas de Transporte de Membrana/genética , Proteínas de Transporte de Membrana/metabolismo , Microscopía Confocal , Mutación , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , Fosforilación/efectos de la radiación , Fototropismo/genética , Fototropismo/fisiología , Fototropismo/efectos de la radiación , Plantas Modificadas Genéticamente , Proteínas Quinasas/genética , Proteínas Serina-Treonina Quinasas , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
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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Ácido Abscísico/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas Bacterianas , Flagelina/metabolismo , Canales Iónicos/metabolismo , Proteínas de la Membrana/metabolismo , Estomas de Plantas/fisiología , Arabidopsis/efectos de los fármacos , Arabidopsis/fisiología , Proteínas Bacterianas/farmacología , Resistencia a la Enfermedad/fisiología , Mutación , Fosfoproteínas Fosfatasas/metabolismo , Enfermedades de las Plantas/microbiología , Proteínas Quinasas/metabolismo , Transducción de Señal , Estrés FisiológicoRESUMEN
Stomata are an attractive experimental system in plant biology, because the responses of guard cells to environmental signals can be directly linked to changes in the aperture of stomatal pores. In this review, the mechanics of stomatal movement are discussed in relation to ion transport in guard cells. Emphasis is placed on the ion pumps, transporters, and channels in the plasma membrane, as well as in the vacuolar membrane. The biophysical properties of transport proteins for H(+), K(+), Ca(2+), and anions are discussed and related to their function in guard cells during stomatal movements. Guard cell signaling pathways for ABA, CO2, ozone, microbe-associated molecular patterns (MAMPs) and blue light are presented. Special attention is given to the regulation of the slow anion channel (SLAC) and SLAC homolog (SLAH)-type anion channels by the ABA signalosome. Over the last decade, several knowledge gaps in the regulation of ion transport in guard cells have been closed. The current state of knowledge is an excellent starting point for tackling important open questions concerning stress tolerance in plants.
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Canales Iónicos/fisiología , Estomas de Plantas/citología , Transducción de Señal/fisiología , Ácido Abscísico/metabolismo , Evolución Biológica , Dióxido de Carbono/metabolismo , Transporte Iónico , Luz , Ozono/metabolismo , Fenómenos Fisiológicos de las Plantas , Agua/fisiologíaRESUMEN
Although there has been long-standing recognition that stimuli-induced cytosolic pH alterations coincide with changes in calcium ion (Ca2+) levels, the interdependence between protons (H+) and Ca2+ remains poorly understood. We addressed this topic using the light-gated channelrhodopsin HcKCR2 from the pseudofungus Hyphochytrium catenoides, which operates as a H+ conductive, Ca2+ impermeable ion channel on the plasma membrane of plant cells. Light activation of HcKCR2 in Arabidopsis guard cells evokes a transient cytoplasmic acidification that sparks Ca2+ release from the endoplasmic reticulum. A H+-induced cytosolic Ca2+ signal results in membrane depolarization through the activation of Ca2+-dependent SLAC1/SLAH3 anion channels, which enabled us to remotely control stomatal movement. Our study suggests a H+-induced Ca2+ release mechanism in plant cells and establishes HcKCR2 as a tool to dissect the molecular basis of plant intracellular pH and Ca2+ signaling.
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Proteínas de Arabidopsis , Arabidopsis , Señalización del Calcio , Calcio , Channelrhodopsins , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Calcio/metabolismo , Channelrhodopsins/genética , Channelrhodopsins/metabolismo , Estomas de Plantas/metabolismo , Protones , Rhinosporidium , Concentración de Iones de HidrógenoRESUMEN
Stomatal closure is known to be associated with early defence responses of plant cells triggered by microbe-associated molecular patterns (MAMPs). However, the molecular mechanisms underlying these guard-cell responses have not yet been elucidated. We therefore studied pathogen-induced changes in ion channel activity in Hordeum vulgare guard cells. Barley mildew (Blumeria graminis) hyphae growing on leaves inhibited light-induced stomatal opening, starting at 9 h after inoculation, when appressoria had developed. Alternatively, stomatal closure was induced by nano-infusion of chitosan via open stomata into the sub-stomatal cavity. Experiments using intracellular double-barreled micro-electrodes revealed that mildew stimulated S-type (slow) anion channels in guard cells. These channels enable the efflux of anions from guard cells and also promote K(+) extrusion by altering the plasma membrane potential. Stimulation of S-type anion channels was also provoked by nano-infusion of chitosan. These data suggest that MAMPs of mildew hyphae penetrating the cuticle provoke activation of S-type anion channels in guard cells. In response, guard cells extrude K(+) salts, resulting in stomatal closure. Plasma membrane anion channels probably represent general targets of MAMP signaling in plants, as these elicitors depolarize the plasma membrane of various cell types.