1
|
Lemtiri-Chlieh F, Arold ST, Gehring C. Mg 2+ Is a Missing Link in Plant Cell Ca 2+ Signalling and Homeostasis-A Study on Vicia faba Guard Cells. Int J Mol Sci 2020; 21:ijms21113771. [PMID: 32471040 PMCID: PMC7312177 DOI: 10.3390/ijms21113771] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2020] [Revised: 05/13/2020] [Accepted: 05/15/2020] [Indexed: 01/04/2023] Open
Abstract
Hyperpolarization-activated calcium channels (HACCs) are found in the plasma membrane and tonoplast of many plant cell types, where they have an important role in Ca2+-dependent signalling. The unusual gating properties of HACCs in plants, i.e., activation by membrane hyperpolarization rather than depolarization, dictates that HACCs are normally open in the physiological hyperpolarized resting membrane potential state (the so-called pump or P-state); thus, if not regulated, they would continuously leak Ca2+ into cells. HACCs are permeable to Ca2+, Ba2+, and Mg2+; activated by H2O2 and the plant hormone abscisic acid (ABA); and their activity in guard cells is greatly reduced by increasing amounts of free cytosolic Ca2+ ([Ca2+]Cyt), and hence closes during [Ca2+]Cyt surges. Here, we demonstrate that the presence of the commonly used Mg-ATP inside the guard cell greatly reduces HACC activity, especially at voltages ≤ −200 mV, and that Mg2+ causes this block. Therefore, we firstly conclude that physiological cytosolic Mg2+ levels affect HACC gating and that channel opening requires either high negative voltages (≥−200 mV) or displacement of Mg2+ away from the immediate vicinity of the channel. Secondly, based on structural comparisons with a Mg2+-sensitive animal inward-rectifying K+ channel, we propose that the likely candidate HACCs described here are cyclic nucleotide gated channels (CNGCs), many of which also contain a conserved diacidic Mg2+ binding motif within their pores. This conclusion is consistent with the electrophysiological data. Finally, we propose that Mg2+, much like in animal cells, is an important component in Ca2+ signalling and homeostasis in plants.
Collapse
Affiliation(s)
- Fouad Lemtiri-Chlieh
- King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE), Thuwal 23955-6900, Saudi Arabia;
- Department of Neuroscience, University of Connecticut School of Medicine, Farmington, CT 06030, USA
- Correspondence: (F.L.-C); (C.G.)
| | - Stefan T. Arold
- King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE), Thuwal 23955-6900, Saudi Arabia;
- King Abdullah University of Science and Technology (KAUST), Computational Bioscience Research Center (CBRC), Thuwal 23955-6900, Saudi Arabia
- Centre de Biochimie Structurale, CNRS, INSERM, Université de Montpellier, 34090 Montpellier, France
| | - Chris Gehring
- King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE), Thuwal 23955-6900, Saudi Arabia;
- Department of Chemistry, Biology & Biotechnology, University of Perugia, 06121 Perugia, Italy
- Correspondence: (F.L.-C); (C.G.)
| |
Collapse
|
2
|
Misra BB, Reichman SM, Chen S. The guard cell ionome: Understanding the role of ions in guard cell functions. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 146:50-62. [PMID: 30458181 DOI: 10.1016/j.pbiomolbio.2018.11.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2018] [Revised: 11/01/2018] [Accepted: 11/16/2018] [Indexed: 12/20/2022]
Abstract
The ionome is critical for plant growth, productivity, defense, and it eventually affects human food quantity and quality. Located on the leaf surface, stomatal guard cells are critical gatekeepers for water, gas, and pathogens. Insights form ionomics (metallomics) is imperative as we enter an omics-driven systems biology era where an understanding of guard cell function and physiology is advanced through efforts in genomics, transcriptomics, proteomics, and metabolomics. While the roles of major cations (K, Ca) and anions (Cl) are well known in guard cell function, the related physiology, movement and regulation of trace elements, metal ions, and heavy metals are poorly understood. The majority of the information on the role of trace elements in guard cells emanates from classical feeding experiments, field or in vitro fortification, micropropagation, and microscopy studies, while novel insights are available from limited metal ion transporter and ion channel studies. Given the rejuvenated and recent interest in the constantly changing ionome in plant mineral balance and eventually in human nutrition and health, we looked into the far from established guard cell ionome in lieu of the modern omics era of high throughput research endeavors. Newer technologies and tools i.e., high resolution mass spectrometry, advanced imaging, and phenomics are now available to delve into the guard cell ionomes. In this review, research efforts on guard cell ionomes were collated and categorized, and we highlight the underlying role of the largely unknown ionome in guard cell function towards a systems physiology understanding of plant health and productivity.
Collapse
Affiliation(s)
- Biswapriya B Misra
- Center for Precision Medicine, Department of Internal Medicine, Section on Molecular Medicine, Wake Forest School of Medicine, Medical Center Boulevard, Winston Salem, 27157, NC, USA; Department of Biology, Genetics Institute, Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, 32610, USA.
| | - Suzie M Reichman
- School of Engineering, RMIT University, GPO Box 2476, Melbourne, 3001, Australia; Centre for Environmental Sustainability and Remediation, RMIT University, GPO Box 2476, Melbourne, 3001, Australia
| | - Sixue Chen
- Department of Biology, Genetics Institute, Plant Molecular and Cellular Biology Program, University of Florida, Gainesville, FL, 32610, USA; Proteomics and Mass Spectrometry, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL, 32610, USA
| |
Collapse
|
3
|
Wolf T, Guinot DR, Hedrich R, Dietrich P, Marten I. Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex. PLANT & CELL PHYSIOLOGY 2005; 46:1682-9. [PMID: 16081526 DOI: 10.1093/pcp/pci184] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Voltage-dependent inward-rectifying (K(in)) and outward-rectifying (K(out)) K(+) channels are capable of mediating K(+) fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K(+) channels provided evidence for the requirement of ATP to maintain K(+) channel activity. Here, the nucleotide and Mg(2+) dependencies of time-dependent K(in) and K(out) channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K(out) channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K(out) channels by fast activation kinetics, inhibition by elevated intracellular Mg(2+) concentration, permeability for K(+) as well as for Na(+) and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K(+) and Na(+) transport in both cell types and species.
Collapse
Affiliation(s)
- Thomas Wolf
- Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Bioscience, University of Wuerzburg, Germany
| | | | | | | | | |
Collapse
|
4
|
Schachtman DP. Molecular insights into the structure and function of plant K(+) transport mechanisms. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1465:127-39. [PMID: 10748250 DOI: 10.1016/s0005-2736(00)00134-6] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Our understanding of plant potassium transport has increased in the past decade through the application of molecular biological techniques. In this review, recent work on inward and outward rectifying K(+) channels as well as high affinity K(+) transporters is described. Through the work on inward rectifying K(+) channels, we now have precise details on how the structure of these proteins determines functional characteristics such as ion conduction, pH sensitivity, selectivity and voltage sensing. The physiological function of inward rectifying K(+) channels in plants has been clarified through the analysis of expression patterns and mutational analysis. Two classes of outward rectifying K(+) channels have now been cloned from plants and their initial characterisation is reviewed. The physiological role of one class of outward rectifying K(+) channel has been demonstrated to be involved in long distance transport of K(+) from roots to shoots. The molecular structure and function of two classes of energised K(+) transporters are also reviewed. The first class is energised by Na(+) and shares structural similarities with K(+) transport mechanisms in bacteria and fungi. Structure-function studies suggest that it should be possible to increase the K(+) and Na(+) selectivity of these transporters, which will enhance the salt tolerance of higher plants. The second class of K(+) transporter is comprised of a large gene family and appears to have a dual affinity for K(+). A suite of molecular techniques, including gene cloning, oocyte expression, RNA localisation and gene inactivation, is now being used to fully characterise the biophysical and physiological function of plants K(+) transport mechanisms.
Collapse
Affiliation(s)
- D P Schachtman
- CSIRO Plant Industry, Horticulture Unit, GPO Box 350, Glen Osmond, Australia.
| |
Collapse
|
5
|
Ultrafast inactivation causes inward rectification in a voltage-gated K(+) channel from Caenorhabditis elegans. J Neurosci 2000. [PMID: 10632580 DOI: 10.1523/jneurosci.20-02-00511.2000] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The exp-2 gene in the nematode Caenorhabditis elegans influences the shape and duration of the action potential of pharyngeal muscle cells. Several loss-of-function mutations in exp-2 lead to broadening of the action potential and to a concomitant slowing of the pumping action of the pharynx. In contrast, a gain-of-function mutation leads to narrow action potentials and shallow pumping. We cloned and functionally characterized the exp-2 gene. The exp-2 gene is homologous to genes of the family of voltage-gated K(+) channels (Kv type). The Xenopus oocyte-expressed EXP-2 channel, although structurally closely related to Kv-type channels, is functionally distinct and very similar to the human ether-à-gogo-related gene (HERG) K(+) channel. In response to depolarization, EXP-2 activates slowly and inactivates very rapidly. On repolarization, recovery from inactivation is also rapid and strongly voltage-dependent. These kinetic properties make the Kv-type EXP-2 channel an inward rectifier that resembles the structurally unrelated HERG channel. Apart from many similarities to HERG, however, the molecular mechanism of fast inactivation appears to be different. Moreover, the single-channel conductance is 5- to 10-fold larger than that of HERG and most Kv-type K(+) channels. It appears that the inward rectification mechanism by rapid inactivation has evolved independently in two distinct classes of structurally unrelated, voltage-gated K(+) channels.
Collapse
|
6
|
Pei ZM, Ward JM, Schroeder JI. Magnesium Sensitizes Slow Vacuolar Channels to Physiological Cytosolic Calcium and Inhibits Fast Vacuolar Channels in Fava Bean Guard Cell Vacuoles. PLANT PHYSIOLOGY 1999; 121:977-986. [PMID: 10557247 PMCID: PMC59462 DOI: 10.1104/pp.121.3.977] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/1999] [Accepted: 07/12/1999] [Indexed: 05/20/2023]
Abstract
Vacuolar ion channels in guard cells play important roles during stomatal movement and are regulated by many factors including Ca(2+), calmodulin, protein kinases, and phosphatases. We report that physiological cytosolic and luminal Mg(2+) levels strongly regulate vacuolar ion channels in fava bean (Vicia faba) guard cells. Luminal Mg(2+) inhibited fast vacuolar (FV) currents with a K(i) of approximately 0.23 mM in a voltage-dependent manner at positive potentials on the cytoplasmic side. Cytosolic Mg(2+) at 1 mM also inhibited FV currents. Furthermore, in the absence of cytosolic Mg(2+), cytosolic Ca(2+) at less than 10 µM did not activate slow vacuolar (SV) currents. However, when cytosolic Mg(2+) was present, submicromolar concentrations of cytosolic Ca(2+) activated SV currents with a K(d) of approximately 227 nM, suggesting a synergistic Mg(2+)-Ca(2+) effect. The activation potential of SV currents was shifted toward physiological potentials in the presence of cytosolic Mg(2+) concentrations. The direction of SV currents could also be changed from outward to both outward and inward currents. Our data predict a model for SV channel regulation, including a cytosolic binding site for Ca(2+) with an affinity in the submicromolar range and a cytosolic low-affinity Mg(2+)-Ca(2+) binding site. SV channels are predicted to contain a third binding site on the vacuolar luminal side, which binds Ca(2+) and is inhibitory. In conclusion, cytosolic Mg(2+) sensitizes SV channels to physiological cytosolic Ca(2+) elevations. Furthermore, we propose that cytosolic and vacuolar Mg(2+) concentrations ensure that FV channels do not function as a continuous vacuolar K(+) leak, which would prohibit stomatal opening.
Collapse
Affiliation(s)
- ZM Pei
- Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0116
| | | | | |
Collapse
|
7
|
Abstract
Potassium channels contribute to the excitability of neurons and signaling in the nervous system. They arise from multiple gene families including one for voltage-gated potassium channels and one for inwardly rectifying potassium channels. Features of potassium permeation, channel gating and regulation, and subunit interaction have been analyzed. Potassium channels of similar design have been found in animals ranging from jellyfish to humans, as well as in plants, yeast, and bacteria. Structural similarities are evident for the pore-forming alpha subunits and for the beta subunits, which could potentially regulate channel activity according to the level of energy and/or reducing power of the cell.
Collapse
Affiliation(s)
- L Y Jan
- Department of Physiology, University of California, San Francisco 94143-0724, USA
| | | |
Collapse
|
8
|
Abstract
Recently developed molecular and genetic approaches have enabled the identification and functional characterization of novel genes encoding ion channels, ion carriers, and water channels of the plant plasma membrane.
Collapse
Affiliation(s)
- S M Assmann
- Biology Department, Pennsylvania State University, 208 Mueller Laboratory, University Park, PA 16802, USA.
| | | |
Collapse
|
9
|
Spector PS, Curran ME, Zou A, Keating MT, Sanguinetti MC. Fast inactivation causes rectification of the IKr channel. J Gen Physiol 1996; 107:611-9. [PMID: 8740374 PMCID: PMC2217012 DOI: 10.1085/jgp.107.5.611] [Citation(s) in RCA: 320] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The mechanism of rectification of HERG, the human cardiac delayed rectifier K+ channel, was studied after heterologous expression in Xenopus oocytes. Currents were measured using two-microelectrode and macropatch voltage clamp techniques. The fully activated current-voltage (I-V) relationship for HERG inwardly rectified. Rectification was not altered by exposing the cytoplasmic side of a macropatch to a divalent-free solution, indicating this property was not caused by voltage-dependent block of outward current by Mg2+ or other soluble cytosolic molecules. The instantaneous I-V relationship for HERG was linear after removal of fast inactivation by a brief hyperpolarization. The time constants for the onset of and recovery from inactivation were a bell-shaped function of membrane potential. The time constants of inactivation varied from 1.8 ms at +50 mV to 16 ms at -20 mV; recovery from inactivation varied from 4.7 ms at -120 mV to 15 ms at -50 mV. Truncation of the NH2-terminal region of HERG shifted the voltage dependence of activation and inactivation by +20 to +30 mV. In addition, the rate of deactivation of the truncated channel was much faster than wild-type HERG. The mechanism of HERG rectification is voltage-gated fast inactivation. Inactivation of channels proceeds at a much faster rate than activation, such that no outward current is observed upon depolarization to very high membrane potentials. Fast inactivation of HERG and the resulting rectification are partly responsible for the prolonged plateau phase typical of ventricular action potentials.
Collapse
Affiliation(s)
- P S Spector
- Cardiology Division, University of Utah, Salt Lake City 84112, USA
| | | | | | | | | |
Collapse
|
10
|
Uozumi N, Gassmann W, Cao Y, Schroeder JI. Identification of strong modifications in cation selectivity in an Arabidopsis inward rectifying potassium channel by mutant selection in yeast. J Biol Chem 1995; 270:24276-81. [PMID: 7592636 DOI: 10.1074/jbc.270.41.24276] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The Arabidopsis thaliana cDNA, KAT1, encodes a hyperpolarization-activated K+ channel. In the present study, we utilized a combination of random site-directed mutagenesis, genetic screening in a potassium uptake-deficient yeast strain, and electrophysiological analysis in Xenopus oocytes to identify strong modifications in cation selectivity of the inward rectifying K+ channel KAT1. Threonine at position 256 was replaced by 11 other amino acid residues. Six of these mutated KAT1 cDNAs complemented a K+ uptake-deficient yeast strain at low concentrations of potassium. Among these, two mutants (T256D and T256G) showed a sensitivity of yeast growth toward high ammonium concentrations and a dramatic increase in current amplitudes of rubidium and ammonium ions relative to K+ by 39-72-fold. These single site mutations gave rise to Rb+- and NH4(+)-selective channels with Rb+ and NH4+ currents that were approximately 10-13-fold greater in amplitude than K+ currents, whereas the NH4+ to K+ current amplitude ratio of wild type KAT1 was 0.28. This strong conversion in cation specificity without loss of general selectivity exceeds those reported for other mutations in the pore domain of voltage-dependent K+ channels. Yeast growth was greatly impaired by sodium in two other mutants at this site (T256E and T256Q), which were blocked by millimolar sodium (K1/2 = 1.1 mM for T256E), although the wild type channel was not blocked by 110 mM sodium. Interestingly, the ability of yeast to grow in the presence of toxic cations correlated to biophysical properties of KAT1 mutants, illustrating the potential for qualitative K+ channel mutant selection in yeast. These data suggest that the size of the side chain of the amino acid at position 256 in KAT1 is important for enabling cation permeation and that this site plays a crucial role in determining the cation selectivity of hyperpolarization-activated potassium channels.
Collapse
Affiliation(s)
- N Uozumi
- Department of Biology, University of California, San Diego, La Jolla 92093-0116, USA
| | | | | | | |
Collapse
|
11
|
Cao Y, Crawford NM, Schroeder JI. Amino Terminus and the First Four Membrane-spanning Segments of the Arabidopsis K+ Channel KAT1 Confer Inward-rectification Property of Plant-Animal Chimeric Channels. J Biol Chem 1995. [DOI: 10.1074/jbc.270.30.17697] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
|