Structure and activity of SLAC1 channels for stomatal signaling in leaves

Stomata in leaves regulate gas exchange between the plant and its atmosphere. Various environmental stimuli elicit abscisic acid (ABA); ABA leads to phosphoactivation of slow anion channel 1 (SLAC1); SLAC1 activity reduces turgor pressure in aperture-defining guard cells; and stomatal closure ensues. We used electrophysiology for functional characterizations of Arabidopsis thaliana SLAC1 (AtSLAC1) and cryoelectron microscopy (cryo-EM) for structural analysis of Brachypodium distachyon SLAC1 (BdSLAC1), at 2.97-Å resolution. We identified 14 phosphorylation sites in AtSLAC1 and showed nearly 330-fold channel-activity enhancement with 4 to 6 of these phosphorylated. Seven SLAC1-conserved arginines are poised in BdSLAC1 for regulatory interaction with the N-terminal extension. This BdSLAC1 structure has its pores closed, in a basal state, spring loaded by phenylalanyl residues in high-energy conformations. SLAC1 phosphorylation fine-tunes an equilibrium between basal and activated SLAC1 trimers, thereby controlling the degree of stomatal opening.

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Molecular basis for the R-type anion channel QUAC1 activity in guard cells

10.1101/2021.09.09.459598 ◽

2021 ◽

Author(s):

Li Qin ◽

Ling-hui Tang ◽

Jia-shu Xu ◽

Xian-hui Zhang ◽

Yun Zhu ◽

...

Keyword(s):

Molecular Basis ◽

Stomatal Closure ◽

Anion Channel ◽

Guard Cells ◽

Channel Activity ◽

Cytoplasmic Domains ◽

Anion Channels ◽

Channel Activation ◽

Environmental Stimuli ◽

Functional Analyses

SUMMARYThe rapid (R)-type anion channel plays a central role in controlling stomatal closure in plant guard cells, thus regulating the exchange of water and photosynthetic gas (CO2) in response to environmental stimuli. The activity of the R- type anion channel is regulated by malate. However, the molecular basis of the R-type anion channel activity remains elusive. Here, we describe the first cryo-EM structure of the R-type anion channel QUAC1 at 3.5 Å resolution in the presence of malate. The structure reveals that the QUAC1 is a symmetrical dimer, forming a single electropositive T-shaped pore for passing anions across the membrane. The transmembrane and cytoplasmic domains are assembled into a twisted bi-layer architecture, with the associated dimeric interfaces nearly perpendicular. Our structural and functional analyses reveal that QUAC1 functions as an inward rectifying anion channel and suggests a mechanism for malate-mediated channel activation. Altogether, our study uncovers the molecular basis for a novel class of anion channels and provides insights into the gating and modulation of the R-type anion channel.

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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 ◽

10.1073/pnas.1807624115 ◽

2018 ◽

Vol 115 (44) ◽

pp. 11129-11137 ◽

Cited By ~ 18

Author(s):

Jingbo Zhang ◽

Nuo Wang ◽

Yinglong Miao ◽

Felix Hauser ◽

J. Andrew McCammon ◽

...

Keyword(s):

Stomatal Closure ◽

Anion Channel ◽

Guard Cells ◽

Channel Activity ◽

Plant Leaves ◽

In Planta ◽

Anion Channels ◽

Accelerated Molecular Dynamics ◽

Bicarbonate Ions ◽

Stomatal Movements

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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Structural and Functional Insights into the Role of Guard Cell Ion Channels in Abiotic Stress-Induced Stomatal Closure

Plants ◽

10.3390/plants10122774 ◽

2021 ◽

Vol 10 (12) ◽

pp. 2774

Author(s):

Hamdy Kashtoh ◽

Kwang-Hyun Baek

Keyword(s):

Ion Channels ◽

Guard Cell ◽

Stomatal Closure ◽

Turgor Pressure ◽

Anion Channel ◽

Weather Conditions ◽

Guard Cells ◽

Water Transpiration ◽

Structure And Functions

A stomatal pore is formed by a pair of specialized guard cells and serves as a major gateway for water transpiration and atmospheric CO2 influx for photosynthesis in plants. These pores must be tightly controlled, as inadequate CO2 intake and excessive water loss are devastating for plants. When the plants are exposed to extreme weather conditions such as high CO2 levels, O3, low air humidity, and drought, the turgor pressure of the guard cells exhibits an appropriate response against these stresses, which leads to stomatal closure. This phenomenon involves a complex network of ion channels and their regulation. It is well-established that the turgor pressure of guard cells is regulated by ions transportation across the membrane, such as anions and potassium ions. In this review, the guard cell ion channels are discussed, highlighting the structure and functions of key ion channels; the SLAC1 anion channel and KAT1 potassium channel, and their regulatory components, emphasizing their significance in guard cell response to various stimuli.

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Faculty Opinions recommendation of Stomatal closure by fast abscisic acid signaling is mediated by the guard cell anion channel SLAH3 and the receptor RCAR1.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.10694957.11793055 ◽

2011 ◽

Author(s):

Julian Schroeder

Keyword(s):

Abscisic Acid ◽

Guard Cell ◽

Stomatal Closure ◽

Anion Channel ◽

Abscisic Acid Signaling

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Faculty Opinions recommendation of The trafficking protein SYP121 of Arabidopsis connects programmed stomatal closure and K⁺ channel activity with vegetative growth.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.13372993.14743108 ◽

2011 ◽

Author(s):

Martin Robert McAinsh

Keyword(s):

Vegetative Growth ◽

Stomatal Closure ◽

K Channel ◽

Channel Activity

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The trafficking protein SYP121 of Arabidopsis connects programmed stomatal closure and K + channel activity with vegetative growth

The Plant Journal ◽

10.1111/j.1365-313x.2011.04786.x ◽

2011 ◽

Vol 69 (2) ◽

pp. 241-251 ◽

Cited By ~ 52

Author(s):

Cornelia Eisenach ◽

Zhong‐Hua Chen ◽

Christopher Grefen ◽

Michael R. Blatt

Keyword(s):

Vegetative Growth ◽

Stomatal Closure ◽

K Channel ◽

Channel Activity

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Analysis of anion channel activity in chondrocytes in vitro model of osteoarthritis

Osteoarthritis and Cartilage ◽

10.1016/j.joca.2018.02.226 ◽

2018 ◽

Vol 26 ◽

pp. S104

Author(s):

K. Kumagai ◽

F. Toyoda ◽

C. Staunton ◽

U. Sharif ◽

R. Lewis ◽

...

Keyword(s):

In Vitro Model ◽

Anion Channel ◽

Channel Activity ◽

Vitro Model

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Modulation of frequency and height of cytosolic calcium spikes by plasma membrane anion channels in guard cells

Bioscience Biotechnology and Biochemistry ◽

10.1093/bbb/zbab118 ◽

2021 ◽

Author(s):

Md Tahjib-Ul-Arif ◽

Shintaro Munemasa ◽

Toshiyuki Nakamura ◽

Yoshimasa Nakamura ◽

Yoshiyuki Murata

Keyword(s):

Plasma Membrane ◽

Stomatal Closure ◽

Anion Channel ◽

Guard Cells ◽

Cytosolic Calcium ◽

Peak Height ◽

Extracellular Calcium ◽

Wild Type ◽

Anion Channels ◽

In The Wild

Abstract Cytosolic calcium ([Ca2+]cyt) elevation activates plasma membrane anion channels in guard cells, which is required for stomatal closure. However, involvement of the anion channels in the [Ca2+]cyt elevation remains unclear. We investigated the involvement using Arabidopsis thaliana anion channel mutants, slac1-4 slah3-3 and slac1-4 almt12-1. Extracellular calcium induced stomatal closure in the wild-type plants but not in the anion channel mutant plants whereas extracellular calcium induced [Ca2+]cyt elevation both in the wild-type guard cells and in the mutant guard cells. The peak height and the number of the [Ca2+]cyt spike were lower and larger in the slac1-4 slah3-3 than in the wild-type and the height and the number in the slac1-4 almt12-1 were much lower and much larger than in the wild-type. These results suggest that the anion channels are involved in the regulation of [Ca2+]cyt elevation in guard cells.

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Anion channel SLAH3 is a regulatory target of chitin receptor-associated kinase PBL27 in microbial stomatal closure

eLife ◽

10.7554/elife.44474 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 12

Author(s):

Yi Liu ◽

Tobias Maierhofer ◽

Katarzyna Rybak ◽

Jan Sklenar ◽

Andy Breakspear ◽

...

Keyword(s):

Stomatal Closure ◽

Anion Channel ◽

Anion Channels ◽

Slow Type ◽

Leaf Level ◽

Short Signal ◽

Molecular Patterns ◽

Fungal Immunity ◽

Anti Fungal ◽

Full Activation

In plants, antimicrobial immune responses involve the cellular release of anions and are responsible for the closure of stomatal pores. Detection of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) induces currents mediated via slow-type (S-type) anion channels by a yet not understood mechanism. Here, we show that stomatal closure to fungal chitin is conferred by the major PRRs for chitin recognition, LYK5 and CERK1, the receptor-like cytoplasmic kinase PBL27, and the SLAH3 anion channel. PBL27 has the capacity to phosphorylate SLAH3, of which S127 and S189 are required to activate SLAH3. Full activation of the channel entails CERK1, depending on PBL27. Importantly, both S127 and S189 residues of SLAH3 are required for chitin-induced stomatal closure and anti-fungal immunity at the whole leaf level. Our results demonstrate a short signal transduction module from MAMP recognition to anion channel activation, and independent of ABA-induced SLAH3 activation.

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