Structure reveals a regulation mechanism of plant outward-rectifying K channel GORK by structural rearrangements in the CNBD-Ankyrin bridge.

Guard cells, which regulate stomatal apertures in plants, possess a sophisticated mechanism for regulating turgor pressure. The outward-rectifying "K" channel GORK, expressed in guard cells of the plant , is a central component that promotes stomatal closure by releasing K to the extracellular space, thereby lowering turgor pressure. To date, the structural basis underlying the regulation of the K transport activity of GORK is unclear.

Potassium homeostasis and signalling: from the whole plant to the subcellular level.

Potassium is an essential macronutrient required for plant growth and development. Over the recent decade, an important signalling role of K has emerged. Here, we discuss some aspects of such signalling at the various levels of plant functional organisation.

Dynamics of homeostats: the basis of electrical, chemical, hydraulic, pH and calcium signaling in plants.

Homeostats are important to control homeostatic conditions. Here, we have analyzed the theoretical basis of their dynamic properties by bringing the K homeostat out of steady state (i) by an electrical stimulus, (ii) by an external imbalance in the K or H gradient or (iii) by a readjustment of transporter activities. The reactions to such changes can be divided into (i) a short-term response (tens of milliseconds), where the membrane voltage changed along with the concentrations of ions that are not very abundant in the cytosol (H and Ca), and (ii) a long-term response (minutes and longer) caused by the slow changes in K concentrations.

Homeostats: The hidden rulers of ion homeostasis in plants.

Ion homeostasis is a crucial process in plants that is closely linked to the efficiency of nutrient uptake, stress tolerance and overall plant growth and development. Nevertheless, our understanding of the fundamental processes of ion homeostasis is still incomplete and highly fragmented. Especially at the mechanistic level, we are still in the process of dissecting physiological systems to analyse the different parts in isolation.

An auxin homeostat allows plant cells to establish and control defined transmembrane auxin gradients.

Extracellular auxin maxima and minima are important to control plant developmental programs. Auxin gradients are provided by the concerted action of proteins from the three major plasma membrane (PM) auxin transporter classes AUX1/LAX, PIN and ATP-BINDING CASSETTE subfamily B (ABCB) transporters. But neither genetic nor biochemical nor modeling approaches have been able to reliably assign the individual roles and interplay of these transporter types.

Temperature sensing: A potassium channel as cold sensor in the rain tree Samanea saman.

The rain tree Samanea saman folds its leaves upon rainfall. New results now indicate that rain perception is in fact a temperature-sensing process, and that Samanea possess an ion channel with a strong temperature sensitivity that is involved in leaf movement.

K and pH homeostasis in plant cells is controlled by a synchronized K /H antiport at the plasma and vacuolar membrane.

Stomatal movement involves ion transport across the plasma membrane (PM) and vacuolar membrane (VM) of guard cells. However, the coupling mechanisms of ion transporters in both membranes and their interplay with Ca and pH changes are largely unclear. Here, we investigated transporter networks in tobacco guard cells and mesophyll cells using multiparametric live-cell ion imaging and computational simulations.

SV channel VfTPC1 is a hyperexcitable variant of plant vacuole Two Pore Channels.

To fire action-potential-like electrical signals, the vacuole membrane requires the two-pore channel TPC1, formerly called SV channel. The TPC1/SV channel functions as a depolarization-stimulated, non-selective cation channel that is inhibited by luminal Ca. In our search for species-dependent functional TPC1 channel variants with different luminal Ca sensitivity, we found in total three acidic residues present in Ca sensor sites 2 and 3 of the Ca-sensitive AtTPC1 channel from that were neutral in its ortholog and also in those of many other Fabaceae.

The Surprising Dynamics of Electrochemical Coupling at Membrane Sandwiches in Plants.

Transport processes across membranes play central roles in any biological system. They are essential for homeostasis, cell nutrition, and signaling. Fluxes across membranes are governed by fundamental thermodynamic rules and are influenced by electrical potentials and concentration gradients.

TPC1-Type Channels in : Interaction between EF-Hands and Ca.

Two-pore channels (TPCs) are members of the superfamily of ligand-gated and voltage-sensitive ion channels in the membranes of intracellular organelles of eukaryotic cells. The evolution of ordinary plant TPC1 essentially followed a very conservative pattern, with no changes in the characteristic structural footprints of these channels, such as the cytosolic and luminal regions involved in Ca sensing. In contrast, the genomes of mosses and liverworts encode also TPC1-like channels with larger variations at these sites (TPC1b channels).

A unique inventory of ion transporters poises the Venus flytrap to fast-propagating action potentials and calcium waves.

Since the 19 century, it has been known that the carnivorous Venus flytrap is electrically excitable. Nevertheless, the mechanism and the molecular entities of the flytrap action potential (AP) remain unknown. When entering the electrically excitable stage, the trap expressed a characteristic inventory of ion transporters, among which the increase in glutamate receptor GLR3.

Transporter networks can serve plant cells as nutrient sensors and mimic transceptor-like behavior.

Sensing of external mineral nutrient concentrations is essential for plants to colonize environments with a large spectrum of nutrient availability. Here, we analyzed transporter networks in computational cell biology simulations to understand better the initial steps of this sensing process. The networks analyzed were capable of translating the information of changing external nutrient concentrations into cytosolic H and Ca signals, two of the most ubiquitous cellular second messengers.

Structural Insights into the Substrate Transport Mechanisms in GTR Transporters through Ensemble Docking.

Glucosinolate transporters (GTRs) are part of the nitrate/peptide transporter (NPF) family, members of which also transport specialized secondary metabolites as substrates. Glucosinolates are defense compounds derived from amino acids. We selected 4-methylthiobutyl (4MTB) and indol-3-ylmethyl (I3M) glucosinolates to study how GTR1 from transports these substrates in computational simulation approaches.

Nutrient cycling is an important mechanism for homeostasis in plant cells.

Homeostasis in living cells refers to the steady state of internal, physical, and chemical conditions. It is sustained by self-regulation of the dynamic cellular system. To gain insight into the homeostatic mechanisms that maintain cytosolic nutrient concentrations in plant cells within a homeostatic range, we performed computational cell biology experiments.

Computational Analyses of the AtTPC1 (Arabidopsis Two-Pore Channel 1) Permeation Pathway.

Two Pore Channels (TPCs) are cation-selective voltage- and ligand-gated ion channels in membranes of intracellular organelles of eukaryotic cells. In plants, the TPC1 subtype forms the slowly activating vacuolar (SV) channel, the most dominant ion channel in the vacuolar membrane. Controversial reports about the permeability properties of plant SV channels fueled speculations about the physiological roles of this channel type.

Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel ACR1.

Guard cells control the aperture of plant stomata, which are crucial for global fluxes of CO and water. In turn, guard cell anion channels are seen as key players for stomatal closure, but is activation of these channels sufficient to limit plant water loss? To answer this open question, we used an optogenetic approach based on the light-gated anion channelrhodopsin 1 (ACR1). In tobacco guard cells that express ACR1, blue- and green-light pulses elicit Cl and NO currents of -1 to -2 nA.

Acidosis-induced activation of anion channel SLAH3 in the flooding-related stress response of Arabidopsis.

Plants, as sessile organisms, gained the ability to sense and respond to biotic and abiotic stressors to survive severe changes in their environments. The change in our climate comes with extreme dry periods but also episodes of flooding. The latter stress condition causes anaerobiosis-triggered cytosolic acidosis and impairs plant function.

Plant HKT Channels: An Updated View on Structure, Function and Gene Regulation.

HKT channels are a plant protein family involved in sodium (Na) and potassium (K) uptake and Na-K homeostasis. Some HKTs underlie salt tolerance responses in plants, while others provide a mechanism to cope with short-term K shortage by allowing increased Na uptake under K starvation conditions. HKT channels present a functionally versatile family divided into two classes, mainly based on a sequence polymorphism found in the sequences underlying the selectivity filter of the first pore loop.

PSC-db: A Structured and Searchable 3D-Database for Plant Secondary Compounds.

Plants synthesize a large number of natural products, many of which are bioactive and have practical values as well as commercial potential. To explore this vast structural diversity, we present PSC-db, a unique plant metabolite database aimed to categorize the diverse phytochemical space by providing 3D-structural information along with physicochemical and pharmaceutical properties of the most relevant natural products. PSC-db may be utilized, for example, in qualitative estimation of biological activities (Quantitative Structure-Activity Relationship, QSAR) or massive docking campaigns to identify new bioactive compounds, as well as potential binding sites in target proteins.

A voltage-dependent Ca homeostat operates in the plant vacuolar membrane.

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 Ca 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 Ca and pH homeostasis of bulging root hair cells of Arabidopsis.

The Venus flytrap trigger hair-specific potassium channel KDM1 can reestablish the K+ gradient required for hapto-electric signaling.

The carnivorous plant Dionaea muscipula harbors multicellular trigger hairs designed to sense mechanical stimuli upon contact with animal prey. At the base of the trigger hair, mechanosensation is transduced into an all-or-nothing action potential (AP) that spreads all over the trap, ultimately leading to trap closure and prey capture. To reveal the molecular basis for the unique functional repertoire of this mechanoresponsive plant structure, we determined the transcriptome of D.

How to Grow a Tree: Plant Voltage-Dependent Cation Channels in the Spotlight of Evolution.

Phylogenetic analysis can be a powerful tool for generating hypotheses regarding the evolution of physiological processes. Here, we provide an updated view of the evolution of the main cation channels in plant electrical signalling: the Shaker family of voltage-gated potassium channels and the two-pore cation (K) channel (TPC1) family. Strikingly, the TPC1 family followed the same conservative evolutionary path as one particular subfamily of Shaker channels (K) and remained highly invariant after terrestrialisation, suggesting that electrical signalling was, and remains, key to survival on land.

Channelrhodopsin-mediated optogenetics highlights a central role of depolarization-dependent plant proton pumps.

In plants, environmental stressors trigger plasma membrane depolarizations. Being electrically interconnected via plasmodesmata, proper functional dissection of electrical signaling by electrophysiology is basically impossible. The green alga evolved blue light-excited channelrhodopsins (ChR1, 2) to navigate.