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.

Alternative Splicing Underpins the ALMT9 Transporter Function for Vacuolar Malic Acid Accumulation in Apple.

Vacuolar malic acid accumulation largely determines fruit acidity, a key trait for the taste and flavor of apple and other fleshy fruits. Aluminum-activated malate transporter 9 (ALMT9/Ma1) underlies a major genetic locus, Ma, for fruit acidity in apple, but how the protein transports malate across the tonoplast is unclear. Here, it is shown that overexpression of the coding sequence of Ma1 (Ma1α) drastically decreases fruit acidity in "Royal Gala" apple, leading to uncovering alternative splicing underpins Ma1's function.

Exploring the Interplay between Polyphenols and Lysyl Oxidase Enzymes for Maintaining Extracellular Matrix Homeostasis.

Collagen, the most abundant structural protein found in mammals, plays a vital role as a constituent of the extracellular matrix (ECM) that surrounds cells. Collagen fibrils are strengthened through the formation of covalent cross-links, which involve complex enzymatic and non-enzymatic reactions. Lysyl oxidase (LOX) is responsible for catalyzing the oxidative deamination of lysine and hydroxylysine residues, resulting in the production of aldehydes, allysine, and hydroxyallysine.

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.

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.

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.

An extracellular cation coordination site influences ion conduction of OsHKT2;2.

Background: HKT channels mediate sodium uniport or sodium and potassium symport in plants. Monocotyledons express a higher number of HKT proteins than dicotyledons, and it is only within this clade of HKT channels that cation symport mechanisms are found. The prevailing ion composition in the extracellular medium affects the transport abilities of various HKT channels by changing their selectivity or ion transport rates.

Yeast strain Saccharomyces cerevisiae BYT45 lacking the cation extrusion systems ENA1-5 and NHA1 is suitable for the characterization of TASK-3 potassium channel antagonists.

Finding new potential antagonists of potassium channels is a continuing task. TASK potassium channels operate over a large physiological range of membrane voltages, why they are thought to contribute to the excitability and resting potential of mammalian membrane potentials. Additionally, they are regulated by extracellular stimuli like changes in pH and K+ concentrations.

Nutrient exchange in arbuscular mycorrhizal symbiosis from a thermodynamic point of view.

To obtain insights into the dynamics of nutrient exchange in arbuscular mycorrhizal (AM) symbiosis, we modelled mathematically the two-membrane system at the plant-fungus interface and simulated its dynamics. In computational cell biology experiments, the full range of nutrient transport pathways was tested for their ability to exchange phosphorus (P)/carbon (C)/nitrogen (N) sources. As a result, we obtained a thermodynamically justified, independent and comprehensive model of the dynamics of the nutrient exchange at the plant-fungus contact zone.

The potassium battery: a mobile energy source for transport processes in plant vascular tissues.

Contents 1049 I. 1049 II. 1050 III.

The receptor-like pseudokinase MRH1 interacts with the voltage-gated potassium channel AKT2.

The potassium channel AKT2 plays important roles in phloem loading and unloading. It can operate as inward-rectifying channel that allows H-ATPase-energized K uptake. Moreover, through reversible post-translational modifications it can also function as an open, K-selective channel, which taps a 'potassium battery', providing additional energy for transmembrane transport processes.

Outward Rectification of Voltage-Gated K+ Channels Evolved at Least Twice in Life History.

Voltage-gated potassium (K+) channels are present in all living systems. Despite high structural similarities in the transmembrane domains (TMD), this K+ channel type segregates into at least two main functional categories-hyperpolarization-activated, inward-rectifying (Kin) and depolarization-activated, outward-rectifying (Kout) channels. Voltage-gated K+ channels sense the membrane voltage via a voltage-sensing domain that is connected to the conduction pathway of the channel.

K₂p channels in plants and animals.

Two-pore domain potassium (K2P) channels are membrane proteins widely identified in mammals, plants, and other organisms. A functional channel is a dimer with each subunit comprising two pore-forming loops and four transmembrane domains. The genome of the model plant Arabidopsis thaliana harbors five genes coding for K2P channels.

Voltage-sensor transitions of the inward-rectifying K+ channel KAT1 indicate a latching mechanism biased by hydration within the voltage sensor.

The Kv-like (potassium voltage-dependent) K(+) channels at the plasma membrane, including the inward-rectifying KAT1 K(+) channel of Arabidopsis (Arabidopsis thaliana), are important targets for manipulating K(+) homeostasis in plants. Gating modification, especially, has been identified as a promising means by which to engineer plants with improved characteristics in mineral and water use. Understanding plant K(+) channel gating poses several challenges, despite many similarities to that of mammalian Kv and Shaker channel models.

The role of K(+) channels in uptake and redistribution of potassium in the model plant Arabidopsis thaliana.

Potassium (K(+)) is inevitable for plant growth and development. It plays a crucial role in the regulation of enzyme activities, in adjusting the electrical membrane potential and the cellular turgor, in regulating cellular homeostasis and in the stabilization of protein synthesis. Uptake of K(+) from the soil and its transport to growing organs is essential for a healthy plant development.

The pH sensor of the plant K+-uptake channel KAT1 is built from a sensory cloud rather than from single key amino acids.

The uptake of potassium ions (K+) accompanied by an acidification of the apoplasm is a prerequisite for stomatal opening. The acidification (approximately 2-2.5 pH units) is perceived by voltage-gated inward potassium channels (K(in)) that then can open their pores with lower energy cost.

A minimal cysteine motif required to activate the SKOR K+ channel of Arabidopsis by the reactive oxygen species H2O2.

Reactive oxygen species (ROS) are essential for development and stress signaling in plants. They contribute to plant defense against pathogens, regulate stomatal transpiration, and influence nutrient uptake and partitioning. Although both Ca(2+) and K(+) channels of plants are known to be affected, virtually nothing is known of the targets for ROS at a molecular level.

Distributed structures underlie gating differences between the kin channel KAT1 and the Kout channel SKOR.

The family of voltage-gated (Shaker-like) potassium channels in plants includes both inward-rectifying (K(in)) channels that allow plant cells to accumulate K(+) and outward-rectifying (K(out)) channels that mediate K(+) efflux. Despite their close structural similarities, K(in) and K(out) channels differ in their gating sensitivity towards voltage and the extracellular K(+) concentration. We have carried out a systematic program of domain swapping between the K(out) channel SKOR and the K(in) channel KAT1 to examine the impacts on gating of the pore regions, the S4, S5, and the S6 helices.