Sugar beet PMT5a and STP13 carriers suitable for proton-driven plasma membrane sucrose and glucose import in taproots.

Sugar beet (Beta vulgaris) is the major sugar-producing crop in Europe and Northern America, as the taproot stores sucrose at a concentration of around 20%. Genome sequence analysis together with biochemical and electrophysiological approaches led to the identification and characterization of the TST sucrose transporter driving vacuolar sugar accumulation in the taproot. However, the sugar transporters mediating sucrose uptake across the plasma membrane of taproot parenchyma cells remained unknown.

Synthesis of Helical Indolophenanthridines Showing Aggregation-Induced Emission.

Helical indolo[2,3-]- and [3,2-]phenanthridines were synthesized from amines by amide formation and Morgan-Walls cyclization. The synthetic routes offer the advantage of late-stage derivatization and do not require protecting groups, which makes the compounds directly suitable for further functionalization. The compounds exhibit remarkable acid-dependent bathochromic shifts of the luminescence, solvatochromism, and aggregation-induced emission (AIE) behavior, which make them especially interesting candidates for studies toward optoelectronic applications.

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.

ALMT-independent guard cell R-type anion currents.

Plant transpiration is controlled by stomata, with S- and R-type anion channels playing key roles in guard cell action. Arabidopsis mutants lacking the ALMT12/QUAC1 R-type anion channel function in guard cells show only a partial reduction in R-type channel currents. The molecular nature of these remaining R-type anion currents is still unclear.

TPC1 vacuole SV channel gains further shape - voltage priming of calcium-dependent gating.

Across phyla, voltage-gated ion channels (VGICs) allow excitability. The vacuolar two-pore channel AtTPC1 from the tiny mustard plant Arabidopsis thaliana has emerged as a paradigm for deciphering the role of voltage and calcium signals in membrane excitation. Among the numerous experimentally determined structures of VGICs, AtTPC1 was the first to be revealed in a closed and resting state, fueling speculation about structural rearrangements during channel activation.

Tobacco leaf tissue rapidly detoxifies direct salt loads without activation of calcium and SOS signaling.

Salt stress is a major abiotic stress, responsible for declining agricultural productivity. Roots are regarded as hubs for salt detoxification, however, leaf salt concentrations may exceed those of roots. How mature leaves manage acute sodium chloride (NaCl) stress is mostly unknown.

Molecular basis of multistep voltage activation in plant two-pore channel 1.

Voltage-gated ion channels confer excitability to biological membranes, initiating and propagating electrical signals across large distances on short timescales. Membrane excitation requires channels that respond to changes in electric field and couple the transmembrane voltage to gating of a central pore. To address the mechanism of this process in a voltage-gated ion channel, we determined structures of the plant two-pore channel 1 at different stages along its activation coordinate.

Voltage-dependent gating of SV channel TPC1 confers vacuole excitability.

In contrast to the plasma membrane, the vacuole membrane has not yet been associated with electrical excitation of plants. Here, we show that mesophyll vacuoles from Arabidopsis sense and control the membrane potential essentially via the K-permeable TPC1 and TPK channels. Electrical stimuli elicit transient depolarization of the vacuole membrane that can last for seconds.

High V-PPase activity is beneficial under high salt loads, but detrimental without salinity.

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 PP 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.

Structure and Function of TPC1 Vacuole SV Channel Gains Shape.

Plants and animals in endosomes operate TPC1/SV-type cation channels. All plants harbor at least one TPC1 gene. Although the encoded SV channel was firstly discovered in the plant vacuole membrane two decades ago, its biological function has remained enigmatic.

Control of basal jasmonate signalling and defence through modulation of intracellular cation flux capacity.

Unknown mechanisms tightly regulate the basal activity of the wound-inducible defence mediator jasmonate (JA) in undamaged tissues. However, the Arabidopsis fatty acid oxygenation upregulated2 (fou2) mutant in vacuolar two-pore channel 1 (TPC1 ) displays high JA pathway activity in undamaged leaves. This mutant was used to explore mechanisms controlling basal JA pathway regulation.

Functional characterisation and cell specificity of BvSUT1, the transporter that loads sucrose into the phloem of sugar beet (Beta vulgaris L.) source leaves.

Sugar beet (Beta vulgaris L.) is one of the most important sugar-producing plants worldwide and provides about one third of the sugar consumed by humans. Here we report on molecular characterisation of the BvSUT1 gene and on the functional characterisation of the encoded transporter.

Silent S-Type Anion Channel Subunit SLAH1 Gates SLAH3 Open for Chloride Root-to-Shoot Translocation.

Higher plants take up nutrients via the roots and load them into xylem vessels for translocation to the shoot. After uptake, anions have to be channeled toward the root xylem vessels. Thereby, xylem parenchyma and pericycle cells control the anion composition of the root-shoot xylem sap [1-6].

Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain.

The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents.

Identification of the transporter responsible for sucrose accumulation in sugar beet taproots.

Sugar beet provides around one third of the sugar consumed worldwide and serves as a significant source of bioenergy in the form of ethanol. Sucrose accounts for up to 18% of plant fresh weight in sugar beet. Most of the sucrose is concentrated in the taproot, where it accumulates in the vacuoles.

Overexpression of a proton-coupled vacuolar glucose exporter impairs freezing tolerance and seed germination.

Arabidopsis vacuoles harbor, besides sugar transporter of the TMT-type, an early response to dehydration like 6 (ERDL6) protein involved in glucose export into the cytosol. However, the mode of transport of ERDL6 and the plant's feedback to overexpression of its activity on essential properties such as, for example, seed germination or freezing tolerance, remain unexplored. Using patch-clamp studies on vacuoles expressing AtERDL6 we demonstrated directly that this carrier operates as a proton-driven glucose exporter.

Open stomata 1 (OST1) kinase controls R-type anion channel QUAC1 in Arabidopsis guard cells.

Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S-type anion channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting 'open stomata' phenotype.

C-terminus-mediated voltage gating of Arabidopsis guard cell anion channel QUAC1.

Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel families—SLAC/SLAH and ALMT—are known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al(3+)-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents.

Regulation of the V-type ATPase by redox modulation.

ATP-hydrolysis and proton pumping by the V-ATPase (vacuolar proton-translocating ATPase) are subject to redox regulation in mammals, yeast and plants. Oxidative inhibition of the V-ATPase is ascribed to disulfide-bond formation between conserved cysteine residues at the catalytic site of subunit A. Subunits containing amino acid substitutions of one of three conserved cysteine residues of VHA-A were expressed in a vha-A null mutant background in Arabidopsis.

Luminal and cytosolic pH feedback on proton pump activity and ATP affinity of V-type ATPase from Arabidopsis.

Proton pumping of the vacuolar-type H(+)-ATPase into the lumen of the central plant organelle generates a proton gradient of often 1-2 pH units or more. Although structural aspects of the V-type ATPase have been studied in great detail, the question of whether and how the proton pump action is controlled by the proton concentration on both sides of the membrane is not understood. Applying the patch clamp technique to isolated vacuoles from Arabidopsis mesophyll cells in the whole-vacuole mode, we studied the response of the V-ATPase to protons, voltage, and ATP.

Barley mildew and its elicitor chitosan promote closed stomata by stimulating guard-cell S-type anion channels.

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.

Cell type-specific regulation of ion channels within the maize stomatal complex.

The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells.

Proton-driven sucrose symport and antiport are provided by the vacuolar transporters SUC4 and TMT1/2.

The vacuolar membrane is involved in solute uptake into and release from the vacuole, which is the largest plant organelle. In addition to inorganic ions and metabolites, large quantities of protons and sugars are shuttled across this membrane. Current models suggest that the proton gradient across the membrane drives the accumulation and/or release of sugars.

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

S-type anion channels are direct targets of abscisic acid (ABA) signaling and contribute to chloride and nitrate release from guard cells, which in turn initiates stomatal closure. SLAC1 was the first component of the guard cell S-type anion channel identified. However, we found that guard cells of Arabidopsis SLAC1 mutants exhibited nitrate conductance.

TPC1-SV channels gain shape.

The most prominent ion channel localized in plant vacuoles is the slow activating SV type. Slow vacuolar (SV) channels were discovered by patch clamp studies as early as 1986. In the following two decades, numerous studies revealed that these calcium- and voltage-activated, nonselective cation channels are expressed in the vacuoles of all plants and every plant tissue.