Cryo-EM structures of the human band 3 transporter indicate a transport mechanism involving the coupled movement of chloride and bicarbonate ions.

The band 3 transporter is a critical integral membrane protein of the red blood cell (RBC), as it is responsible for catalyzing the exchange of bicarbonate and chloride anions across the plasma membrane. To elucidate the structural mechanism of the band 3 transporter, detergent solubilized human ghost membrane reconstituted in nanodiscs was applied to a cryo-EM holey carbon grid to define its composition. With this approach, we identified and determined structural information of the human band 3 transporter. Here, we present 5 different cryo-EM structures of the transmembrane domain of dimeric band 3, either alone or bound with chloride or bicarbonate. Interestingly, we observed that human band 3 can form both symmetric and asymmetric dimers with a different combination of outward-facing (OF) and inward-facing (IF) states. These structures also allow us to obtain the first model of a human band 3 molecule at the IF conformation. Based on the structural data of these dimers, we propose a model of ion transport that is in favor of the elevator-type mechanism.

Age-, region-, and day/night-related variation of the chloride reversal potential in the rat suprachiasmatic nucleus.

The master control of mammalian circadian rhythms is the suprachiasmatic nucleus (SCN), which is formed by the ventral and dorsal regions. In SCN neurons, GABA has an important function and even excitatory actions in adulthood. However, the physiological role of this neurotransmitter in the developing SCN is unknown. Here, we recorded GABAergic postsynaptic currents (in the perforated-patch configuration using gramicidin) to determine the chloride reversal potential (ECl) and also assessed the immunological expression of the Na-K-Cl cotransporter 1 (NKCC1) at early ages of the rat (postnatal days (P) 3 to 25), during the day and night, in the two SCN regions. We detected that ECl greatly varied with age and depending on the SCN region and time of day. Broadly speaking, ECl was more hyperpolarized with age, except for the oldest age studied (P20-25) in both day and night in the ventral SCN, where it was less negative. Likewise, ECl was more hyperpolarized in the dorsal SCN both during the day and at night; while ECl was more negative at night both in the ventral and the dorsal SCN. Moreover, the total NKCC1 fluorescent expression was higher during the day than at night. These results imply that NKCC1 regulates the circadian and developmental fluctuations in the [Cl-]i to fine-tune ECl, which is crucial for either excitatory or inhibitory GABAergic actions to occur in the SCN.

Morphology of Four Strains of Phellinoid Agaricomycetes and Microstructural and Physiological Properties of Their Exudates.

To study and compare the morphology of the phellinoid Agaricomycetes strains and find other strategies to improve Phellinus spp. growth and metabolism. In this study, the morphological characteristics of four Phellinus igniarius strains (phellinoid Agaricomycetes) were observed under a light microscope. The exudates from these fungi were observed using light microscopy, scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The exudates were initially transparent with a water-like appearance, and became darker with time at neutral pH. Microscopy of air-dried exudates revealed regular shapes and crystals. Cl- (chloride) and K+ were the two key elements analyzed using EDS. Polyphenol oxidase (POD), catalase (CAT), and laccase activities were detected in mycelia from each of the four Phellinus strains. The K+ content of the three strains was higher than that of the wild strain. Cl- content correlated negatively with that of K+. Laccase activities associated with each mycelia and its corresponding media differed under cold and contaminated conditions.

Cl--dependent amplification of excitatory synaptic potentials at distal dendrites revealed by voltage imaging.

The processing of synaptic signals in somatodendritic compartments determines neuronal computation. Although the amplification of excitatory signals by local voltage-dependent cation channels has been extensively studied, their spatiotemporal dynamics in elaborate dendritic branches remain obscure owing to technical limitations. Using fluorescent voltage imaging throughout dendritic arborizations in hippocampal pyramidal neurons, we demonstrate a unique chloride ion (Cl-)-dependent remote computation mechanism in the distal branches. Excitatory postsynaptic potentials triggered by local laser photolysis of caged glutamate spread along dendrites, with gradual amplification toward the distal end while attenuation toward the soma. Tour de force subcellular patch-clamp recordings from thin branches complemented by biophysical model simulations revealed that the asymmetric augmentation of excitation relies on tetrodotoxin-resistant sodium ion (Na+) channels and Cl- conductance accompanied by a more hyperpolarized dendritic resting potential. Together, this study reveals the cooperative voltage-dependent actions of cation and anion conductance for dendritic supralinear computation, which can locally decode the spatiotemporal context of synaptic inputs.

Macrophage WNK1 senses intracellular hypo-chlorine to regulate vulnerability to sepsis attack during hypochloremia.

Sepsis is one of the leading causes of death in critical patients worldwide and its occurrence is related to the excessive activation of macrophages. Chloride loss worsens the prognosis of patients with sepsis but the underlying mechanism is currently unclear. In this study, we founded that macrophages deficient in intracellular Cl- secrete more inflammatory cytokines such as IL-1ß, IL-6 and TNF-α compared with control group. The intracellular chloride level decreased in WNK1 deficiency or activity inhibited macrophages with more severe inflammatory response after LPS treatment. Remimazolam, as classic GABAa receptor agonist, alleviates excessive inflammation cascade by promoting macrophage chloride influx during sepsis progression. Collectively, this study proves that macrophage WNK1 acts as a negative regulator of inflammatory response by sensing chloride to maintain intracellular chloride balance during sepsis coupled with hypochloremia.

Catalysis of an SN2 pathway by geometric preorganization.

Bimolecular nucleophilic substitution (SN2) mechanisms occupy a central place in the historical development and teaching of the field of organic chemistry1. Despite the importance of SN2 pathways in synthesis, catalytic control of ionic SN2 pathways is rare and notably uncommon even in biocatalysis2,3, reflecting the fact that any electrostatic interaction between a catalyst and the reacting ion pair necessarily stabilizes its charge and, by extension, reduces polar reactivity. Nucleophilic halogenase enzymes navigate this tradeoff by desolvating and positioning the halide nucleophile precisely on the SN2 trajectory, using geometric preorganization to compensate for the attenuation of nucleophilicity4. Here we show that a small-molecule (646 Da) hydrogen-bond-donor catalyst accelerates the SN2 step of an enantioselective Michaelis-Arbuzov reaction by recapitulating the geometric preorganization principle used by enzymes. Mechanistic and computational investigations show that the hydrogen-bond donor diminishes the reactivity of the chloride nucleophile yet accelerates the rate-determining dealkylation step by reorganizing both the phosphonium cation and the chloride anion into a geometry that is primed to enter the SN2 transition state. This new enantioselective Arbuzov reaction affords highly enantioselective access to an array of H-phosphinates, which are in turn versatile P-stereogenic building blocks amenable to myriad derivatizations. This work constitutes, to our knowledge, the first demonstration of catalytic enantiocontrol of the phosphonium dealkylation step, establishing a new platform for the synthesis of P-stereogenic compounds.

Effects of temperature, chloride and perchlorate salt concentration on the metabolic activity of Deinococcus radiodurans.

The extremophile bacterium Deinococcus radiodurans is characterized by its ability to survive and sustain its activity at high levels of radiation and is considered an organism that might survive in extraterrestrial environments. In the present work, we studied the combined effects of temperature and chlorine-containing salts, with focus on perchlorate salts which have been detected at high concentrations in Martian regolith, on D. radiodurans activity (CO2 production rates) and viability after incubation in liquid cultures for up to 30 days. Reduced CO2 production capacity and viability was observed at high perchlorate concentrations (up to 10% w/v) during incubation at 0 or 25 °C. Both the metabolic activity and viability were reduced as the perchlorate and chloride salt concentration increased and temperature decreased, and an interactive effect of temperature and salt concentration on the metabolic activity was found. These results indicate the ability of D. radiodurans to remain metabolically active and survive in low temperature environments rich in perchlorate.

Chloride intracellular channel 4 participates in the regulation of lipopolysaccharide-induced inflammatory responses in human bronchial epithelial cells.

The airway epithelium is located at the interactional boundary between the external and internal environments of the organism and is often exposed to harmful environmental stimuli. Inflammatory response that occurs after airway epithelial stress is the basis of many lung and systemic diseases. Chloride intracellular channel 4 (CLIC4) is abundantly expressed in epithelial cells. The purpose of this study was to investigate whether CLIC4 is involved in the regulation of lipopolysaccharide (LPS)-induced inflammatory response in airway epithelial cells and to clarify its potential mechanism. Our results showed that LPS induced inflammatory response and decreased CLIC4 levels in vivo and in vitro. CLIC4 silencing aggravated the inflammatory response in epithelial cells, while overexpression of CLIC4 combined with LPS exposure significantly decreased the inflammatory response compared with cells exposed to LPS without CLIC4 overexpression. By labeling intracellular chloride ions with chloride fluorescent probe MQAE, we showed that CLIC4 mediated intracellular chloride ion-regulated LPS-induced cellular inflammatory response.

Chloride Gradient Is Involved in Ammonium Influx in Human Erythrocytes.

The ammonia/ammonium (NH3/NH4+, AM) concentration in human erythrocytes (RBCs) is significantly higher than in plasma. Two main possible mechanisms for AM transport, including simple and facilitated diffusion, are described; however, the driving force for AM transport is not yet fully characterized. Since the erythroid ammonium channel RhAG forms a structural unit with anion exchanger 1 (eAE1) within the ankyrin core complex, we hypothesized the involvement of eAE1 in AM transport. To evaluate the functional interaction between eAE1 and RhAG, we used a unique feature of RBCs to swell and lyse in isotonic NH4+ buffer. The kinetics of cell swelling and lysis were analyzed by flow cytometry and an original laser diffraction method, adapted for accurate volume sensing. The eAE1 role was revealed according to (i) the changes in cell swelling and lysis kinetics, and (ii) changes in intracellular pH, triggered by eAE1 inhibition or the modulation of eAE1 main ligand concentrations (Cl- and HCO3-). Additionally, the AM import kinetics was analyzed enzymatically and colorimetrically. In NH4+ buffer, RBCs concentration-dependently swelled and lysed when [NH4+] exceeded 100 mM. Cell swelling and hemolysis were tightly regulated by chloride concentration. The complete substitution of chloride with glutamate prevented NH4+-induced cell swelling and hemolysis, and the restoration of [Cl-] dose-dependently amplified the rates of RBC swelling and lysis and the percentage of hemolyzed cells. Similarly, eAE1 inhibition impeded cell swelling and completely prevented hemolysis. Accordingly, eAE1 inhibition, or a lack of chloride anions in the buffer, significantly decreased NH4+ import. Our data indicate that the eAE1-mediated chloride gradient is required for AM transport. Taken together, our data reveal a new player in AM transport in RBCs.

Vitamin D is involved in the regulation of Cl- uptake in zebrafish (Danio rerio).

Cl- is a major anion in the bodily fluids of vertebrates, and maintaining its homeostasis is essential for normal physiological functions. Fishes inhabiting freshwater (FW) passively lose body fluid ions, including Cl-, to the external environment because of the electrochemical gradient of ions across the body surface. Therefore, FW fishes have to actively absorb Cl- from the surroundings to maintain ion homeostasis in their bodily fluids. Hormonal control is vital for modulating ion uptake in fish. Vitamin D is involved in the regulation of Ca2+ uptake and acid secretion in fish. In the present study, we found that the levels of bioactive vitamin D, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3), significantly increased in zebrafish embryos and adults after exposure to water containing low levels of Cl-. Moreover, the administration of 1α,25(OH)2D3 treatment (20 µg/L) in zebrafish embryos, and intraperitoneal (i.p.) injection of 1α,25(OH)2D3 (5 µg/kg body mass) in zebrafish adults, resulting the increased Cl- content in bodily fluid in zebrafish. Na+-Cl- cotransporter 2b (NCC2b) and Cl- channel 2c (CLC2c) are specifically expressed during Cl- uptake by ionocytes in zebrafish. Our results indicated that the mRNA and protein expression of NCC2b and CLC2c considerably increased in the zebrafish with exogenous 1α,25(OH)2D3 treatment. Additionally, exogenous 1α,25(OH)2D3 administration increased the number of NCC2b- and CLC2c-expressing cells in yolk skins of zebrafish embryos and the gill filaments of zebrafish adults. Transcript signals of vitamin D receptors (VDRs) were identified in NCC2b-expressing cells. Knockdown of VDRa and VDRb significantly reduced the expression of NCC2b and CLC2c and the number of NCC2b- and CLC2c-expressing cells. These results indicate that vitamin D can affect Cl- uptake in zebrafish and extend our knowledge of the role of vitamin D in fish physiology.

Modulation of TMEM16B channel activity by the calcium-activated chloride channel regulator 4 (CLCA4) in human cells.

The Ca2+-activated Cl- channel regulator CLCA1 potentiates the activity of the Ca2+-activated Cl- channel (CaCC) TMEM16A by directly engaging the channel at the cell surface, inhibiting its reinternalization and increasing Ca2+-dependent Cl- current (ICaCC) density. We now present evidence of functional pairing between two other CLCA and TMEM16 protein family members, namely CLCA4 and the CaCC TMEM16B. Similar to CLCA1, (i) CLCA4 is a self-cleaving metalloprotease, and the N-terminal portion (N-CLCA4) is secreted; (ii) the von Willebrand factor type A (VWA) domain in N-CLCA4 is sufficient to potentiate ICaCC in HEK293T cells; and (iii) this is mediated by the metal ion-dependent adhesion site motif within VWA. The results indicate that, despite the conserved regulatory mechanism and homology between CLCA1 and CLCA4, CLCA4-dependent ICaCC are carried by TMEM16B, rather than TMEM16A. Our findings show specificity in CLCA/TMEM16 interactions and suggest broad physiological and pathophysiological links between these two protein families.

Electroneutral Na+/Cl- cotransport activity of zebrafish Slc12a10.1 expressed in Xenopus oocytes.

Na+/Cl- cotransporter 2 (Ncc2 or Slc12a10) is a membrane transport protein that belongs to the electroneutral cation-chloride cotransporter family. The Slc12a10 gene (slc12a10) is widely present in bony vertebrates but is deleted or pseudogenized in birds, some bony fishes, and most mammals. Slc12a10 is highly homologous to Ncc (Slc12a3 or Ncc1); however, there are only a few reports measuring the activity of Slc12a10. In this study, we focused on zebrafish Slc12a10.1 (zSlc12a10.1) and analyzed its activity using Xenopus oocyte electrophysiology. Analysis using Na+-selective microelectrodes showed that intracellular sodium activity (aNai) in zSlc12a10.1 oocytes was significantly decreased in Na+- or Cl--free medium and recovered when Na+ or Cl- was readded to the medium. Similar analysis using a Cl--selective microelectrode showed that intracellular chloride activity (aCli) in zSlc12a10.1 oocytes significantly decreased in Na+- or Cl--free medium and recovered when Na+ or Cl- was readded to the medium. When a similar experiment was performed with a voltage clamp, the membrane current did not change when aNai of zSlc12a10.1 oocytes was decreased in Na+-free medium. Molecular phylogenetic and synteny analyses suggest that gene duplication between slc12a10.2 and slc12a10.3 in zebrafish is a relatively recent event, whereas gene duplication between slc12a10.1 and the ancestral gene of slc12a10.2/slc12a10.3 occurred at least about 2 million years ago. slc12a10 deficiency was observed in species belonging to Ictaluridae, Salmoniformes, Osmeriformes, Batrachoididae, Syngnathiformes, Gobiesociformes, Labriformes, and Tetraodontiformes. These results indicate that zebrafish Slc12a10.1 is an electroneutral Na+/Cl-cotransporter and establish its evolutionary position among various teleost slc12a10 paralogs.NEW & NOTEWORTHY Na+/Cl- cotransporter 2 (Slc12a10; Ncc2) is a protein highly homologous to Ncc (Slc12a3; Ncc1); however, there are only a few reports measuring the activity of Slc12a10. Electrophysiological analysis of Xenopus oocytes expressing zebrafish Slc12a10.1 showed that Slc12a10.1 acts as an electroneutral Na+/Cl-cotransporter. This is the third report on the activity of Slc12a10, following previous reports on Slc12a10 in eels.

Molecular mechanism of anion permeation through aquaporin 6.

Aquaporins (AQPs) are recognized as transmembrane water channels that facilitate selective water permeation through their monomeric pores. Among the AQP family, AQP6 has an intriguing characteristic as an anion channel, which is allosterically controlled by pH conditions and is eliminated by a single amino acid mutation. However, the molecular mechanism of anion permeation through AQP6 remains unclear. Using molecular dynamics simulations in the presence of a transmembrane voltage utilizing an ion concentration gradient, we show that chloride ions permeate through the pore corresponding to the central axis of the AQP6 homotetramer. Under low pH conditions, a subtle opening of the hydrophobic selectivity filter (SF), located near the extracellular part of the central pore, becomes wetted and enables anion permeation. Our simulations also indicate that a single mutation (N63G) in human AQP6, located at the central pore, significantly reduces anion conduction, consistent with experimental data. Moreover, we demonstrate that the pH-sensing mechanism in which the protonation of H184 and H189 under low pH conditions allosterically triggers the gating of the SF region. These results suggest a unique pH-dependent allosteric anion permeation mechanism in AQP6 and could clarify the role of the central pore in some of the AQP tetramers.

Low potassium activation of proximal mTOR/AKT signaling is mediated by Kir4.2.

The renal epithelium is sensitive to changes in blood potassium (K+). We identify the basolateral K+ channel, Kir4.2, as a mediator of the proximal tubule response to K+ deficiency. Mice lacking Kir4.2 have a compensated baseline phenotype whereby they increase their distal transport burden to maintain homeostasis. Upon dietary K+ depletion, knockout animals decompensate as evidenced by increased urinary K+ excretion and development of a proximal renal tubular acidosis. Potassium wasting is not proximal in origin but is caused by higher ENaC activity and depends upon increased distal sodium delivery. Three-dimensional imaging reveals Kir4.2 knockouts fail to undergo proximal tubule expansion, while the distal convoluted tubule response is exaggerated. AKT signaling mediates the dietary K+ response, which is blunted in Kir4.2 knockouts. Lastly, we demonstrate in isolated tubules that AKT phosphorylation in response to low K+ depends upon mTORC2 activation by secondary changes in Cl- transport. Data support a proximal role for cell Cl- which, as it does along the distal nephron, responds to K+ changes to activate kinase signaling.

Regulation of Neuronal Chloride Homeostasis by Pro- and Mature Brain-Derived Neurotrophic Factor (BDNF) via KCC2 Cation-Chloride Cotransporters in Rat Cortical Neurons.

The strength of inhibitory neurotransmission depends on intracellular neuronal chloride concentration, primarily regulated by the activity of cation-chloride cotransporters NKCC1 (Sodium-Potassium-Chloride Cotransporter 1) and KCC2 (Potassium-Chloride Cotransporter 2). Brain-derived neurotrophic factor (BDNF) influences the functioning of these co-transporters. BDNF is synthesized from precursor proteins (proBDNF), which undergo proteolytic cleavage to yield mature BDNF (mBDNF). While previous studies have indicated the involvement of BDNF signaling in the activity of KCC2, its specific mechanisms are unclear. We investigated the interplay between both forms of BDNF and chloride homeostasis in rat hippocampal neurons and in utero electroporated cortices of rat pups, spanning the behavioral, cellular, and molecular levels. We found that both pro- and mBDNF play a comparable role in immature neurons by inhibiting the capacity of neurons to extrude chloride. Additionally, proBDNF increases the endocytosis of KCC2 while maintaining a depolarizing shift of EGABA in maturing neurons. Behaviorally, proBDNF-electroporated rat pups in the somatosensory cortex exhibit sensory deficits, delayed huddling, and cliff avoidance. These findings emphasize the role of BDNF signaling in regulating chloride transport through the modulation of KCC2. In summary, this study provides valuable insights into the intricate interplay between BDNF, chloride homeostasis, and inhibitory synaptic transmission, shedding light on the underlying cellular mechanisms involved.

Chloride Modulates Central pH Sensitivity and Plasticity of Brainstem Breathing-Related Biorhythms in Zebra Finch Embryos.

All terrestrial vertebrate life must transition from aquatic gas exchange in the embryonic environment to aerial or pulmonary respiration at birth. In addition to being able to breathe air, neonates must possess functional sensory feedback systems for maintaining acid-base balance. Respiratory neurons in the brainstem act as pH sensors that can adjust breathing to regulate systemic pH. The central pH sensitivity of breathing-related motor output develops over the embryonic period in the zebra finch (Taeniopygia guttata). Due to the key role of chloride ions in electrochemical stability and developmental plasticity, we tested chloride's role in the development of central pH sensitivity. We blocked gamma-aminobutyric acid-A receptors and cation-chloride cotransport that subtly modulated the low-pH effects on early breathing biorhythms. Further, chloride-free artificial cerebrospinal fluid altered the pattern and timing of breathing biorhythms and blocked the stimulating effect of acidosis in E12-14 brainstems. Early and middle stage embryos exhibited rebound plasticity in brainstem motor outputs during low-pH treatment, which was eliminated by chloride-free solution. Results show that chloride modulates low-pH sensitivity and rebound plasticity in the zebra finch embryonic brainstem, but work is needed to determine the cellular and circuit mechanisms that control functional chloride balance during acid-base disturbances.

Salt tolerance in mungbean is associated with controlling Na and Cl transport across roots, regulating Na and Cl accumulation in chloroplasts and maintaining high K in root and leaf mesophyll cells.

Salinity tolerance requires coordinated responses encompassing salt exclusion in roots and tissue/cellular compartmentation of salt in leaves. We investigated the possible control points for salt ions transport in roots and tissue tolerance to Na+ and Cl- in leaves of two contrasting mungbean genotypes, salt-tolerant Jade AU and salt-sensitive BARI Mung-6, grown in nonsaline and saline (75 mM NaCl) soil. Cryo-SEM X-ray microanalysis was used to determine concentrations of Na, Cl, K, Ca, Mg, P, and S in various cell types in roots related to the development of apoplastic barriers, and in leaves related to photosynthetic performance. Jade AU exhibited superior salt exclusion by accumulating higher [Na] in the inner cortex, endodermis, and pericycle with reduced [Na] in xylem vessels and accumulating [Cl] in cortical cell vacuoles compared to BARI Mung-6. Jade AU maintained higher [K] in root cells than BARI Mung-6. In leaves, Jade AU maintained lower [Na] and [Cl] in chloroplasts and preferentially accumulated [K] in mesophyll cells than BARI Mung-6, resulting in higher photosynthetic efficiency. Salinity tolerance in Jade AU was associated with shoot Na and Cl exclusion, effective regulation of Na and Cl accumulation in chloroplasts, and maintenance of high K in root and leaf mesophyll cells.

GhCLCc-1, a Chloride Channel Gene from Upland Cotton, Positively Regulates Salt Tolerance by Modulating the Accumulation of Chloride Ions.

The ionic toxicity induced by salinization has adverse effects on the growth and development of crops. However, researches on ionic toxicity and salt tolerance in plants have focused primarily on cations such as sodium ions (Na+), with very limited studies on chloride ions (Cl-). Here, we cloned the homologous genes of Arabidopsis thaliana AtCLCc, GhCLCc-1A/D, from upland cotton (Gossypium hirsutum), which were significantly induced by NaCl or KCl treatments. Subcellular localization showed that GhCLCc-1A/D were both localized to the tonoplast. Complementation of Arabidopsis atclcc mutant with GhCLCc-1 rescued its salt-sensitive phenotype. In addition, the silencing of the GhCLCc-1 gene led to an increased accumulation of Cl- in the roots, stems, and leaves of cotton seedlings under salt treatments, resulting in compromised salt tolerance. And ectopic expression of the GhCLCc-1 gene in Arabidopsis reduced the accumulation of Cl- in transgenic lines under salt treatments, thereby enhancing salt tolerance. These findings elucidate that GhCLCc-1 positively regulates salt tolerance by modulating Cl- accumulation and could be a potential target gene for improving salt tolerance in plants.

Tuft cell-derived acetylcholine promotes epithelial chloride secretion and intestinal helminth clearance.

Epithelial cells secrete chloride to regulate water release at mucosal barriers, supporting both homeostatic hydration and the "weep" response that is critical for type 2 immune defense against parasitic worms (helminths). Epithelial tuft cells in the small intestine sense helminths and release cytokines and lipids to activate type 2 immune cells, but whether they regulate epithelial secretion is unknown. Here, we found that tuft cell activation rapidly induced epithelial chloride secretion in the small intestine. This response required tuft cell sensory functions and tuft cell-derived acetylcholine (ACh), which acted directly on neighboring epithelial cells to stimulate chloride secretion, independent of neurons. Maximal tuft cell-induced chloride secretion coincided with immune restriction of helminths, and clearance was delayed in mice lacking tuft cell-derived ACh, despite normal type 2 inflammation. Thus, we have uncovered an epithelium-intrinsic response unit that uses ACh to couple tuft cell sensing to the secretory defenses of neighboring epithelial cells.

Chloride reduces plant nitrate requirement and alleviates low nitrogen stress symptoms.

Chloride (Cl-) is traditionally categorized as an antagonist of nitrate (NO3-) because Cl- hinders plant NO3- transport and accumulation. However, we have recently defined Cl- as a beneficial macronutrient for higher plants, due to specific functions that lead to more efficient use of water, nitrogen (N) and CO2 under optimal N and water supply. When accumulated in leaves at macronutrient levels, Cl- promotes growth through osmotic, physiological, metabolic, anatomical and cellular changes that improve plant performance under optimal NO3- nutrition. Nitrate over-fertilization in agriculture can adversely affect crop yield and nature, while its deficiency limits plant growth. To study the relationship between Cl- nutrition and NO3- availability, we have characterized different physiological responses such as growth and yield, N-use efficiency, water status, photosynthesis, leaf anatomy, pigments and antioxidants in tomato plants treated with or without 5 mM Cl- salts and increasing NO3- treatments (3-15 mM). First, we have demonstrated that 5 mM Cl- application can reduce the use of NO3- in the nutrient solution by up to half without detriment to plant growth and yield in tomato and other horticultural plants. Second, Cl- application reduced stress symptoms and improved plant growth under low-NO3- conditions. The Cl--dependent resistance to low-N stress resulted from: more efficient use of the available NO3-; improved plant osmotic and water status regulation; improved stomatal conductance and photosynthetic rate; and better antioxidant response. We proposed that beneficial Cl- levels increase the crop ability to grow better with lower NO3- requirements and withstand N deficiency, promoting a more sustainable and resilient agriculture.