Salinity is a major constraint to crop productivity. Beneficial plant–fungus interactions represent a promising strategy to enhance stress resilience. Here, we investigated fungal endophytes isolated from the roots of Oryza sativa cultivated in saline-prone marshlands of the Guadalquivir River, Spain. From a collection of 38 isolates, five salt-tolerant strains exhibiting plant growth-promoting activity were identified, including a previously uncharacterized Reticulascus sp. strain S5. Co-cultivation assays with the non-native host plant Arabidopsis thaliana demonstrated that S5 increased the root and shoot biomass under salt stress. To elucidate the underlying molecular mechanisms, a comprehensive RNA-Seq analysis of the roots and shoots under control and saline conditions was performed. Fungal colonization induced pronounced transcriptomic changes, particularly in the shoots, including rewiring of the auxin- and abscisic acid-related pathways and the induction of genes associated with cell wall remodeling. Concurrently, defense-related processes, including glucosinolate biosynthesis and ethylene signaling, were broadly repressed, suggesting attenuated stress perception in colonized plants. In the roots, S5 inoculation suppressed the expression of genes involved in root hair development and cell wall organization, indicating a fungus-driven reconfiguration of root development. Moreover, comparative analysis with Fusarium sp. K-23, a fungus that has previously been demonstrated to promote plant growth under salinity stress, revealed distinct root-associated mechanisms but convergence on a shared regulatory module in shoots involving ABA-responsive transcription factors and osmotic stress regulators. Collectively, our findings demonstrate that Reticulascus sp. S5 enhances plant salt stress tolerance through the coordinated transcriptional reprogramming of growth, hormone signaling, and stress responses, highlighting a possible potential of habitat-adapted endophytes for sustainable crop improvement.

Serendipita indica, a widely studied beneficial root-colonizing fungal endophyte, promotes plant growth under saline conditions by reducing Na+ accumulation in host plants, including Arabidopsis thaliana. This reduction in Na + levels likely contributes to salt detoxification, but the underlying mechanisms remain unclear. Previous studies have demonstrated that SOS1, a key Na+ transporter and major determinant of salt tolerance in plants, is not involved in this reduction. To explore whether other plant transporters might participate in Na+ reduction, we first characterized the full Arabidopsis transportome, with putative substrates and subcellular localizations, and performed a comprehensive transcriptomic analysis of the full set of transporter proteins. In this study, we investigated and excluded the possible contribution of HKT1, another relevant Na+ transporter implicated in salt adaptation in Arabidopsis. By examining differentially expressed transporters under salt stress, we identified a subset of candidate genes potentially involved in Na+ transport. Among these, we evaluated the role of CNGC10 and CNGC13 using mutant lines under both S. indica- and non-colonized conditions. Interestingly, both transporters appeared to be involved in the endophyte-induced decrease in Na+ accumulation although, other, yet-unidentified transporters may also contribute to this phenomenon.

Salinity is a major constraint to crop productivity. Beneficial plant–fungus interactions represent a promising strategy to enhance stress resilience. Here, we investigated fungal endophytes isolated from Oryza sativa cultivated in saline-prone marshlands of the Guadalquivir River, Spain. From a collection of 38 isolates, five salt-tolerant strains exhibiting plant growth-promoting activity were identified, including a previously uncharacterized Reticulascus sp. strain S5. Co-cultivation assays with Arabidopsis thaliana demonstrated that S5 increased root and shoot biomass under salt stress. To elucidate the underlying mechanisms, a comprehensive RNA-seq analysis of roots and shoots under control and saline conditions was performed. Fungal colonization induced pronounced transcriptomic changes, particularly in shoots, including the rewiring of auxin- and abscisic acid-related pathways and the induction of genes associated with cell wall remodelling. Concurrently, defence-related processes, including glucosinolate biosynthesis and ethylene signalling, were broadly repressed, suggesting attenuated stress perception in colonized plants. In roots, S5 infection suppressed genes involved in root hair development and cell wall organization, indicating a fungus-driven reconfiguration of root development. Comparative analysis with the growth-promoting Fusarium sp. K-23 revealed distinct root-associated mechanisms but convergence on a shared regulatory module in shoots involving ABA-responsive transcription factors and osmotic stress regulators. Collectively, our findings demonstrate that Reticulascus sp. S5 enhances plant salt stress tolerance through coordinated transcriptional reprogramming of growth, hormone signalling, and stress responses, highlighting the potential of habitat-adapted endophytes for sustainable crop improvement.

Soil salinity is a significant abiotic stress factor that impedes plant growth and crop yield, particularly in arid and semi-arid regions. Recent reports indicate that 8.7

Global climate change exacerbates abiotic stresses, as drought, heat, and salt stresses are anticipated to increase significantly in the coming years. Plants coexist with a diverse range of microorganisms. Multiple inter-organismic relationships are known to confer benefits to plants, including growth promotion and enhanced tolerance to abiotic stresses. In this study, we investigated the mutualistic interactions between three fungal endophytes originally isolated from distinct arid environments and an agronomically relevant crop, Solanum lycopersicum. We demonstrated a significant increase in shoot biomass under drought conditions in co-cultivation with Penicillium chrysogenum isolated from Antarctica, Penicillium minioluteum isolated from the Atacama Desert, Chile, and Serendipita indica isolated from the Thar Desert, India. To elucidate plant gene modules commonly induced by the different endophytes that could explain the observed drought tolerance effect in tomato, a comprehensive transcriptomics analysis was conducted. This analysis led to the identification of a shared gene module in the fungus-infected tomato plants. Within this module, gene network analysis enabled us to identify genes related to abscisic acid (ABA) signaling, ABA transport, auxin signaling, ion homeostasis, proline biosynthesis, and jasmonic acid signaling, providing insights into the molecular basis of drought tolerance commonly mediated by fungal endophytes. Our findings highlight a conserved response in the mutualistic interactions between endophytic fungi isolated from unrelated environments and tomato roots, resulting in improved shoot biomass production under drought stress.

ENA transporters are a group of P-type ATPases that are characterized by actively moving Na+ or K+ out of the cell against their concentration gradient. The existence of these transporters was initially attributed to some fungi, although more recently they have also been identified in mosses, liverworts, and some protozoa. Given the current increase in the number of organisms whose genomes are completely sequenced, we set out to expand our knowledge about the existence of ENA in organisms belonging to other phylogenetic groups. For that, a hidden Markov model profile was constructed to identify homologous sequences to ENA proteins in protein databases. This analysis allowed us to identify the existence of ENA-type ATPases in the most primitive groups of fungi, as well as in other eukaryotic organisms not described so far. In addition, this study has allowed the identification of a possible new group of P-ATPases, initially proposed as ENA but which maintain phylogenetic distances with these proteins. Finally, this work has also addressed this study of the structure of ENA proteins, which remained unknown due to the lack of crystallographic data. For this purpose, a 3D structure prediction of the NcENA1 protein of the fungus Neurospora crassa was performed using AlphaFold2 software v2.3.1. From this structure, the electrostatic potential of the protein was analyzed. With all these data, the protein regions and the amino acids involved in the transport of Na+ or K+ ions across the membrane were proposed for the first time. Targeted mutagenesis of some of these residues has confirmed their relevant participation in the transport function of ENA proteins.

Serendipita indica is an endophytic root symbiont fungus that enhances the growth of various plants under different stress conditions, including salinity. Here, the functional characterization of two fungal Na+/H+ antiporters, SiNHA1 and SiNHX1 has been carried out to study their putative role in saline tolerance. Although their gene expression does not respond specifically to saline conditions, they could contribute, together with the previously characterized Na+ efflux systems SiENA1 and SiENA5, to relieve Na+ from the S. indica cytosol under this stressed condition. In parallel, an in-silico study has been carried out to define its complete transportome. To further investigate the repertoire of transporters expressed in free-living cells of S. indica and during plant infection under saline conditions, a comprehensive RNA-seq approach was taken. Interestingly, SiENA5 was the only gene significantly induced under free-living conditions in response to moderate salinity at all the tested time points, revealing that it is one of the main salt-responsive genes of S. indica. In addition, the symbiosis with Arabidopsis thaliana also induced SiENA5 gene expression, but significant changes were only detected after long periods of infection, indicating that the association with the plant somehow buffers and protects the fungus against the external stress. Moreover, the significant and strongest induction of the homologous gene SiENA1 occurred during symbiosis, regardless the exposure to salinity. The obtained results suggest a novel and relevant role of these two proteins during the establishment and maintenance of fungus-plant interaction.

There is mounting evidence that the root-colonizing endosymbiotic fungus Serendipita indica improves plant growth. The beneficial effects have been observed when plants are growing in optimal conditions or under nutritionally deficient soils (e.g., phosphate poor soil) or exposed to stressful environmental conditions such as drought or salinity. However, until now its role in the nutrition of other plant essential macronutrient, such as K + , has not been fully clarified. Here, we study the role of the fungus in the K + nutrition of Arabidopsis thaliana plants, during growth under K + limiting conditions. As a first step, we studied the high-affinity K + uptake of the plant and fungus when growing separately and in symbiosis. In the search for putative fungal actors involved in K + nutrition, we also have cloned and functionally characterized the K + transporters of S. indica Si HAK1, Si TRK1, Si TRK2, and Si TOK1, among which it has been shown that Si HAK1 is the main transporter involved in the K + uptake in the high affinity range of concentrations. In addition, a gene expression study of these transporters and other candidates that could participate in the K + homeostasis of the fungus has been carried out. The results indicated that, contrary to what happens with P nutrition, S. indica seems not to improve neither the growth nor the plant K + reserves during K + starvation. Instead, this nutritionally restrictive condition favored fungal colonization, suggesting that the fungus obtains the greatest benefit in K + supply during symbiosis.

Serendipita indica (formerly Piriformospora indica) is an endophytic fungus that colonizes plant roots producing a beneficial effect on plant growth and development under optimal and suboptimal conditions provoked by any biotic or abiotic stress, such as salt stress. Salinity induces osmotic and ionic imbalances in plants, mainly by altering the Na+ and K+ contents. However, the mechanism by which Serendipita improves plant growth has yet to be elucidated. Previous works suggest that this fungus improves the plant osmotic state but not much is known about whether it participates in readjustment of the ionic imbalance in plants. Here, we report that co-cultivation with Serendipita reduces the Na+ content of Arabidopsis plants under saline conditions. Additionally, we describe the functional characterization of the two Serendipita ENA ATPases, which are homologous to the main proteins involved in the salt tolerance of other fungi. Their heterologous expression in salt-sensitive yeast mutants shows that SiENA1 is involved in Na+ and K+ efflux, while SiENA5 seems to only be involved in Na+ detoxification. Both are induced and might have a relevant function at alkaline pH, condition in which there are few chlamydospores in the mycelium, as well as during co-cultivation with plants exposed to saline conditions.

K+ is an essential cation and the most abundant in plant cells. After N, its corresponding element, K, is the nutrient required in the largest amounts by plants. Despite the numerous roles of K in crop production, improvements in the uptake and efficiency of use of K have not been major focuses in conventional or transgenic breeding studies in the past. In research on the mineral nutrition of plants in general, and K in particular, this nutrient has been shown to be essential to soil-dwelling-microorganisms (fungi, bacteria, protozoa, nematodes, etc.) that form mutualistic associations and that can influence the availability of mineral nutrients for plants. Therefore, this article aims to provide an overview of the role of soil microorganisms in supplying K+ to plants, considering both the potassium-solubilizing microorganisms and the potassium-facilitating microorganisms that are in close contact with the roots of plants. These microorganisms can influence the active transporter-mediated transfer of K+. Regarding the latter group of microorganisms, special focus is placed on the role of endophytic fungus. This review also includes a discussion on productivity through sustainable agriculture.

K+ is widely used by plant cells, whereas Na+ can easily reach toxic levels during plant growth, which typically occurs in saline environments; however, the effects and functions in the chloroplast have been only roughly estimated. Traditionally, the occurrence of ionic fluxes across the chloroplast envelope or the thylakoid membranes has been mostly deduced from physiological measurements or from knowledge of chloroplast metabolism. However, many of the proteins involved in these fluxes have not yet been characterized. Based on genomic and RNA sequencing (RNA-seq) analyses, we present a comprehensive compilation of genes encoding putative ion transporters and channels expressed in the chloroplasts of the moss Physcomitrella patens, with a special emphasis on those related to Na+ and K+ fluxes. Based on the functional characterization of nhad mutants, we also discuss the putative role of NHAD transporters in Na+ homeostasis and osmoregulation of this organelle and the putative contribution of chloroplasts to salt tolerance in this moss. We demonstrate that NaCl does not affect the chloroplast functionality in Physcomitrella despite significantly modifying expression of ionic transporters and cellular morphology, specifically the chloroplast ultrastructure, revealing a high starch accumulation. Additionally, NHAD transporters apparently do not play any essential roles in salt tolerance.

patens. Study of NHAD Transporters in Na and K Homeostasis. Running head: Chloroplast Na and K transporters in Physcomitrella Corresponding author: B. Benito Centro de Biotecnología y Genómica de Plantas/ Universidad Politécnica de Madrid (UPM) Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA)/ Campus Montegancedo UPM/ 28223-Pozuelo de Alarcón, Madrid/Spain/+34 91 336 45 35/+34 91 715 77 21/ begona.benito@upm.es Subject areas: environmental and stress responses/ membrane and transport Number of black and white figures: 0 Number of color figures: 4 Tables: 3 Supplementary material: 1 Figure and 4 tables

K(+) is an essential macronutrient for plants. It is acquired by specific uptake systems located in roots. Although the concentrations of K(+) in the soil solution are widely variable, K(+) nutrition is secured by uptake systems that exhibit different affinities for K(+). Two main systems have been described for root K(+) uptake in several species: the high-affinity HAK5-like transporter and the inward-rectifier AKT1-like channel. Other unidentified systems may be also involved in root K(+) uptake, although they only seem to operate when K(+) is not limiting. The use of knock-out lines has allowed demonstrating their role in root K(+) uptake in Arabidopsis and rice. Plant adaptation to the different K(+) supplies relies on the finely tuned regulation of these systems. Low K(+)-induced transcriptional up-regulation of the genes encoding HAK5-like transporters occurs through a signal cascade that includes changes in the membrane potential of root cells and increases in ethylene and reactive oxygen species concentrations. Activation of AKT1 channels occurs through phosphorylation by the CIPK23/CBL1 complex. Recently, activation of the Arabidopsis HAK5 by the same complex has been reported, pointing to CIPK23/CBL as a central regulator of the plant's adaptation to low K(+). Na(+) is not an essential plant nutrient but it may be beneficial for some plants. At low concentrations, Na(+) improves growth, especially under K(+) deficiency. Thus, high-affinity Na(+) uptake systems have been described that belong to the HKT and HAK families of transporters. At high concentrations, typical of saline environments, Na(+) accumulates in plant tissues at high concentrations, producing alterations that include toxicity, water deficit and K(+) deficiency. Data concerning pathways for Na(+) uptake into roots under saline conditions are still scarce, although several possibilities have been proposed. The apoplast is a significant pathway for Na(+) uptake in rice grown under salinity conditions, but in other plant species different mechanisms involving non-selective cation channels or transporters are under discussion.

MAIN CONCLUSION:Arabidopsis plants in NaCl suffering half growth inhibition do not suffer osmotic stress and seldom shoot Na (+) toxicity; overaccumulation of Na (+) plus K (+) might trigger the inhibition. It is widely assumed that salinity inhibits plant growth by osmotic stress and shoot Na(+) toxicity. This study aims to examine the growth inhibition of Arabidopsis thaliana by NaCl concentrations that allow the completion of the life cycle. Unaffected Col-0 wild-type plants were used to define nontoxic Na(+) contents; Na(+) toxicities in shoots and roots were analyzed in hkt1 and sos1 mutants, respectively. The growth inhibition of Col-0 plants at 40 mM Na(+) was mild and equivalent to that produced by 8 and 4 mM Na(+) in hkt1 and sos1 plants, respectively. Therefore, these mutants allowed to study the toxicity of Na(+) in the absence of an osmotic challenge. Col-0 and Ts-1 accessions showed very different Na(+) contents but similar growth inhibitions; Ts-1 plants showed very high leaf Na(+) contents but no symptoms of Na(+) toxicity. Ak-1, C24, and Fei-0 plants were highly affected by NaCl showing evident symptoms of shoot Na(+) toxicity. Increasing K(+) in isotonic NaCl/KCl combinations dramatically decreased the Na(+) content in all Arabidopsis accessions and eliminated the signs of Na(+) toxicity in most of them but did not relieve growth inhibition. This suggested that the dominant inhibition in these conditions was either osmotic or of an ionic nature unspecific for Na(+) or K(+). Col-0 and Ts-1 plants growing in sorbitol showed a clear osmotic stress characterized by a notable decrease of their water content, but this response did not occur in NaCl. Overaccumulation of Na(+) plus K(+) might trigger growth reduction in NaCl-treated plants.

High-affinity K+ (HAK) transporters are encoded by a large family of genes and are ubiquitous in the plant kingdom. These HAK-type transporters participate in low- and high-affinity potassium (K+) uptake and are crucial for the maintenance of K+ homeostasis under hostile conditions. In this study, the full-length cDNA of CcHAK1 gene was isolated from roots of the habanero pepper (Capsicum chinense). CcHAK1 expression was positively regulated by K+ starvation in roots and was not inhibited in the presence of NaCl. Phylogenetic analysis placed the CcHAK1 transporter in group I of the HAK K+ transporters, showing that it is closely related to Capsicum annuum CaHAK1 and Solanum lycopersicum LeHAK5. Characterization of the protein in a yeast mutant deficient in high-affinity K+ uptake (WΔ3) suggested that CcHAK1 function is associated with high-affinity K+ uptake, with Km and Vmax for Rb of 50 μM and 0.52 nmol mg-1 min-1, respectively. K+ uptake in yeast expressing the CcHAK1 transporter was inhibited by millimolar concentrations of the cations ammonium ([Formula: see text]) and cesium (Cs+) but not by sodium (Na+). The results presented in this study suggest that the CcHAK1 transporter may contribute to the maintenance of K+ homeostasis in root cells in C. chinense plants undergoing K+-deficiency and salt stress.

A raiz de la observacion clinica de que el ejercicio cronico y de alto nivel parece relacionarse con la aparicion de ciertas arritmias, desarrollamos un modelo experimental de ejercicio dinamico con objeto de: 1) determinar si el ejercicio cronico y de alta intensidad puede promover el desarrollo de un sustrato promotor de arritmias; 2) estudiar si efectivamente existe mayor susceptibilidad a presentar arritmias, en especial fibrilacion auricular, en respuesta al ejercicio; 3) estudiar los mecanismos implicados en la aparicion de arritmias, en especial fibrilacion auricular; 4) evaluar las repercusiones del cese de la actividad deportiva en cuanto a susceptibilidad arritmica se refiere. Nuestros resultados confirman el desarrollo de un sustrato potencialmente arritmogenico en respuesta al ejercicio cronico, con aparicion de fibrosis auricular y en ventriculo derecho. Ademas, pudimos comprobar la mayor susceptibilidad a presentar fibrilacion auricular en respuesta al ejercicio cronico, la cual se vio favorecida tanto por el propio remodelado arritmogenico como por el aumento del tono vagal. Gran parte del remodelado estructural y autonomico observado tras el ejercicio, remitio tras el cese de la actividad deportiva, y con ello la susceptibilidad arritmica.

Pulmonary vein isolation has evolved over the past years as an alternative for the treatment of symptomatic recurrences of atrial fibrillation refractory to antiarrhythmic drug treatment. Both radiofrequency energy and cryoballoon ablation have proven useful in this setting. We present the case of a 55-year-old male patient undergoing cryoballoon ablation complicated with pulmonary hemorrhage. The cause of this rare complication may be found in the damage of vascular venous structures near the ablation zone or, alternatively, in hemorrhagic damage of the pulmonary vein surrounding tissue (or less probably to direct injury of the lingular bronchus). The extremely low temperatures achieved in this case (which are often associated with deep balloon position inside the veins) are alarming and should alert the physician about the possibility of an excessively intrapulmonary vein deployment of the cryoablation balloon.

In the earth's crust and in seawater, K+ and Na+ are by far the most available monovalent inorganic cations. Physico-chemically, K+ and Na+ are very similar, but K+ is widely used by plants whereas Na+ can easily reach toxic levels. Indeed, salinity is one of the major and growing threats to agricultural production. In this article, we outline the fundamental bases for the differences between Na+ and K+. We present the foundation of transporter selectivity and summarize findings on transporters of the HKT type, which are reported to transport Na+ and/or Na+ and K+, and may play a central role in Na+ utilization and detoxification in plants. Based on the structural differences in the hydration shells of K+ and Na+, and by comparison with sodium channels, we present an ad hoc mechanistic model that can account for ion permeation through HKTs.