Halophytes: Potential Resources for Salt Stress Tolerance Genes and Promoters

Juncus rigidus high biomass and cellulose productivity under wastewater salinity stress - A paradigm shift to the valorization of RO reject water

The use of water purifiers is intensively catching up and disposing of reverse osmosis reject water is of great concern. Reject water management using conventional methods is costly and harmful to the environment. To address this issue, the present study aims to utilize reverse osmosis reject wastewater using an eco-friendly approach. Juncus rigidus was treated with reject wastewater containing different salinity levels. Wastewater-treated plant dry biomass increased with increasing reject water salinity, and 625.3 g dry biomass recovered in treatment-B (~18,520 ppm). However, ~23,220 ppm wastewater salinity was lethal to the plants. The cellulose was extracted by alkali hydrolysis. The cellulose content in the wastewater-treated biomass was significantly higher in Treatment-B compared to both the control and Treatment-A (~12,744 ppm). The water salinity enhanced the cellulose (26.49 %) production in J. rigidus. Cellulose purity was confirmed using spectroscopic and thermogravimetric means. XRD shows highest crystallinity Index (77.29) with a d-spacing of 4.7 Å and 5.7 nm crystallite size in treatment-B. FTIR results reveal well-defined relevant peaks for OH, CH, CO, CH2, C-O-C, CO groups in treatment-B cellulose. Salinity impacts carboxyl groups in treatment B cellulose with a sharper and intense peak at 1644 cm-1 responsible for water absorption. Treatment-B exhibits higher thermal stability due to increased crystallinity. DSC shows endothermic depolymerization of cellulose with distinct peaks for different treatments. Morphological traits got better with increasing salinity with no adverse effect on cellulose. Salinity moderately affected the water absorption capacity of cellulose. All cellulose samples were devoid of gram-negative bacteria known by microbial test. This pioneering work underscores the plant's remarkable capacity not only to accomplish the circular economy by the valorization of wastewater obtained from various water purifiers for Juncus cultivation for cellulose production for diverse applications but also to generate income from wastewater.

Multivariate statistical analysis of bioavailability of heavy metals and mineral characterization in selected species of coastal flora

This study presents a thorough investigation into the concentration of heavy metals and mineral composition within four distinct coastal flora species: Cyperus conglomeratus, Halopyrum mucronatum, Sericostem pauciflorum, and Salvadora persica. Employing rigorous statistical methodologies such as Pearson coefficient correlation, principal component analysis (PCA), analysis of variance (ANOVA), and interclass correlation (ICC), we aimed to elucidate the bioavailability of heavy metals, minerals, and relevant physical characteristics. The analysis focused on essential elements including copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), magnesium (Mg2+), calcium (Ca2+), sodium (Na+), potassium (K+), and chloride (Cl-), all of which are known to play pivotal roles in the ecological dynamics of coastal ecosystems. Through PCA, we discerned distinctive patterns within PC1 to PC4, collectively explaining an impressive 99.65% of the variance observed in heavy metal composition across the studied flora species. These results underscore the profound influence of environmental factors on the mineral composition of coastal flora, offering critical insights into the ecological processes shaping these vital ecosystems. Furthermore, significant correlations among mineral contents in H. mucronatum; K+ with content of Na+ (r = 0.989) and Mg2+ (r = 0.984); as revealed by ICC analyses, contributed to a nuanced understanding of variations in electrical conductivity (EC), pH levels, and ash content among the diverse coastal flora species. By shedding light on heavy metal and mineral dynamics in coastal flora, this study not only advances our scientific understanding but also provides a foundation for the development of targeted environmental monitoring and management strategies aimed at promoting the ecological sustainability and resilience of coastal ecosystems in the face of ongoing environmental challenges.

HgS2, a novel salt-responsive gene from the Halophyte Halogeton glomeratus, confers salt tolerance in transgenic Arabidopsis

Halophyte Halogeton glomeratus mostly grows in saline desert areas in arid and semi-arid regions and is able to adapt to adverse conditions such as salinity and drought. Earlier transcriptomic studies revealed activation of the HgS2 gene in the leaf of H. glomeratus seedlings when exposed to saline conditions. To identify the properties of HgS2 in H. glomeratus, we used yeast transformation and overexpression in Arabidopsis. Yeast cells genetically transformed with HgS2 exhibited K+ uptake and Na+ efflux compared with control (empty vector). Stable overexpression of HgS2 in Arabidopsis improved its resistance to salt stress and led to a notable rise in seed germination in salinity conditions compared to the wild type (WT). Transgenic Arabidopsis regulated ion homeostasis in plant cells by increasing Na+ absorption and decreasing K+ efflux in leaves, while reducing Na+ absorption and K+ efflux in roots. In addition, overexpression of HgS2 altered transcription levels of stress response genes and regulated different metabolic pathways in roots and leaves of Arabidopsis. These results offer new insights into the role of HgS2 in plants' salt tolerance.

Nitrate modulates the physiological tolerance responses of the halophytic species Sarcocornia fruticosa to copper excess

Coexistence impact of pollutants of different nature on halophytes tolerance to metal excess has not been thoroughly examined, and plant functional responses described so far do not follow a clear pattern. Using the Cu-tolerant halophyte Sarcocornia fruticosa as a model species, we conducted a greenhouse experiment to evaluate the impact of two concentration of copper (0 and 12 mM CuSO4) in combination with three nitrate levels (2, 14 and 50 mM KNO3) on plant growth, photosynthetic apparatus performance and ROS-scavenging enzymes system. The results revealed that S. fruticosa was able to grow adequately even when exposed to high concentrations of copper and nitrate. This response was linked to the plant capacity to uptake and retain a large amount of copper in its roots (up to 1500 mg kg-1 Cu), preventing its transport to aerial parts. This control of translocation was further magnified with nitrate concentration increment. Likewise, although Cu excess impaired S. fruticosa carbon assimilation capacity, the plant was able to downregulate its light-harvesting complexes function, as indicated its lowers ETR values, especially at 12 mM Cu + 50 mM NO3. This downregulation would contribute to avoid excess energy absorption and transformation. In addition, this strategy of avoiding excess energy was accompanied by the upregulation of all ROS-scavenging enzymes, a response that was further enhanced by the increase in nitrate concentration. Therefore, we conclude that the coexistence of nitrate would favor S. fruticosa tolerance to copper excess, and this effect is mediated by the combined activation of several tolerance mechanisms.

Modulation of physio-biochemical and photosynthesis parameters by overexpressing SbPIP2 gene improved abiotic stress tolerance of transgenic tobacco

The present study aims to explore the potential of a plasma-membrane localized PIP2-type aquaporin protein sourced from the halophyte Salicornia brachiata to alleviate salinity and water deficit stress tolerance in a model plant through transgenic intervention. Transgenic plants overexpressing SbPIP2 gene showed improved physio-biochemical parameters like increased osmolytes (proline, total sugar, and amino acids), antioxidants (polyphenols), pigments and membrane stability under salinity and drought stresses compared to control plants [wild type (WT) and vector control (VC) plants]. Multivariate statistical analysis showed that, under water and salinity stresses, osmolytes, antioxidants and pigments were correlated with SbPIP2-overexpressing (SbPIP2-OE) plants treated with salinity and water deficit stress, suggesting their involvement in stress tolerance. As aquaporins are also involved in CO2 transport, SbPIP2-OE plants showed enhanced photosynthesis performance than wild type upon salinity and drought stresses. Photosynthetic gas exchange (net CO2 assimilation rate, PSII efficiency, ETR, and non-photochemical quenching) were significantly higher in SbPIP2-OE plants compared to control plants (wild type and vector control plants) under both unstressed and stressed conditions. The higher quantum yield for reduction of end electron acceptors at the PSI acceptor side [Φ( R0 )] in SbPIP2-OE plants compared to control plants under abiotic stresses indicates a continued PSI functioning, leading to retained electron transport rate, higher carbon assimilation, and less ROS-mediated injuries. In conclusion, the SbPIP2 gene functionally validated in the present study could be a potential candidate for engineering abiotic stress resilience in important crops.

Exploring salt tolerance mechanisms using machine learning for transcriptomic insights: case study in Spartina alterniflora

Salt stress poses a significant threat to global cereal crop production, emphasizing the need for a comprehensive understanding of salt tolerance mechanisms. Accurate functional annotations of differentially expressed genes are crucial for gaining insights into the salt tolerance mechanism. The challenge of predicting gene functions in under-studied species, especially when excluding infrequent GO terms, persists. Therefore, we proposed the use of NetGO 3.0, a machine learning-based annotation method that does not rely on homology information between species, to predict the functions of differentially expressed genes under salt stress. Spartina alterniflora, a halophyte with salt glands, exhibits remarkable salt tolerance, making it an excellent candidate for in-depth transcriptomic analysis. However, current research on the S. alterniflora transcriptome under salt stress is limited. In this study we used S. alterniflora as an example to investigate its transcriptional responses to various salt concentrations, with a focus on understanding its salt tolerance mechanisms. Transcriptomic analysis revealed substantial changes impacting key pathways, such as gene transcription, ion transport, and ROS metabolism. Notably, we identified a member of the SWEET gene family in S. alterniflora, SA_12G129900.m1, showing convergent selection with the rice ortholog SWEET15. Additionally, our genome-wide analyses explored alternative splicing responses to salt stress, providing insights into the parallel functions of alternative splicing and transcriptional regulation in enhancing salt tolerance in S. alterniflora. Surprisingly, there was minimal overlap between differentially expressed and differentially spliced genes following salt exposure. This innovative approach, combining transcriptomic analysis with machine learning-based annotation, avoids the reliance on homology information and facilitates the discovery of unknown gene functions, and is applicable across all sequenced species.

Temporal Changes in Biochemical Responses to Salt Stress in Three Salicornia Species

Halophytes adapt to salinity using different biochemical response mechanisms. Temporal measurements of biochemical parameters over a period of exposure to salinity may clarify the patterns and kinetics of stress responses in halophytes. This study aimed to evaluate short-term temporal changes in shoot biomass and several biochemical variables, including the contents of photosynthetic pigments, ions (Na+, K+, Ca2+, and Mg2+), osmolytes (proline and glycine betaine), oxidative stress markers (H2O2 and malondialdehyde), and antioxidant enzymes (superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase) activities of three halophytic Salicornia species (S. persica, S. europaea, and S. bigelovii) in response to non-saline, moderate (300 mM NaCl), and high (500 mM NaCl) salinity treatments at three sampling times. Salicornia plants showed maximum shoot biomass under moderate salinity conditions. The results indicated that high Na+ accumulation in the shoots, coupled with the relative retention of K+ and Ca2+ under salt stress conditions, contributed significantly to ionic and osmotic balance and salinity tolerance in the tested Salicornia species. Glycine betaine accumulation, both constitutive and salt-induced, also seems to play a crucial role in osmotic adjustment in Salicornia plants subjected to salinity treatments. Salicornia species possess an efficient antioxidant enzyme system that largely relies on the ascorbate peroxidase and peroxidase activities to partly counteract salt-induced oxidative stress. The results also revealed that S. persica exhibited higher salinity tolerance than S. europaea and S. bigelovii, as shown by better plant growth under moderate and high salinity. This higher tolerance was associated with higher peroxidase activities and increased glycine betaine and proline accumulation in S. persica. Taking all the data together, this study allowed the identification of the biochemical mechanisms contributing significantly to salinity tolerance of Salicornia through the maintenance of ion and osmotic homeostasis and protection against oxidative stress.

Exogenous Sodium and Calcium Alleviate Drought Stress by Promoting the Succulence of Suaeda salsa

Succulence is a key trait involved in the response of Suaeda salsa to salt stress. However, few studies have investigated the effects of the interaction between salt and drought stress on S. salsa growth and succulence. In this study, the morphology and physiology of S. salsa were examined under different salt ions (Na+, Ca2+, Mg2+, Cl-, and SO42-) and simulated drought conditions using different polyethylene glycol concentrations (PEG; 0%, 5%, 10%, and 15%). The results demonstrate that Na+ and Ca2+ significantly increased leaf succulence by increasing leaf water content and enlarging epidermal cell size compared to Mg2+, Cl-, and SO42-. Under drought (PEG) stress, with an increase in drought stress, the biomass, degree of leaf succulence, and water content of S. salsa decreased significantly in the non-salt treatment. However, with salt treatment, the results indicated that Na+ and Ca2+ could reduce water stress due to drought by stimulating the succulence of S. salsa. In addition, Na+ and Ca2+ promoted the activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), which could reduce oxidative stress. In conclusion, Na+ and Ca2+ are the main factors promoting succulence and can effectively alleviate drought stress in S. salsa.

Comparative transcriptome analysis reveals the adaptive mechanisms of halophyte Suaeda dendroides encountering high saline environment

Suaeda dendroides, a succulent euhalophyte of the Chenopodiaceae family, intermittently spread around northern Xinjiang, China, has the ability to grow and develop in saline and alkali environments. The objective of this study was therefore to investigate the underlying molecular mechanisms of S. dendroides response to high salt conditions. 27 sequencing libraries prepared from low salt (200 mM NaCl) and high salt (800 mM NaCl) treated plants at 5 different stages were sequenced using Illumina Hiseq 2000. A total of 133,107 unigenes were obtained, of which 4,758 were DEGs. The number of DEGs in the high salt group (3,189) was more than the low salt treatment group (733) compared with the control. GO and KEGG analysis of the DEGs at different time points of the high salt treatment group showed that the genes related to cell wall biosynthesis and modification, plant hormone signal transduction, ion homeostasis, organic osmolyte accumulation, and reactive oxygen species (ROS) detoxification were significantly expressed, which indicated that these could be the main mechanisms of S. dendroides acclimate to high salt stress. The study provides a new perspective for understanding the molecular mechanisms of halophytes adapting to high salinity. It also provides a basis for future investigations of key salt-responsive genes in S. dendroides.

Introducing the halophyte Salicornia europaea to investigate combined impact of salt and tidal submergence conditions

Tolerance mechanisms to single abiotic stress events are being investigated in different plant species, but how plants deal with multiple stress factors occurring simultaneously is still poorly understood. Here, we introduce Salicornia europaea as a species with an extraordinary tolerance level to both flooding and high salt concentrations. Plants exposed to 0.5MNaCl (mimicking sea water concentrations) grew larger than plants not exposed to salt. Adding more salt reduced growth, but concentrations up to 2.5MNaCl were not lethal. Regular tidal flooding with salt water (0.5MNaCl) did not affect growth or chlorophyll fluorescence, whereas continuous flooding stopped growth while plants survived. Quantitative polymerase chain reaction (qPCR) analysis of plants exposed to 1% oxygen in air revealed induction of selected hypoxia responsive genes, but these genes were not induced during tidal flooding, suggesting that S. europaea did not experience hypoxic stress. Indeed, plants were able to transport oxygen into waterlogged soil. Interestingly, sequential exposure to salt and hypoxic air changed the expression of several but not all genes as compared to their expression upon hypoxia only, demonstrating the potential to use S . europaea to investigate signalling-crosstalk between tolerance reactions to multiple environmental perturbations.

Progress and prospects in harnessing wild relatives for genetic enhancement of salt tolerance in rice

Salt stress is the second most devastating abiotic stress after drought and limits rice production globally. Genetic enhancement of salinity tolerance is a promising and cost-effective approach to achieve yield gains in salt-affected areas. Breeding for salinity tolerance is challenging because of the genetic complexity of the response of rice plants to salt stress, as it is governed by minor genes with low heritability and high G × E interactions. The involvement of numerous physiological and biochemical factors further complicates this complexity. The intensive selection and breeding efforts targeted towards the improvement of yield in the green-revolution era inadvertently resulted in the gradual disappearance of the loci governing salinity tolerance and a significant reduction in genetic variability among cultivars. The limited utilization of genetic resources and narrow genetic base of improved cultivars have resulted in a plateau in response to salinity tolerance in modern cultivars. Wild species are an excellent genetic resource for broadening the genetic base of domesticated rice. Exploiting novel genes of underutilized wild rice relatives to restore salinity tolerance loci eliminated during domestication can result in significant genetic gain in rice cultivars. Wild species of rice, Oryza rufipogon and Oryza nivara, have been harnessed in the development of a few improved rice varieties like Jarava and Chinsura Nona 2. Furthermore, increased access to sequence information and enhanced knowledge about the genomics of salinity tolerance in wild relatives has provided an opportunity for the deployment of wild rice accessions in breeding programs, while overcoming the cross-incompatibility and linkage drag barriers witnessed in wild hybridization. Pre-breeding is another avenue for building material that are ready for utilization in breeding programs. Efforts should be directed towards systematic collection, evaluation, characterization, and deciphering salt tolerance mechanisms in wild rice introgression lines and deploying untapped novel loci to improve salinity tolerance in rice cultivars. This review highlights the potential of wild relatives of Oryza to enhance tolerance to salinity, track the progress of work, and provide a perspective for future research.

Spatial assessment and chemical characterization of degraded (salt-affected) soils at post-reclamation stage of the Indo-Gangetic Plain in Haryana State

Dynamics of soil salinity and sodicity is a common feature driven by anthropogenic causes such as soil reclamation, the effect of extreme climate events, disturbed salt, and water balance in irrigated areas that are devoid of any good quality groundwater source and adequate natural surface drainage condition in a semiarid climatic region. Periodic soil salinity assessment is therefore vital to know the current soil salinity status, plan reclamation, and/or management strategies for sustained agricultural growth and livelihood security. Temporal studies using Indian Remote Sensing (IRS) LISS III data, at pre- (1997) and post-reclamation (2017) stages have indicated spatial changes as reclaimed areas (~ 35%) and dynamics of soil salinity as increased areas (~ 61%) under irrigation across the Gangetic plain of Haryana State. The prominent areas of reclaimed sodic soil soils were located in the old alluvial plain which covered Panipat (12.32%), Karnal (6.01%), and Jind (5.9%) districts. Based on pH, ECe, and ESP values, these were classified as slight (Sso1, 8.75%), moderate (Sso2, 24.73%), and strong (Sso3, 18.20%) sodic soils, respectively. Significant salinity-inflictions (emerging areas) were identified at low-lying, poorly drained, irrigated soils in south and central Haryana that cover Jhajjar (13.99%), Sirsa (11.06%), Hisar (10.15%), Rohtak (8.73%), Bhiwani (6.43%), Palwal (4.31%), and Rewari (3.01%) districts. Slight (Ssa1, 16.82%), and moderate (Ssa2, 22.13%), categories are dominant soils, respectively. Among the landforms, significant areas (28.24%) were identified in the old alluvial plain with sand dunes (OAPSD), aeo-fluvial plain (AFP, 8.6%), and fluvio-aeolian plain (FAP, 6.0%), respectively. Dominant areas of reclaimed soils (14.4%) were identified in OAPSD. The soil analysis data indicated that these soil are moderate to strongly sodic (pH 8.7-11.0) and saline (ECe 4-26 dS m-1). The reclaimed sodic soils showed prominent improvement in soil pH and sodicity levels (pH 8.3-9.2) at 0-15 cm depth and are commonly located in the Ghaggar and Yamuna river plains. Poor quality groundwater with high Residual Sodium Carbonate (RSC) was dominant at selected locations under the arid and semiarid climate. The database can also be used as a reference database for further monitoring of soil salinity status particularly in the irrigated regions. Currently, it is also used as a primary database for harmonization, monitoring, and reconciling of similar soils of the world under the Global Soil Partnership projects.

Deep learning-enabled discovery and characterization of HKT genes in Spartina alterniflora

Spartina alterniflora is a halophyte that can survive in high-salinity environments, and it is phylogenetically close to important cereal crops, such as maize and rice. It is of scientific interest to understand why S. alterniflora can live under such extremely stressful conditions. The molecular mechanism underlying its high-saline tolerance is still largely unknown. Here we investigated the possibility that high-affinity K+ transporters (HKTs), which function in salt tolerance and maintenance of ion homeostasis in plants, are responsible for salt tolerance in S. alterniflora. To overcome the imprecision and unstable of the gene screening method caused by the conventional sequence alignment, we used a deep learning method, DeepGOPlus, to automatically extract sequence and protein characteristics from our newly assemble S. alterniflora genome to identify SaHKTs. Results showed that a total of 16 HKT genes were identified. The number of S. alterniflora HKTs (SaHKTs) is larger than that in all other investigated plant species except wheat. Phylogenetically related SaHKT members had similar gene structures, conserved protein domains and cis-elements. Expression profiling showed that most SaHKT genes are expressed in specific tissues and are differentially expressed under salt stress. Yeast complementation expression analysis showed that type I members SaHKT1;2, SaHKT1;3 and SaHKT1;8 and type II members SaHKT2;1, SaHKT2;3 and SaHKT2;4 had low-affinity K+ uptake ability and that type II members showed stronger K+ affinity than rice and Arabidopsis HKTs, as well as most SaHKTs showed preference for Na+ transport. We believe the deep learning-based methods are powerful approaches to uncovering new functional genes, and the SaHKT genes identified are important resources for breeding new varieties of salt-tolerant crops.

A novel ABA-induced transcript factor from Millettia pinnata, MpAITR1, enhances salt and drought tolerance through ABA signaling in transgenic Arabidopsis

Abiotic stress, such as salt and drought stress, seriously limits plant growth and crop yield. Abscisic acid (ABA) is essential in regulating plant responses to abiotic stress via signal perception, transduction, and transcriptional regulation. Pongamia (Millettia pinnata) is a kind of semi-mangrove plant with strong stress tolerance and can grow in fresh and sea water. However, the molecular mechanism of the ABA signaling pathway mediating the environmental tolerance of Pongamia is still scarce so far. AITR (ABA-Induced Transcription Repressor) was a recently identified small conserved family of transcription factor in angiosperms, which played controversial roles in response to abiotic stresses in different species. Here, we identified an ABA-induced gene, MpAITR1, which encoded a nucleus localization transcriptional factor in Pongamia. MpAITR1 was highly induced by ABA and salt treatments in roots and leaves. Heterologous expression of MpAITR1 in Arabidopsis increased sensitivity to ABA, moreover, enhanced tolerance to salt and drought stress. The expression levels of some ABA-responsive and stress-responsive genes were altered in transgenic plants compared to wild-type plants under the ABA, salt, and drought stress, which was consistent with the stress-tolerant phenotype of transgenic plants. These results reveal that MpAITR1 positively modulates ABA signaling pathways and enhances the tolerance to salt and drought stress by regulating downstream target genes. Taken together, MpAITR1 from the semi-mangrove plant Pongamia serves as a potential candidate for stress-tolerant crop breeding.

ROS Homeostasis and Antioxidants in the Halophytic Plants and Seeds

Reactive oxygen species (ROS) are excited or partially reduced forms of atmospheric oxygen, which are continuously produced during aerobic metabolism like many physiochemical processes operating throughout seed life. Previously, it was believed that ROS are merely cytotoxic molecules, however, now it has been established that they perform numerous beneficial functions in plants including many critical roles in seed physiology. ROS facilitate seed germination via cell wall loosening, endosperm weakening, signaling, and decreasing abscisic acid (ABA) levels. Most of the existing knowledge about ROS homeostasis and functions is based on the seeds of common plants or model ones. There is little information about the role of ROS in the germination process of halophyte seeds. There are several definitions for halophytic plants, however, we believed "halophytes are plants that can grow in very saline environment and complete their life cycle by adopting various phenological, morphological and physiological mechanisms at canopy, plant, organelle and molecular scales". Furthermore, mechanisms underlying ROS functions such as downstream targets, cross-talk with other molecules, and alternative routes are still obscure. The primary objective of this review is to decipher the mechanisms of ROS homeostasis in halophytes and dry seeds, as well as ROS flux in germinating seeds of halophytes.

Desalination, Water Re-use, and Halophyte Cultivation in Salinized Regions: A Highly Productive Groundwater Treatment System

Groundwater salinization is a problem affecting access to water in many world regions. Though desalination by conventional reverse osmosis (RO) can upgrade groundwater quality for drinking, its disadvantages include unmanaged brine discharge and accelerated groundwater depletion. Here, we propose a new approach combining RO, forward osmosis (FO), and halophyte cultivation, in which FO optimally adjusts the concentration of the RO reject brine for irrigation of Salicornia or Sarcocornia. The FO also re-uses wastewater, thus, reducing groundwater extraction and the wastewater effluent volume. To suit different groundwater salinities in the range 1-8 g/L, three practical designs are proposed and analyzed. Results include specific groundwater consumption (SGC), specific energy consumption (SEC), wastewater volume reduction, peak RO pressure, permeate water quality, efficiency of water resource utilization, and halophyte yield. Compared to conventional brackish water RO, the results show superior performance in almost all aspects. For example, SGC is reduced from 1.25 to 0.9 m3 per m3 of drinking water output and SEC is reduced from 0.79 to 0.70 kW h/m3 by a FO-RO-FO system treating groundwater of salinity 8 g/L. This system can produce 1.1 m3 of high-quality drinking water and up to 4.9 kg of edible halophyte per m3 of groundwater withdrawn.

Isolation and molecular characterization of an FSK2-type dehydrin from Atriplex halimus

Dehydrins form the group II LEA protein family and are known to play multiple roles in plant stress tolerance and enzyme protection. They harbor a variable number of conserved lysine rich motifs (K-segments) and may also contain three additional conserved motifs (Y-, F- and S-segments). In this work, we report the isolation and characterization of an FSK₂-type dehydrin from the halophytic species Atriplex halimus, which we designate as AhDHN1. In silico analysis of the protein sequence revealed that AhDHN1 contains large number of hydrophilic residues, and is predicted to be intrinsically disordered. In addition, it has an FSK₂ architecture with one F-segment, one S-segment, and two K-segments. The expression analysis showed that the AhDHN1 transcript is induced by salt and water stress treatments in the leaves of Atriplex seedlings. Moreover, circular dichroism spectrum performed on recombinant AhDHN1 showed that the dehydrin lacks any secondary structure, confirming its intrinsic disorder nature. However, there is a gain of α-helicity in the presence of membrane-like SDS micelles. In vitro assays revealed that AhDHN1 is able to effectively protect enzymatic activity of the lactate dehydrogenase against cold, heat and dehydration stresses. Our findings strongly suggest that AhDHN1 can be involved in the adaptation mechanisms of halophytes to adverse environments.

Opportunities for the use of selenium nanoparticles in agriculture

Due to the growing number of the world's population, there is an urgent need for high-quality food to meet global food security. Traditional fertilizers and pesticides face the problems of low utilization efficiency and possible hazards to non-target organisms. Selenium (Se) is an essential trace element for animals and humans. As a result, Se nanoparticles (SeNPs) have aroused intense interest and found opportunities in agricultural use. Herein, we summarized representative studies on the potential application of SeNPs in agriculture, including mitigating biotic and abiotic stresses in plants, promoting seed germination and plant growth, and improving Se contents and nutritional values in crops, and the underlying mechanisms were also discussed. Finally, future directions are highlighted to get a deep insight into this field.

Lipid metabolism and antioxidant system contribute to salinity tolerance in halophytic grass seashore paspalum in a tissue-specific manner

Soil salinization is a growing issue that limits agriculture globally. Understanding the mechanism underlying salt tolerance in halophytic grasses can provide new insights into engineering plant salinity tolerance in glycophytic plants. Seashore paspalum (Paspalum vaginatum Sw.) is a halophytic turfgrass and genomic model system for salt tolerance research in cereals and other grasses. However, the salt tolerance mechanism of this grass largely unknown. To explore the correlation between Na⁺ accumulation and salt tolerance in different tissues, we utilized two P. vaginatum accessions that exhibit contrasting tolerance to salinity. To accomplish this, we employed various analytical techniques including ICP-MS-based ion analysis, lipidomic profiling analysis, enzyme assays, and integrated transcriptomic and metabolomic analysis. Under high salinity, salt-tolerant P. vaginatum plants exhibited better growth and Na⁺ uptake compared to salt-sensitive plants. Salt-tolerant plants accumulated heightened Na⁺ accumulation in their roots, leading to increased production of root-sourced H₂O₂, which in turn activated the antioxidant systems. In salt-tolerant plants, metabolome profiling revealed tissue-specific metabolic changes, with increased amino acids, phenolic acids, and polyols in roots, and increased amino acids, flavonoids, and alkaloids in leaves. High salinity induced lipidome adaptation in roots, enhancing lipid metabolism in salt-tolerant plants. Moreover, through integrated analysis, the importance of amino acid metabolism in conferring salt tolerance was highlighted. This study significantly enhances our current understanding of salt-tolerant mechanisms in halophyte grass, thereby offering valuable insights for breeding and genetically engineering salt tolerance in glycophytic plants.

A holistic and sustainable approach linked to drought tolerance of Mediterranean crops

The rapid increase in average temperatures and the progressive reduction in rainfalls caused by climate change is reducing crop yields worldwide, particularly in regions with hot and semi-arid climates such as the Mediterranean area. In natural conditions, plants respond to environmental drought stress with diverse morphological, physiological, and biochemical adaptations in an attempt to escape, avoid, or tolerate drought stress. Among these adaptations to stress, the accumulation of abscisic acid (ABA) is of pivotal importance. Many biotechnological approaches to improve stress tolerance by increasing the exogenous or endogenous content of ABA have proved to be effective. In most cases the resultant drought tolerance is associated with low productivity incompatible with the requirements of modern agriculture. The on-going climate crisis has provoked the search for strategies to increase crop yield under warmer conditions. Several biotechnological strategies, such as the genetic improvement of crops or the generation of transgenic plants for genes involved in drought tolerance, have been attempted with unsatisfactory results suggesting the need for new approaches. Among these, the genetic modification of transcription factors or regulators of signaling cascades provide a promising alternative. To reconcile drought tolerance with crop yield, we propose mutagenesis of genes controlling key signaling components downstream of ABA accumulation in local landraces to modulate responses. We also discuss the advantages of tackling this challenge with a holistic approach involving different knowledge and perspectives, and the problem of distributing the selected lines at subsidized prices to guarantee their use by small family farms.

Roles of S-Adenosylmethionine and Its Derivatives in Salt Tolerance of Cotton

Salinity is a major abiotic stress that restricts cotton growth and affects fiber yield and quality. Although studies on salt tolerance have achieved great progress in cotton since the completion of cotton genome sequencing, knowledge about how cotton copes with salt stress is still scant. S-adenosylmethionine (SAM) plays important roles in many organelles with the help of the SAM transporter, and it is also a synthetic precursor for substances such as ethylene (ET), polyamines (PAs), betaine, and lignin, which often accumulate in plants in response to stresses. This review focused on the biosynthesis and signal transduction pathways of ET and PAs. The current progress of ET and PAs in regulating plant growth and development under salt stress has been summarized. Moreover, we verified the function of a cotton SAM transporter and suggested that it can regulate salt stress response in cotton. At last, an improved regulatory pathway of ET and PAs under salt stress in cotton is proposed for the breeding of salt-tolerant varieties.

Soilless Cultivated Halophyte Plants: Volatile, Nutritional, Phytochemical, and Biological Differences

The use of halophyte plants appears as a potential solution for degraded soil, food safety, freshwater scarcity, and coastal area utilization. These plants have been considered an alternative crop soilless agriculture for sustainable use of natural resources. There are few studies carried out with cultivated halophytes using a soilless cultivation system (SCS) that report their nutraceutical value, as well as their benefits on human health. The objective of this study was to evaluate and correlate the nutritional composition, volatile profile, phytochemical content, and biological activities of seven halophyte species cultivated using a SCS (Disphyma crassifolium L., Crithmum maritimum L., Inula crithmoides L., Mesembryanthemum crystallinum L., Mesembryanthemum nodiflorum L., Salicornia ramosissima J. Woods, and Sarcocornia fruticosa (Mill.) A. J. Scott.). Among these species, results showed that S. fruticosa had a higher content in protein (4.44 g/100 g FW), ash (5.70 g/100 g FW), salt (2.80 g/100 g FW), chloride (4.84 g/100 g FW), minerals (Na, K, Fe, Mg, Mn, Zn, Cu), total phenolics (0.33 mg GAE/g FW), and antioxidant activity (8.17 µmol TEAC/g FW). Regarding the phenolic classes, S. fruticosa and M. nodiflorum were predominant in the flavonoids, while M. crystallinum, C. maritimum, and S. ramosissima were in the phenolic acids. Moreover, S. fruticosa, S. ramosissima, M. nodiflorum, M. crystallinum, and I. crithmoides showed ACE-inhibitory activity, an important target control for hypertension. Concerning the volatile profile, C. maritimum, I. crithmoides, and D. crassifolium were abundant in terpenes and esters, while M. nodiflorum, S. fruticosa, and M. crystallinum were richer in alcohols and aldehydes, and S. ramosissima was richer in aldehydes. Considering the environmental and sustainable roles of cultivated halophytes using a SCS, these results indicate that these species could be considered an alternative to conventional table salt, due to their added nutritional and phytochemical composition, with potential contribution for the antioxidant and anti-hypertensive effects.

Halophytes as new model plant species for salt tolerance strategies

Soil salinity is becoming a growing issue nowadays, severely affecting the world's most productive agricultural landscapes. With intersecting and competitive challenges of shrinking agricultural lands and increasing demand for food, there is an emerging need to build resilience for adaptation to anticipated climate change and land degradation. This necessitates the deep decoding of a gene pool of crop plant wild relatives which can be accomplished through salt-tolerant species, such as halophytes, in order to reveal the underlying regulatory mechanisms. Halophytes are generally defined as plants able to survive and complete their life cycle in highly saline environments of at least 200-500 mM of salt solution. The primary criterion for identifying salt-tolerant grasses (STGs) includes the presence of salt glands on the leaf surface and the Na⁺ exclusion mechanism since the interaction and replacement of Na⁺ and K⁺ greatly determines the survivability of STGs in saline environments. During the last decades or so, various salt-tolerant grasses/halophytes have been explored for the mining of salt-tolerant genes and testing their efficacy to improve the limit of salt tolerance in crop plants. Still, the utility of halophytes is limited due to the non-availability of any model halophytic plant system as well as the lack of complete genomic information. To date, although Arabidopsis (Arabidopsis thaliana) and salt cress (Thellungiella halophila) are being used as model plants in most salt tolerance studies, these plants are short-lived and can tolerate salinity for a shorter duration only. Thus, identifying the unique genes for salt tolerance pathways in halophytes and their introgression in a related cereal genome for better tolerance to salinity is the need of the hour. Modern technologies including RNA sequencing and genome-wide mapping along with advanced bioinformatics programs have advanced the decoding of the whole genetic information of plants and the development of probable algorithms to correlate stress tolerance limit and yield potential. Hence, this article has been compiled to explore the naturally occurring halophytes as potential model plant species for abiotic stress tolerance and to further breed crop plants to enhance salt tolerance through genomic and molecular tools.

RNA-seq analysis and reconstruction of gene networks involved in response to salinity stress in quinoa (cv. Titicaca)

To better understand the mechanisms involved in salinity stress, the adaptability of quinoa cv. Titicaca-a halophytic plant-was investigated at the transcriptome level under saline and non-saline conditions. RNA-sequencing analysis of leaf tissue at the four-leaf stage by Illumina paired-end method was used to compare salt stress treatment (four days after stress at 13.8 dsm^-1) and control. Among the obtained 30,846,354 transcripts sequenced, 30,303 differentially expressed genes from the control and stress treatment samples were identified, with 3363 genes expressed ≥ 2 and false discovery rate (FDR) of < 0.001. Six differential expression genes were then selected and qRT-PCR was used to confirm the RNA-seq results. Some of the genes (Include; CML39, CBSX5, TRX1, GRXC9, SnRKγ1 and BAG6) and signaling pathways discussed in this paper not been previously studied in quinoa. Genes with ≥ 2 were used to design the gene interaction network using Cytoscape software, and AgriGO software and STRING database were used for gene ontology. The results led to the identification of 14 key genes involved in salt stress. The most effective hub genes involved in salt tolerance were the heat shock protein gene family. The transcription factors that showed a significant increase in expression under stress conditions mainly belonged to the WRKY, bZIP and MYB families. Ontology analysis of salt stress-responsive genes and hub genes revealed that metabolic pathways, binding, cellular processes and cellular anatomical entity are among the most effective processes involved in salt stress.

Response to Hypersalinity of Four Halophytes Growing in Hydroponic Floating Systems: Prospects in the Phytomanagement of High Saline Wastewaters and Extreme Environments

Hypersaline environments occur naturally worldwide in arid and semiarid regions or in artificial areas where the discharge of highly saline wastewaters, such as produced water (PW) from oil and gas industrial setups, has concentrated salt (NaCl). Halophytes can tolerate high NaCl concentrations by adopting ion extrusion and inclusion mechanisms at cell, tissue, and organ levels; however, there is still much that is not clear in the response of these plants to salinity and completely unknown issues in hypersaline conditions. Mechanisms of tolerance to saline and hypersaline conditions of four different halophytes (Suaeda fruticosa (L.) Forssk, Halocnemum strobilaceum (Pall.) M. Bieb., Juncus maritimus Lam. and Phragmites australis (Cav.) Trin. ex Steudel) were assessed by analysing growth, chlorophyll fluorescence and photosynthetic pigment parameters, nutrients, and sodium (Na) uptake and distribution in different organs. Plants were exposed to high saline (257 mM or 15 g L^-1 NaCl) and extremely high or hypersaline (514, 856, and 1712 mM or 30, 50, and 100 g L^-1 NaCl) salt concentrations in a hydroponic floating culture system for 28 days. The two dicotyledonous S. fruticosa and H. strobilaceum resulted in greater tolerance to hypersaline concentrations than the two monocotyledonous species J. maritimus and P. australis. Plant biomass and major cation (K, Ca, and Mg) distributions among above- and below-ground organs evidenced the osmoprotectant roles of K in the leaves of S. fruticosa, and of Ca and Mg in the leaves and stem of H. strobilaceum. In J. maritimus and P. australis the rhizome modulated the reduced uptake and translocation of nutrients and Na to shoot with increasing salinity levels. S. fruticosa and H. strobilaceum absorbed and accumulated elevated Na amounts in the aerial parts at all the NaCl doses tested, with high bioaccumulation (from 0.5 to 8.3) and translocation (1.7-16.2) factors. In the two monocotyledons, Na increased in the root and rhizome with the increasing concentration of external NaCl, dramatically reducing the growth in J. maritimus at both 50 and 100 g L^-1 NaCl and compromising the survival of P. australis at 30 g L^-1 NaCl and over after two weeks of treatment.

Does Potassium Modify the Response of Zinnia (Zinnia elegans Jacq.) to Long-Term Salinity?

Salinity is one of the major abiotic stress factors hindering crop production, including ornamental flowering plants. The present study examined the response to salt stress of Zinnia elegans 'Lilliput' supplemented with basic (150 mg·dm^-3) and enhanced (300 mg·dm^-3) potassium doses. Stress was imposed by adding 0.96 and 1.98 g of NaCl per dm^-3 of the substrate. The substrate's electrical conductivity was 1.1 and 2.3 dS·m^-1 for lower potassium levels and 1.2 and 2.4 dS·m^-1 for higher potassium levels. Salt stress caused a significant and dose-dependent reduction in leaf RWC, increased foliar Na and Cl concentrations, and reduced K. About 15% and 25% of cell membrane injury at lower and higher NaCl doses, respectively, were accompanied by only slight chlorophyll reduction. Salt stress-induced proline increase was accompanied by increased P5CS activity and decreased PDH activity. More than a 25% reduction in most growth parameters at EC 1.1-1.2 dS·m^-1 but only a slight decrease in chlorophyll and a 25% reduction in the decorative value (number of flowers produced, flower diameter) only at EC 2.3-2.4 dS·m^-1 were found. Salt stress-induced leaf area reduction was accompanied by increased cell wall lignification. An enhanced potassium dose caused a reduction in leaf Na and Cl concentrations and a slight increase in K. It was also effective in membrane injury reduction and proline accumulation. Increasing the dose of potassium did not improve growth and flowering parameters but affected the lignification of the leaf cell walls, which may have resulted in growth retardation. Zinnia elegans 'Lilliput' may be considered sensitive to long-term salt stress.

Impact of Polyploidy Induction for Salinity Stress Mitigation in Soybean (Glycine max L. Merrill)

Polyploidy induction is recognized as one of the major evolutionary processes leading to remarkable morphological, physiological, and genetic variations in plants. Soybean (Glycine max L.), also known as soja bean or soya bean, is an annual leguminous crop of the pea family (Fabaceae) that shares a paleopolypoidy history, dating back to approximately 56.5 million years ago with other leguminous crops such as cowpea and other Glycine specific polyploids. This crop has been documented as one of the polyploid complex species among legumes whose gene evolution and resultant adaptive growth characteristics following induced polyploidization has not been fully explored. Furthermore, no successfully established in vivo or in vitro based polyploidy induction protocols have been reported to date, particularly, with the intention to develop mutant plants showing strong resistance to abiotic salinity stress. This review, therefore, describes the role of synthetic polyploid plant production in soybean for the mitigation of high soil salt stress levels and how this evolving approach could be used to further enhance the nutritional, pharmaceutical and economic industrial value of soybeans. This review also addresses the challenges involved during the polyploidization process.

Salt-Tolerant Plants, Halophytes, as Renewable Natural Resources for Cancer Prevention and Treatment: Roles of Phenolics and Flavonoids in Immunomodulation and Suppression of Oxidative Stress towards Cancer Management

Halophytes and xerophytes, plants with adequate tolerance to high salinity with strong ability to survive in drought ecosystem, have been recognized for their nutritional and medicinal values owing to their comparatively higher productions of secondary metabolites, primarily the phenolics, and the flavonoids, as compared to the normal vegetation in other climatic regions. Given the consistent increases in desertification around the world, which are associated with increasing salinity, high temperature, and water scarcity, the survival of halophytes due to their secondary metabolic contents has prioritized these plant species, which have now become increasingly important for environmental protection, land reclamation, and food and animal-feed security, with their primary utility in traditional societies as sources of drugs. On the medicinal herbs front, because the fight against cancer is still ongoing, there is an urgent need for development of more efficient, safe, and novel chemotherapeutic agents, than those currently available. The current review describes these plants and their secondary-metabolite-based chemical products as promising candidates for developing newer cancer therapeutics. It further discusses the prophylactic roles of these plants, and their constituents in prevention and management of cancers, through an exploration of their phytochemical and pharmacological properties, with a view on immunomodulation. The important roles of various phenolics and structurally diverse flavonoids as major constituents of the halophytes in suppressing oxidative stress, immunomodulation, and anti-cancer effects are the subject matter of this review and these aspects are outlined in details.

Improving abiotic stress tolerance of forage grasses - prospects of using genome editing

Due to an increase in the consumption of food, feed, and fuel and to meet global food security needs for the rapidly growing human population, there is a necessity to obtain high-yielding crops that can adapt to future climate changes. Currently, the main feed source used for ruminant livestock production is forage grasses. In temperate climate zones, perennial grasses grown for feed are widely distributed and tend to suffer under unfavorable environmental conditions. Genome editing has been shown to be an effective tool for the development of abiotic stress-resistant plants. The highly versatile CRISPR-Cas system enables increasingly complex modifications in genomes while maintaining precision and low off-target frequency mutations. In this review, we provide an overview of forage grass species that have been subjected to genome editing. We offer a perspective view on the generation of plants resilient to abiotic stresses. Due to the broad factors contributing to these stresses the review focuses on drought, salt, heat, and cold stresses. The application of new genomic techniques (e.g., CRISPR-Cas) allows addressing several challenges caused by climate change and abiotic stresses for developing forage grass cultivars with improved adaptation to the future climatic conditions. Genome editing will contribute towards developing safe and sustainable food systems.

GT Transcription Factors of Rosa rugosa Thunb. Involved in Salt Stress Response

Rosa rugosa was a famous aromatic plant while poor salt tolerance of commercial cultivars has hindered its culture in saline-alkali soil. In many plants, the roles of GT (or trihelix) genes in salt stresses responses have been emerging. In the wild R. rugosa, a total of 37 GTs (RrGTs) were grouped into GT-1, GT-2, GTγ, SH4, and SIP1 lineages. SIP1 lineage expanded by transposition. The motifs involved in the binding of GT cis-elements were conserved. Four RrGTs (RrGT11/14/16/18) significantly differentially expressed in roots or leaves under salt stress. The responsive patterns within 8 h NaCl treatment indicated that RrGTγ-4 (RrGT18) and RrGT-1 (RrGT16) were significantly induced by salt in roots of R. rugosa. Subcellular localizations of RrSIP1 (RrGT11) and RrGTγ-4 were on chloroplasts while RrGT-1 and RrSIP2 (RrGT14) located on cell nucleus. Regulation of ion transport could be the most important role of RrSIPs and RrGTγ-4. And RrGT-1 could be a halophytic gene with higher transcription abundance than glycophytic GT-1. These results provide key clue for further investigations of roles of RrGTs in salt stress response and would be helpful in the understanding the salt tolerance regulation mechanism of R. rugosa.

Exploiting constructed wetlands for industrial effluent phytodesalination in Jing-Jin-Ji urban agglomeration, China

The unsustainable exploitation of water resources and growing salinization impacting China's Beijing-Tianjin-Hebei (Jing-Jin-Ji) agglomeration threatens the region's economic growth and drives the exploration of alternative resources. The region's industries face a financial burden due to increasing constraints on water exploitation and discharge regulations. These have resulted in increased industrial salt concentration rejections/discharges, meanwhile, constructed wetlands (CWs), deployed as a perfunctory receptacle for industrial effluents in the region, are underexploited for treating/removing salts. Also, halophytic plants local to the region have promising chloride uptake (60.6 g/kg and 256.0 g/kg of plant dry weight) and can reduce water conductivity by 40%. Exploitation of CWs, using local halophytes has not been explored for phytodesalination purposes in the region. Hence, this study analyses the water resource and salinization crisis in the agglomeration and further evaluates workable potential and critical technical considerations for using local halophytes in CWs to treat industrial salt-laden effluents. While acknowledging this intervention for removing industrial effluent salt may not meet compliance in the region, effluent post-phytodesalination presents opportunities for industries to meet regulatory stipulations on water reuse rates. Furthermore, such effluent may be used for irrigation and can ameliorate the salinization and groundwater exploitation crisis as a cleaner recharge source.

Genetic analyses of morphological traits, and phenotypic screening of tossa jute germplasm grown under salinity stress

Corchorus olitorius L. jute is a natural fiber crop that is very susceptible to salinity stress. Salinity in soil is a serious threat to tossa jute cultivation in salt-prone regions of Bangladesh. Development of salinity stress tolerant tossa jute variety is a crying need in Bangladesh. Hence, 22 tossa jute genotypes were investigated in an augmented design against 7.86-7.93 dSm^-1 salinity stress at coastal regions of Bangladesh during 2017-2019. Salt-tolerant jute genotypes were phenotypically screened out based on survivability, vegetative growth, plant height, base diameter, and fiber yield capacity. Among all genotypes, Acc. 4160 and Acc. 2311 showed good fiber yield (18.0 and 13.8 g plant-1, respectively) with the lowest mortality rate (5.67 and 8.0%, respectively). Acc. 1381, Acc. 2307, Acc. 1334, Acc. 1381 and the pre-released varieties, namely O-9897, BJRI Tossa Pat 5, JRO-524 (Green) were also found good for the aforesaid traits. Among the studied characters, high heritability in a broad sense, genetic advance (%) of mean and significant associations were found which contribute to fiber yield significantly. According to the Clustering and principal component analyses, the relatively salt-tolerant genotypes of cluster II (Acc. 4160, Acc. 2311, Acc. 2307, JRO-524 (Green), Acc. 4327, BJRI Tossa Pat 5, Acc. 1334 & Acc. 1381) could be used as breeding materials and sources of salt-tolerant genes to develop salt-tolerant tossa jute variety.

Alkaloid production and response to natural adverse conditions in Peganum harmala: in silico transcriptome analyses

Peganum harmala is a valuable wild plant that grows and survives under adverse conditions and produces pharmaceutical alkaloid metabolites. Using different assemblers to develop a transcriptome improves the quality of assembled transcriptome. In this study, a concrete and accurate method for detecting stress-responsive transcripts by comparing stress-related gene ontology (GO) terms and public domains was designed. An integrated transcriptome for P. harmala including 42 656 coding sequences was created by merging de novo assembled transcriptomes. Around 35 000 transcripts were annotated with more than 90% resemblance to three closely related species of Citrus, which confirmed the robustness of the assembled transcriptome; 4853 stress-responsive transcripts were identified. CYP82 involved in alkaloid biosynthesis showed a higher number of transcripts in P. harmala than in other plants, indicating its diverse alkaloid biosynthesis attributes. Transcription factors (TFs) and regulatory elements with 3887 transcripts comprised 9% of the transcriptome. Among the TFs of the integrated transcriptome, cystein2/histidine2 (C2H2) and WD40 repeat families were the most abundant. The Kyoto Encyclopedia of Genes and Genomes (KEGG) MAPK (mitogen-activated protein kinase) signaling map and the plant hormone signal transduction map showed the highest assigned genes to these pathways, suggesting their potential stress resistance. The P. harmala whole-transcriptome survey provides important resources and paves the way for functional and comparative genomic studies on this plant to discover stress-tolerance-related markers and response mechanisms in stress physiology, phytochemistry, ecology, biodiversity, and evolution. P. harmala can be a potential model for studying adverse environmental cues and metabolite biosynthesis and a major source for the production of various alkaloids.

Comparative Analysis of Physiological, Hormonal and Transcriptomic Responses Reveal Mechanisms of Saline-Alkali Tolerance in Autotetraploid Rice (Oryza sativa L.)

Saline-alkali soil has posed challenges to the growth of agricultural crops, while polyploidy often show greater adaptability in diverse and extreme environments including saline-alkali stress, but its defense mechanisms in rice remain elusive. Herein, we explored the mechanisms of enhanced saline-alkali tolerance of autotetraploid rice 93-11T relative to diploid rice 93-11D, based on physiological, hormonal and transcriptomic profilings. Physiologically, the enhanced saline-alkali tolerance in 93-11T was manifested in higher soluble sugar accumulation and stronger superoxide dismutase (SOD) and peroxidase (POD) activities in leaves during 24 h after saline-alkali shock. Furthermore, various hormone levels in leaves of 93-11T altered greatly, such as the negative correlation between salicylic acid (SA) and the other four hormones changed to positive correlation due to polyploidy. Global transcriptome profiling revealed that the upregulated differentially expressed genes (DEGs) in leaves and roots of 93-11T were more abundant than that in 93-11D, and there were more DEGs in roots than in leaves under saline-alkali stress. Genes related to phytohormone signal transduction of auxin (AUX) and SA in roots, lignin biosynthesis in leaves or roots, and wax biosynthesis in leaves were obviously upregulated in 93-11T compared with 93-11D under saline-alkali condition. Collectively, 93-11T subjected to saline-alkali stress possibly possesses higher osmotic regulation ability due to cuticular wax synthesis, stronger negative regulation of reactive oxygen species (ROS) production by increasing the SA levels and maintaining relative lower levels of IAA, and higher antioxidant capacity by increasing activities of SOD and POD, as well as lignin biosynthesis. Our research provides new insights for exploring the mechanisms of saline-alkali tolerance in polyploid rice and discovering new gene targets for rice genetic improvement.

Characterization of a Stress-Enhanced Promoter from the Grass Halophyte, Spartina alterniflora L

Stress-inducible promoters are vital for the desirable expression of genes, especially transcription factors, which could otherwise compromise growth and development when constitutively overexpressed in plants. Here, we report on the characterization of the promoter region of a stress-responsive gene SaAsr1 from monocot halophyte cordgrass (Spartina alterniflora). Several cis-acting elements, such as ABRE (ABA-responsive element), DRE-CRT (dehydration responsive-element/C-Repeat), LTRE (low temperature-responsive element), ERE (ethylene-responsive element), LRE (light-responsive element), etc. contributed at varying degrees to salt-, drought- and ABA-enhanced expression of gusA reporter gene in Arabidopsis thaliana under the full-length promoter, pAsr11875 and its deletion derivatives with an assortment of cis-regulatory motifs. The smallest promoter, pAsr1491, with three cis-acting elements (a CCAAT box-heat responsive, an LRE, and a copper responsive element) conferred drought-enhanced expression of gusA; pAsr1755 (with an ABRE and a DRE) presented the highest expression in ABA and drought; and pAsr1994 with seven ABREs and two DREs conferred optimal induction of gusA, especially under drought and ABA. Arabidopsis transgenics expressing a known abiotic stress-responsive gene, SaADF2 (actin depolymerization factor 2), under both pAsr11875 and p35S promoters outperformed the wild type (WT) with enhanced drought and salt tolerance contributed by higher relative water content and membrane stability with no significant difference between pAsr11875:SaADF2 or p35S:SaADF2 lines. However, pAsr11875:SaADF2 lines produced healthy plants with robust shoot systems under salt stress and control compared to slightly stunted growth of the p35S:SaADF2 plants. This reestablished the evidence that transgene expression under a stress-inducible promoter is a better strategy for the genetic manipulation of crops.

Mining for salt-tolerant genes from halophyte Zoysia matrella using FOX system and functional analysis of ZmGnTL

Zoysia matrella is a salt-tolerant turfgrass grown in areas with high soil salinity irrigated with effluent water. Previous studies focused on explaining the regulatory mechanism of Z. matrella salt-tolerance at phenotypic and physiological levels. However, the molecular mechanism associated with salt tolerance of Z. matrella remained unclear. In this study, a high-efficient method named FOX (full-length cDNA overexpression) hunting system was used to search for salt-tolerant genes in Z. matrella. Eleven candidate genes, including several known or novel salt-tolerant genes involved in different metabolism pathways, were identified. These genes exhibited inducible expression under salt stress condition. Furthermore, a novel salt-inducible candidate gene ZmGnTL was transformed into Arabidopsis for functional analysis. ZmGnTL improved salt-tolerance through regulating ion homeostasis, reactive oxygen species scavenging, and osmotic adjustment. In summary, we demonstrated that FOX is a reliable system for discovering novel genes relevant to salt tolerance and several candidate genes were identified from Z. matrella that can assist molecular breeding for plant salt-tolerance improvement.

High-quality ice plant reference genome analysis provides insights into genome evolution and allows exploration of genes involved in the transition from C3 to CAM pathways

Ice plant (Mesembryanthemum crystallinum), a member of the Aizoaceae family, is a typical halophyte crop and a model plant for studying the mechanism of transition from C3 photosynthesis to crassulacean acid metabolism (CAM). Here, we report a high-quality chromosome-level ice plant genome sequence. This 98.05% genome sequence is anchored to nine chromosomes, with a total length of 377.97 Mb and an N50 scaffold of 40.45 Mb. Almost half of the genome (48.04%) is composed of repetitive sequences, and 24 234 genes have been annotated. Subsequent to the ancient whole-genome triplication (WGT) that occurred in eudicots, there has been no recent whole-genome duplication (WGD) or WGT in ice plants. However, we detected a novel WGT event that occurred in the same order in Simmondsia chinensis, which was previously overlooked. Our findings revealed that ice plants have undergone chromosome rearrangements and gene removal during evolution. Combined with transcriptome and comparative genomic data and expression verification, we identified several key genes involved in the CAM pathway and constructed a comprehensive network. As the first genome of the Aizoaceae family to be released, this report will provide a rich data resource for comparative and functional genomic studies of Aizoaceae, especially for studies on salt tolerance and C3-to-CAM transitions to improve crop yield and resistance.

Evaluation of Halophyte Biopotential as an Unused Natural Resource: The Case of Lobularia maritima

Halophytes are plant species widely distributed in saline habitats, such as beaches, postindustrial wastelands, irrigated lands, salt flats, and others. Excessive salt level, known to limit plant growth, is not harmful to halophytes, which have developed a variety of defense mechanisms allowing them to colonize harsh environments. Plants under stress are known to respond with several morpho-anatomical adaptations, but also to enhance the production of secondary metabolites to better cope with difficult conditions. Owing to these adaptations, halophytes are an interesting group of undemanding plants with a high potential for application in the food and pharmaceutical industries. Therefore, this review aims to present the characteristics of halophytes, describe changes in their gene expression, and discuss their synthesized metabolites of pharmacognostic and pharmacological significance. Lobularia maritima is characterized as a widely spread halophyte that has been shown to exhibit various pharmacological properties in vitro and in vivo. It is concluded that halophytes may become important sources of natural products for the treatment of various ailments and for supplementing the human diet with necessary non-nutrients and minerals. However, extensive studies are needed to deepen the knowledge of their biological potential in vivo, so that they can be introduced to the pharmaceutical and food industries.

Adaptive Response and Transcriptomic Analysis of Flax (Linum usitatissimum L.) Seedlings to Salt Stress

Soil salinity constrains agricultural development in arid regions. Flax is an economically important crop in many countries, and screening or breeding salinity-resistant flax cultivars is necessary. Based on the previous screening of flaxseed cultivars C71 (salt-sensitive) and C116 (salt-tolerant) as test materials, flax seedlings stressed with different concentrations of NaCl (0, 100, 150, 200, and 250 mmol/L) for 21 days were used to investigate the effects of salt stress on the growth characteristics, osmotic regulators, and antioxidant capacity of these flax seedlings and to reveal the adaptive responses of flax seedlings to salt stress. The results showed that plant height and root length of flax were inhibited, with C116 showing lower growth than C71. The concentrations of osmotic adjustment substances such as soluble sugars, soluble proteins, and proline were higher in the resistant material, C116, than in the sensitive material, C71, under different concentrations of salt stress. Consistently, C116 showed a better rapid scavenging ability for reactive oxygen species (ROS) and maintained higher activities of antioxidant enzymes to balance salt injury stress by inhibiting growth under salt stress. A transcriptome analysis of flax revealed that genes related to defense and senescence were significantly upregulated, and genes related to the growth and development processes were significantly downregulated under salt stress. Our results indicated that one of the important adaptations to tolerance to high salt stress is complex physiological remediation by rapidly promoting transcriptional regulation in flax.

Comprehensive Analysis of the Hsp20 Gene Family in Canavalia rosea Indicates Its Roles in the Response to Multiple Abiotic Stresses and Adaptation to Tropical Coral Islands

Heat shock protein 20 (Hsp20) is a major family of heat shock proteins that mainly function as molecular chaperones and are markedly accumulated in cells when organisms are subjected to environmental stress, particularly heat. Canavalia rosea is an extremophile halophyte with good adaptability to environmental high temperature and is widely distributed in coastal areas or islands in tropical and subtropical regions. In this study, we identified a total of 41 CrHsp20 genes in the C. rosea genome. The gene structures, phylogenetic relationships, chromosome locations, and conserved motifs of each CrHsp20 or encoding protein were analyzed. The promoters of CrHsp20s contained a series of predicted cis-acting elements, which indicates that the expression of different CrHsp20 members is regulated precisely. The expression patterns of the CrHsp20 family were analyzed by RNA sequencing both at the tissue-specific level and under different abiotic stresses, and were further validated by quantitative reverse transcription PCR. The integrated expression profiles of the CrHsp20s indicated that most CrHsp20 genes were greatly upregulated (up to dozens to thousands of times) after 2 h of heat stress. However, some of the heat-upregulated CrHsp20 genes showed completely different expression patterns in response to salt, alkaline, or high osmotic stresses, which indicates their potential specific function in mediating the response of C. rosea to abiotic stresses. In addition, some of CrHsp20s were cloned and functionally characterized for their roles in abiotic stress tolerance in yeast. Taken together, these findings provide a foundation for functionally characterizing Hsp20s to unravel their possible roles in the adaptation of this species to tropical coral reefs. Our results also contribute to the understanding of the complexity of the response of CrHsp20 genes to other abiotic stresses and may help in future studies evaluating the functional characteristics of CrHsp20s for crop genetic improvement.

Bacterial diversity and community structure in the rhizosphere of the halophyte Halocnemum strobilaceum in an Algerian arid saline soil

Hypersaline ecosystems host a particular microbiota, which can be specifically recruited by halophytes. In order to broaden our knowledge of hypersaline ecosystems, an in natura study was conducted on the microbiota associated with the halophyte Halocnemum strobilaceum from alkaline-saline arid soil in Algeria. We collected and identified a total of 414 strains isolated from root tissues (RT), root-adhering soil (RAS), non-adhering rhizospheric soil (NARS) and bulk soil (BS) using different NaCl concentrations. Our data showed that halophilic and halotolerant bacterial isolates in BS and the rhizosphere belonged to 32 genera distributed in Proteobacteria (49%), Firmicutes (36%), Actinobacteria (14%) and Bacteroidetes (1%). Bacterial population size and species diversity were greatly increased in the rhizosphere (factor 100). The reservoir of diversity in BS was dominated by the genera Bacillus and Halomonas. Bacillus/Halomonas ratio decreased with the proximity to the roots from 2.2 in BS to 0.3 at the root surface. Salt screening of the strains showed that species belonging to nine genera were able to grow up to 5.1 M NaCl. Thus, we found that H. strobilaceum exerted a strong effect on the diversity of the recruited microbiota with an affinity strongly attributed to the genus Halomonas.

Salinity Tolerance of Halophytic Grass Puccinellia nuttalliana Is Associated with Enhancement of Aquaporin-Mediated Water Transport by Sodium

In salt-sensitive plants, root hydraulic conductivity is severely inhibited by NaCl, rapidly leading to the loss of water balance. However, halophytic plants appear to effectively control plant water flow under salinity conditions. In this study, we tested the hypothesis that Na⁺ is the principal salt factor responsible for the enhancement of aquaporin-mediated water transport in the roots of halophytic grasses, and this enhancement plays a significant role in the maintenance of water balance, gas exchange, and the growth of halophytic plants exposed to salinity. We examined the effects of treatments with 150 mM of NaCl, KCl, and Na₂SO₄ to separate the factors that affect water relations and, consequently, physiological and growth responses in three related grass species varying in salt tolerance. The grasses included relatively salt-sensitive Poa pratensis, moderately salt-tolerant Poa juncifolia, and the salt-loving halophytic grass Puccinellia nuttalliana. Our study demonstrated that sustained growth, chlorophyll concentrations, gas exchange, and water transport in Puccinellia nuttalliana were associated with the presence of Na in the applied salt treatments. Contrary to the other examined grasses, the root cell hydraulic conductivity in Puccinellia nuttalliana was enhanced by the 150 mM NaCl and 150 mM Na₂SO₄ treatments. This enhancement was abolished by the 50 µM HgCl₂ treatment, demonstrating that Na was the factor responsible for the increase in mercury-sensitive, aquaporin-mediated water transport. The observed increases in root Ca and K concentrations likely played a role in the transcriptional and (or) posttranslational regulation of aquaporins that enhanced root water transport capacity in Puccinellia nuttalliana. The study demonstrates that Na plays a key role in the aquaporin-mediated root water transport of the halophytic grass Puccinellia nuttalliana, contributing to its salinity tolerance.

Ion homeostasis in differently adapted populations of Suaeda vera Forssk. ex J.F. Gmel. for phytoremediation of hypersaline soils

Salt-accumulator species are of great interest for the phytoremediation of salt-affected soils to reclaim soil salinization, a major constraints causing germination retardation and growth restriction of plants as well as habitat degradation. Higher biomass production at ECe 23-36 dS m^-1 indicated that this species grows better in high to moderate salinity that was linked to osmotic adjustment through higher ion accumulation (Na⁺, Cl^‒, and Ca²⁺) and organic osmolytes (free amino acids and proline). Plants from highly and moderately saline habitats exhibited broader metaxylem vessels, which was associated with eased conduction of solutes leading to better growth. Leaf anatomical characteristics generally increased with increasing salinity except at the highest ECe 55 dS m^-1. The increased leaf lamina thickness contributed to succulence because of increased storage parenchymatous spongy tissues (that can store high amounts of water), water contents and it is a reflection of maintaining ion homeostasis and colonizing hyper-saline soil. Reduced stomatal density and area under high salinity are critical to cope with environmental hazards. Under high salinity, compartmentalization of excessive Na⁺ and Cl^- ions and accumulation of compatible osmolytes are directly related to high degree of salinity tolerance, and hence are useful for phyto-amelioration of salinity-impacted lands.

Halophytes.tn: an innovative database for Tunisian halophyte plant identification, distribution and characterization

Halophytes.tn (http://halophytes.rnrt.tn/) is a web-based database of Tunisian halophyte species. Halophytes are salt-tolerant plants able to grow above 85 mM of salt, even up to 2 M as for Tecticornia spp. Tunisia, a North African country located on the Mediterranean border, covering ∼165 000 km², harbors several types of saline habitats and biotopes where halophytes preferably vegetate. With ∼6000 worldwide and over 420 Tunisian species, halophytes represent a huge potential in several fields, including desalination, phytoremediation, agrofarming, medicinal use, industrial applications, pharmacology and even nanotechnology. We describe the practical and technical steps followed and bioinformatics tools used to conceive and design the first Tunisian halophytes database, enabling species identification and characterization. As a first version, information about botany, morphology, ecophysiology and biochemistry were provided for the identified species with their sites of growing in Tunisia, first step of biodiversity conservation, management and valorization. The database will be regularly maintained, updated and enriched to achieve the goal of whole Tunisian halophyte species and fit the needs of scientists and all category of users.Database URL: http://halophytes.rnrt.tn/

NHX-Type Na+/H+ Antiporter Gene Expression Under Different Salt Levels and Allelic Diversity of HvNHX in Wild and Cultivated Barleys

Salinity tolerance is a multifaceted trait attributed to various mechanisms. Wild barley is highly specialized to grow under severe environmental conditions of Tibet and is well-known for its diverse germplasm with high tolerance to abiotic stresses. The present study focused on determining the profile of the expression of isoforms of the HvNHX gene in 36 wild and two cultivated barley under salt stress. Our findings revealed that in leaves and roots, expression of HvNHX1 and HvNHX3 in XZ16 and CM72 was upregulated at all times as compared with sensitive ones. The HvNHX2 and HvNHX4 isoforms were also induced by salt stress, although not to the same extent as HvNHX1 and HvNHX3. Gene expression analysis revealed that HvNHX1 and HvNHX3 are the candidate genes that could have the function of regulators of ions by sequestration of Na⁺ in the vacuole. HvNHX1 and HvNHX3 showed a wide range of sequence variations in an amplicon, identified via single-nucleotide polymorphisms (SNPs). Evaluation of the sequencing data of 38 barley genotypes, including Tibetan wild and cultivated varieties, showed polymorphisms, including SNPs, and small insertion and deletion (INDEL) sites in the targeted genes HvNHX1 and HvNHX3. Comprehensive analysis of the results revealed that Tibetan wild barley has distinctive alleles of HvNHX1 and HvNHX3 which confer tolerance to salinity. Furthermore, less sodium accumulation was observed in the root of XZ16 than the other genotypes as visualized by CoroNa-Green, a sodium-specific fluorophore. XZ16 is the tolerant genotype, showing least reduction of root and leaf dry weight under moderate (150 mM) and severe (300 mM) NaCl stress. Evaluation of genetic variation and identification of salt tolerance mechanism in wild barley could be promoting approaches to unravel the novel alleles involved in salinity tolerance.

Impact of Nanomaterials on the Regulation of Gene Expression and Metabolomics of Plants under Salt Stress

Plant salinity resistance results from a combination of responses at the physiological, molecular, cellular, and metabolic levels. This article focuses on plant stress tolerance mechanisms for controlling ion homeostasis, stress signaling, hormone metabolism, anti-oxidative enzymes, and osmotic balance after nanoparticle applications. Nanoparticles are used as an emerging tool to stimulate specific biochemical reactions related to plant ecophysiological output because of their small size, increased surface area and absorption rate, efficient catalysis of reactions, and adequate reactive sites. Regulated ecophysiological control in saline environments could play a crucial role in plant growth promotion and survival of plants under suboptimal conditions. Plant biologists are seeking to develop a broad profile of genes and proteins that contribute to plant salt resistance. These plant metabolic profiles can be developed due to advancements in genomic, proteomic, metabolomic, and transcriptomic techniques. In order to quantify plant stress responses, transmembrane ion transport, sensors and receptors in signaling transduction, and metabolites involved in the energy supply require thorough study. In addition, more research is needed on the plant salinity stress response based on molecular interactions in response to nanoparticle treatment. The application of nanoparticles as an aspect of genetic engineering for the generation of salt-tolerant plants is a promising area of research. This review article addresses the use of nanoparticles in plant breeding and genetic engineering techniques to develop salt-tolerant crops.