Important Role In Salt Tolerance Research Articles

Salt-tolerance mechanisms in quinoa: Is glycinebetaine the missing piece of the puzzle?

Salinization of arable land has been progressively increasing, which, along with the effects of climate change, poses a serious risk to food production. Quinoa is a halophyte species that grows and is productive in highly saline soils. This study addresses the mechanisms of response and adaptation to high salinity. We show that the differential distribution of sodium in plants depends on the variety, observing that varieties such as Pandela Rosada limit the passage transit of sodium to the aerial part of the plant, a mechanism that seems to be regulated by sodium transporters such as HKT1s or SOS1. Like other halophytes of the Amaranthaceae family, quinoa plants have salt glands (bladder cells), which have been reported to play an important role in salt tolerance. However, our study shows that the contribution of bladder glands to salt accumulation is rather low. The 1H-NMR metabolome study of quinoa subjected to salt stress showed important modifications in the contents of amino acids, sugars, organic acids, and quaternary ammonium compounds (glycinebetaine). The compound with a higher presence was glycinebetaine, which makes up 6% of the leaf dry matter under saline conditions. Our findings suggest that glycinebetaine can act as an osmolyte and/or osmoprotectant, facilitating plant development under high saline ambient.

Evolutionary analysis of the OSCA gene family in sunflower (Helianthus annuus L) and expression analysis under NaCl stress.

Hyperosmolality-gated calcium-permeable channels (OSCA) are Ca2+ nonselective cation channels that contain the calcium-dependent DUF221 domain, which plays an important role in plant response to stress and growth. However, the OSCA gene has not been fully identified and analyzed in sunflowers. In this study, we comprehensively analyzed the number, structure, collinearity, and phylogeny of the OSCA gene family in the sunflower, six Compositae species (Arctium lappa, Chrysanthemum morifolium, Cichorium endivia, Cichorium intybus, Lactuca sativa var. Angustata, and Carthamus tinctorius), and six other plants (soybean, Arabidopsis thaliana, rice, grape, and maize). The expression of the sunflower OSCA gene in nine different tissues, six different hormones, and NaCl stress conditions were analyzed based on transcriptome data and qRT-PCR. A total of 15 OSCA proteins, distributed on 10 chromosomes, were identified in the sunflower, and all of them were located in the endoplasmic reticulum. Using the phylogenetic tree, collinearity, gene structure, and motif analysis of the six Compositae species and six other plants, we found that the sunflower OSCA protein had only three subfamilies and lacked the Group 4 subfamily, which is conserved in the evolution of Compositae and subject to purification selection. The OSCA gene structure and motif analysis of the sunflower and six Compositae showed that there was a positive correlation between the number of motifs of most genes and the length of the gene, different subfamilies had different motifs, and the Group 4 subfamily had the smallest number of genes and the simplest gene structure. RNA-seq and qRT-PCR analysis showed that the expression levels of most OSCA genes in the sunflower changed to varying degrees under salt stress, and HaOSCA2.6 and HaOSCA3.1 were the most important in the sunflower's response to salt stress. The coexpression network of the sunflower genes under salt stress was constructed based on weighted gene co-expression network analysis (WGCNA). In conclusion, our findings suggest that the OSCA gene family is conserved during the sunflower's evolution and plays an important role in salt tolerance. These results will deepen our understanding of the evolutionary relationship of the sunflower OSCA gene family and provide a basis for their functional studies under salt stress.

Biochemical and molecular responses of Rosa damascena mill. cv. Kashan to salicylic acid under salinity stress

BackgroundToday, salinity stress is one of the most important abiotic stresses in the world, because it causes damage to many agricultural products and reduces their yields. Oxidative stress causes tissue damages in plants, which occurs with the production of reactive oxygen species (ROS) when plants are exposed to environmental stresses such as salinity. Today, it is recommended to use compounds that increase the resistance of plants to environmental stresses and improve plant metabolic activities. Salicylic acid (SA), as an intracellular and extracellular regulator of the plant response, is known as one of these effective compounds. Damask rose (Rosa damascena Mill.) is a medicinal plant from the Rosaceae, and its essential oils and aromatic compounds are used widely in the cosmetic and food industries in the world. Therefore, considering the importance of this plant from both medicinal and ornamental aspects, for the first time, we investigated one of the native cultivars of Iran (Kashan). Since one of the most important problems in Damask rose cultivation is the occurrence of salinity stress, for the first time, we investigated the interaction of several levels of NaCl salinity (0, 4, 8, and 12 ds m− 1) with SA (0, 0.5, 1, and 2 mM) as a stress reducer.ResultsSince salinity stress reduces plant growth and yield, in this experiment, the results showed that the increase in NaCl concentration caused a gradual decrease in photosynthetic and morphological parameters and an increase in ion leakage. Also, increasing the level of salinity stress up to 12 ds m− 1 affected the amount of chlorophyll, root length and leaf total area, all of which reduced significantly compared to plants under no stress. However, many studies have highlighted the application of compounds that reduce the negative effects of stress and increase plant resistance and tolerance against stresses. In this study, the application of SA even at low concentration (0.5 mM) could neutralize the negative effects of salinity stress in the Rosa damascena. In this regard, the results showed that salinity increases the activity of antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) and the concentration of proline, protein and glycine betaine (GB). Overexpression of antioxidant genes (Ascorbate Peroxidase (APX), CAT, Peroxidase (POD), Fe-SOD and Cu-SOD) showed an important role in salt tolerance in Damascus rose. In addition, 0.5 mm SA increased the activity of enzymatic and non-enzymatic systems and increased salinity tolerance.ConclusionsThe change in weather conditions due to global warming and increased dryness contributes to the salinization of the earth’s surface soils. Therefore, it is of particular importance to measure the threshold of tolerance of roses to salinity stress and the effect of stress-reducing substances in plants. In this context, SA has various roles such as increasing the content of pigments, preventing ethylene biosynthesis, increasing growth, and activating genes involved in stress, which modifies the negative effects of salinity stress. Also, according to the results of this research, even in the concentration of low values, positive results can be obtained from SA, so it can be recommended as a relatively cheap and available material to improve production in saline lands.

Identification of a Negative Regulator for Salt Tolerance at Seedling Stage via a Genome-Wide Association Study of Thai Rice Populations.

Salt stress is a major limiting factor in crop production and yield in many regions of the world. The objective of this study was to identify the genes responsible for salt tolerance in Thai rice populations. We performed a genome-wide association study with growth traits, relative water content, and cell membrane stability at the seedling stage, and predicted 25 putative genes. Eleven of them were located within previously reported salt-tolerant QTLs (ST-QTLs). OsCRN, located outside the ST-QTLs, was selected for gene characterization using the Arabidopsis mutant line with T-DNA insertion in the orthologous gene. Mutations in the AtCRN gene led to the enhancement of salt tolerance by increasing the ability to maintain photosynthetic pigment content and relative water content, while the complemented lines with ectopic expression of OsCRN showed more susceptibility to salt stress detected by photosynthesis performance. Moreover, the salt-tolerant rice varieties showed lower expression of this gene than the susceptible rice varieties under salt stress conditions. The study concludes that by acting as a negative regulator, OsCRN plays an important role in salt tolerance in rice.

Pepper bHLH transcription factor CabHLH035 contributes to salt tolerance by modulating ion homeostasis and proline biosynthesis.

Members of the bHLH family of transcription factors play important roles in multiple aspects of plant biological processes, for instance, abiotic stress responses. Previously, we characterized CaNAC035, a gene that positively regulates stress tolerance and identified CabHLH035, a CaNAC035-interacting protein in pepper (Capsicum annuum L.). In this study, we describe the role of CabHLH035 in the response to salt stress. Our results show that the expression of CabHLH035 increased following salt treatment. Transient expression of CabHLH035 (CabHLH035-To) in pepper enhanced salt tolerance, ectopic expression of CabHLH035 in Arabidopsis increased the salt stress tolerance, whereas knocking down the expression of CabHLH035 in pepper plants resulted in decreased salt tolerance. Homologs of the Salt Overly Sensitive 1 (SOS1) and pyrroline-5-carboxylate acid synthetase (P5CS) genes showed drastically increased expression in transgenic Arabidopsis plants expressing CabHLH035 and CabHLH035-To plants, but expression decreased in CabHLH035-silenced plants. Our results also showed that CabHLH035 can directly bind to the CaSOS1 and CaP5CS gene promoters and positively activate their expression. We found that transgenic Arabidopsis plants, ectopic expression of CabHLH035 and pepper plants transiently overexpressing CabHLH035 (CabHLH035-To) showed lower Na+ and higher proline contents in response to NaCl treatment, while CabHLH035-silenced plants had higher Na+ and lower proline concentrations. Overall, CabHLH035 plays important roles in salt tolerance through its effects on the intracellular Na+ :K+ ratio and proline biosynthesis.

The key regulator LcERF056 enhances salt tolerance by modulating reactive oxygen species-related genes in Lotus corniculatus

BackgroundThe APETALA2/ethylene response factor (AP2/ERF) family are important regulatory factors involved in plants’ response to environmental stimuli. However, their roles in salt tolerance in Lotus corniculatus remain unclear.ResultsHere, the key salt-responsive transcription factor LcERF056 was cloned and characterised. LcERF056 belonging to the B3–1 (IX) subfamily of ERFs was considerably upregulated by salt treatment. LcERF056-fused GFP was exclusively localised to nuclei. Furthermore, LcERF056- overexpression (OE) transgenic Arabidopsis and L. corniculatus lines exhibited significantly high tolerance to salt treatment compared with wild-type (WT) or RNA interference expression (RNAi) transgenic lines at the phenotypic and physiological levels. Transcriptome analysis of OE, RNAi, and WT lines showed that LcERF056 regulated the downstream genes involved in several metabolic pathways. Chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR) and yeast one-hybrid (Y1H) assay demonstrated that LcERF056 could bind to cis-element GCC box or DRE of reactive oxygen species (ROS)-related genes such as lipid-transfer protein, peroxidase and ribosomal protein.ConclusionOur results suggested that the key regulator LcERF056 plays important roles in salt tolerance in L. corniculatus by modulating ROS-related genes. Therefore, it may be a useful target for engineering salt-tolerant L. corniculatus or other crops.

Revealing the salt tolerance mechanism of Tamarix hispida by large-scale identification of genes conferring salt tolerance.

The identification of genes conferring salt tolerance is important to reveal plant salt tolerance mechanisms. Here, we employed yeast expression system combined with high-throughput sequencing to identify genes conferring salt tolerance from Tamarix hispida Willd. A total of 1224 potential genes conferring salt tolerance were identified. Twenty-one genes were randomly selected for functional characterization using transient transformation in T. hispida and stable transformation in Arabidopsis thaliana (L.) Heynh. More than 90% of studied genes are found to confer tolerance to salt stress, indicating that the identified genes are reliable. More than 75% of the identified genes were highly expressed in roots rather than in leaves, suggesting roots play an important role in salt tolerance. The genes belonging to 'response to stimulus' were highly accumulated , and these accounted for 32% of the total identified genes. In addition, the processes of 'protein translation', 'osmotic adjustment', 'scavenging of free radicals', 'photosynthesis, detoxification of cells', 'protection of cellular macromolecules' and 'maintenance of cellular pH' play important roles in salt tolerance. This study provides useful information on the salt tolerance mechanism of T. hispida and offers a valuable resource for exploring genes used in salt tolerance breeding.

Growth and transcriptome analysis of tomato under seawater stress

The tomato industry has been seriously affected by continuous soil salinization and seawater irritation. This study analyzed the salt tolerance mechanism of tomato from physiological and molecular aspects and screened out the salt tolerance genes; this information provides a foundation for future research on tomato salt tolerance and environmental adaptability. In this study, tomato was used as the experimental material, and treated with seawater accounted for 0%, 10%, 20%, or 30% of the nutrient solution volume respectively. The results showed that when the seawater percentage was less than 20%, it had little effect on the growth of tomato; when the seawater percentage was more than 20%, it could severely inhibit tomato growth, thereby affecting the ion balance in plants. The results showed that 33,810 unigenes were obtained after transcriptome high-throughput sequencing and assembly. In total, 31,631 unigenes were successfully annotated by comparison of the obtained unigenes with six gene databases. According to the Gene Ontology (GO) database, unigenes in the tomato transcriptome could be roughly divided into three categories (biological process, cellular component, and molecular function) with 45 branches. Analyzing genetic differences revealed that 509 unigenes were significantly differentially expressed under seawater stress, among which 40.67% were up-regulated and 59.33% were down-regulated. Moreover, we also found that the differentially expressed genes (DEGs) were mainly enriched in six pathways: growth, response to stimulus, signaling, membrane, transcription factor activity and protein binding. The expression profiles of the selected DEGs in the samples were characterized and verified by qRT-PCR. These DEGs and metabolic pathways may play an important role in salt tolerance of tomato. The functional characteristics of these genes and pathways will provide a new target for improving salt tolerance of tomato through gene regulation.

Transcriptomic insights into the molecular aspects of salt stress responses in Kandelia candel roots

The mangrove plant Kandelia candel is a type of woody halophyte that grows in tropical and subtropical ocean intertidal zones and exhibits a high salt tolerance. In this study, 61,970 unigenes were obtained from the roots of 60-day-old K. candel seedlings treated with 0 (control), 200, 400, and 600 mM NaCl for 3 days with an N50 of 1510 bp. Moreover, 454, 311, and 2663 genes were differentially expressed under 200, 400, and 600 mM NaCl treatments, respectively. These differentially expressed genes were primarily involved in plant hormone signal transduction, carbohydrate and energy metabolism, amino acid metabolism, stress response, and defense. The levels of 12 important differentially expressed genes were confirmed by qRT-PCR, showing that the changing trend was generally consistent with the results of the transcriptomic analysis. In addition, physiological parameters involved in energy metabolism, amino acid metabolism, and the reactive oxygen species scavenging process were significantly increased under salt stress treatment, and the trend was consistent with the results of transcription and qRT-PCR. This study indicated that K. candel roots could tolerate high salt stress by enhancing ethylene signal transduction, maintaining a stable energy supply, increasing antioxidant capacity. Specially, we found that accumulation of ?-aminobutyric acid and glutamate, but not proline, might play an important role in salt tolerance in the roots of K. candel.

OsC2DP, a Novel C2 Domain-Containing Protein Is Required for Salt Tolerance in Rice.

Salt stress is one of the major factors limiting crop production globally, including rice (Oryza sativa). Although a number of genes involved in salt tolerance have been functionally identified, the mechanism underlying salt tolerance in rice is still poorly understood. Here, we reported a novel C2 domain-containing protein, OsC2DP required for salt tolerance in rice. OsC2DP was predominately expressed in the roots and its expression was repressed by salt stress. Transient expression of OsC2DP in rice protoplast cells showed that it was localized in the cytosol. Immunostaining further showed that OsC2DP was able to translocate from the cytosol to plasma membrane under salt conditions. Knockout of OsC2DP did not affect Na+ concentration in the roots, but increased shoot Na+ concentration, resulting in a significant sensitivity of rice to salt stress. Furthermore, the quantitative Real-time PCR and transcriptomic analysis showed that the expression level of some genes related to salt tolerance were indirectly regulated by OsC2DP, especially OsSOS1 and OsNHX4. These results indicate that OsC2DP has an important role in salt tolerance and these findings provide new insights into the regulation of OsC2DP gene for rice breeding with high salt tolerance.

Variable salinity responses and comparative gene expression in woodland strawberry genotypes

Commercial strawberry cultivars are sensitive to salinity. These plants are octoploid (2n = 8x = 56) making analysis of complex traits such as salt tolerance difficult. Hence, the objective of this study was to evaluate eight woodland diploid strawberry genotypes for their physiological and genetic responses under high salinity conditions. Shoot salt tolerance (ST) index of eight genotypes irrigated with water of electrical conductivity (ECiw) of 8 dS m−1 ranged from 0.41 to 0.86. Average Cl concentration in leaves was more than 11-fold higher than Na concentration, indicating that Cl− toxicity is more critical than Na+ for diploid strawberries. Improved water use efficiency (WUE) due to reduced stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) was associated with improved ST index. Expression analyses of eleven genes involved in Na+ and Cl− transport revealed differences in component traits responsible for salt tolerance. Increased expressions of SOS2, NHX1 and NHX2 in salt-tolerant genotypes suggest that Na+ sequestration in vacuoles may play an important role in salt tolerance in strawberry. Additionally, a chloride channel gene (CLC_C) was shown to be critical for salt tolerance. Understanding the genetic mechanisms regulating salt tolerance will be critical in developing strawberry germplasm more tolerant to salinity.

Whole genomes and transcriptomes reveal adaptation and domestication of pistachio

BackgroundPistachio (Pistacia vera), one of the most important commercial nut crops worldwide, is highly adaptable to abiotic stresses and is tolerant to drought and salt stresses.ResultsHere, we provide a draft de novo genome of pistachio as well as large-scale genome resequencing. Comparative genomic analyses reveal stress adaptation of pistachio is likely attributable to the expanded cytochrome P450 and chitinase gene families. Particularly, a comparative transcriptomic analysis shows that the jasmonic acid (JA) biosynthetic pathway plays an important role in salt tolerance in pistachio. Moreover, we resequence 93 cultivars and 14 wild P. vera genomes and 35 closely related wild Pistacia genomes, to provide insights into population structure, genetic diversity, and domestication. We find that frequent genetic admixture occurred among the different wild Pistacia species. Comparative population genomic analyses reveal that pistachio was domesticated about 8000 years ago and suggest that key genes for domestication related to tree and seed size experienced artificial selection.ConclusionsOur study provides insight into genetic underpinning of local adaptation and domestication of pistachio. The Pistacia genome sequences should facilitate future studies to understand the genetic basis of agronomically and environmentally related traits of desert crops.

Distribution and re-transportation of sodium in three Malus species with different salt tolerance

To further dissect the mechanism of salt tolerance in Malus, the comparison was made regarding the differences between the salt-tolerant and salt-sensitive species in sodium accumulation and extrusion capability in the roots and stem base as well as the sodium re-transportation from shoot to roots by using 22Na labeling-based feeding of leaves and roots-split experiments. The results demonstrated that the salt-tolerant Malus species could accumulate more 22Na in the main roots, lateral roots, stem base phloem and xylem, and extrude more sodium out than the salt-sensitive one. In addition, the salt-tolerant Malus species had the higher sodium re-transportation rate from shoot to roots. Altogether, it is concluded that the stronger sodium accumulation and extrusion in the roots and the stronger sodium re-transportation from shoot to roots in the salt-tolerant species play important roles in salt tolerance of Malus species.

Spinach (Spinacea oleracea L.) Response to Salinity: Nutritional Value, Physiological Parameters, Antioxidant Capacity, and Gene Expression

Scarcity of good-quality irrigation water is a major impediment to meet food demand for a growing world population. Recycled waters may be available locally more affordably, but their higher salinity is a concern. Salinity effects on spinach mineral composition, antioxidant capacity, photosynthesis, and gene expression have not been established. Spinach cv. Raccoon was greenhouse-grown and irrigated with four levels of water salinity of electrical conductivities (ECiw) of 1.4 (control) or ranging from 3.6 to 9.4 dS m−1, combined with three levels of K (3, 5, and 7 meq L−1). Irrigation waters had 2, 20, 40, and 80 meq L−1 of NaCl. After 23 treatment days, plants significantly accumulated Na and Cl in shoots and roots with increasing salinity, regardless of the K concentration in the irrigation water. Plants exhibited no visual symptoms of salt toxicity and there were no differences in shoot growth. Plants maintained their overall concentrations of mineral nutrients, physiological parameters, and oxalic acid across salinity treatments. Leaves retained all their antioxidant capacity at 20 meq L−1 NaCl, and 74% to 66% at 40 and 80 meq L−1 NaCl, respectively. Expression analyses of ten genes, that play important role in salt tolerance, indicated that although some genes were upregulated in plants under salinity, compared to the control, there was no association between Na or K tissue concentrations and gene expression. Results clearly show that spinach maintains its growth, mineral composition, and antioxidant capacity up to ECiw = 9.4 dS m−1. As this salinity is equivalent to a soil salinity of 4.5 dS m−1, spinach can tolerate over two-fold its previously-considered salinity threshold. Thus, growers can cultivate spinach using recycled, saline, waters without detriment to shoot biomass accumulation, and nutritional value.

Carbon and nitrogen removal through “Candidatus Brocadia sinica”-dominated simultaneous anammox and denitrification (SAD) process treating saline wastewater

“Candidatus Brocadia sinica”-dominated simultaneous anammox and denitrification (SAD) process was used to treat nitrogen-rich saline wastewater. The reactor was operated at 30 ± 0.5 °C with influent pH of 7.5 ± 0.1. ‘Ca. B. sinica’ could adapt to high saline surroundings after 42 cycles’ operation. With 100% seawater, nitrogen removal rate and organic removal rate were 0.71 kg/(m3·d) and 0.27 kg/(m3·d), respectively. Both were closed to those without seawater. Independent of salinity, percentage of nitrogen removal by anammox was higher than that by denitrification during the whole treatment period. ‘Ca. B. sinica’ had good tolerance to salinity. However, maximum removal rate of NH4+-N declined with growing salinity. Modified Boltzmann model was proper to analyze the effect resulting from salinity on the maximum removal rate of NH4+-N. Granular sludge characterized by anammox granule embedded in denitrifying granule might play an important role in salt tolerance of anammox bacteria.

Selection and mechanism exploration for salt-tolerant genes in tomato

ABSTRACTHigh salinity is a major destructive environmental factor limiting the growth and productivity of plants. In this study, we selected 8 significantly enriched salt stress-related pathways and 17 differentially expressed genes based on RNA sequencing (RNA-Seq). We verified the salt tolerance of the selected key genes using qRT-PCR and combined molecular biology and physiology to explore the salt tolerance mechanism of ASR2-like and ASR3-like genes using the salt-tolerant tomato cultivar LA2711 and the salt-sensitive tomato cultivar ZS-5. The results showed that exogenous ABA significantly increased all physiological indexes but decreased the transcript levels of two target genes compared with untreated controls under salt stress, suggesting that the two genes play an important role in salt tolerance in the form of negative dependence on ABA. Combined with the ABA adaptation pattern and the relationship between the target gene and ABA in the process of response to salt stress, we concluded that ASR2-like and ASR3-like might respond to salt stress by increasing the activities of ROS-scavenging enzymes and proline content via negative dependence on ABA. Taken together, these results provide a good resource for the genetic improvement of tomato and a theoretical basis for obtaining tomato varieties with high resistance to salt.

Overexpression of cysteine protease gene from Salix matsudana enhances salt tolerance in transgenic Arabidopsis

Salix matsudana is a salt-tolerant arbor tree species. We are interested in understanding its mechanisms of salt-tolerance. Here, we isolated a full-length 1080-bp cDNA for a salt stress-responsive cysteine protease gene from S. matsudana, designated SmCP. The deduced 359-amino-acid SmCP protein was essentially identical to cysteine proteases of other plant species and was predicted to contain inhibitor-I29 and peptidase-C1A domains with three active catalytic sites found in eukaryotic cysteine proteases. Expression profile analysis revealed that SmCP expression is constitutive and overexpression in roots takes place under salt stress. Expression of SmCP in Escherichia coli cells led to enhanced salinity tolerance. In addition, transgenic Arabidopsis thaliana lines overexpressing SmCP displayed enhanced tolerance to salt stress, with increased germination rates, antioxidant enzyme (superoxide dismutase) activity, chlorophyll content and ion flux in the root, and reduced malondialdehyde (MDA) levels and electric conductivity compared with control plants. These results indicate that SmCP likely plays an important role in salt tolerance in S. matsudana.

Molecular characterization and functional analysis of a cation-chloride cotransporter gene from trifoliate orange (Poncirus trifoliata L.)

A cation-chloride cotransporter gene PtrCCC from trifoliate orange was identified, its ectopic expression confers salt tolerance in transgenic tobacco. Salinity is one of the most serious environmental stresses that limit crop growth. Cation-chloride cotransporters (CCCs) are membrane proteins that are involved in plant development and salt tolerance. Here we provide an insight into the molecular characterization and functional analysis of CCC-encoding gene (PtrCCC) from trifoliate orange (Poncirus trifoliata L.). The open-reading frame of PtrCCC is 2943 bp in length, which encodes a protein of 980 amino acids. Phylogenetic analysis revealed that PtrCCC is closely related to CCCs from its allied genera as well as woody perennials. Quantitative real-time PCR (qRT-PCR) analysis demonstrated that PtrCCC was expressed in all tested tissues, with higher expression level in root tip and leaf tip. Its expression was up-regulated in the leaves of trifoliate orange under the presence of KCl conditions. Ectopic expression of PtrCCC gene in tobacco exhibited an improvement in salt tolerance. The transgenic plants had higher dry biomass in the roots and shoots than that in wild type plants. Moreover, under KCl and NaCl + KCl stress conditions, the accumulation of shoot Cl− was remarkably decreased in the transgenic lines as compared with the wild type plants. Collectively, these results suggest that PtrCCC plays an important role in salt tolerance, which is partially attributed to its role in ions homeostasis.

Domain-switch analysis of PeNHX3 from Populus euphratica reveals the critical role of the transmembrane domain 11 in Na+ and Li+ transport

Populus euphratica, the well-known tree halophyte, tolerates the stress of high levels of salt. We previously showed that the transmembrane domain 11 (TM11) of PeNHX3, a Na+,K+/H+ antiporter from P. euphratica, was crucial for Na+ and Li+ transport in a yeast growth assay. Here, we examined the role of TM11 in catalyzing Na+ and Li+ transport in transgenic Arabidopsis. We found that PeNHX3 localized to the tonoplasts in Arabidopsis. Overexpression of PeNHX3 in Arabidopsis improved seedling growth and enhanced salt tolerance and Li+ detoxification. However, overexpression of PeNHX3 did not improve Arabidopsis growth at KCl concentrations higher than 0.1mM, suggesting a low K+ transport activity for PeNHX3 in plants. We performed in planta domain-switch analysis by replacing the C-terminal domain of AtNHX1 with a C-terminal segment of PeNHX3 containing the TM11 domain. We demonstrated that TM11 was critical for the Na+ and Li+ transport activities by PeNHX3. Taken together, PeNHX3 plays an important role in salt tolerance and Li+ detoxification in plants. TM11 controls the Na+ and Li+ transport activities of PeNHX3 in Arabidopsis.

Salt tolerance response revealed by RNA-Seq in a diploid halophytic wild relative of sweet potato

Crop wild relatives harbor exotic and novel genetic resources, which hold great potential for crop improvement. Ipomoea imperati is a wild diploid relative of sweet potato with the capability of high salinity tolerance. We compared the transcriptomes of I. imperati under salt stress vs. control to identify candidate genes and pathways involved in salt response. De novo assembly produced 67,911 transcripts with a high depth of coverage. A total of 39,902 putative genes were assigned annotations, and 936 and 220 genes involved in salt response in roots and leaves, respectively. Functional analysis indicated a whole system response during salt stress in I. imperati, which included four metabolic processes: sensory initiation, transcriptional reprogramming, cellular protein component change, and cellular homeostasis regulation. We identified a number of candidate genes involved in the ABA signaling pathway, as well as transcription factors, transporters, antioxidant enzymes, and enzymes associated with metabolism of synthesis and catalysis. Furthermore, two membrane transporter genes, including vacuole cation/proton exchanger and inositol transporter, were considered to play important roles in salt tolerance. This study provided valuable information not only for understanding the genetic basis of ecological adaptation but also for future application in sweet potato and other crop improvements.