Molecular Mechanisms Underlying Salt Tolerance Research Articles

Understanding salt tolerance mechanism using transcriptome profiling and de novo assembly of wild tomato Solanum chilense.

Soil salinity affects the plant growth and productivity detrimentally, but Solanum chilense, a wild relative of cultivated tomato (Solanum lycopersicum L.), is known to have exceptional salt tolerance. It has precise adaptations against direct exposure to salt stress conditions. Hence, a better understanding of the mechanism to salinity stress tolerance by S. chilense can be accomplished by comprehensive gene expression studies. In this study 1-month-old seedlings of S. chilense and S. lycopersicum were subjected to salinity stress through application of sodium chloride (NaCl) solution. Through RNA-sequencing here we have studied the differences in the gene expression patterns. A total of 386 million clean reads were obtained through RNAseq analysis using the Illumina HiSeq 2000 platform. Clean reads were further assembled de novo into a transcriptome dataset comprising of 514,747 unigenes with N50 length of 578 bp and were further aligned to the public databases. Genebank non-redundant (Nr), Viridiplantae, Gene Ontology (GO), KOG, and KEGG databases classification suggested enrichment of these unigenes in 30 GO categories, 26 KOG, and 127 pathways, respectively. Out of 265,158 genes that were differentially expressed in response to salt treatment, 134,566 and 130,592 genes were significantly up and down-regulated, respectively. Upon placing all the differentially expressed genes (DEG) in known signaling pathways, it was evident that most of the DEGs involved in cytokinin, ethylene, auxin, abscisic acid, gibberellin, and Ca2+ mediated signaling pathways were up-regulated. Furthermore, GO enrichment analysis was performed using REVIGO and up-regulation of multiple genes involved in various biological processes in chilense under salinity were identified. Through pathway analysis of DEGs, “Wnt signaling pathway” was identified as a novel pathway for the response to the salinity stress. Moreover, key genes for salinity tolerance, such as genes encoding proline and arginine metabolism, ROS scavenging system, transporters, osmotic regulation, defense and stress response, homeostasis and transcription factors were not only salt-induced but also showed higher expression in S. chilense as compared to S. lycopersicum. Thus indicating that these genes may have an important role in salinity tolerance in S. chilense. Overall, the results of this study improve our understanding on possible molecular mechanisms underlying salt tolerance in plants in general and tomato in particular.

Characterizing the metabolites related to rice salt tolerance with introgression lines exhibiting contrasting performances in response to saline conditions

Rice is susceptible to salt stress at the seedling stage. To explore the molecular mechanisms underlying salt tolerance, the metabolic responses to salt stress were investigated with a metabolite-profiling technique. Gas chromatography–mass spectrometry was used to profile metabolite changes in five rice lines with a similar genetic background, but with obviously diverse growth performances under saline conditions. A total of 84 metabolites were detected in rice leaf extracts under control and saline conditions. The data revealed that amino acids were enriched more in three salt-tolerant lines (G58, G1710, and IR64) than in two salt-sensitive lines (G45 and G52) under control conditions, suggesting that there were basal metabolite differences between the tolerant and sensitive lines. Additionally, significantly higher allantoin levels in G58, G1710, and IR64 under both stress and control conditions were observed, implying allantoin was important for the better growth of the three rice lines. Moreover, sorbitol, melezitose, and pipecolic acid levels increased considerably in response to salt stress in the five lines, indicating they contribute to rice responses to salt stress significantly. Interestingly, the similar metabolic patterns were regulated by salt stress in the salt-sensitive and salt-tolerant lines, and the main difference was quantitative. The sensitive lines had more pronounced increases during the early stages of the stress treatment than the tolerant lines. Thus, monitoring the metabolome changes of plants may provide crucial insights into how plants tolerate stress. The results presented herein provide valuable information for further elucidating the molecular mechanisms underlying rice salt tolerance.

Physiological and transcriptomic analyses reveal the mechanisms underlying the salt tolerance of Zoysia japonica Steud

BackgroundAreas with saline soils are sparsely populated and have fragile ecosystems, which severely restricts the sustainable development of local economies. Zoysia grasses are recognized as excellent warm-season turfgrasses worldwide, with high salt tolerance and superior growth in saline-alkali soils. However, the mechanism underlying the salt tolerance of Zoysia species remains unknown.ResultsThe phenotypic and physiological responses of two contrasting materials, Zoysia japonica Steud. Z004 (salt sensitive) and Z011 (salt tolerant) in response to salt stress were studied. The results show that Z011 was more salt tolerant than was Z004, with the former presenting greater K+/Na+ ratios in both its leaves and roots. To study the molecular mechanisms underlying salt tolerance further, we compared the transcriptomes of the two materials at different time points (0 h, 1 h, 24 h, and 72 h) and from different tissues (leaves and roots) under salt treatment. The 24-h time point and the roots might make significant contributions to the salt tolerance. Moreover, GO and KEGG analyses of different comparisons revealed that the key DEGs participating in the salt-stress response belonged to the hormone pathway, various TF families and the DUF family.ConclusionsZoysia salt treatment transcriptome shows the 24-h and roots may make significant contributions to the salt tolerance. The auxin signal transduction family, ABA signal transduction family, WRKY TF family and bHLH TF family may be the most important families in Zoysia salt-stress regulation.

A Glycine max sodium/hydrogen exchanger enhances salt tolerance through maintaining higher Na+ efflux rate and K+/Na+ ratio in Arabidopsis

BackgroundSoybean (Glycine max (L.)) is one the most important oil-yielding cash crops. However, the soybean production has been seriously restricted by salinization. It is therefore crucial to identify salt tolerance-related genes and reveal molecular mechanisms underlying salt tolerance in soybean crops. A better understanding of how plants resist salt stress provides insights in improving existing soybean varieties as well as cultivating novel salt tolerant varieties. In this study, the biological function of GmNHX1, a NHX-like gene, and the molecular basis underlying GmNHX1-mediated salt stress resistance have been revealed.ResultsWe found that the transcription level of GmNHX1 was up-regulated under salt stress condition in soybean, reaching its peak at 24 h after salt treatment. By employing the virus-induced gene silencing technique (VIGS), we also found that soybean plants became more susceptible to salt stress after silencing GmNHX1 than wild-type and more silenced plants wilted than wild-type under salt treatment. Furthermore, Arabidopsis thaliana expressing GmNHX1 grew taller and generated more rosette leaves under salt stress condition compared to wild-type. Exogenous expression of GmNHX1 resulted in an increase of Na+ transportation to leaves along with a reduction of Na+ absorption in roots, and the consequent maintenance of a high K+/Na+ ratio under salt stress condition. GmNHX1-GFP-transformed onion bulb endothelium cells showed fluorescent pattern in which GFP fluorescence signals enriched in vacuolar membranes. Using the non-invasive micro-test technique (NMT), we found that the Na+ efflux rate of both wild-type and transformed plants after salt treatment were significantly higher than that of before salt treatment. Additionally, the Na+ efflux rate of transformed plants after salt treatment were significantly higher than that of wild-type. Meanwhile, the transcription levels of three osmotic stress-related genes, SKOR, SOS1 and AKT1 were all up-regulated in GmNHX1-expressing plants under salt stress condition.ConclusionVacuolar membrane-localized GmNHX1 enhances plant salt tolerance through maintaining a high K+/Na+ ratio along with inducing the expression of SKOR, SOS1 and AKT1. Our findings provide molecular insights on the roles of GmNHX1 and similar sodium/hydrogen exchangers in regulating salt tolerance.

CmRAV1 shows differential expression in two melon (Cucumis melo L.) cultivars and enhances salt tolerance in transgenic Arabidopsis plants.

The growth and development of melon (Cucumis melo L.) are severely affected by soil salinization in many areas of the world, but the understanding of the molecular mechanisms underlying salt tolerance in melon remains limited. In this study, a new RAV (related to ABI3/VP1) gene, CmRAV1, was identified in melon. Protein structure homology analysis revealed that CmRAV1 contains an AP2 domain and a B3 domain, and subcellular localization assay revealed that CmRAV1 is localized in the nucleus. The transcript level of CmRAV1 was closely correlated with NaCl treatment, and the expression pattern of CmRAV1 differed between two cultivars (salt-tolerant and salt-sensitive cultivars) under NaCl treatment. In addition, yeasts transformed with CmRAV1 showed notably improved growth on medium containing 200mM NaCl compared with wild-type ones. The overexpression of CmRAV1 in transgenic Arabidopsis thaliana resulted in enhanced salt tolerance at the seed germination and seedling growth stages. This study demonstrated that the expression of CmRAV1 was associated with saline stress and can potentially be utilized to improve plant salt tolerance.

Methods for grafting Arabidopsis thaliana and Eutrema salsugineum

BackgroundGrafting, an ancient agronomic technique, is an artificial mode of asexual reproduction in plants. Recently, grafting research has gradually shifted from modifying agronomic traits to the study of molecular mechanism. Grafting is an excellent tool to study long-range signaling processes in plants. And the grafting between species will help elucidate the molecular mechanisms underlying contrasting differences between different species. Arabidopsis thaliana is a salt-sensitive model glycophyte and Eutrema salsugineum (previously Thellungiella salsuginea, salt cress) is a salt-tolerant model halophyte. Successful grafting of these two model plants will help further study the physiological and molecular mechanisms underlying salt tolerance in plants. The aim of this study was to demonstrate two sterile micro-grafting methods for Arabidopsis and salt cress.ResultsWe developed the methods for sterile grafting between A. thaliana and E. salsugineum; this is the first report on inter-generic grafting between Arabidopsis and Eutrema. The method involves cut-in grafting under sterile conditions. The grafted plant part was placed in half strength Murashige and Skoog medium with 1% agar and 1% sugar, and then cultured vertically with 22 °C/18 °C short-day/night cycles. The plants were then transferred to half strength Hoagland nutrient solution for hydroponics. The reported method is simple and easy to operate. Self-grafted Arabidopsis–Arabidopsis and Eutrema–Eutrema plants were used as controls, which were obtained with an improved hypocotyl-cutting grafting method. Ion contents in grafted plants were detected by inductively coupled plasma optical emission spectroscopy. The results showed that the ion content in salt cress and Arabidopsis changed to different degrees after grafting.ConclusionsThe inter-species grafting technique described here makes it possible to study hybrid plants between Arabidopsis and Eutrema and will contribute to further understanding of long-distance communications in plants. This technique also provides a reference for improving plant varieties using grafting, such as gardening plants, as well as fruit and vegetable crops.

Dissecting molecular mechanisms underlying salt tolerance in rice: a comparative transcriptional profiling of the contrasting genotypes

BackgroundSalinity expansion in arable land is a threat to crop plants. Rice is the staple food crop across several countries worldwide; however, its salt sensitive nature severely affects its growth under excessive salinity. FL478 is a salt tolerant indica recombinant inbred line, which can be a good source of salt tolerance at the seedling stage in rice. To learn about the genetic basis of its tolerance to salinity, we compared transcriptome profiles of FL478 and its sensitive parent (IR29) using RNA-seq technique.ResultsA total of 1714 and 2670 genes were found differentially expressed (DEGs) under salt stress compared to normal conditions in FL478 and IR29, respectively. Gene ontology analysis revealed the enrichment of transcripts involved in salinity response, regulation of gene expression, and transport in both genotypes. Comparative transcriptome analysis revealed that 1063 DEGs were co-expressed, while 338/252 and 572/908 DEGs were exclusively up/down-regulated in FL478 and IR29, respectively. Further, some biological processes (e.g. iron ion transport, response to abiotic stimulus, and oxidative stress) and molecular function terms (e.g. zinc ion binding and cation transmembrane transporter activity) were specifically enriched in FL478 up-regulated transcripts. Based on the metabolic pathways analysis, genes encoding transport and major intrinsic proteins transporter superfamily comprising aquaporin subfamilies and genes involved in MAPK signaling and signaling receptor kinases were specifically enriched in FL478. A total of 1135 and 1894 alternative splicing events were identified in transcripts of FL478 and IR29, respectively. Transcripts encoding two potassium transporters and two major facilitator family transporters were specifically up-regulated in FL478 under salt stress but not in the salt sensitive genotype. Remarkably, 11 DEGs were conversely regulated in the studied genotypes; for example, OsZIFL, OsNAAT, OsGDSL, and OsELIP genes were up-regulated in FL478, while they were down-regulated in IR29.ConclusionsThe achieved results suggest that FL478 employs more efficient mechanisms (especially in signal transduction of salt stress, influx and transport of k+, ionic and osmotic homeostasis, as well as ROS inhibition) to respond to the salt stress compared to its susceptible parent.

Transcript profiling reveals an important role of cell wall remodeling and hormone signaling under salt stress in garlic

Salt stress is one of the environmental factors that evidently limit plant growth and yield. Despite the fact that understanding plant response to salt stress is important to agricultural practice, the molecular mechanisms underlying salt tolerance in garlic remain unclear. In this study, garlic seedlings were exposed to 200 mM NaCl stress for 0, 1, 4, and 12 h, respectively. RNA-seq was applied to analyze the transcriptional response under salinity conditions. A total of 13,114 out of 25,530 differentially expressed unigenes were identified to have pathway annotation, which were mainly involved in purine metabolism, starch and sucrose metabolism, plant hormone signal transduction, flavone and flavonol biosynthesis, isoflavonoid biosynthesis, MAPK signaling pathway, and circadian rhythm. In addition, 272 and 295 differentially expressed genes were identified to be cell wall and hormone signaling-related, respectively, and their interactions under salinity stress were extensively discussed. The results from the current work would provide new resources for the breeding aimed at improving salt tolerance in garlic.

Isolation and Comparative Analysis of Two Na+/H+ Antiporter NHX2 Genes from Pyrus betulaefolia

The vacuolar Na+/H+ antiporter NHX gene is a salt tolerance determinant in higher plants. Pyrus betulaefolia, a popular rootstock in Asia, can improve pear salt tolerance through grafting. In this study, two novel NHX genes were isolated from P. betulaefolia using its NaCl-treated transcriptome information. Both PbNHX2.1 and PbNHX2.2 have typical DNA structures and conservative protein motifs often found in vacuolar Na+/H+ antiporters. They are classified as the same NHXs in the phylogenetic tree. Furthermore, both PbNHX2s localized to the plant cell tonoplast. The NaCl treatment strongly induced the expression of PbNHX2.1 in shoots and PbNHX2.2 in the whole plant, but the transcript levels of PbNHX2.2 were much higher. This result meant that they have diverse functions during sodium ion transport in P. betulaefolia. The PbNHX2.2 transcription was influenced by polyethylene glycol and abscisic acid (ABA). An ABA cis-acting element was found in its promoter region, which indicated that PbNHX2.2 transcriptional regulation under salt and osmotic stresses may be ABA-dependent. Yeast recombined experiments revealed that PbNHX2.1 and PbNHX2.2 restored, with different efficacies, the Na+-sensitive phenotype of a endosomal/vacuolar Na+/H+ antiporter mutant, AXT3. These PbNHX2s proteins, especially PbNHX2.2, facilitated Na+ ion transport and maintained intracellular K+ status. The results suggest that PbNHX2.2 was a salt tolerance determinant and had a major function in the vacuolar compartmentalization of Na+. The information on gene features, transcriptional pattern, and the basic function of the NHX family members in P. betulaefolia will help reveal the molecular mechanism underlying salt tolerance in this species.

Effect of salt-stress on gene expression in citrus roots revealed by RNA-seq.

Citrus, as one of the most economically important fruits worldwide, is adversely affected by salinity stress. However, its molecular mechanisms underlying salinity tolerance are still not clear. In this study, next-generation RNA-seq technology was applied to analyze the gene expression profiling of citrus roots at 3 time points over a 24-h period of salt treatment. A total of 1831 differentially expressed genes (DEGs) were identified. Among them, 1195 and 1090 DEGs were found at 4 and 24h, of which 454 were overlapped. Based on functional annotation, the salt overly sensitive (SOS) and reactive oxygen species (ROS) signaling pathways were found to be involved. Meanwhile, we found that hormone metabolism and signaling played important roles in salt stress. In addition, a multitude of transcription factors (TFs) including WRKY, NAC, MYB, AP2/ERF, bZIP, GATA, bHLH, ZFP, SPL, CBF, and CAMTA were identified. The genes related to cell wall loosening and stiffening (xyloglucan endotransglucosylase/hydrolases, peroxidases) were also involved in salt stress. Our data not only provided a genetic resource for discovering salt tolerance-related genes, but also furthered our understanding of the molecular mechanisms underlying salt tolerance in citrus.

Transcriptomic and proteomic feature of salt stress-regulated network in Jerusalem artichoke (Helianthus tuberosus L.) root based on de novo assembly sequencing analysis.

Ribosome activation and sugar metabolic process mainly act on the regulation of salt tolerance in the bioenergy crop Helianthus tuberosus L. as dissected by integrated transcriptomic and proteomic analyses. Helianthus tuberosus L. is an important halophyte plant that can survive in saline-alkali soil. It is vitally necessary to build an available genomic resource to investigate the molecular mechanisms underlying salt tolerance in H. tuberosus. De novo assembly and annotation of transcriptomes were built for H. tuberosus using a HiSeq4000 platform. 293,823 transcripts were identified and annotated into 190,567 unigenes. In addition, iTRAQ-labeled quantitative proteomics was carried out to detect global protein profiling as a response to salt stress. Comparative omics analysis showed that 5432 genes and 43 proteins were differentially expressed in H. tuberosus under salt stress, which were enriched in the following processes: carbohydrate metabolism, ribosome activation and translation, oxidation-reduction and ion binding. The reprogramming of transcript and protein works suggested that the induced activity of ribosome and sugar signaling may endue H. tuberosus with salt tolerance. With high-quality sequencing and annotation, the obtained transcriptomics and proteomics provide a robust genomic resource for dissecting the regulatory molecular mechanism of H. tuberosus in response to salt stress.

Transcriptomics analysis of salt stress tolerance in the roots of the mangrove Avicennia officinalis

Salinity affects growth and development of plants, but mangroves exhibit exceptional salt tolerance. With direct exposure to salinity, mangrove roots possess specific adaptations to tolerate salt stress. Therefore, studying the early effects of salt on mangrove roots can help us better understand the tolerance mechanisms. Using two-month-old greenhouse-grown seedlings of the mangrove tree Avicennia officinalis subjected to NaCl treatment, we profiled gene expression changes in the roots by RNA-sequencing. Of the 6547 genes that were differentially regulated in response to salt treatment, 1404 and 5213 genes were significantly up- and down-regulated, respectively. By comparative genomics, 93 key salt tolerance-related genes were identified of which 47 were up-regulated. Upon placing all the differentially expressed genes (DEG) in known signaling pathways, it was evident that most of the DEGs involved in ethylene and auxin signaling were up-regulated while those involved in ABA signaling were down-regulated. These results imply that ABA-independent signaling pathways also play a major role in salt tolerance of A. officinalis. Further, ethylene response factors (ERFs) were abundantly expressed upon salt treatment and the Arabidopsis mutant aterf115, a homolog of AoERF114 is characterized. Overall, our results would help in understanding the possible molecular mechanism underlying salt tolerance in plants.

Transcriptome-wide profiling and expression analysis of two accessions of Paulownia australis under salt stress

Paulownia australis has important economic and ecological values. In this study, the morphological and physiological changes of the leaves in diploid and autotetraploid P. australis under salt stress were analyzed. To detect related genes and gain a comprehensive perspective on the molecular mechanisms underlying salt tolerance in P. australis, transcriptome-wide gene expression profiling was conducted in the leaves of the diploid and autotetraploid P. australis under control and salinity conditions, respectively. Evaluation of the responses against salinity stress revealed the superiority of autotetraploid over diploid in terms of salinity tolerance. Changes in physiological parameters in diploid P. australis (PA2) and tetraploid P. australis (PA4) plants in response to salt stress were measured. Transcriptome data revealed that many of the common unigenes which were involved in accumulation of compatible solutes, oxidative stress detoxification, ion homeostasis, and signal transduction showed significant differences between the two accessions in response to salt stress. A number of salt-responsive unigenes were identified in two accessions of P. australis under salt stress. Furthermore, the differentially expressed unigenes found to be common in both accessions may be useful genetic resources for further genetic improvement of Paulownia using transgenic approaches.

Transcriptome analysis of hexaploid hulless oat in response to salinity stress.

BackgroundOat is a cereal crop of global importance used for food, feed, and forage. Understanding salinity stress tolerance mechanisms in plants is an important step towards generating crop varieties that can cope with environmental stresses. To date, little is known about the salt tolerance of oat at the molecular level. To better understand the molecular mechanisms underlying salt tolerance in oat, we investigated the transcriptomes of control and salt-treated oat using RNA-Seq.ResultsUsing Illumina HiSeq 4000 platform, we generated 72,291,032 and 356,891,432 reads from non-stressed control and salt-stressed oat, respectively. Assembly of 64 Gb raw sequence data yielded 128,414 putative unique transcripts with an average length of 1,189 bp. Analysis of the assembled unigenes from the salt stressed and control libraries indicated that about 65,000 unigenes were differentially expressed at different stages. Functional annotation showed that ABC transporters, plant hormone signal transduction, plant-pathogen interactions, starch and sucrose metabolism, arginine and proline metabolism, and other secondary metabolite pathways were enriched under salt stress. Based on the RPKM values of assembled unigenes, 24 differentially expressed genes under salt stress were selected for quantitative RT-PCR validation, which successfully confirmed the results of RNA-Seq. Furthermore, we identified 18,039 simple sequence repeats, which may help further elucidate salt tolerance mechanisms in oat.ConclusionsOur global survey of transcriptome profiles of oat plants in response to salt stress provides useful insights into the molecular mechanisms underlying salt tolerance in this crop. These findings also represent a rich resource for further analysis of salt tolerance and for breeding oat with improved salt tolerance through the use of salt-related genes.

Expression partitioning of homeologs and tandem duplications contribute to salt tolerance in wheat (Triticum aestivum L.).

Salt stress dramatically reduces crop yield and quality, but the molecular mechanisms underlying salt tolerance remain largely unknown. To explore the wheat transcriptional response to salt stress, we performed high-throughput transcriptome sequencing of 10-day old wheat roots under normal condition and 6, 12, 24 and 48 h after salt stress (HASS) in both a salt-tolerant cultivar and salt-sensitive cultivar. The results demonstrated global gene expression reprogramming with 36,804 genes that were up- or down-regulated in wheat roots under at least one stress condition compared with the controls and revealed the specificity and complexity of the functional pathways between the two cultivars. Further analysis showed that substantial expression partitioning of homeologous wheat genes occurs when the plants are subjected to salt stress, accounting for approximately 63.9% (2,537) and 66.1% (2,624) of the homeologous genes in ‘Chinese Spring’ (CS) and ‘Qing Mai 6’ (QM). Interestingly, 143 salt-responsive genes have been duplicated and tandemly arrayed on chromosomes during wheat evolution and polyploidization events, and the expression patterns of 122 (122/143, 85.3%) tandem duplications diverged dynamically over the time-course of salinity exposure. In addition, constitutive expression or silencing of target genes in Arabidopsis and wheat further confirmed our high-confidence salt stress-responsive candidates.

The involvement of TsFtsH8 in Thellungiella salsuginea tolerance to cold and high light stresses

Thellungiella salsuginea is a plant that commonly grows in harsh environments of salinity and low temperature. Although the molecular mechanism underlying salt tolerance in T. salsuginea has been extensively explored, our understanding of how this species tolerates cold stress is limited. In a previous study, Wong et al. (2006) identified a cold-inducible TsFtsH8 gene in T. salsuginea. Based on the role of AtFtsH in D1 protein turnover and in maintaining the normal function of photosystem II, we hypothesized that TsFtsH8 might be related to cold tolerance in T. salsuginea. In the present study, RNAi lines of TsFtsH8 were generated and its tolerance to cold was evaluated. The results showed that in early spring, TsFtsH8-RNAi lines underwent leaf variegation, severe chlorophyll decomposition, organelle deterioration, decrease in the maximum photochemical efficiency of photosystem II (Fv/Fm) and in the proportion of open photosystem II reaction centers (qP), and incomplete degradation of the 23 kDa fragment of the D1 protein. These findings suggest that TsFtsH8 is involved in the development of T. salsuginea in the early spring.

Physiological analysis and transcriptome comparison of two muskmelon (Cucumis melo L.) cultivars in response to salt stress

Melon (Cucumis melo L.) is an important vegetable crop that ranks second in salt tolerance among the Cucurbitaceae. Previous studies on the two muskmelon cultivars 'Bing XueCui' (BXC) and 'Yu Lu' (YL) revealed that they had different characteristics under salt stress, but the molecular basis underlying their different physiological responses is unclear. Here, we combined a physiological study with a genome-wide transcriptome analysis to understand the molecular basis of genetic variation that responds to salt stress in the melon. BXC performed better under salt stress than YL in terms of biomass and photosynthetic characteristics, because it exhibited less reduction in transpiration rate, net photosynthesis rate, and stomatal conductance under 150-mM NaCl stress than YL. A transcriptome comparison of the leaves of the cultivars revealed that 1171 genes responded to salt stress in BXC while 1487 genes were identified as salt-stress-responsive in YL. A real-time polymerase chain reaction analysis of 12 of the responsive genes revealed that there was a strong, positive correlation with RNA sequencing data. The genes were involved in several pathways, including photosynthesis, the biosynthesis of secondary metabolites, metabolism, and plant hormone signal transduction, and their expression levels differed between the two cultivars in response to salt stress. This study provides a molecular perspective of two melon cultivars in response to salt stress, and its results could be used to investigate the complex molecular mechanisms underlying salt tolerance in the melon.

Analyzing serial cDNA libraries revealed reactive oxygen species and gibberellins signaling pathways in the salt response of Upland cotton (Gossypium hirsutum L.)

By comparing series full-length cDNA libraries stressed and control, the dynamic process of salt stress response in Upland cotton was studied, and reactive oxygen species and gibberellins signaling pathways were proposed. The Upland cotton is the most important fiber plant with highly salt tolerance. However, the molecular mechanism underlying salt tolerance in domesticated cotton was unclear. Here, seven full-length cDNA libraries were constructed for seedling roots of Upland cotton 'Zhong G 5' at 0, 3, 12 and 48h after the treatment of control or 150mM NaCl stress. About 3300 colonies in each library were selected robotically for 5'-end pyrosequencing, resulting in 20,358 expressed sequence tags (ESTs) totally. And 8516 uniESTs were then assembled, including 2914 contigs and 5602 singletons, and explored for Gene Ontology (GO) function. GO comparison between serial stress libraries and control reflected the growth regulation, stimulus response, signal transduction and biology regulation processes were conducted dynamically in response to salt stress. MYB, MYB-related, WRKY, bHLH, GRAS and ERF families of transcription factors were significantly enriched in the early response. 65 differentially expressed genes (DEGs), mainly associated with reactive oxygen species (ROS) scavenging, gibberellins (GAs) metabolism, signal transduction, transcription regulation, stress response and transmembrane transport, were identified and confirmed by quantitative real-time PCR. Overexpression of selected DEGs increased tolerance against salt stress in transgenic yeast. Results in this study supported that a ROS-GAs interacting signaling pathway of salt stress response was activated in Upland cotton. Our results provided valuable gene resources for further investigation of the molecular mechanism of salinity tolerance.

Effect of salt treatment on the glucosinolate-myrosinase system in Thellungiella salsuginea

Background and aims Glucosinolates are specialized plant metabolites derived from amino acids. Found in many important crop species (e.g., oilseed rape, broccoli and cabbage), glucosinolates and their degradation products have important roles in plant defense and interactions with the environment. The objective of this research was to study the effects of salt stress on the glucosinolate-myrosinase system in Thellungiella halophila, which has been characterized as a model organism for studying the molecular mechanisms underlying salt tolerance in plants.