Salt Stress-responsive Genes Research Articles

Overexpression of Grapevine VvIAA18 Gene Enhanced Salt Tolerance in Tobacco.

In plants, auxin/indoleacetic acid (Aux/IAA) proteins are transcriptional regulators that regulate developmental process and responses to phytohormones and stress treatments. However, the regulatory functions of the Vitis vinifera L. (grapevine) Aux/IAA transcription factor gene VvIAA18 have not been reported. In this study, the VvIAA18 gene was successfully cloned from grapevine. Subcellular localization analysis in onion epidermal cells indicated that VvIAA18 was localized to the nucleus. Expression analysis in yeast showed that the full length of VvIAA18 exhibited transcriptional activation. Salt tolerance in transgenic tobacco plants and Escherichia. coli was significantly enhanced by VvIAA18 overexpression. Real-time quantitative PCR analysis showed that overexpression of VvIAA18 up-regulated the salt stress-responsive genes, including pyrroline-5-carboxylate synthase (NtP5CS), late embryogenesis abundant protein (NtLEA5), superoxide dismutase (NtSOD), and peroxidase (NtPOD) genes, under salt stress. Enzymatic analyses found that the transgenic plants had higher SOD and POD activities under salt stress. Meanwhile, component analysis showed that the content of proline in transgenic plants increased significantly, while the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) decreased significantly. Based on the above results, the VvIAA18 gene is related to improving the salt tolerance of transgenic tobacco plants. The VvIAA18 gene has the potential to be applied to enhance plant tolerance to abiotic stress.

Evaluation and QTL Mapping of Salt Tolerance in Yardlong Bean [Vigna unguiculata (L.) Walp. Subsp. unguiculata Sesquipedalis Group] Seedlings

Salinity is a major abiotic stress that limits productivity in yardlong bean. Identification of the quantitative trait loci (QTL) underlying salt tolerance is a prerequisite for successful marker-assisted selection when breeding for salt-tolerance. The objective of this study was to use a set of insertions and deletions (InDels) found in salt stress-responsive genes to construct a linkage map and identify reliable markers that can guide breeding efforts for novel, high-yield, salt-tolerant varieties of yardlong bean (Vigna unguiculata). A linkage map was constructed from 103 InDel markers in an F2 population consisting of 143 plants produced by crossing yardlong bean varieties Suzi 41 (salt tolerant) and Sujiang 1419 (salt sensitive). The markers were clustered across 9 chromosomes spanning 975.7 cM in total length, with an average distance between adjacent markers of 9.5 cM. Using this linkage map, we identified six major QTLs associated with control of salt tolerance-related traits on chromosomes (Chr.) 08, 09, and 11, which explained 9.9% ~ 72.7% of the phenotypic variation. Four major QTLs showed co-location in the region between VUIn584 and VUIn724 on Chr.09, associated with the traits of salt tolerance rating (STR), leaf chlorophyll content (SPAD), aerial biomass fresh weight (AFW), and root fresh weight (RFW). These QTLs provide a valuable reference for marker-assisted breeding, QTL fine mapping, and the cloning and characterization of salt-tolerance candidate genes.

Potassium Transporter LrKUP8 Is Essential for K+ Preservation in Lycium ruthenicum, A Salt-Resistant Desert Shrub.

Salt stress is a major constraint for many crops and trees. A wild species of Goji named Lycium ruthenicum is an important economic halophyte in China and has an extremely high tolerance to salinity. L. ruthenicum grows in saline soil and is known as a potash-rich species. However, its salt adaptation strategies and ion balance mechanism remains poorly understood. Potassium (K+) is one of the essential macronutrients for plant growth and development. In this study, a putative salt stress-responsive gene encoding a HAK (high-affinity K+)/KUP (K+ uptake)/KT (K+ transporter) transporter was cloned and designated as LrKUP8. This gene belongs to the cluster II group of the KT/HAK/KUP family. The expression of LrKUP8 was strongly induced under high NaCl concentrations. The OE-LrKUP8 calli grew significantly better than the vector control calli under salt stress conditions. Further estimation by ion content and micro-electrode ion flux indicated a relative weaker K+ efflux in the OE-LrKUP8 calli than in the control. Thus, a key gene involved in K+ uptake under salt condition was functionally characterized using a newly established L. ruthenicum callus transformation system. The importance of K+ regulation in L. ruthenicum under salt tolerance was highlighted.

A Physic Nut Stress-Responsive HD-Zip Transcription Factor, JcHDZ07, Confers Enhanced Sensitivity to Salinity Stress in Transgenic Arabidopsis

Homeodomain-leucine zipper (HD-Zip) transcription factors are reported to play crucial roles in the growth, development, and stress responses of plants. However, there is little knowledge of the molecular mechanisms involved in physic nut’s stress tolerance generally, or the functions of its HD-Zip genes. In the present study, a HD-Zip family transcription factor, designated JcHDZ07, was isolated from physic nut. Expression profile analysis showed that salinity stress inhibited the expression of JcHDZ07. Transient expression of JcHDZ07-YFP in Arabidopsis protoplast cells revealed that JcHDZ07 was a nuclear-localized protein. Additionally, no obvious difference in growth and development between wild-type and JcHDZ07-overexpressing plants was observed in the absence of stress. Our results further indicated that JcHDZ07 overexpressing transgenic plants had lower proline contents, lower survival rates, and activities of catalase and superoxide dismutase, but higher relative electrical leakage and malonaldehyde contents compared with wild-type plants under salinity stress conditions, suggesting that overexpression of JcHDZ07 confers enhanced sensitivity to salinity stress in transgenic Arabidopsis. Expression of salt stress-responsive genes were upregulated in leaves of transgenic plants under salinity stress, but less strongly than in wild-type plants. Collectively, our results suggest that JcHDZ07 functions as an important regulator during the process of plant responses to salinity stress.

Genome-wide identification and expression profile of HD-ZIP genes in physic nut and functional analysis of the JcHDZ16 gene in transgenic rice

BackgroundHomeodomain-leucine zipper (HD-ZIP) transcription factors play important roles in the growth, development and stress responses of plants, including (presumably) physic nut (Jatropha curcas), which has high drought and salinity tolerance. However, although physic nut’s genome has been released, there is little knowledge of the functions, expression profiles and evolutionary histories of the species’ HD-ZIP genes.ResultsIn this study, 32 HD-ZIP genes were identified in the physic nut genome (JcHDZs) and divided into four groups (I-IV) based on phylogenetic analysis with homologs from rice, maize and Arabidopsis. The analysis also showed that most of the JcHDZ genes were closer to members from Arabidopsis than to members from rice and maize. Of the 32 JcHDZ genes, most showed differential expression patterns among four tissues (root, stem cortex, leaf, and seed). Expression profile analysis based on RNA-seq data indicated that 15 of the JcHDZ genes respond to at least one abiotic stressor (drought and/or salinity) in leaves at least at one time point. Transient expression of a JcHDZ16-YFP fusion protein in Arabidopsis protoplasts cells showed that JcHDZ16 is localized in the nucleus. In addition, rice seedlings transgenically expressing JcHDZ16 had lower proline contents and activities of antioxidant enzymes (catalase and superoxide dismutase) together with higher relative electrolyte leakage and malondialdehyde contents under salt stress conditions (indicating higher sensitivity) than wild-type plants. The transgenic seedlings also showed increased sensitivity to exogenous ABA, and increases in the transcriptional abundance of several salt stress-responsive genes were impaired in their responses to salt stress. Further data on JcHDZ16-overexpressing plants subjected to salt stress treatment verified the putative role of JcHDZ genes in salt stress responses.ConclusionOur results may provide foundations for further investigation of functions of JcHDZ genes in responses to abiotic stress, and promote application of JcHDZ genes in physic nut breeding.

CYSTM3 negatively regulates salt stress tolerance in Arabidopsis.

CYSTM3, a small mitochondrial protein, acts as a negative regulator in salt stress response by preventing Na+ efflux and disturbing reactive oxygen species (ROS) homeostasis in Arabidopsis. Cysteine-rich transmembrane module (CYSTM) is a not well characterized small peptide family in plants. In this study, we identified a novel mitochondrion-localized CYSTM member CYSTM3 from Arabidopsis, which was ubiquitously expressed in different tissues and dramatically induced by salt stress. Transgenic plants overexpressing CYSTM3 (OE) displayed hypersensitivity to salt stress compared with wild type (WT) plants, whereas a knockout mutant cystm3 was more tolerant to high salinity than WT. Moreover, OE lines accumulated higher contents of Na+ and ROS than WT and cystm3 upon exposure to high salinity. Further analysis revealed that CYSTM3 could deter root Na+ efflux and inhibit the activities of a range of ROS scavenging enzymes in Arabidopsis. In addition, the transcripts of nuclear salt stress-responsive genes were over-activated in cystm3 than those in WT and OE lines. Taken together, Arabidopsis CYSTM3 acts as a negative regulator in salt stress tolerance.

Effective Agrobacterium-mediated transformation protocols for callus and roots of halophyte ice plant (Mesembryanthemum crystallinum)

BackgroundIce plant (Mesembryanthemum crystallinum L.) is a model plant for studying salt-tolerant mechanisms in higher plants. Many salt stress-responsive ice plant genes have been identified with molecular and biochemical approaches. However, no further functional characterization of these genes in host plant due to lack of easy and effective transformation protocols.ResultsTo establish efficient transformation system of ice plants, three types of ice plant materials, hypocotyl-derived callus, aseptically-grown seedlings and pot-grown juvenile plants, were used to develop Agrobacterium-mediated transformation protocols. The highest transient transformation efficiency was with 5-day-old ice plant callus co-incubated with an Agrobacterium tumefaciens at 2.5 × 109 cells mL−1 for 48 h. The 3-day-old ice plant seedlings with root tip removed were successfully infected with A. tumefaciens or A. rhizogenes, and obtained 85% and 33–100% transient transformation rates, respectively. The transient transformation assays in ice plant callus and seedlings demonstrated that the concentrations of Agrobacteria, the durations of co-incubation time, and the plant growth stages were three important factors affecting the transient transformation efficiencies. Additionally, pot-grown juvenile plants were syringe-injected with two A. rhizogenes strains A8196 and NCPPB 1855, to establish transformed roots. After infections, ice plants were grown hydroponically and showed GUS expressions in transformed roots for 8 consecutive weeks.ConclusionsOur Agrobacterium-mediated transformation protocols utilized hypocotyl-derived callus and seedlings as plant materials, which can be easily obtained in large quantity. The average successful transient transformation rates were about 2.4–3.0% with callus and 33.3–100.0% with seedlings. We also developed a rapid and efficient protocol to generate transgenic roots by A. rhizogenes infections without laborious and challenging tissue culture techniques. This protocol to establish composite ice plant system demonstrates excellent improvements in efficiency, efficacy, and ease of use over previous ice plant transformation protocols. These Agrobacterium-mediated transformation protocols can be versatile and efficient tools for exploring gene functions at cellular and organ levels of ice plants.

Identification of Salt Stress Response Genes in Rosa chinensis Leaves by Comparative RNA-seq Analysis of Transcriptome Dynamics

Rosa chinensis Jacq., originating from China, occupied a pivotal position in the floral industry all over the world. Drought and soil salinization is a major problem in the Chinese rose planting industry. Therefore, the study on resistance is important to improve R. chinensis breeding. In this work, leaves of twelve samples with three biological repetitions were collected for transcriptome sequencing. In total 83.14 Gigabyte (G) Illumina sequence data were generated and 74 850 unigenes were successfully annotated. Differentially expressed gene (DEG) analysis was performed by comparing the transcriptomes of the 0, 2, 4 and 7 days salt treatment, based upon which several potential candidate genes involved in salt tolerance response had been identified. DEGs involved in plant hormone signal transduction, photosynthesis, and catalytic activity were examined in depth. The experimental result indicated that the R. chinensis showed strong stress signals after being subjected to salt stress. In the initial stage of salt treatment (two days), plant protective process began to take effect, which was embodied in the regulation of oxidoreductase activities and plant hormone signal transduction pathway. In addition, the expression level of P5CS was up-regulated in R. chinensis, but the proline metabolic pathway was not affected. In the late stage of salt treatment (four and seven days), the photosynthesis – antenna proteins pathway has been greatly affected, and the down-regulated PYL, Snrk2 and MRP lead to the salt tolerance decline, which was consistent with the leaf wilting performance of the R. chinensis in four and seven days of treatment. All the candidate genes were verified by RT-qPCR.

Transcriptome Sequence Analysis Elaborates a Complex Defensive Mechanism of Grapevine (Vitis vinifera L.) in Response to Salt Stress.

Salinity is ubiquitous abiotic stress factor limiting viticulture productivity worldwide. However, the grapevine is vulnerable to salt stress, which severely affects growth and development of the vine. Hence, it is crucial to delve into the salt resistance mechanism and screen out salt-resistance prediction marker genes; we implicated RNA-sequence (RNA-seq) technology to compare the grapevine transcriptome profile to salt stress. Results showed 2472 differentially-expressed genes (DEGs) in total in salt-responsive grapevine leaves, including 1067 up-regulated and 1405 down-regulated DEGs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations suggested that many DEGs were involved in various defense-related biological pathways, including ROS scavenging, ion transportation, heat shock proteins (HSPs), pathogenesis-related proteins (PRs) and hormone signaling. Furthermore, many DEGs were encoded transcription factors (TFs) and essential regulatory proteins involved in signal transduction by regulating the salt resistance-related genes in grapevine. The antioxidant enzyme analysis showed that salt stress significantly affected the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione S-transferase (GST) activities in grapevine leaves. Moreover, the uptake and distribution of sodium (Na+), potassium (K+) and chlorine (Cl−) in source and sink tissues of grapevine was significantly affected by salt stress. Finally, the qRT-PCR analysis of DE validated the data and findings were significantly consistent with RNA-seq data, which further assisted in the selection of salt stress-responsive candidate genes in grapevine. This study contributes in new perspicacity into the underlying molecular mechanism of grapevine salt stress-tolerance at the transcriptome level and explore new approaches to applying the gene information in genetic engineering and breeding purposes.

Gene expression analysis reveals diversified responsiveness to salt stress in rice genotypes

Salt stress is a major factor affecting rice (Oryza sativa) growth and productivity, limiting its distribution globally. Rice production is primarily gets affected due to its vulnerability to salinity stress at seedling stage, as well as reproductive stage leading to reduction in yield. We report the analysis of 12 diverse rice genotypes collected from different parts of coastal places of northern Andra Pradesh and southern Orissa in India for salt tolerance and categorized their tolerance levels on the basis of reduction in growth and transcript expression pattern. The analysis identified four contrasting salt tolerant genotypes and other eight genotypes exhibited moderate tolerance. Two tolerant and two sensitive genotypes were biochemically explored and used further for gene expression analysis. Proline content showed significant difference between salt tolerant and sensitive genotypes suggesting high tolerance level in tolerant CR1014 and Kudrat-5. The gene-expression analysis of selected CR1014 (salt-tolerant) and Kudrat-5 (salt-sensitive) genotypes differed at transcript expression levels for antioxidant specific A2YPX2/plant peroxidase—POX (19.03-fold) and SODCP/superoxide dismutase (SOD) copper/zinc binding (3.77-fold) in shoots of Kudrat-5 and CATA1/catalase (2.49-fold) and SODCP/SOD copper/zinc binding (4.83-fold) in CR1014 in stress conditions). The salt-stress responsive-specific transcripts HAK17/K+ potassium transporter, A2XMP7/heat shock protein DnaJ, cysteine-rich domain and Q10D68/serine hydroxymethyltransferase in CR1014 after treatment showed increased expression. Interestingly, the transcripts specific for methionine biosynthesis mainly A2Z9C9/Cys/Met metabolism, pyridoxal phosphate-dependent enzyme and B8AF89/spermine synthase induced their expression in Kudrat-5 under salinity stress, where the similar trend was not reflected in salt-tolerant genotype. Thus, the present study highlights on transcript expression pattern for salt-stress responsive candidate genes in two-contrasting rice genotypes selected from the pool of farmer’s cultivated varieties along the coastal belts of India.

Global transcriptome analysis of grapevine (Vitis vinifera L.) leaves under salt stress reveals differential response at early and late stages of stress in table grape cv. Thompson Seedless

Among the different abiotic stresses, salt stress has a significant effect on the growth and yield of grapevine (Vitis vinifera L.). In this study, we employed RNA sequence based transcriptome analysis to study salinity stress response in grape variety Thompson Seedless. Salt stress adversely affected the growth related and physiological parameters and the effect on physiological parameters was significant within 10 days of stress imposition. A total of 343 genes were differentially expressed in response to salt stress. Among the differentially expressed genes (DEGs) only 42 genes were common at early and late stages of stress. The gene enrichment analysis revealed that GO terms related to transcription factors were over-represented. Among the DEGs, 52 were transcription factors belonging to WRKY, EREB, MYB, NAC and bHLH families. Salt stress significantly affected several pathways like metabolic pathways, biosynthesis of secondary metabolites, membrane transport development related pathways etc. 343 DEGs were distributed on all the 19 chromosomes, however clustered regions of DEGs were present on chromosomes 2, 5, 6 and 12 suggesting probable QTLs for imparting tolerance to salt and other abiotic stresses. Real-time PCR of selected genes in control and treated samples of grafted and own root vines demonstrated that rootstock influenced expression of salt stress responsive genes. Microsatellite regions were identified in ten selected salt responsive genes and highly polymorphic markers were identified using fifteen grape genotypes. This information will be useful for the identification of key genes involved in salt stress tolerance in grape. The identified DEGs could also be useful for genome wide analysis for the identification of polymorphic markers for their subsequent use in molecular breeding for developing salt tolerant grape genotypes.

Arabidopsis non-TZF gene AtC3H17 functions as a positive regulator in salt stress response

Functional studies of CCCH-type zinc finger proteins in abiotic stress responses have largely focused on tandem CCCH-type zinc finger (TZF) genes, whereas the study of functional roles of non-TZF genes in abiotic stress responses has largely been neglected. Here, we investigated the functional roles of AtC3H17, a non-TZF gene of Arabidopsis, in salt stress responses. AtC3H17 expression significantly increased under NaCl, mannitol, and ABA treatments. AtC3H17-overexpressing transgenic plants (OXs) were more tolerant under NaCl and MV treatment conditions than the wild type (WT). atc3h17 mutants were more sensitive under NaCl and MV treatment conditions compared with the WT. The transcription of the salt stress-responsive genes in ABA-dependent pathway, such as RAB18, COR15A, and RD22, was significantly higher in AtC3H17 OXs than in WT both under NaCl-free condition and after NaCl treatment. Our results demonstrate that AtC3H17 functions as a positive regulator in salt stress response, via the up-regulation of ABA-dependent salt stress-response pathway.

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.

Salt stress-induced FERROCHELATASE 1 improves resistance to salt stress by limiting sodium accumulation in Arabidopsis thaliana

Ferrochelatase-1 as a terminal enzyme of heme biosynthesis regulates many essential metabolic and physiological processes. Whether FC1 is involved in plant response to salt stress has not been described. This study shows that Arabidopsis overexpressing AtFC1 displays resistance to high salinity, whereas a T-DNA insertion knock-down mutant fc1 was more sensitive to salt stress than wild-type plants. AtFC1 conferred plant salt resistance by reducing Na+ concentration, enhancing K+ accumulation and preventing lysis of the cell membrane. Such observations were associated with the upregulation of SOS1, which encodes a plasma membrane Na+/H+ antiporter. AtFC1 overexpression led to a reduced expression of several well known salt stress-responsive genes such as NHX1 and AVP1, suggesting that AtFC1-regulated low concentration of Na+ in plants might not be through the mechanism for Na+ sequestration. To investigate the mechanism leading to the role of AtFC1 in mediating salt stress response in plants, a transcriptome of fc1 mutant plants under salt stress was profiled. Our data show that mutation of AtFC1 led to 490 specific genes up-regulated and 380 specific genes down-regulated in fc1 mutants under salt stress. Some of the genes are involved in salt-induced oxidative stress response, monovalent cation-proton (Na+/H+) exchange, and Na+ detoxification.

RiceMetaSys for salt and drought stress responsive genes in rice: a web interface for crop improvement

BackgroundGenome-wide microarray has enabled development of robust databases for functional genomics studies in rice. However, such databases do not directly cater to the needs of breeders. Here, we have attempted to develop a web interface which combines the information from functional genomic studies across different genetic backgrounds with DNA markers so that they can be readily deployed in crop improvement. In the current version of the database, we have included drought and salinity stress studies since these two are the major abiotic stresses in rice.ResultsRiceMetaSys, a user-friendly and freely available web interface provides comprehensive information on salt responsive genes (SRGs) and drought responsive genes (DRGs) across genotypes, crop development stages and tissues, identified from multiple microarray datasets. ‘Physical position search’ is an attractive tool for those using QTL based approach for dissecting tolerance to salt and drought stress since it can provide the list of SRGs and DRGs in any physical interval. To identify robust candidate genes for use in crop improvement, the ‘common genes across varieties’ search tool is useful. Graphical visualization of expression profiles across genes and rice genotypes has been enabled to facilitate the user and to make the comparisons more impactful. Simple Sequence Repeat (SSR) search in the SRGs and DRGs is a valuable tool for fine mapping and marker assisted selection since it provides primers for survey of polymorphism. An external link to intron specific markers is also provided for this purpose. Bulk retrieval of data without any limit has been enabled in case of locus and SSR search.ConclusionsThe aim of this database is to facilitate users with a simple and straight-forward search options for identification of robust candidate genes from among thousands of SRGs and DRGs so as to facilitate linking variation in expression profiles to variation in phenotype.Database URL: http://14.139.229.201

MdMYB4 enhances apple callus salt tolerance by increasing MdNHX1 expression levels

Exposure to high salt concentrations is one of the main stresses adversely affecting crop growth, development, and yield. In this study, a putative salt stress-responsive gene (MdMYB4) encoding an R2R3-MYB transcription factor was cloned and characterized. This gene belongs to the SG2 subgroup, and its C-terminal contains a conserved SG2 motif. The relative MdMYB4 expression levels in Malus × domestica Borkh. ‘Orin’ calli cultured under various NaCl concentrations were analyzed. Saline conditions upregulated the expression of MdMYB4, and the effects of the encoded transcription factor on salt tolerance were determined in MdMYB4-overexpressing (OE-MYB4) ‘Orin’ calli. The OE-MYB4 calli grew significantly better than the wild-type calli under salt stress conditions. Additionally, an analysis of the cis-acting elements in the MdNHX1 and MdSOS1 promoters revealed MYB-binding sites. However, the electrophoretic mobility shift assay results indicated that MdMYB4 can bind only to the MdNHX1 promoter. Moreover, the MdNHX1 expression levels were higher in OE-MYB4 calli than in wild-type calli at 150, 200, and 250 mM NaCl. In contrast, there were no significant changes to the MdSOS1 expression levels in OE-MYB4 calli. In conclusion, MdMYB4 is an R2R3-MYB transcription factor that mediates salt tolerance by activating the MdNHX1 promoter. Our findings may provide a theoretical basis for enriching the genetic resources associated with stress tolerance and for improving stress resistance in apple cultivars.

Characterization of salt tolerance and Fusarium wilt resistance of a sweetpotato mutant

The variant LM1 was previously obtained using embryogenic cell suspension cultures of sweetpotato variety Lizixiang by gamma-ray induced mutation, and then its characteristics were stably inherited through six clonal generations, thus this mutant was named LM1. In this study, systematic characterization of salt tolerance and Fusarium wilt resistance were performed between Lizixiang and mutant LM1. LM1 exhibited significantly higher salt tolerance compared to Lizixiang. The content of proline and activities of superoxide dismutase (SOD) and photosynthesis were significantly increased, while malonaldehyde (MDA) and H2O2 contents were significantly decreased compared to that of Lizixiang under salt stress. The inoculation test with Fusarium wilt showed that its Fusarium wilt resistance was also improved. The lignin, total phenolic, jasmonic acid (JA) contents and SOD activity were significantly higher, while H2O2 content was significantly lower in LM1 than that in Lizixiang. The expression level of salt stress-responsive and disease resistance-related genes was significantly higher in LM1 than that in Lizixiang under salt and Fusarium wilt stresses, respectively. This result provides a novel and valuable material for improving the salt tolerance and Fusarium wilt resistance of sweetpotato.

Phospholipases Dζ1 and Dζ2 have distinct roles in growth and antioxidant systems in Arabidopsis thaliana responding to salt stress.

Phospholipases Dζ play different roles in Arabidopsis salt tolerance affecting the regulation of ion transport and antioxidant responses. Lipid signalling mediated by phospholipase D (PLD) plays essential roles in plant growth including stress and hormonal responses. Here we show that PLDζ1 and PLDζ2 have distinct effects on Arabidopsis responses to salinity. A transcriptome analysis of a double pldζ1pldζ2 mutant revealed a cluster of genes involved in abiotic and biotic stresses, such as the high salt-stress responsive genes DDF1 and RD29A. Another cluster of genes with a common expression pattern included ROS detoxification genes involved in electron transport and biotic and abiotic stress responses. Total superoxide dismutase (SOD) activity was induced early in the shoots and roots of all pldζ mutants exposed to mild or severe salinity with the highest SOD activity measured in pldζ2 at 14days. Lipid peroxidation in shoots and roots was higher in the pldζ1 mutant upon salt treatment and pldζ1 accumulated H2O2 earlier than other genotypes in response to salt. Salinity caused less deleterious effects on K+ accumulation in shoots and roots of the pldζ2 mutant than of wild type, causing only a slight variation in Na+/K+ ratio. Relative growth rates of wild-type plants, pldζ1, pldζ2 and pldζ1pldζ2 mutants were similar in control conditions, but strongly affected by salt in WT and pldζ1. The efficiency of photosystem II, estimated by measuring the ratio of chlorophyll fluorescence (F v/F m ratio), was strongly decreased in pldζ1 under salt stress. In conclusion, PLDζ2 plays a key role in determining Arabidopsis sensitivity to salt stress allowing ion transport and antioxidant responses to be finely regulated.

A ζ-carotene desaturase gene, IbZDS, increases β-carotene and lutein contents and enhances salt tolerance in transgenic sweetpotato

ζ-Carotene desaturase (ZDS) is one of the key enzymes in carotenoid biosynthesis pathway. However, the ZDS gene has not been applied to carotenoid improvement of plants. Its roles in tolerance to abiotic stresses have not been reported. In this study, the IbZDS gene was isolated from storage roots of sweetpotato (Ipomoea batatas (L.) Lam.) cv. Nongdafu 14. Its overexpression significantly increased β-carotene and lutein contents and enhanced salt tolerance in transgenic sweetpotato (cv. Kokei No. 14) plants. Significant up-regulation of lycopene β-cyclase (β-LCY) and β-carotene hydroxylase (β-CHY) genes and significant down-regulation of lycopene ε-cyclase (ε-LCY) and ε-carotene hydroxylase (ε-CHY) genes were found in the transgenic plants. Abscisic acid (ABA) and proline contents and superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were significantly increased, whereas malonaldehyde (MDA) content was significantly decreased in the transgenic plants under salt stress. The salt stress-responsive genes encoding pyrroline-5-carboxylate reductase (P5CR), SOD, CAT, ascorbate peroxidase (APX) and POD were found to be significantly up-regulated in the transgenic plants under salt stress. This study indicates that the IbZDS gene has the potential to be applied for improving β-carotene and lutein contents and salt tolerance in sweetpotato and other plants.

Transcriptomic analysis of salt stress responsive genes in Rhazya stricta.

Rhazya stricta is an evergreen shrub that is widely distributed across Western and South Asia, and like many other members of the Apocynaceae produces monoterpene indole alkaloids that have anti-cancer properties. This species is adapted to very harsh desert conditions making it an excellent system for studying tolerance to high temperatures and salinity. RNA-Seq analysis was performed on R. stricta exposed to severe salt stress (500 mM NaCl) across four time intervals (0, 2, 12 and 24 h) to examine mechanisms of salt tolerance. A large number of transcripts including genes encoding tetrapyrroles and pentatricopeptide repeat (PPR) proteins were regulated only after 12 h of stress of seedlings grown in controlled greenhouse conditions. Mechanisms of salt tolerance in R. stricta may involve the upregulation of genes encoding chaperone protein Dnaj6, UDP-glucosyl transferase 85a2, protein transparent testa 12 and respiratory burst oxidase homolog protein b. Many of the highly-expressed genes act on protecting protein folding during salt stress and the production of flavonoids, key secondary metabolites in stress tolerance. Other regulated genes encode enzymes in the porphyrin and chlorophyll metabolic pathway with important roles during plant growth, photosynthesis, hormone signaling and abiotic responses. Heme biosynthesis in R. stricta leaves might add to the level of salt stress tolerance by maintaining appropriate levels of photosynthesis and normal plant growth as well as by the participation in reactive oxygen species (ROS) production under stress. We speculate that the high expression levels of PPR genes may be dependent on expression levels of their targeted editing genes. Although the results of PPR gene family indicated regulation of a large number of transcripts under salt stress, PPR actions were independent of the salt stress because their RNA editing patterns were unchanged.