Role In Salt Stress Tolerance Research Articles

Genome-Wide Mining of Wheat DUF966 Gene Family Provides New Insights Into Salt Stress Responses.

Domain of unknown function (DUF) proteins constitute a great deal of families of functionally uncharacterized proteins in eukaryotes. The DUF966 gene family is found in monocotyledons, dicotyledons, mosses, and other species. However, little is known about the functions of DUF966 genes in wheat (Triticum aestivum L.). In this study, we identified and characterized the TaDUF966 gene family members in wheat by in silico analysis. A total of 28 TaDUF966 proteins were identified in wheat. Phylogenetic analysis divided these proteins into two groups (Groups I and II). Proteins in each group showed a highly conserved DUF966 domain and conserved motif distribution, implying their functional conservation. Analysis of gene expression profiling data showed that some TaDUF966 genes were induced by salt stress. We further confirmed the role of TaDUF966-9B in salt stress using virus induced gene silencing (VIGS) assay. Compared with the empty vector control, the TaDUF966-9B knockdown plants exhibited severe leaf curling at 10 days post-inoculation with BSMV under salt stress, suggesting that TaDUF966 genes play a vital role in salt stress tolerance in wheat. Taken together, these results expand our knowledge of the evolution of the DUF966 gene family in wheat and promote the potential application of these genes in wheat genetic improvement.

Chlorophyll a fluorescence of safflower affected by salt stress and hormonal treatments

Salicylic and jasmonic acids are classified as stress hormones, which can affect numerous physiological characteristics of plants such as electron transporting systems in thylakoid membrane under normal and stressful conditions. A greenhouse experiment was conducted with factorial arrangement based on a randomized complete block design with three replications to assess the possible effects of salicylic acid (1 mM) and jasmonic acid (0.5 mM) on different parameters of chlorophyll a fluorescence in safflower (Carthamus tinctorius L. cv. Goldasht) under salt stress [0, 4, 8, and 12 dS m−1 NaCl (about 0, 40, 80 and 120 mM NaCl, respectively)]. Leaf chlorophyll content index, relative water content, leaf area and seed yield were decreased with increasing salinity. Salinity caused a significant decrease in the variable fluorescence, the maximum quantum yield of photosystem II, efficiency of water-splitting complex on the donor side of the photosystem II and total performance index (PItotal). The highest time needed to reach maximum fluorescence was recorded at 12 dS m−1. Maximum fluorescence and PItotal were increased, but initial fluorescence and maximum fluorescence were significantly decreased by salicylic acid and jasmonic acid treatments under saline conditions. Salicylic acid and jasmonic acid considerably improved the variable fluorescence, maximum quantum yield of photosystem II, the efficiency of water-splitting complex, PItotal, physiological parameters and seed yield under salinity. In this way, foliar application of salicylic acid and jasmonic acid could play a key role in salt stress tolerance of safflower plants.

Comparative time-course transcriptome analysis in contrasting Carex rigescens genotypes in response to high environmental salinity.

Soil salinization is one of most crucial environmental problems around the world and negatively affects plant growth and production. Carex rigescens is a turfgrass with favorable stress tolerance and great application prospect in salinity soil remediation and utilization; however, the molecular mechanisms behind its salt stress response are unknown. We performed a time-course transcriptome analysis between salt tolerant 'Huanghua' (HH) and salt sensitive 'Beijing' (BJ) genotypes. Physiological changes within 24h were observed, with the HH genotype exhibiting increased salt tolerance compared to BJ. 5764 and 10752 differentially expressed genes were approved by transcriptome in BJ and HH genotype, respectively, and dynamic analysis showed a discrepant profile between two genotypes. In the BJ genotype, genes related to carbohydrate metabolism and stress response were more active and ABA signal transduction pathway might play a more important role in salt stress tolerance than in HH genotype. In the HH genotype, unique increases in the regulatory network of transcription factors, hormone signal transduction, and oxidation-reduction processes were observed. Moreover, trehalose and pectin biosynthesis and chitin catabolic related genes were specifically involved in the HH genotype, which may have contributed to salt tolerance. Moreover, some candidate genes like mannan endo-1,4-beta-mannosidase and EG45-like domain-containing protein are highlighted for future research about salt stress resistance in C. rigescens and other plant species. Our study revealed unique salt adaptation and resistance characteristics of two C. rigescens genotypes and these findings could help to enrich the currently available knowledge and clarify the detailed salt stress regulatory mechanisms in C. rigescens and other plants.

Transcriptional responses of Rosa rugosa to salt stress and salt shock

ABSTRACT Rugosa rugosa has high tolerance to various stresses; however, the molecular mechanisms of this behavior under adverse conditions are unclear. The objective of this study is to investigate expression patterns of stress-related genes in response to salinity stress. Changes in transcript levels of R. rugose, grown under different salt stress conditions (0, 25, 50, and 100 mM NaCl) over a long exposure period (30 days), have been investigated. In addition, the effects of salt shock stress on seedlings exposed to a high level (200 mM) of NaCl for a relatively short duration (3 h) have also been investigated. Expression levels of selected differentially expressed genes have been determined using relative reverse transcription polymerase chain reaction (RT-PCR). It has been observed that seedlings exposed to salt stress for a long duration exhibited no signs of stress in both leaves and roots. In addition, expression of NHX1 in R. rugosa increased in the presence of NaCl. Furthermore, transcripts of EXP4, GPP, NHX1, NAC, and DREB genes also increased under high levels of NaCl. In contrast, expression levels of MYB and TIR decreased during this salt shock treatment. Of particular interest is the increase in levels of transcripts of NHX1 in leaves of seedlings grown under both salt stress and salt shock conditions, thus suggesting that this gene plays an important role in salt stress tolerance in R. rugosa. These findings will support efforts in enhancing salt tolerance in roses, and perhaps in other members of the Rosaceae family.

QTL analysis for rice salinity tolerance and fine mapping of a candidate locus qSL7 for shoot length under salt stress

Salinity is one of the major abiotic stresses limiting rice production worldwide. Understanding the genetic basis of salinity tolerance is key for rice breeding. In this study, a recombinant inbred line (RIL) population derived from a super hybrid rice Liang–You–Pei–Jiu (LYP9) parents 93-11 and PA64s, exhibited variation in phenotypes including shoot length (SL), root length (RL), shoot fresh weight (SFW), root fresh weight (RFW), shoot dry weight (SDW), and root dry weight (RDW) under 50 and 100 mM NaCl stress. QTL analysis identified a total of 38 QTLs for these 6 traits under two distinct concentrations of salt, distributing on chromosomes 1, 2, 3, 4, 5, 6, 7 and 10. A total of 21 QTLs were found in 6 stable loci. A novel major QTL, qSL7 for shoot length on chromosome 7 was identified in two distinct concentrations. A chromosome segment substitution line (CSSL) harboring the qSL7 locus from PA64s with 93-11 background was developed and exhibited higher SL value, higher K+ concentration, and lower Na+ concentration compared to 93-11. With BC5F2:3 derived from CSSL-qSL7/93-11, the qSL7 was fine mapped within a 252.9 kb region on chromosome 7 where 40 annotated genes located including, LOC_Os07g43530, which encodes a DNA-binding domain containing protein reported previously as a transcription factor playing a positive role in salt stress tolerance. Our study provides new genetic resources for improvement of salinity tolerance in rice breeding.

PpAKR1A, a Novel Aldo-Keto Reductase from Physcomitrella Patens, Plays a Positive Role in Salt Stress.

The moss Physcomitrella patens is tolerant of highly saline environments. In plants, salinity stress may induce the production of toxic reactive carbonyl species (RCS) and oxidative damage. Aldo-keto reductases (AKRs) are a large group of NADP-dependent oxidoreductases involved in RCS detoxification. However, many members in this superfamily remain uncharacterized. In this study, we cloned and characterised a putative AKR1 from P. patens, named PpAKR1A. Notably, the transcription level of PpAKR1A was induced by salt and methylglyoxal (MG) stress, and the recombinant PpAKR1A protein catalysed the reduction of toxic aldehydes. PpAKR1A knockout mutants of P. patens (ppakr1a) were sensitive to NaCl and MG treatment, as indicated by much lower concentrations of chlorophyll and much higher concentrations of MG and H2O2 than those in WT plants. Meanwhile, ppakr1a plants exhibited decreases in the MG-reducing activity and reactive oxygen species-scavenging ability in response to salt stress, possibly due to decreases in the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Our results indicate that PpAKR1A is an aldo-keto reductase that detoxifies MG and thus plays an important role in salt stress tolerance in P. patens.

Genome-Wide Mining and Identification of Protein Kinase Gene Family Impacts Salinity Stress Tolerance in Highly Dense Genetic Map Developed from Interspecific Cross between G. hirsutum L. and G. darwinii G. Watt

Abiotic stress is an important limiting factor in crop growth and yield around the world. Owing to the continued genetic erosion of the upland cotton germplasm due to intense selection and inbreeding, attention has shifted towards wild cotton progenitors which offer unique traits that can be introgressed into the cultivated cotton to improve their genetic performance. The purpose of this study was to characterize the Pkinase gene family in a previously developed genetic map of the F2 population derived from a cross between two cotton species: Gossypium hirsutum (CCRI 12-4) and Gossypium darwinii (5-7). Based on phylogenetic analysis, Pkinase (PF00069) was found to be the dominant domain with 151 genes in three cotton species, categorized into 13 subfamilies. Structure analysis of G. hirsutum genes showed that a greater percentage of genes and their exons were highly conserved within the group. Syntenic analysis of gene blocks revealed 99 duplicated genes among G. hirsutum, Gossypium arboreum and Gossypium raimondii. Most of the genes were duplicated in segmental pattern. Expression pattern analysis showed that the Pkinase gene family possessed species-level variation in induction to salinity and G. darwinii had higher expression levels as compared to G. hirsutum. Based on RNA sequence analysis and preliminary RT-qPCR verification, we hypothesized that the Pkinase gene family, regulated by transcription factors (TFs) and miRNAs, might play key roles in salt stress tolerance. These findings inferred comprehensive information on possible structure and function of Pkinase gene family in cotton under salt stress.

Lipid Droplets Mediate Salt Stress Tolerance in Parachlorella kessleri.

Microalgae are known to respond to salinity stress via mechanisms that include accumulation of compatible solutes and synthesis of antioxidants. Here, we describe a salinity-tolerance mechanism mediated by lipid droplets (LDs). In the alga Parachlorella kessleri grown under salt-stress conditions, we observed significant increases in cell size and LD content. LDs that were closely grouped along the plasma membrane shrank as the plasma membrane expanded, and some LDs were engulfed by vacuoles. Transcriptome analysis showed that genes encoding lysophospholipid acyltransferases (LPLATs) and phospholipase A2 were significantly up-regulated following salt stress. Diacylglycerol kinase and LPLAT were identified in the proteome of salt-induced LDs, alongside vesicle trafficking and plastidial proteins and histone H2B. Analysis of fatty acid composition revealed an enrichment of C18:1 and C18:2 at the expense of C18:3 in response to salt stress. Pulse-chase experiments further suggested that variations of fatty acid composition were associated with LDs. Acetate stimulation research further confirmed a positive role of LDs in cell growth under salt stress. These results suggest that LDs play important roles in salt-stress tolerance, through harboring proteins, participating in cytoplasmic component recycling, and providing materials and enzymes for membrane modification and expansion.

Exploiting Differential Gene Expression to Discover Ionic and Osmotic-Associated Transcripts in the Halophyte Grass Aeluropus littoralis

BackgroundSalinity as a most significant environmental challenges affects the growth and productivity of plants worldwide. In this study, the ionic and iso-osmotic effects of salt stress were investigated in Aeluropus littoralis L., a halophyte grass species from Poaceae family, by cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique. To dissect the two different effects (ionic and osmotic) exerted by salt stress, various ionic agents including 200 and 400 mM sodium chloride (NaCl), 200 and 400 mM potassium chloride (KCl) as well as 280 and 406 gl− 1 (− 0.9 and − 1.4 MPa) polyethylene glycol 6000 (PEG) as their iso-osmotic concentrations were applied.ResultsApplication of KCl and PEG significantly reduced the fresh weight (FW) of A. littoralis seedlings compared to control while NaCl treatment markedly enhanced the FW. At the transcriptome level, different observations of changes in gene expression have been made in response of A. littoralis to ionic and osmotic stresses. Out of 69 transcript derived fragments (TDFs), 42 TDFs belong to 9 different groups of genes involved in metabolism (11.6%), transcription (10.2%), ribosomal protein (8.7%), protein binding (8.7%) transporter (5.8%), translation (5.8%), signal transduction (4.3%), nucleosome assembly protein (2.9%) and catabolism (2.9%). The 44 and 28 percent of transcripts were expressed under ionic stress (NaCl-specific and KCl-specific) and osmotic stress (common with NaCl, KCl and PEG), respectively which indicating a greater response of plants to ionic stress than osmotic stress. Expression pattern of eight candidate TDFs including; SYP81, CAND1, KATN, ISB1, SAMDC, GLY1, HAK18 and ZF30 was evaluated by RT-qPCR at high salinity levels and recovery condition.ConclusionDifferential regulation of these TDFs was observed in root and shoot which confirm their role in salt stress tolerance and provide initial insights into the transcriptome of A. littoralis. Expression pattern of ionic and osmotic-related TDFs at A. littoralis can be taken as an indication of their functional relevance at different salt and drought stresses.

Identification of phosphorylated proteins in response to salt stress in wheat embryo and endosperm during seed germination

Seed germination is a new beginning for the crop life cycle, which is closely related to seed sprouting and subsequent plant growth and development, and ultimately affects grain yield and quality. Salt stress is one of the most important abiotic stress factors that restrict crop production. Therefore, it is highly important to improve crop salt tolerance and sufficient utilization of saline-alkali land. In this study, we identified the phosphorylated proteins involved in salt stress response by combining SEM, 2-DE, Pro-Q Diamond staining and tandem mass spectrometry. The results showed that salt stress significantly inhibited seed germination and starch degradation. In total, 14 phosphorylated protein spots (11 unique proteins) in the embryo and 6 phosphorylated protein spots (4 unique proteins) in the endosperm were identified, which mainly involved in stress/defense, protein metabolism and energy metabolism. The phosphorylation of some proteins such as cold regulated proteins, 27K protein, EF-1β and superoxide dismutase could play important roles in salt stress tolerance.

Comprehensive Analysis of MYB Gene Family and Their Expressions Under Abiotic Stresses and Hormone Treatments in Tamarix hispida.

The MYB transcription factors (TFs) is a plant TF families, which involves in hormone signal transduction, and abiotic stress tolerance, etc. However, there are few studies on the MYB TFs family and its regulatory mechanism in Tamarix hispida. In this study, 14 MYB genes (named ThMYB1 - ThMYB14) were cloned and characterized from T. hispida. The transcription profiles of ThMYBs in T. hispida under different abiotic stress conditions were monitored using qRT-PCR. Most of studied ThMYBs were significantly downregulated and/or upregulated by salt and osmotic stress, ABA, GA3 and JA treatments in at least one organ. Especially, ThMYB13 was induced in the leaves and roots of T. hispida when exposed to NaCl treatment at all study periods, indicating that it may involve in salt stress. To further study ThMYB13 function, ThMYB13 overexpression and knock-down plants and control plants transformed with an empty pROKII were obtained using a transient transformation system. Overexpression of ThMYB13 in T. hispida displayed the lowest O2-, H2O2 and MDA accumulation, minimal cell death, the most stable K+/Na+ ratio and the lowest electrolyte leakage rate among the three kinds of transient expression in T. hispida. Conversely, the RNAi-silencing, transiently transformed plants displayed the opposite physiological changes. Therefore, ThMYB13 might play a role in salt stress tolerance in transgenic T. hispida plants.

High Performance of Photosynthesis and Osmotic Adjustment Are Associated With Salt Tolerance Ability in Rice Carrying Drought Tolerance QTL: Physiological and Co-expression Network Analysis.

Understanding specific biological processes involving in salt tolerance mechanisms is important for improving traits conferring tolerance to salinity, one of the most important abiotic stresses in plants. Under drought and salinity stresses, plants share overlapping responsive mechanisms such as physiological changes and activation of signaling molecules, which induce and transmit signals through regulator genes in a regulatory network. In this study, two near isogenic lines of rice carrying chromosome segments of drought tolerance QTL on chromosome 8 from IR68586-F2-CA-31 (DH103) in the genetic background of sensitive cultivar “Khao Dawk Mali 105; KDML105” (designated as CSSL8-94 and CSSL8-95) were used to investigate physiological responses to salt stress [namely growth, Na+/K+ ratio, water status, osmotic adjustment, photosynthetic parameters, electrolyte leakage (EL), malondialdehyde (MDA), proline and sugar accumulations], compared with the standard salt tolerant (Pokkali; PK) and their recurrent parent (KDML105) rice cultivars. Physiological examination indicated that both CSSLs showed superior salt-tolerant level to KDML105. Our results suggested that salt tolerance ability of these CSSL lines may be resulted from high performance photosynthesis, better osmotic adjustment, and less oxidative stress damage under salt conditions. Moreover, to explore new candidate genes that might take part in salt tolerance mechanisms, we performed co-expression network analysis for genes identified in the CSSL rice, and found that Os08g419090, the gene involved with tetrapyrrole and porphyrin biosynthetic process (chlorophyll biosynthetic process), Os08g43230 and Os08g43440 (encoded TraB family protein and cytochrome P450, respectively) might have unprecedented roles in salt stress tolerance.

The wheat salinity-induced R2R3-MYB transcription factor TaSIM confers salt stress tolerance in Arabidopsis thaliana

MYB transcription factors are a large family of proteins involved in plant development and responses to stress. In this study, the wheat salinity-induced R2R3-MYB transcription factor TaSIM was functionally characterized, with a focus on its role in salt stress tolerance. TaSIM protein enters the nucleus and binds to the MYB-binding site II motif. Expression analysis revealed that TaSIM was induced by drought, high salinity, low temperature, and abscisic acid treatment. Overexpression of TaSIM improved salt stress tolerance in transgenic plants. Furthermore, the transcript levels of genes involved in abscisic acid (ABA)-dependent (RD22) and ABA-independent (RD29A) signaling were higher in TaSIM-overexpressing plants than in the wild type. These results suggest that TaSIM positively modulates salt stress tolerance and has potential applications in molecular breeding to enhance salt tolerance in crops.

Physiological and molecular responses of Betula platyphylla Suk to salt stress

Our study found that birch employs different physiological pathways to tolerance salt stress in roots and leaves, and the genes closely correlated with these physiological changes were identified. Birches are fast-growing woody plants that are adapted to adverse environments, and are widely distributed from north Europe to northeast Asia. However, the salt stress tolerance mechanism of birch has little been studied. Here, we investigated the physiological and molecular response of white birch (Betula Platyphylla) to salt stress. Long-term salt stress inhibited photosynthetic activity, and decreased stomatal conductance of birch. Abscisic acid was induced in birch during the early salt stress period, and Ca2+ level was increased slowly but maintained at a higher level for a long time. Under salt conditions, the salt-overly-sensitive pathway was activated in birch roots; reactive oxygen species (ROS) was highly accumulated, and superoxide dismutase is the main ROS scavenger in roots, while peroxidase is the main ROS scavenger in leaves. Proline plays a role in salt tolerance in both roots and leaves; however, soluble sugars and trehalose also have roles in salt stress tolerance, but mainly in leaves. Additionally, the genes that might have essential roles in controlling some of these physiological changes were identified, which represent good candidate genes to characterize the salt tolerance mechanism of birch. This study increased our understanding of the salt tolerance mechanism of birch plants.

Potassium and zinc increase tolerance to salt stress in wheat (Triticum aestivum L.)

Potassium and zinc are essential elements in plant growth and metabolism and plays a vital role in salt stress tolerance. To investigate the physiological mechanism of salt stress tolerance, a pot experiment was conducted. Potassium and zinc significantly minimize the oxidative stress and increase root, shoot and spike length in wheat varieties. Fresh and dry biomass were significantly increased by potassium followed by zinc as compared to control C. The photosynthetic pigment and osmolyte regulator (proline, total phenolic, and total carbohydrate) were significantly enhanced by potassium and zinc. Salt stress increases MDA content in wheat varieties while potassium and zinc counteract the adverse effect of salinity and significantly increased membrane stability index. Salt stress decreases the activities of antioxidant enzymes (superoxide dismutase, catalase and ascorbate peroxidase) while the exogenous application of potassium and zinc significantly enhanced the activities of these enzymes. A significant positive correlation was found of spike length with proline (R2 = 0.966 ∗∗∗), phenolic (R2 = 0.741∗) and chlorophyll (R2 = 0.853∗∗). The MDA content showed significant negative correlation (R2 = 0.983∗∗∗) with MSI. It is concluded that potassium and zinc reduced toxic effect of salinity while its combine application showed synergetic effect and significantly enhanced salt tolerance.

OsPEX11, a Peroxisomal Biogenesis Factor 11, Contributes to Salt Stress Tolerance in Oryza sativa.

Peroxisomes are single membrane-bound organelles, whose basic enzymatic constituents are catalase and H2O2-producing flavin oxidases. Previous reports showed that peroxisome is involved in numerous processes including primary and secondary metabolism, plant development and abiotic stress responses. However, knowledge on the function of different peroxisome genes from rice and its regulatory roles in salt and other abiotic stresses is limited. Here, a novel prey protein, OsPEX11 (Os03g0302000), was screened and identified by yeast two-hybrid and GST pull-down assays. Phenotypic analysis of OsPEX11 overexpression seedlings demonstrated that they had better tolerance to salt stress than wild type (WT) and OsPEX11-RNAi seedlings. Compared with WT and OsPEX11-RNAi seedlings, overexpression of OsPEX11 had lower level of lipid peroxidation, Na+/K+ ratio, higher activities of antioxidant enzymes (SOD, POD, and CAT) and proline accumulation. Furthermore, qPCR data suggested that OsPEX11 acted as a positive regulator of salt tolerance by reinforcing the expression of several well-known rice transporters (OsHKT2;1, OsHKT1;5, OsLti6a, OsLti6b, OsSOS1, OsNHX1, and OsAKT1) involved in Na+/K+ homeostasis in transgenic plants under salinity. Ultrastructural observations of OsPEX11-RNAi seedlings showed that they were less sensitive to salt stress than WT and overexpression lines. These results provide experimental evidence that OsPEX11 is an important gene implicated in Na+ and K+ regulation, and plays a critical role in salt stress tolerance by modulating the expression of cation transporters and antioxidant defense. Thus, OsPEX11 could be considered in transgenic breeding for improvement of salt stress tolerance in rice crop.

Over-expression of Topoisomerase II Enhances Salt Stress Tolerance in Tobacco.

Topoisomerases are unique enzymes having an ability to remove or add DNA supercoils and untangle the snarled DNA. They can cut, shuffle, and religate DNA strands and remove the torsional stress during DNA replication, transcription or recombination events. In the present study, we over-expressed topoisomerase II (TopoII) in tobacco (Nicotiana tabaccum) and examined its role in growth and development as well as salt (NaCl) stress tolerance. Several putative transgenic plants were generated and the transgene integration and expression was confirmed by PCR and Southern blot analyses, and RT-PCR analysis respectively. Percent seed germination, shoot growth, and chlorophyll content revealed that transgenic lines over-expressing the NtTopoIIα-1 gene exhibited enhanced tolerance to salt (150 and 200 mM NaCl) stress. Moreover, over-expression of TopoII lead to the elevation in proline and glycine betaine levels in response to both concentrations of NaCl as compared to wild-type. In response to NaCl stress, TopoII over-expressing lines showed reduced lipid peroxidation derived malondialdehyde (MDA) generation. These results suggest that TopoII plays a pivotal role in salt stress tolerance in plants.

Comparative Proteomic Analysis Reveals Differential Root Proteins in Medicago sativa and Medicago truncatula in Response to Salt Stress.

Salt stress is an important abiotic stress that causes decreased crop yields. Root growth and plant activities are affected by salt stress through the actions of specific genes that help roots adapt to adverse environmental conditions. For a more comprehensive understanding of proteins affected by salinity, we used two-dimensional gel electrophoresis and mass spectrometry to characterize the proteome-level changes associated with salt stress response in Medicago sativa cv. Zhongmu-1 and Medicago truncatula cv. Jemalong A17 roots. Our physiological and phenotypic observations indicated that Zhongmu-1 was more salt tolerant than Jemalong A17. We identified 93 and 30 proteins whose abundance was significantly affected by salt stress in Zhongmu-1 and Jemalong A17 roots, respectively. The tandem mass spectrometry analysis of the differentially accumulated proteins resulted in the identification of 60 and 26 proteins in Zhongmu-1 and Jemalong A17 roots, respectively. Function analyses indicated molecule binding and catalytic activity were the two primary functional categories. These proteins have known functions in various molecular processes, including defense against oxidative stress, metabolism, photosynthesis, protein synthesis and processing, and signal transduction. The transcript levels of four identified proteins were determined by quantitative reverse transcription polymerase chain reaction. Our results indicate that some of the identified proteins may play key roles in salt stress tolerance.

Expression of dehydrins, HSP70, Cu/Zn SOD, and RuBisCO in leaves of tobacco (Nicotiana tabacum L.) dihaploids under salt stress

Salinity is an abiotic factor that has a negative impact on plant growth and seed germination, leading to limited crop production. The effect of salt stress (100 and 200 mM NaCl) on the expression of dehydrins (DHNs), heat-shock protein 70 (HSP70), superoxide dismutase (Cu/Zn SOD), and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) was investigated in leaves of tobacco (Nicotiana tabacum L.) F1 hybrid DH10 and four dihaploid lines (207B, 238C, 239K, 244B) under in vitro conditions. After 33 d, the dihaploid lines as well as DH10 showed enhanced expression of 70-kDa DHN in response to 200 mM NaCl stress. This was especially evident in line 207B, which previously proved to be tolerant to salt stress, suggesting that DHNs have an important role in salt stress tolerance. Also, line 207B as well as lines 238C and 244B responded to 200 mM NaCl stress by increased expression of Cu/Zn SOD, indicating its possible role in providing salt stress tolerance. On the other hand, salt stress induced in line 239K resulted in a significantly higher expression of RuBisCO, indicating that differential susceptibility of dihaploids to increased levels of NaCl might be the result of their different genetic traits. Decreased expression of HSP70 in salt-treated tobacco dihaploids indicates that HSP70 is not included in protection against salt stress.

Overexpression of an MYB-Related Gene FvMYB1 from Fraxinus velutina Increases Tolerance to Salt Stress in Transgenic Tobacco

MYB transcription factors (TFs) in plants play important roles in abiotic stress tolerance. Here, we report that an MYB-related TF gene, named FvMYB1, was isolated from the salt-tolerant tree species Fraxinus velutina Torr. The real-time PCR analysis showed that the FvMYB1 transcript increased remarkably in response to salt treatment. Subsequently, the FvMYB1 gene was transferred into the tobacco genome via the Agrobacterium-mediated approach. PCR and Southern blot verified that the FvMYB1 gene had been expressed in transgenic tobacco. The overexpressing transgenic seedlings displayed better salt tolerance in root length, shoot fresh weight, and shoot/root ratio compared to the wild type. Moreover, along with the superoxide dismutase and peroxidase activities and proline content that were significantly increased in the transgenic plants, the transcriptions of a series of stress-responsive genes were up-regulated under salt treatment. Further, an analysis of the upstream sequence of the FvMYB1 gene revealed that the promoter could enhance GUS gene expression in transgenic tobacco with NaCl treatment. These results indicate that FvMYB1 functions as a transcriptional activator that plays a regulatory role in salt stress tolerance of F. velutina.