Cloning and characterization of a salt stress-inducible small GTPase gene from the model grass species Lolium temulentum

Recent progress in understanding salinity tolerance in plants: Story of Na+/K+ balance and beyond

High salt concentrations in the growing medium can severely affect the growth and development of plants. It is imperative to understand the different components of salt-tolerant network in plants in order to produce the salt-tolerant cultivars. High-affinity potassium transporter- and myelocytomatosis proteins have been shown to play a critical role for salinity tolerance through exclusion of sodium (Na⁺) ions from sensitive shoot tissues in plants. Numerous genes, that limit the uptake of salts from soil and their transport throughout the plant body, adjust the ionic and osmotic balance of cells in roots and shoots. In the present review, we have tried to provide a comprehensive report of major research advances on different mechanisms regulating plant tolerance to salinity stress at proteomics, metabolomics, genomics and transcriptomics levels. Along with the role of ionic homeostasis, a major focus was given on other salinity tolerance mechanisms in plants including osmoregulation and osmo-protection, cell wall remodeling and integrity, and plant antioxidative defense. Major proteins and genes expressed under salt-stressed conditions and their role in enhancing salinity tolerance in plants are discussed as well. Moreover, this manuscript identifies and highlights the key questions on plant salinity tolerance that remain to be discussed in the future.

Progress in understanding salt stress response in plants using biotechnological tools

Salinization is a worldwide environmental problem, which is negatively impacting crop yield and thus posing a threat to the world's food security. Considering the rising threat of salinity, it is need of time, to understand the salt tolerant mechanism in plants and find avenues for the development of salinity resistant plants. Several plants tolerate salinity in a different manner, thereby halophytes and glycophytes evolved altered mechanisms to counter the stress. Therefore, in this review article, physiological, metabolic, and molecular aspects of the plant adaptation to salt stress have been discussed. The conventional breeding techniques for developing salt tolerant plants has not been much successful, due to its multigenic trait. The inflow of data from plant sequencing projects and annotation of genes led to the identification of many putative genes having a role in salt stress. The bioinformatics tools provided preliminary information and were helpful for making salt stress-specific databases. The microRNA identification and characterization led to unraveling the finer intricacies of the network. The transgenic approach finally paved a way for overexpressing some important genes viz. DREB, MYB, COMT, SOS, PKE, NHX, etc. conferred salt stress tolerance. In this review, we tried to show the effect of salinity on plants, considering ion homeostasis, antioxidant defense response, proteins involved, possible utilization of transgenic plants, and bioinformatics for coping with this stress factor. An overview of previous studies related to salt stress is presented in order to assist researchers in providing a potential solution for this increasing environmental threat.

Effect of salinity stress on plants and its tolerance strategies: a review

The environmental stress is a major area of scientific concern because it constraints plant as well as crop productivity. This situation has been further worsened by anthropogenic activities. Therefore, there is a much scientific saddle on researchers to enhance crop productivity under environmental stress in order to cope with the increasing food demands. The abiotic stresses such as salinity, drought, cold, and heat negatively influence the survival, biomass production and yield of staple food crops. According to an estimate of FAO, over 6% of the world's land is affected by salinity. Thus, salinity stress appears to be a major constraint to plant and crop productivity. Here, we review our understanding of salinity impact on various aspects of plant metabolism and its tolerance strategies in plants.

Enhanced oxidative stress resistance through activation of a zinc deficiency transcription factor in Brachypodium distachyon

Identification of viable strategies to increase stress resistance of crops will become increasingly important for the goal of global food security as our population increases and our climate changes. Considering that resistance to oxidative stress is oftentimes an indicator of health and longevity in animal systems, characterizing conserved pathways known to increase oxidative stress resistance could prove fruitful for crop improvement strategies. This report argues for the usefulness and practicality of the model organism Brachypodium distachyon for identifying and validating stress resistance factors. Specifically, we focus on a zinc deficiency B. distachyon basic leucine zipper transcription factor, BdbZIP10, and its role in oxidative stress in the model organism B. distachyon. When overexpressed, BdbZIP10 protects plants and callus tissue from oxidative stress insults, most likely through distinct and direct activation of protective oxidative stress genes. Increased oxidative stress resistance and cell viability through the overexpression of BdbZIP10 highlight the utility of investigating conserved stress responses between plant and animal systems.

Salt-stress induced changes in the leaf proteome of diploid and tetraploid mandarins with contrasting Na+ and Cl- accumulation behaviour

To understand the genotypic variation of citrus to mild salt stress, a proteomic approach has been carried out in parallel on two citrus genotypes ('Cleopatra' and 'Willow leaf' mandarins), which differ for Na(+) and Cl(-) accumulation, and their cognate autotetraploids (4×). Using two-dimensional electrophoresis approximately 910 protein spots were reproducibly detected in control and salt-stressed leaves of all genotypes. Among them, 44 protein spots showing significant variations at least in one genotype were subjected to mass spectrometry analysis for identification. Salt-responsive proteins were involved in several functions, including photosynthetic processes, ROS scavenging, stress defence, and signalling. Genotype factors affect the salt-responsive pattern, especially that of carbon metabolism. The no ion accumulator 'Cleopatra' mandarin genotype showed the highest number of salt-responsive proteins, and up-regulation of Calvin cycle-related proteins. Conversely the ion accumulator 'Willow leaf' mandarin showed high levels of several photorespiration-related enzymes. A common set of proteins (twelve spots) displayed higher levels in salt-stressed leaves of 2× and 4× 'Cleopatra' and 4× 'Willow leaf' mandarin. Interestingly, antioxidant enzymes and heat shock proteins showed higher constitutive levels in 4× 'Cleopatra' mandarin and 4× 'Willow leaf' mandarin compared with the cognate 2× genotype. This work provides for the first time information on the effect of 8 weeks of salt stress on citrus genotypes contrasting for ion accumulation and their cognate autotetraploids. Results underline that genetic factors have a predominant effect on the salt response, although a common stress response independent from genotype was also found.

Abiotic stresses activate a MAPkinase in the model grass species Lolium temulentum

Forage and turf grasses are utilized in diverse environments that expose them to a variety of abiotic stresses, however very little is known concerning the perception or molecular responses to these various stresses. In the model grass species Lolium temulentum, a 46kDa mitogen-activated protein kinase (MAPK) was activated in the leaf within 10min of exposing the roots to salt stress. When plants were subjected cold stress, no significant activation of the MAPK was observed. However, the 46kDa MAPK was rapidly activated in the leaves of plants within 3min of exposure to heat stress. Previously, mechanical wounding has been shown to rapidly activate a 46kDa and a 44kDa MAPK in L. temulentum. The wound activation of the MAPKs was delayed and diminished in plants undergoing cold treatment. In plants subjected simultaneously to 40°C and wounding, the activation of the 46kDa MAPK was enhanced. However if plants were subjected to heat and cold stress for more than 2h or exposed to 300mM NaCl for 24h prior to wounding, the wound activation of the 46kDa and a 44kDa MAPKs were significantly inhibited. These results suggest that the 46kDa MAPK plays a role in the response to various environmental stimuli.

Toxic effect of NaCl on ion metabolism, antioxidative enzymes and gene expression of perennial ryegrass

Two-month old seedlings of perennial ryegrass (Lolium perenne L.) were subjected to four different levels of salinity for 7 days. The NaCl treatments reduced turf quality and normalized transpiration rates. Both chlorophyll (Chl) a and Chl b contents decreased in the grass exposed to 255 mM relative to the control. An increase in the lipid peroxidationin was observed. The activity of leaf superoxide dismutase increased while, peroxidase and catalase activities decreased in response to NaCl treatments. The expression of Chl Cu/ZnSOD, Cyt Cu/ZnSOD, FeSOD, CAT, POD, GPX and GR was up-regulated for NaCl-treated grass. Salt stress increased accumulation of Na(+) and decreased K(+)/Na(+) ratio, Mg(2+) and P content in both shoots and roots of perennial ryegrass. The findings of this study suggest that salt stress may cause toxicity to perennial ryegrass through oxidative injury and damage to Chl and cell membrane integrity.

Analysis of gene expression by ESTs from suppression subtractive hybridization library in Chenopodium album L. under salt stress

To identify genes expression in Chenopodium album exposed to NaCl stress and screen ESTs related to salt stress, a subtractive suppression hybridization (SSH) library of C. album under salt stress was constructed in the present study. Random EST sequencing produced 825 high-quality ESTs with GenBank ID GE746311-GE747007, which had 301 bp of average size and were clustered into 88 contigs and 550 singletons. They were classified into 12 categories according to their function annotations. 635 ESTs (76.97%) showed similarities to gene sequences in the non-redundancy database, while 190 ESTs (23.03%) showed low or no similarities. The transcriptional profiles of 56 ESTs randomly selected from 347 unknown or novel ESTs of SSH library under varying NaCl concentration and at different time points were analyzed. The results indicated that a high proportion of tested ESTs were activated by salt stress. Four in 56 ESTs responded to NaCl were also enhanced in expression level when exposed to ABA and PEG stresses. The above four ESTs were validated by northern blotting which was consistent with the results of RT-PCR. The results suggested that genes corresponded to these ESTs might be involved in stress response or regulation. The complete sequences and detailed function of these ESTs need to be further studied.

Cloning and genetic diversity analysis of a new P5CS gene from common bean (Phaseolus vulgaris L.)

Delta(1)-pyrroline-5-carboxylate synthetase (P5CS) is the rate-limiting enzyme involved in the biosynthesis of proline in plants. By the 3' rapid amplification of cDNA ends (3'-RACE) approach, a 2,246-bp cDNA sequence was obtained from common bean (Phaseolus vulgaris L.), denominated PvP5CS2 differing from another P5CS gene that we cloned previously from common bean (PvP5CS). The predicted amino acid sequence of PvP5CS2 has an overall 93.2% identity GmP5CS (Glycine max L. P5CS). However, PvP5CS2 shows only 83.7% identity in amino acid sequence to PvP5CS, suggesting PvP5CS2 represents a homolog of the soybean P5CS gene. Abundant indel (insertion and deletion events) and SNP (single nucleotide polymorphisms) were found in the cloned PvP5CS2 genome sequence when comparing 24 cultivated and 3 wild common bean accessions and these in turn reflected aspects of common bean evolution. Sequence alignment showed that genotypes from the same gene pool had similar nucleotide variation, while genotypes from different gene pools had distinctly different nucleotide variation for PvP5CS2. Furthermore, diversity along the gene sequence was not evenly distributed, being low in the glutamic-g-semialdehyde dehydrogenase catalyzing region, moderate in the Glu-5-kinase catalyzing region and high in the intervening region. Neutrality tests showed that PvP5CS2 was a conserved gene undergoing negative selection. A new marker (Pv97) was developed for genetic mapping of PvP5CS2 based on an indel between DOR364 and G19833 sequences and the gene was located between markers Bng126 and BMd045 on chromosome b01. The relationship of PvP5CS2 and a previously cloned pyrroline-5-carboxylate synthetase gene as well as the implications of this work on selecting for drought tolerance in common bean are discussed.

Cloning the PvP5CS gene from common bean (Phaseolus vulgaris) and its expression patterns under abiotic stresses

A full-length cDNA denominated PvP5CS for Delta(1)-pyrroline-5-carboxylate synthetase (P5CS), an enzyme involved in the biosynthesis of proline, was cloned from common bean using a candidate gene approach. PvP5CS contains an open reading frame encoding a 716 amino acid polypeptide. Sequence analysis showed that PvP5CS shares 95.1% homology in nucleotide sequence and 93.2% identity in amino acid sequence with the mothbean (Vigna aconitifolia) P5CS. The expression patterns of PvP5CS in common bean treated with drought, cold (4 degrees C), and salt (200 mM NaCl) stresses were examined using real-time quantitative PCR. These abiotic stresses caused significant up-regulation of the expression of PvP5CS in leaves. The PvP5CS mRNA transcript increased to 2.5 times the control level after 4d drought stress. A rapid up-regulation of PvP5CS, to about 16.3 times the control at 2h post-treatment was observed under salt stress. A significant increase in PvP5CS expression (11.7-fold) was detected after 2h of cold stress. The peaks of proline accumulation appeared at 8d for drought, 24h for cold and 9h for salt stress, somewhat later than the peaks of PvP5CS expression. These results suggest that PvP5CS was a stress-inducible gene regulating the accumulation of proline in plants subjected to stress. Finally, subcellular localization assays showed that the PvP5CS protein was present in the nucleus and at the plasmalemma.