Perception Of Salt Stress Research Articles

Salt stress perception and metabolic regulation network analysis of a marine probiotic Meyerozyma guilliermondii GXDK6.

Extremely salt-tolerant microorganisms play an important role in the development of functional metabolites or drug molecules. In this work, the salt stress perception and metabolic regulation network of a marine probiotic Meyerozyma guilliermondii GXDK6 were investigated using integrative omics technology. Results indicated that GXDK6 could accept the salt stress signals from signal transduction proteins (e.g., phosphorelay intermediate protein YPD1), thereby contributing to regulating the differential expression of its relevant genes (e.g., CTT1, SOD) and proteins (e.g., catalase, superoxide dismutase) in response to salt stress, and increasing the salt-tolerant viability of GXDK6. Omics data also suggested that the transcription (e.g., SMD2), translation (e.g., MRPL1), and protein synthesis and processing (e.g., inner membrane protein OXA1) of upregulated RNAs may contribute to increasing the salt-tolerant survivability of GXDK6 by improving protein transport activity (e.g., Small nuclear ribonucleoprotein Sm D2), anti-apoptotic ability (e.g., 54S ribosomal protein L1), and antioxidant activity (e.g., superoxide dismutase). Moreover, up to 65.9% of the differentially expressed genes/proteins could stimulate GXDK6 to biosynthesize many salt tolerant-related metabolites (e.g., β-alanine, D-mannose) and drug molecules (e.g., deoxyspergualin, calcitriol), and were involved in the metabolic regulation of GXDK6 under high NaCl stress. This study provided new insights into the exploration of novel functional products and/or drugs from extremely salt-tolerant microorganisms.Graphical Abstract.

Plant salt response: Perception, signaling, and tolerance.

Salt stress is one of the significant environmental stressors that severely affects plant growth and development. Plant responses to salt stress involve a series of biological mechanisms, including osmoregulation, redox and ionic homeostasis regulation, as well as hormone or light signaling-mediated growth adjustment, which are regulated by different functional components. Unraveling these adaptive mechanisms and identifying the critical genes involved in salt response and adaption are crucial for developing salt-tolerant cultivars. This review summarizes the current research progress in the regulatory networks for plant salt tolerance, highlighting the mechanisms of salt stress perception, signaling, and tolerance response. Finally, we also discuss the possible contribution of microbiota and nanobiotechnology to plant salt tolerance.

Identifying Novel Genes and Proteins Involved in Salt Stress Perception and Signaling of Rice Seedlings.

Rice is one of the most important crops worldwide. Crop production is constrained markedly, however, by abiotic stresses such as salinity. To elucidate early stress response signaling networks involved in rice, we report in this study an original quantitative proteomic analysis of the rice seedlings subjected to short-term salt stress. We detected 570 differentially regulated proteins (DRPs) in the root sample. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis demonstrated that DRPs of the root were mainly involved in membrane trafficking, kinase activity, and ion toxicity responses. Interactome analysis revealed the central role of root proteins involved in membrane trafficking in the early response to salinity, such as cell surface receptor-like kinases (RLKs), phosphatidylinositols (PIs), calcium-dependent protein kinases 1 and 5, calcineurin B-like protein-interacting proteins, protein phosphatase 2C (PP2C) inhibitors, and abscisic acid receptors (PYL5/10), indicating activation of S-type anion channel. Furthermore, the proteogenomic analysis revealed 128 unique genome search-specific peptides with high-quality mass spectromety (MS/MS) spectra. We identified 38 novel protein-coding genes, refined the annotation of 17 existing gene models, and suggested several novel stress-responsive proteins, such as RLK5, peroxidase 27, and growth-regulating factor 2. Novel peptides had an ortholog match in the curated protein sequence set of other plant species. In conclusion, this study identifies novel stress-responsive proteins and genes of rice, thus warrant future consideration as candidates for molecular breeding of stress-tolerant crop varieties.

Transcriptome of Cenostigma pyramidale roots, a woody legume, under different salt stress times.

Salinity stress has a significant impact on the gain of plant biomass. Our study provides the first root transcriptome of Cenostigma pyramidale, a tolerant woody legume from a tropical dry forest, under three different salt stress times (30 min, 2 h, and 11 days). The transcriptome was assembled using the RNA sequencing (RNA-Seq) de novo pipeline from GenPipes. We observed 932, 804, and 3157 upregulated differentially expressed genes (DEGs) and 164, 273, and 1332 downregulated DEGs for salt over 30 min, 2 h, and 11 days, respectively. For DEGs annotated with the Viridiplantae clade in the early stress periods, the response to salt stress was mainly achieved by stabilizing homeostasis of such ions like Na+ and K+ , signaling by Ca2+ , transcription factor modulation, water transport, and oxidative stress. For salt stress at 11 days, we observed a higher modulation of transcription factors including the WRKY, MYB, bHLH, NAC, HSF, and AP2-EREBP families, as well as DEGs involved in hormonal responses, water transport, sugar metabolism, proline, and reactive oxygen scavenging mechanisms. Five selected DEGs (K+ transporter, aquaporin, glutathione S-transferase, cyclic nucleotide-gated channel, and superoxide dismutase) were validated by qPCR. Our results indicated that C. pyramidale had an early perception of salt stress modulating ionic channels and transporters, and as the stress progressed, the focus turned to the antioxidant system, aquaporins, and complex hormone responses. The results of this first root transcriptome provide clues on how this native species modulate gene expression to achieve salt stress tolerance.

The contribution of SERF1 to root-to-shoot signaling during salinity stress in rice

Stress perception and communication play important roles in the adaptation of plants to changing environmental conditions. Plant roots are the first organs to detect changes in the soil water potential induced by salt stress. In the presence of salinity stress, root-to-shoot communication occurs to adjust the growth of the whole plant. So far, the phytohormone abscisic acid (ABA), hydraulic signals and reactive oxygen species (ROS) have been proposed to mediate this communication under salt stress. Recently, we identified the rice transcription factor SALT-RESPONSIVE ERF1 (SERF1), which regulates a ROS-dependent transcriptional cascade in roots required for salinity tolerance. Upon salt stress, SERF1 knockout mutant plants show an increased leaf temperature as compared with wild type. As this occurs within the first 20 min of salt stress, we here evaluated the involvement of SERF1 in the perception of salt stress in the shoot. By metabolic profiling and expression analysis we show that the action of SERF1 in signal communication to the shoot is independent from ABA, but does affect the accumulation of ROS-related metabolites and transcripts under short-term salt stress.

Salt-responsive ERF1 regulates reactive oxygen species-dependent signaling during the initial response to salt stress in rice.

Early detection of salt stress is vital for plant survival and growth. Still, the molecular processes controlling early salt stress perception and signaling are not fully understood. Here, we identified salt-responsive ERF1 (SERF1), a rice (Oryza sativa) transcription factor (TF) gene that shows a root-specific induction upon salt and hydrogen peroxide (H2O2) treatment. Loss of SERF1 impairs the salt-inducible expression of genes encoding members of a mitogen-activated protein kinase (MAPK) cascade and salt tolerance-mediating TFs. Furthermore, we show that SERF1-dependent genes are H2O2 responsive and demonstrate that SERF1 binds to the promoters of MAPK kinase kinase6 (MAP3K6), MAPK5, dehydration-responsive element bindinG2A (DREB2A), and zinc finger protein179 (ZFP179) in vitro and in vivo. SERF1 also directly induces its own gene expression. In addition, SERF1 is a phosphorylation target of MAPK5, resulting in enhanced transcriptional activity of SERF1 toward its direct target genes. In agreement, plants deficient for SERF1 are more sensitive to salt stress compared with the wild type, while constitutive overexpression of SERF1 improves salinity tolerance. We propose that SERF1 amplifies the reactive oxygen species-activated MAPK cascade signal during the initial phase of salt stress and translates the salt-induced signal into an appropriate expressional response resulting in salt tolerance.

THE ROLE OF CALCIUM IN PLANTS' SALT TOLERANCE

High concentrations of sodium (Na) are toxic to most plant species, making soil salinity a major abiotic stress in plant productivity world wide. It has been shown that, calcium (Ca2+) is an important determinant for plant salt tolerance and confers protective effects on plants under growing in sodic soils. Calcium plays an essential role in processes that preserve the structural and functional integrity of plant cell membranes, stabilizes cell wall structures, regulates ion transport and selectivity, and controls ion-exchange behavior as well as cell wall enzyme activities. The nature of these responses will vary depending on the plant genotype. One of the essential functions of Ca2+ is acting as a second messenger in stress signaling. Genetic evidence suggests that perception of salt stress leads to a cytosolic calcium-signal that activates the calcium sensor protein SOS3. SOS3 binds to and activates a ser/thr protein kinase SOS2. The activated SOS2 kinase regulates the activities of SOS1, a plasma membrane Na+/H+ antiporter, and NHX1, a tonoplast Na+/H+ antiporter. This results in either Na+ efflux out of cytosol or its compartmentation in vacuole.

Proteomic Study of the Impact of Hik33 Mutation in Synechocystis sp. PCC 6803 under Normal and Salt Stress Conditions

Cyanobacteria are the only prokaryotes possessing plasma, thylakoid, and outer membranes. The plasma membrane of a cyanobacterial cell is essential for the biogenesis of cyanobacterial photosystems and serves as a barrier against environmental stress. We previously identified dozens of salt-responsive proteins in the plasma membrane of Synechocystis sp. PCC 6803. Five histidine kinases (Hiks) including Hik33 were also proposed to be involved in the perception of salt stress in Synechocystis. In this study, we analyzed proteomic profiles of the plasma membrane from a hik33-knockout mutant (ΔHik33) under normal and salt-stress conditions. Using 2D-DIGE followed by mass spectrometry analysis, we identified 26 differentially expressed proteins in ΔHik33 mutant cells. Major changes, due to the Hik33 mutation, included the substrate-binding proteins of ABC transporters, such as GgtB and FutA1, regulatory proteins including MorR and Rre13, as well as several hypothetical proteins. Under salt-stress conditions, the Hik33 mutation reduced levels of 7 additional proteins, such as NrtA, nitrate/sulfonate/bicarbonate-binding protein and LexA, and enhanced levels of 9 additional proteins including SphX. These observations suggest a substantial rearrangement in the plasma membrane proteome of Synechocystis due to the loss of hik33. Furthermore, a comprehensive molecular network was revealed in ΔHik33 mutant coping with salt stress.

A Receptor-Like Kinase That Functions in Adaptation to Salt Stress in Legumes

show that Srlk is rapidly induced by salt stress in M. truncatula roots, rather than in response to mannitol or cold temperature. Experiments with the Srlk-promoter fused to a b-glucuronidase marker gene showed that Srlk expression is strongly induced in root epidermal cells in response to salt. Repression of Srlk using RNA interference (RNAi) and mutations of Srlk introduced through TILLING prevented the inhibition of root growth under high salt conditions (see figure). In addition, Srlk mutant plants were found to accumulate significantly less sodium than control plants. Finally, several other salt-induced genes showed drastically reduced levels of induction following salt stress in the Srlk mutants relative to controls. RLKs possess an extracellular domain connected via a transmembrane domain to a cytoplasmic kinase. Plants contain hundreds of RLKs, which are thought to have overlapping or distinct roles in perceiving environmental and developmental signals and transducing these signals to downstream effectors (reviewed in Morillo and Tax, 2006). The results of de Lorenzo et al. suggest that Srlk may play a primary role in the perception of salt stress by M. truncatula roots and the ability of the plant to accumulate sodium under high salt conditions. Plant response to high salt and other stresses is highly complex, making genetic modification of plants for improved stress tolerance difficult to achieve (Wang et al., 2003). It will be important to identify downstream signaling partners and target genes of Srlk in the response and adaptation to salt stress. This work opens a new pathway for investigation and enhanced prospects for the development of improved salt tolerance in

The involvement of calcium in the regulation of GPX1 expression

Detrimental effects of salinity on plants are known to be partially alleviated by external Ca(2+). Previously we demonstrated that in citrus cells, phospholipid hydroperoxide glutathione peroxidase (GPX1) is induced by salt and its activation can be monitored by pGPX1::GUS fusion in transformed tobacco cells. In this paper we further characterized the induction of GPX1 by additional treatments, which are known to affect Ca(2+) transport. Omission of Ca(2+) changed the pattern of the transient salt-induced expression of GPX1 and chelation of Ca(2+) by EGTA, or treatment with caffeine, abolished the salt-induced GPX1 transcript. On the other hand, La(3+) was found to be as potent as NaCl in inducing GPX1 transcription and the combined effect of La(3+) and NaCl seemed to be additive. Pharmacological perturbation of either external or internal Ca(2+) pools by La(3+), EGTA, caffeine, Ca(2+) channel blockers, or a Ca(2+)-ATPase inhibitor rendered the imposed salt stress more severe. Except for La(3+), all these Ca(2+) effectors had no effect on their own. In addition, the fluidizer benzyl alcohol dramatically increased the NaCl-induced GPX1 transcription. Taken together, our results show that: 1) the mode of action of La(3+) on GPX1 expression differs from its established role as a Ca(2+) channel blocker, 2) membrane integrity has an important role in the perception of salt stress, and 3) internal stores of Ca(2+) are involved in activating GPX1 expression in response to salt stress. We propose that the common basis for these effects lies in the membrane bound Ca(2+).

Sodium sensing induces different changes in free cytosolic calcium concentration and pH in salt‐tolerant and ‐sensitive rice (Oryza sativa) cultivars

Perception of salt stress in plant cells induces a change in the free cytosolic Ca2+, [Ca2+]cyt, which transfers downstream reactions toward salt tolerance. Changes in cytosolic H+ concentration, [H+]cyt, are closely linked to the [Ca2+]cyt dynamics under various stress signals. In this study, salt‐induced changes in [Ca2+]cyt, and [H+]cyt and vacuolar [H+] concentrations were monitored in single protoplasts of rice (Oryza sativa L. indica cvs. Pokkali and BRRI Dhan29) by fluorescence microscopy. Changes in cytosolic [Ca2+] and [H+] were detected by use of the fluorescent dyes acetoxy methyl ester of calcium‐binding benzofuran and acetoxy methyl ester of 2′, 7′‐bis‐(2‐carboxyethyl)‐5‐(and‐6) carboxyfluorescein, respectively, and for vacuolar pH, fluorescent 6‐carboxyfluorescein and confocal microscopy were used. Addition of NaCl induced a higher increase in [Ca2+]cyt in the salt‐tolerant cv. Pokkali than in the salt‐sensitive cv. BRRI Dhan29. From inhibitor studies, we conclude that the internal stores appear to be the major source for [Ca2+]cyt increase in Pokkali, although the apoplast is more important in BRRI Dhan29. The [Ca2+]cyt measurements in rice also suggest that Na+ should be sensed inside the cytosol, before any increase in [Ca2+]cyt occurs. Moreover, our results with individual mesophyll protoplasts suggest that ionic stress causes an increase in [Ca2+]cyt and that osmotic stress sharply decreases [Ca2+]cyt in rice. The [pH]cyt was differently shifted in the two rice cultivars in response to salt stress and may be coupled to different activities of the H+‐ATPases. The changes in vacuolar pH were correlated with the expressional analysis of rice vacuolar H+‐ATPase in these two rice cultivars.

Salinity-induced ion flux patterns from the excised roots of Arabidopsis sos mutants

The SOS signal-transduction pathway is known to be important for ion homeostasis and salt tolerance in plants. However, there is a lack of in planta electrophysiological data about how the changes in signalling and ion transport activity are integrated at the cellular and tissue level. In this study, using the non-invasive ion flux MIFE technique, we compared net K+, H+ and Na+ fluxes from elongation and mature root zones of Arabidopsis wild type Columbia and sos mutants. Our results can be summarised as follows: (1) SOS mutations affect the function of the entire root, not just the root apex; (2) SOS signalling pathway is highly branched; (3) Na+ effects on SOS1 may by-pass the SOS2/SOS3 complex in the root apex; (4) SOS mutation affects H+ transport even in the absence of salt stress; (5) SOS1 mutation affects intracellular K+ homeostasis with a plasma membrane depolarisation-activated outward-rectifying K+ channel being a likely target; (6) H+ pump also may be a target of SOS signalling. We provide an improved model of SOS signalling and discuss physiological mechanisms underlying salt stress perception and signalling in plants. Our work shows that in planta studies are essential for understanding the functional genomics of plant salt tolerance.

Identical Hik-Rre Systems Are Involved in Perception and Transduction of Salt Signals and Hyperosmotic Signals but Regulate the Expression of Individual Genes to Different Extents in Synechocystis

In previous studies, we characterized five histidine kinases (Hiks) and the cognate response regulators (Rres) that control the expression of approximately 70% of the hyperosmotic stress-inducible genes in the cyanobacterium Synechocystis sp. PCC 6803. In the present study, we screened a gene knock-out library of Rres by RNA slot-blot hybridization and with a genome-wide DNA microarray and identified three Hik-Rre systems, namely, Hik33-Rre31, Hik10-Rre3, and Hik16-Hik41-Rre17, as well as another system that included Rre1, that were involved in perception of salt stress and transduction of the signal. We found that these Hik-Rre systems were identical to those that were involved in perception and transduction of the hyperosmotic stress signal. We compared the induction factors of the salt stress- and hyperosmotic stress-inducible genes that are located downstream of each system and found that these genes responded to the two kinds of stress to different respective extents. In addition, the Hik33-Rre31 system regulated the expression of genes that were specifically induced by hyperosmotic stress, whereas the system that included Rre1 regulated the expression of one or two genes that were specifically induced either by salt stress or by hyperosmotic stress. Our observations suggest that the perception of salt and hyperosmotic stress by the Hik-Rre systems is complex and that salt stress and hyperosmotic stress are perceived as distinct signals by the Hik-Rre systems.

Understanding and Improving Salt Tolerance in Plants

One‐fifth of irrigated agriculture is adversely affected by soil salinity. Hence, developing salt‐tolerant crops is essential for sustaining food production. Progress in breeding for salt‐tolerant crops has been hampered by the lack of understanding of the molecular basis of salt tolerance and lack of availability of genes that confer salt tolerance. Genetic evidence suggests that perception of salt stress leads to a cytosolic calcium‐signal that activates the calcium sensor protein SOS3. SOS3 binds to and activates a ser/thr protein kinase SOS2. The activated SOS2 kinase regulates activities of SOS1, a plasma membrane Na+/H+ antiporter, and NHX1, a tonoplast Na+/H+ antiporter. This results in Na+ efflux and vacuolar compartmentation. A putative osmosensory histidine kinase (AtHK1)‐MAPK cascade probably regulates osmotic homeostasis and ROS scavenging. Osmotic stress and ABA (abscisic acid)‐mediated regulation of LEA (late‐embryogenesis‐abundant)‐type proteins also play important roles in plant salt tolerance. Genetic engineering of ion transporters and their regulators, and of the CBF (C‐repeat‐binding factor) regulons, holds promise for future development of salt‐tolerant crops.

식물의 고염 스트레스에 대한 반응 및 적응기작

Plant responses to salinity stress is critical in determining the growth and development. Therefore, adaptability of plant to salinity stress is directly related with agriculture productivity. Salt adaptation is a result of the integrated functioning of numerous determinants that are regulated coordinately through an appropriate responsive signal transduction cascade. The cascade perceives the saline environment and exerts control over the essential mechanisms that are responsible for ion homeostasis and osmotic adjustment. Although little is known about the component elements of salt stress perception and the signaling cascade(s) in plant, the use of Arabidopsis plant as a molecular genetic tool has been provided important molecular nature of salt tolerance effectors and regulatory pathways. In this review, I summarize recent advances in understanding the molecular mechanisms of salt adaptation.

Identification of histidine kinases that act as sensors in the perception of salt stress in Synechocystis sp. PCC 6803.

In plants and microorganisms, salt stress regulates the expression of large numbers of genes. However, the machinery that senses salt stress remains to be characterized. In this study we identified sensory histidine kinases that are involved in the perception of salt stress in the cyanobacterium Synechocystis sp. strain PCC 6803. A library of strains with mutations in all 43 histidine kinases was screened by DNA microarray analysis of genomewide gene expression under salt stress. The results suggested that four histidine kinases, namely, Hik16, Hik33, Hik34, and Hik41, perceived and transduced salt signals. However, Hik33, Hik34, and Hik16 acting with Hik41 regulated the expression of different sets of genes. These histidine kinases regulated the expression of approximately 20% of the salt-inducible genes, whereas the induction of the remaining salt-inducible genes was unaffected by mutations in any of the histidine kinases, suggesting that additional sensory mechanisms might operate in the perception of salt stress. We also used DNA microarrays to investigate the effect of various salts on gene expression. Our results indicate that Hik33 responds to sodium salts and not to KCl, whereas the Hik16/Hik41 system responds only to NaCl.

Ionic and osmotic components of salt stress specifically modulate net ion fluxes from bean leaf mesophyll

ABSTRACTIonic mechanisms of salt stress perception were investigated by non‐invasive measurements of net H+, K+, Ca2+, Na+, and Cl− fluxes from leaf mesophyll of broad bean (Vicia faba L.) plants using vibrating ion‐selective microelectrodes (the MIFE technique). Treatment with 90 m M NaCl led to a significant increase in the net K+ efflux and enhanced activity of the plasma membrane H+‐pump. Both these events were effectively prevented by high (10 m M) Ca2+ concentrations in the bath. At the same time, no significant difference in the net Na+ flux has been found between low‐ and high‐calcium treatments. It is likely that plasma membrane K+ and H+ transporters, but not the VIC channels, play the key role in the amelioration of negative salt effects by Ca2+ in the bean mesophyll. Experiments with isotonic mannitol application showed that cell ionic responses to hyperosmotic treatment are highly stress‐specific. The most striking difference in response was shown by K+ fluxes, which varied from an increased net K+ efflux (NaCl treatment) to a net K+ influx (mannitol treatment). It is concluded that different ionic mechanisms are involved in the perception of the ‘ionic’ and ‘osmotic’ components of salt stress.