Stress Signaling In Plants Research Articles

Global Plant Stress Signaling: Reactive Oxygen Species at the Cross-Road.

Current technologies have changed biology into a data-intensive field and significantly increased our understanding of signal transduction pathways in plants. However, global defense signaling networks in plants have not been established yet. Considering the apparent intricate nature of signaling mechanisms in plants (due to their sessile nature), studying the points at which different signaling pathways converge, rather than the branches, represents a good start to unravel global plant signaling networks. In this regard, growing evidence shows that the generation of reactive oxygen species (ROS) is one of the most common plant responses to different stresses, representing a point at which various signaling pathways come together. In this review, the complex nature of plant stress signaling networks will be discussed. An emphasis on different signaling players with a specific attention to ROS as the primary source of the signaling battery in plants will be presented. The interactions between ROS and other signaling components, e.g., calcium, redox homeostasis, membranes, G-proteins, MAPKs, plant hormones, and transcription factors will be assessed. A better understanding of the vital roles ROS are playing in plant signaling would help innovate new strategies to improve plant productivity under the circumstances of the increasing severity of environmental conditions and the high demand of food and energy worldwide.

Regulation of the drought response of sweet pepper (Capsicum annuum L.) by foliar-applied hormones, in Mediterranean-climate greenhouse conditions

Plant hormones play an important role in regulating stress responses and signaling in plants; many of them act to alleviate environmental stresses. However, the specific effects and physiological changes could be significantly altered according to the crop species, application concentration and frequency, and cultivation conditions. In this study, we investigated the effect of leaf-applied abscisic acid (ABA), gibberellic acid (GA3), and indole-3-acetic acid (IAA) on plant growth before, during, and after water stress. The objective was to determine their effects on pepper plants (Capsicum annuum L.) in commercial greenhouse conditions, specifically their ability to mitigate water stress, through the study of different stress traits—such as plant growth, gas exchange parameters, chlorophyll content and fluorescence, ascorbate peroxidase activity, total phenolic compounds, and lipid peroxidation. While ABA and IAA heightened the water shortage in the leaves along the experiment, GA3 diminished it. The effects of ABA involved short-term responses, such as stomatal closure and decreased transpiration, and long-term changes, affecting the ratios and concentrations of chlorophylls. Moreover, GA3 complicated the crop management since the plants suffered high stress when treated with this hormone. The results obtained represent a first approach to studying the effect of foliar hormone application in sweet pepper and its ability to regulate (mitigate or amplify) the water stress suffered by the plant under greenhouse conditions.

β-Substituting alanine synthases: roles in cysteine metabolism and abiotic and biotic stress signalling in plants.

Cysteine is required for the synthesis of proteins and metabolites, and is therefore an indispensable compound for growth and development. The β-substituting alanine synthase (BSAS) gene family encodes enzymes known as O-acetylserine thiol lyases (OASTLs), which carry out cysteine biosynthesis in plants. The functions of the BSAS isoforms have been reported to be crucial in assimilation of S and cysteine biosynthesis, and homeostasis in plants. In this review we explore the functional variation in this classic pyridoxal-phosphate-dependent enzyme family of BSAS isoforms. We discuss how specialisation and divergence in BSAS catalytic activities makes a more dynamic set of biological routers that integrate cysteine metabolism and abiotic and biotic stress signalling in Arabidopsis thaliana (L.) Heynh. and also other species. Our review presents a universal scenario in which enzymes modulating cysteine metabolism promote survival and fitness of the species by counteracting internal and external stress factors.

Improved drought and salt tolerance of Arabidopsis thaliana by ectopic expression of a cotton (Gossypium hirsutum) CBF gene

Osmotic stress associated with drought or salinity is a major factor that limits plant growth and productivity. CBF transcription factors play key roles in plant stress signaling transduction pathway. In this work, the data revealed that GhCBF3 identified in cotton (Gossypium hirsutum L.) was remarkably induced by NaCl, mannitol and abscisic acid (ABA). Histochemical assay of GUS activity revealed that GhCBF3 promoter was active in stomata guard cells of the GhCBF3p:GUS transgenic seedlings, and its activity was salt- and osmotic-inducible. Overexpression of GhCBF3 in Arabidopsis resulted in the increased drought- and high salinity-tolerance, but led to an ABA-sensitive phenotype of the transgenic plants. In the presence of NaCl and mannitol, rates of seed germination and cotyledon greening of the GhCBF3 overexpression transgenic plants were higher than those of wild type. Relative water content, proline content and chlorophyll content in the GhCBF3 transgenic seedlings were higher than those in wild type. The GhCBF3 transgenic plants showed greater salt- and drought-tolerance, compared with wild type. In the presence of ABA, stomatal aperture in leaves of the transgenic plants was smaller than that in wild type, and expression levels of AREB1 and AREB2 in the transgenic leaves was remarkably higher than those in wild type. Furthermore, expression of some stress-related genes was altered in the GhCBF3 transgenic plants. These data suggested that GhCBF3 may be involved in regulating stomata closure, thereby enhance plant salt and drought tolerance via ABA signaling pathway.

Plant Raf-like kinase integrates abscisic acid and hyperosmotic stress signaling upstream of SNF1-related protein kinase2.

Plant response to drought and hyperosmosis is mediated by the phytohormone abscisic acid (ABA), a sesquiterpene compound widely distributed in various embryophyte groups. Exogenous ABA as well as hyperosmosis activates the sucrose nonfermenting 1 (SNF1)-related protein kinase2 (SnRK2), which plays a central role in cellular responses against drought and dehydration, although the details of the activation mechanism are not understood. Analysis of a mutant of the moss Physcomitrella patens with reduced ABA sensitivity and reduced hyperosmosis tolerance revealed that a protein kinase designated "ARK" (for "ABA and abiotic stress-responsive Raf-like kinase") plays an essential role in the activation of SnRK2. ARK encoded by a single gene in P. patens belongs to the family of group B3 Raf-like MAP kinase kinase kinases (B3-MAPKKKs) mediating ethylene, disease resistance, and salt and sugar responses in angiosperms. Our findings indicate that ARK, as a novel regulatory component integrating ABA and hyperosmosis signals, represents the ancestral B3-MAPKKKs, which multiplied, diversified, and came to have specific functions in angiosperms.

ABA Regulates Subcellular Redistribution of OsABI-LIKE2, a Negative Regulator in ABA Signaling, to Control Root Architecture and Drought Resistance in Oryza sativa.

The phytohormone ABA is a key stress signal in plants. Although the identification of ABA receptors led to significant progress in understanding the Arabidopsis ABA signaling pathway, there are still many unsolved mysteries regarding ABA signaling in monocots, such as rice. Here, we report that a rice ortholog of AtABI1 and AtABI2, named OsABI-LIKE2 (OsABIL2), plays a negative role in rice ABA signaling. Overexpression of OsABIL2 not only led to ABA insensitivity, but also significantly altered plant developmental phenotypes, including stomatal density and root architecture, which probably caused the hypersensitivity to drought stress. OsABIL2 interacts with OsPYL1, SAPK8 and SAPK10 both in vitro and in vivo, and the phosphatase activity of OsABIL2 was repressed by ABA-bound OsPYL1. However, unlike many other solely nuclear-localized clade A type 2C protein phosphatases (PP2Cs), OsABIL2 is localized in both the nucleus and cytosol. Furthermore, OsABIL2 interacts with and co-localized with OsPYL1 mainly in the cytosol, and ABA treatment regulates the nucleus-cytosol distribution of OsABIL2, suggesting a different mechanism for the activation of ABA signaling. Taken together, this study provides significant insights into rice ABA signaling and indicates the important role of OsABIL2 in regulating root development.

Transcriptome Profiling of the Endophyte Burkholderia phytofirmans PsJN Indicates Sensing of the Plant Environment and Drought Stress.

ABSTRACTIt is widely accepted that bacterial endophytes actively colonize plants, interact with their host, and frequently show beneficial effects on plant growth and health. However, the mechanisms of plant-endophyte communication and bacterial adaption to the plant environment are still poorly understood. Here, whole-transcriptome sequencing of B. phytofirmans PsJN colonizing potato (Solanum tuberosum L.) plants was used to analyze in planta gene activity and the response of strain PsJN to plant stress. The transcriptome of PsJN colonizing in vitro potato plants showed a broad array of functionalities encoded in the genome of strain PsJN. Transcripts upregulated in response to plant drought stress were mainly involved in transcriptional regulation, cellular homeostasis, and the detoxification of reactive oxygen species, indicating an oxidative stress response in PsJN. Genes with modulated expression included genes for extracytoplasmatic function (ECF) group IV sigma factors. These cell surface signaling elements allow bacteria to sense changing environmental conditions and to adjust their metabolism accordingly. TaqMan quantitative PCR (TaqMan-qPCR) was performed to identify ECF sigma factors in PsJN that were activated in response to plant stress. Six ECF sigma factor genes were expressed in PsJN colonizing potato plants. The expression of one ECF sigma factor was upregulated whereas that of another one was downregulated in a plant genotype-specific manner when the plants were stressed. Collectively, our study results indicate that endophytic B. phytofirmans PsJN cells are active inside plants. Moreover, the activity of strain PsJN is affected by plant drought stress; it senses plant stress signals and adjusts its gene expression accordingly.

Wheat NAC transcription factor TaNAC29 is involved in response to salt stress

Soil salinity is considered as one of the most severe abiotic stress factors, which limit plant growth and cause significant losses in crop yield. NAC transcription factors have been proven to play vital roles in abiotic stress signaling in plants. As a staple crop, wheat production is severely constrained by salt stress whereas only a few NAC genes have been characterized functionally. To promote the application of NAC genes in wheat improvement by genetic engineering, a NAC gene designated TaNAC29 was characterized in common wheat. Expression analysis showed that TaNAC29 gene was involved in response to salt, drought and ABA treatments. TaNAC29 protein displays transactivation activity. To determine its role, transgenic Arabidopsis overexpressing TaNAC29 controlled by the CaMV-35S promoter was generated and subjected to salt stress for morphological and physiological assays. Morphological analysis showed that transgenic plants had enhanced tolerance to salt stress, as indicated by improved physiological traits, including more green leaves, reduced H2O2 accumulation, strengthened cell membrane stability and higher SOD, POD, CAT and APX activities. Moreover, the transcript levels of stress-related genes were significantly higher in TaNAC29 overexpression line than those in WT under salt treatment. Taken together, our results demonstrate that TaNAC29 confers salt stress tolerance through reducing H2O2 accumulation and membrane damage by enhancing the antioxidant system, and participating in regulating the abiotic stress-responsive signaling pathway.

Genome-wide identification, expression profiling, and SSR marker development of the bZIP transcription factor family in Medicago truncatula

The basic leucine zipper (bZIP) transcription factors have been shown to play great roles in pathogen defense, light and stress signalling, seed maturation and flower development in plants. However, no reports about this transcription factor family have been reported in grass species, including the model dicotyledonous grass species Medicago truncatula. In the present study, we have identified 75 bZIP transcription factor-encoding genes in the M. truncatula genome. The phylogenetic analysis of these bZIP protein sequences permits classification of them into 12 groups. The chromosome distribution analyses suggesting that bZIP genes in M. truncatula are not recently generated by gene duplication. The results of the identification of intron/exon structural and conserved motifs showed that there is a high group-specificity in all MtbZIP genes. Expression of bZIP transcription factor-encoding genes indicates specific or coexpression patterns of MtbZIP genes involved in organ development, drought-responses and salt-responses. In addition, 104 SSRs specific to 53 MtbZIP genes were detected and 97 primer pairs were developed. The validation of 30 randomly selected primer pairs in 20 alfalfa cultivars showed 17 of them were true-to-type SSR loci and highly transferable among alfalfa cultivars. These results will be important for further cloning and functional characterization of bZIP transcription factors in M. truncatula.

Genetic reduction of inositol triphosphate (InsP₃) increases tolerance of tomato plants to oxidative stress.

We demonstrate here that the reduction of InsP 3 , the key component of the phosphoinositol pathway, results in changes in ROS-scavenging machinery and, subsequently, increases the tolerance of tomato plants to light stress. Different plant stress signaling pathways share similar elements and, therefore, 'cross-talk' between the various pathways can exist. Links between the phosphoinositol signaling pathway and light signaling were recently found. Tomato plants expressing InsP 5-ptase and exhibiting reduction in the level of inositol 1,4,5-triphosphate (InsP3) demonstrated enhanced tolerance to stress caused by continuous light exposure. To understand the molecular basis of observed stress tolerance in tomato lines with decreased amount of InsP3, we monitored the expression of enzymatic antioxidants as well as important factors in light signaling associated with non-enzymatic antioxidants (secondary metabolites). Here, we demonstrated that InsP 5-ptase transgenic plants accumulate less hydroxide peroxide and maintain higher chlorophyll content during stress caused by continuous light exposure. This observation can be explained by documented activation of multiple enzymatic antioxidants (LeAPX1, SICAT2, LeSOD) at levels of gene expression and enzymatic activities during continuous light exposure. In addition, we noticed the up-regulation of photoreceptors LePHYB and LeCHS1, key enzymes in flavonoid biosynthesis pathway, transcription factors LeHY5, SIMYB12, and early light-inducible protein (LeELIP) genes in transgenic tomato seedlings exposed to blue or red light. Our study confirmed the existence of a correlation between phosphoinositol signaling pathway modification, increased tolerance to stress caused by continuous light exposure, activation of ROS-scavenging enzymes, and up-regulation of molecular activators of non-enzymatic antioxidants in InsP 5-ptase expressing tomato lines.

Identification and characterization of an ABA-activated MAP kinase cascade in Arabidopsis thaliana.

Abscisic acid (ABA) is a major phytohormone involved in important stress-related and developmental plant processes. Recent phosphoproteomic analyses revealed a large set of ABA-triggered phosphoproteins as putative mitogen-activated protein kinase (MAPK) targets, although the evidence for MAPKs involved in ABA signalling is still scarce. Here, we identified and reconstituted in vivo a complete ABA-activated MAPK cascade, composed of the MAP3Ks MAP3K17/18, the MAP2K MKK3 and the four C group MAPKs MPK1/2/7/14. In planta, we show that ABA activation of MPK7 is blocked in mkk3-1 and map3k17mapk3k18 plants. Coherently, both mutants exhibit hypersensitivity to ABA and altered expression of a set of ABA-dependent genes. A genetic analysis further reveals that this MAPK cascade is activated by the PYR/PYL/RCAR-SnRK2-PP2C ABA core signalling module through protein synthesis of the MAP3Ks, unveiling an atypical mechanism for MAPK activation in eukaryotes. Our work provides evidence for a role of an ABA-induced MAPK pathway in plant stress signalling.

Stress-induced Oryza sativa BAT1 dual helicase exhibits unique bipolar translocation.

HLA-B associated transcript 1 (BAT1) protein, also named as spliceosome RNA helicase UAP56, is a member of the DExD/H-box family of helicases. However, regulation under stress, biochemical properties, and functions of plant homologue of BAT1 are poorly understood. Here, we report the purification and detailed biochemical characterization of the Oryza sativa homologue of BAT1 (OsBAT1/UAP56) protein (52kDa) and regulation of its transcript under abiotic stress. OsBAT1 transcript levels are enhanced in rice seedlings in response to abiotic stress including salt stress and abscisic acid. Purified OsBAT1 protein exhibits the DNA- and RNA-dependent ATPase, RNA helicase, and DNA- and RNA-binding activities. Interestingly OsBAT1 also exhibits unique DNA helicase activity, which has not been reported so far in any BAT1 homologue. Moreover, OsBAT1 translocates in both the 3' to 5' and 5' to 3' directions, which is also a unique property. The K m value for OsBAT1 DNA helicase is 0.9753nM and for RNA helicase is 1.7536nM, respectively. This study demonstrates several unique characteristics of OsBAT1 especially its ability to unwind both DNA and RNA duplexes; bipolar translocation and its transcript upregulation under abiotic stresses indicate that it is a multifunctional protein. Overall, this study represents significant contribution in advancing our knowledge regarding functions of OsBAT1 in RNA and DNA metabolism and its putative role in abiotic stress signaling in plants.

Distribution and evolution of the lectin family in soybean (Glycine max).

Lectins are a diverse group of proteins that bind specific carbohydrates and are found throughout all kingdoms. In plants, lectins are involved in a range of important processes such as plant defense and stress signaling. Although the genome sequence of Glycine max (soybean) has been published, little is known about the abundance and expansion patterns of lectin genes in soybean. Using BLAST and hidden Markov models, a total of 359 putative lectin genes have been identified. Furthermore, these sequences could be classified in nine of the twelve plant lectin families identified today. Analysis of the domain organization demonstrated that most of the identified lectin genes encode chimerolectins, consisting of one or multiple lectin domains combined with other known protein domains. Both tandem and segmental duplication events have contributed to the expansion of the lectin gene family. These data provide a detailed understanding of the domain architecture and molecular evolution of the lectin gene family in soybean.

Transcription factors and anthocyanin genes related to low-temperature tolerance in rd29A:RdreB1BI transgenic strawberry

Dehydration-responsive element-binding (DREB) transcription factors play critical roles in plant stress responses and signal transduction. To further understand how DREB regulates genes expression to promote cold-hardiness, Illumina/Solexa sequencing technology was used to compare the transcriptomes of non-transgenic and rd29A:RdreB1BI transgenic strawberry plants exposed to low temperatures. Approximately 3.5 million sequence tags were obtained from non-transgenic (NT) and transgenic (T) strawberry untreated (C) or low-temperature treated (LT) leaf samples. Over 1000 genes were differentially expressed between the NT-C and T-C plants, and also the NT-C and NT-LT, as well as the T-C and T-LT plants. Analysis of the genes up-regulated following low-temperature treatment revealed that the majority are linked to metabolism, biosynthesis, transcription and signal transduction. Uniquely up-regulated transcription factors as well as anthocyanin biosynthetic pathway genes are discussed. Accumulation of anthocyanin in the stolon and the base of the petiole differed between non-treated NT and T plants, and this correlated with gene expression patterns. The differentially expressed genes that encode transcription factors and anthocyanin enzymes may contribute to the cold hardiness of RdreB1BI transgenic strawberry. The transcriptome data provide a valuable resource for further studies of strawberry growth and development and DREB-mediated gene regulation under low-temperature stress.

A Buckwheat (Fagopyrum esculentum) DRE-Binding Transcription Factor Gene, FeDREB1, Enhances Freezing and Drought Tolerance of Transgenic Arabidopsis

CBF/DREB transcription factors play essential roles in plant stress signaling transduction pathway. We isolated and identified a CBF/DREB homologous gene, FeDREB1, from Fagopyrum esculentum. Protein sequence alignment and phylogenetic analyses revealed that the FeDREB1 was grouped into the DREB (A-1) lineage. Moreover, subcellular localization observations suggested that FeDREB1 localizes in the nucleus. Yeast one-hybrid assays showed that FeDREB1 protein specifically binds to the DRE sequence and could activate the expression of reporter genes in yeast. These results further suggested that the FeRDEB1 protein was a CBF/DREB transcription factor. Expression analysis revealed that the transcript levels of the FeRDEB1 gene increased rapidly following low-/high-temperature treatment, drought stress, and exogenous ABA treatment. Over-expression of the FeDREB1 gene significantly enhanced the drought and freezing tolerance of transgenic Arabidopsis but resulted in its growth retardation. Moreover, the transgenic Arabidopsis lines were also highly sensitive to ABA application. Digital gene expression profiling (DGE) analysis indicated that increased transcript levels of many ABA-independent/-dependent stress-responsive genes in 35S::FeRDEB1 transgenic Arabidopsis, revealing that the FeDREB1 may participate in an ABA-dependent/-independent pathways.

Effects of plant stress signal molecules on the production of wilforgine in an endophytic actinomycete isolated from Tripterygium wilfordii Hook.f.

The endophytic actinomycete F4-20 was isolated from Tripterygium wilfordii Hook.f. and was confirmed to produce wilforgine, a secondary metabolite discovered in its host. F4-20 showed a close phylogenetic relationship to Streptomyces species. To seek elicitors that may enhance the production of wilforgine in F4-20, four plant stress molecules were applied to the in vitro liquid cultures. Results showed that methyl jasmonate (MeJA), salicylic acid (SA), and hydrogen peroxide (H2O2) inhibited bacterial growth, whereas glutathione (GSH) treatment significantly increased bacterial growth. The wilforgine contents in the mycelia of F4-20 were reduced by MeJA and GSH but were induced by SA and H2O2. When added in the end of the culture period (7 day), 1mM SA and 5mM H2O2 resulted in 69.35±1.71 and 71.80±3.35µg/g DW of wilforgine production, 1.55 and 1.60 fold to that of control (44.83±1.35µg/g DW), respectively. Though this improved production was about 6.5 times lower than that of the natural root (454.00µg/g dry root bark), it provided an alternative method for the production of valuable plant secondary metabolites.

H2O2 inhibits ABA-signaling protein phosphatase HAB1.

Due to its ability to be rapidly generated and propagated over long distances, H2O2 is an important second messenger for biotic and abiotic stress signaling in plants. In response to low water potential and high salt concentrations sensed in the roots of plants, the stress hormone abscisic acid (ABA) activates NADPH oxidase to generate H2O2, which is propagated in guard cells in leaves to induce stomatal closure and prevent water loss from transpiration. Using a reconstituted system, we demonstrate that H2O2 reversibly prevents the protein phosphatase HAB1, a key component of the core ABA-signaling pathway, from inhibiting its main target in guard cells, SnRK2.6/OST1 kinase. We have identified HAB1 C186 and C274 as H2O2-sensitive thiols and demonstrate that their oxidation inhibits both HAB1 catalytic activity and its ability to physically associate with SnRK2.6 by formation of intermolecular dimers.

Hyperspectral detection of a subsurface CO2 leak in the presence of water stressed vegetation.

Remote sensing of vegetation stress has been posed as a possible large area monitoring tool for surface CO2 leakage from geologic carbon sequestration (GCS) sites since vegetation is adversely affected by elevated CO2 levels in soil. However, the extent to which remote sensing could be used for CO2 leak detection depends on the spectral separability of the plant stress signal caused by various factors, including elevated soil CO2 and water stress. This distinction is crucial to determining the seasonality and appropriateness of remote GCS site monitoring. A greenhouse experiment tested the degree to which plants stressed by elevated soil CO2 could be distinguished from plants that were water stressed. A randomized block design assigned Alfalfa plants (Medicago sativa) to one of four possible treatment groups: 1) a CO2 injection group; 2) a water stress group; 3) an interaction group that was subjected to both water stress and CO2 injection; or 4) a group that received adequate water and no CO2 injection. Single date classification trees were developed to identify individual spectral bands that were significant in distinguishing between CO2 and water stress agents, in addition to a random forest classifier that was used to further understand and validate predictive accuracies. Overall peak classification accuracy was 90% (Kappa of 0.87) for the classification tree analysis and 83% (Kappa of 0.77) for the random forest classifier, demonstrating that vegetation stressed from an underground CO2 leak could be accurately discerned from healthy vegetation and areas of co-occurring water stressed vegetation at certain times. Plants appear to hit a stress threshold, however, that would render detection of a CO2 leak unlikely during severe drought conditions. Our findings suggest that early detection of a CO2 leak with an aerial or ground-based hyperspectral imaging system is possible and could be an important GCS monitoring tool.

Tospo viral infection instigates necrosis and premature senescence by micro RNA controlled programmed cell death in Vigna unguiculata

Tospoviruses are the only plant infecting viruses belonging to the family Bunyavirideae. The most characteristic symptoms of tospoviral infection in different hosts are necrosis and premature senescence. To understand the mechanistic model of symptom development and the role of programmed cell death (PCD) during infection, we compared the levels of biochemical intermediates and stress responsive micro RNAs (miRNAs) with their target transcripts in Vigna unguiculata during Groundnut bud necrosis virus (GBNV) infection at the infection and systemic site. Appearance of chlorotic spots was the first visual symptom of GBNV infection. These spots turned to necrotic as the infection progressed. Premature senescence, starting from appearance of yellow mosaic followed by complete yellowing was observed in the systemic leaves. Necrosis (cell death) in the form of hypersensitive response (HR) was observed at the infection site, as judged by the accumulation of reactive oxygen species (ROS). In addition, we also found increased activities of antioxidant enzymes, such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) that are associated with detoxification of ROS. At this stage, down-regulation of miR398a regulating COX-5b, (Cytochrome C oxidase subunit 5b), responsible for oxidative stress resistance was also observed. The other three studied stress responsive miRNAs; miR319a.2, miR399f, miR482 also showed down-regulation with respective induction in the expression of transcripts they regulate; metacaspase-8, PHO2 (PHOSPATE 2; ubiquitin conjugating enzyme) and an NBS-LRR gene, respectively. Production of plant stress signals and differential expression of stress indicators during the HR response at infection (inoculation) sites and PCD at systemic sites is discussed.

Cloning and characterization of NtSnRK2.7 and NtSnRK2.8 genes involved in abiotic stress responses from Nicotiana tabacum

Sucrose non-fermenting1-related protein kinase 2 (SnRK2) plays a key role in abiotic stress signaling in plants. In this study, gene structures, phylogeny, conserved motifs and promoters of NtSnRK2.7 and NtSnRK2.8 in tobacco have been analyzed. Phylogenetic analysis showed that NtSnRK2.7 and NtSnRK2.8 belong to subclass I and subclass III of SnRK2, respectively. They exhibited similar genomic structures, consisting of 9 exons and 8 introns. Subcellular localization showed the presence of NtSnRK2s in the cell membrane, cytoplasm and nucleus. Quantitative real-time PCR was used to analyze the expression patterns of NtSnRK2s in tobacco. NtSnRK2s were constitutively expressed strongly in roots, weakly in stems, and marginally in leaves. Abiotic stress response analyses revealed that NtSnRK2.7 and NtSnRK2.8 were involved in response to various abiotic stresses with different patterns: there was evidence that NtSnRK2.7 participated in abscisic acid-independent signaling pathways, while the transcription of NtSnRK2.8 was induced by abscisic acid treatment; NtSnRK2.7 responded much faster to salt and cold stress. Furthermore, expression of NtSnRK2.8 increased intensely and reached its maximum at 1 h under drought stress indicating that it is sensitive to osmotic stress. Our results suggest that NtSnRK2.7 and NtSnRK2.8 are involved in multiple stress response pathways in distinct ways.