Dehydrins represent hydrophilic proteins acting mainly during cell dehydration and stress response. Dehydrins are generally thermostable; however, the so-called dehydrin-like (dehydrin-related) proteins show variable thermolability. Both groups immunoreact with antibodies directed against the K-segment of dehydrins. Plant mitochondrial dehydrin-like proteins are poorly characterized. The purpose of this study was to extend previous reports on plant dehydrins by comparing the level of immunoprecipitated dehydrin-like proteins in cauliflower (Brassica oleracea var. botrytis), Arabidopsis thaliana and yellow lupin (Lupinus luteus) mitochondria under cold and heat stress.
All the analyzed plant species showed constitutive accumulation of thermostable mitochondrial putative dehydrins ranging from 50 to 70 kDa. The mitochondrial dehydrin-like proteins observed in cauliflower and Arabidopsis ranged from 10 to 100 kDa and in lupin imbibed seeds and hypocotyls - from 20 to 90 kDa. Cold treatment increased mainly the accumulation of 10-100 kDa cauliflower and Arabidopsis dehydrin-like proteins, in the patterns different in cauliflower leaf and inflorescence mitochondria. However, in lupin mitochondria, cold affected mainly 25-50 kDa proteins and seemed to induce the appearance of some novel dehydrin-like proteins. The influence of frost stress on cauliflower leaf mitochondrial dehydrin- like proteins was less significant. The impact of heat stress was less significant in lupin and Arabidopsis than in cauliflower inflorescence mitochondria. Cauliflower mitochondrial dehydrin-like proteins are localized mostly in the mitochondrial matrix; it seems that some of them may interact with mitochondrial membranes.
All the results reveal an unexpectedly broad spectrum of dehydrin-like proteins accumulated during some abiotic stress in the mitochondria of the plant species analyzed. They display only limited similarity in size to those reported previously in maize, wheat and rye mitochondria. Some small thermolabile dehydrin-like proteins were induced under stress conditions applied and therefore they are likely to be involved in stress response.
Dehydrins as a group of late embryogenesis abundant II proteins represent important dehydration-inducible proteins whose accumulation is induced by developmental processes (embryo maturation) as well as by several abiotic stress factors (low temperatures, drought, salinity). In the review, an overview of studies aimed at investigation of dehydrin accumulation patterns at transcript and protein levels as well as their possible functions in common wheat (Triticum aestivum), durum wheat (T. durum), and barley (Hordeum vulgare) plants exposed to various abiotic stress factors (cold, frost, drought, salinity) is provided. Possible roles of dehydrin proteins in an acquisition and maintenance of an enhanced frost tolerance are analyzed in the context of plant developmental processes (vernalization). Quantitative and qualitative differences as well as post-translational modifications in accumulated dehydrin proteins between barley cultivars revealing differential tolerance to drought and salinity are also discussed. Current knowledge on dehydrin role in wheat and barley response to major dehydrative stresses is summarized and the major challenges in dehydrin research are outlined.
dehydrin dynamics; proteins; transcripts; abiotic stress; barley; wheat
Plantlets of Populus yunnanensis Dode were examined in a greenhouse for 48 h to analyze their physiological and proteomic responses to sustained heat, drought, and combined heat and drought. Compared with the application of a single stress, simultaneous treatment with both stresses damaged the plantlets more heavily. The plantlets experienced two apparent response stages under sustained heat and drought. During the first stage, malondialdehyde and reactive oxygen species (ROS) contents were induced by heat, but many protective substances, including antioxidant enzymes, proline, abscisic acid (ABA), dehydrin, and small heat shock proteins (sHSPs), were also stimulated. The plants thus actively defended themselves against stress and exhibited few pathological morphological features, most likely because a new cellular homeostasis was established through the collaborative operation of physiological and proteomic responses. During the second stage, ROS homeostasis was overwhelmed by substantial ROS production and a sharp decline in antioxidant enzyme activities, while the synthesis of some protective elements, such as proline and ABA, was suppressed. As a result, photosynthetic levels in P. yunnanensis decreased sharply and buds began to die, despite continued accumulation of sHSPs and dehydrin. This study supplies important information about the effects of extreme abiotic environments on woody plants.
Dehydration proteins (dehydrins) are group 2 members of the late embryogenesis abundant (LEA) protein family. The protein architecture of dehydrins can be described by the presence of three types of conserved sequence motifs that have been named the K-, Y-, and S-segments. By definition, a dehydrin must contain at least one copy of the lysine-rich K-segment. Abiotic stresses such as drought, cold, and salinity cause the upregulation of dehydrin mRNA and protein levels. Despite the large body of genetic and protein evidence of the importance of these proteins in stress response, the in vivo protective mechanism is not fully known. In vitro experimental evidence from biochemical assays and localization experiments suggests multiple roles for dehydrins, including membrane protection, cryoprotection of enzymes, and protection from reactive oxygen species. Membrane binding by dehydrins is likely to be as a peripheral membrane protein, since the protein sequences are highly hydrophilic and contain many charged amino acids. Because of this, dehydrins in solution are intrinsically disordered proteins, that is, they have no well-defined secondary or tertiary structure. Despite their disorder, dehydrins have been shown to gain structure when bound to ligands such as membranes, and to possibly change their oligomeric state when bound to ions. We review what is currently known about dehydrin sequences and their structures, and examine the various ligands that have been shown to bind to this family of proteins.
abiotic stress; cold; dehydration; dehydrins; intrinsically disordered proteins; late embryogenesis abundant; localization; structure
Dehydrins are thought to play an essential role in the plant response, acclimation and tolerance to different abiotic stresses, such as cold and drought. These proteins contain conserved and repeated segments in their amino acid sequence, used for their classification. Thus, dehydrins from angiosperms present different repetitions of the segments Y, S, and K, while gymnosperm dehydrins show A, E, S, and K segments. The only fragment present in all the dehydrins described to date is the K-segment. Different works suggest the K-segment is involved in key protective functions during dehydration stress, mainly stabilizing membranes. In this work, we describe for the first time two Pinus pinaster proteins with truncated K-segments and a third one completely lacking K-segments, but whose sequence homology leads us to consider them still as dehydrins. qRT-PCR expression analysis show a significant induction of these dehydrins during a severe and prolonged drought stress. By in silico analysis we confirmed the presence of these dehydrins in other Pinaceae species, breaking the convention regarding the compulsory presence of K-segments in these proteins. The way of action of these unusual dehydrins remains unrevealed.
dehydrins; K-segments; drought; gene expression; qRT-PCR; Pinus
• Background and Aims Dehydrins, or group 2 late embryogenic abundant proteins (LEA), are hydrophilic Gly-rich proteins that are induced in vegetative tissues in response to dehydration, elevated salt, and low temperature, in addition to being expressed during the late stages of seed maturation. With the aim of characterizing and studying genes involved in osmotic stress tolerance in coffee, several full-length cDNA-encoding dehydrins (CcDH1, CcDH2 and CcDH3) and an LEA protein (CcLEA1) from Coffea canephora (robusta) were isolated and characterized.
• Methods The protein sequences deduced from the full-length cDNA were analysed to classify each dehydrin/LEA gene product and RT–PCR was used to determine the expression pattern of all four genes during pericarp and grain development, and in several other tissues of C. arabica and C. canephora. Primer-assisted genome walking was used to isolate the promoter region of the grain specific dehydrin gene (CcDH2).
• Key Results The CcDH1 and CcDH2 genes encode Y3SK2 dehydrins and the CcDH3 gene encodes an SK3 dehydrin. CcDH1 and CcDH2 are expressed during the final stages of arabica and robusta grain development, but only the CcDH1 transcripts are clearly detected in other tissues such as pericarp, leaves and flowers. CcDH3 transcripts are also found in developing arabica and robusta grain, in addition to being detected in pericarp, stem, leaves and flowers. CcLEA1 transcripts were only detected during a brief period of grain development. Finally, over 1 kb of genomic sequence potentially encoding the entire grain-specific promoter region of the CcDH2 gene was isolated and characterized.
• Conclusions cDNA sequences for three dehydrins and one LEA protein have been obtained and the expression of the associated genes has been determined in various tissues of arabica and robusta coffees. Because induction of dehydrin gene expression is associated with osmotic stress in other plants, the dehydrin sequences presented here will facilitate future studies on the induction and control of the osmotic stress response in coffee. The unique expression pattern observed for CcLEA1, and the expression of a related gene in other plants, suggests that this gene may play an important role in the development of grain endosperm tissue. Genomic DNA containing the grain-specific CcDH2 promoter region has been cloned. Sequence analysis indicates that this promoter contains several putative regulatory sites implicated in the control of both seed- and osmotic stress-specific gene expression. Thus, the CcDH2 promoter is likely to be a useful tool for basic studies on the control of gene expression during both grain maturation and osmotic stress in coffee.
Dehydrins; late embryogenic abundant protein (LEA); seed development; Coffea; C. canephora; C. arabica; Rubiaceae
Plants accumulate dehydrins in response to osmotic stresses. Dehydrins are divided into five different classes, which are thought to be regulated in different manners. To better understand differences in transcriptional regulation of the five dehydrin classes, de novo motif discovery was performed on 350 dehydrin promoter sequences from a total of 51 plant genomes. Overrepresented motifs were identified in the promoters of five dehydrin classes. The Kn dehydrin promoters contain motifs linked with meristem specific expression, as well as motifs linked with cold/dehydration and abscisic acid response. KS dehydrin promoters contain a motif with a GATA core. SKn and YnSKn dehydrin promoters contain motifs that match elements connected with cold/dehydration, abscisic acid and light response. YnKn dehydrin promoters contain motifs that match abscisic acid and light response elements, but not cold/dehydration response elements. Conserved promoter motifs are present in the dehydrin classes and across different plant lineages, indicating that dehydrin gene regulation is likely also conserved.
Dehydrins (DHNs) protect plant cells from desiccation damage during environmental stress, and also participate in host resistance to various pathogens. In this study, we aimed to identify and characterize the DHN gene families from Vitis vinifera and wild V. yeshanensis, which is tolerant to both drought and cold, and moderately resistant to powdery mildew.
Four DHN genes were identified in both V. vinifera and V. yeshanensis, which shared a high sequence identity between the two species but little homology between the genes themselves. These genes were designated DHN1, DHN2, DHN3 and DHN4. All four of the DHN proteins were highly hydrophilic and were predicted to be intrinsically disordered, but they differed in their isoelectric points, kinase selectivities and number of functional motifs. Also, the expression profiles of each gene differed appreciably from one another. Grapevine DHN1 was not expressed in vegetative tissues under normal growth conditions, but was induced by drought, cold, heat, embryogenesis, as well as the application of abscisic acid (ABA), salicylic acid (SA), and methyl jasmonate (MeJA). It was expressed earlier in V. yeshanensis under drought conditions than in V. vinifera, and also exhibited a second round of up-regulation in V. yeshanensis following inoculation with Erysiphe necator, which was not apparent in V. vinifera. Like DHN1, DHN2 was induced by cold, heat, embryogenesis and ABA; however, it exhibited no responsiveness to drought, E. necator infection, SA or MeJA, and was also expressed constitutively in vegetative tissues under normal growth conditions. Conversely, DHN3 was only expressed during seed development at extremely low levels, and DHN4 was expressed specifically during late embryogenesis. Neither DHN3 nor DHN4 exhibited responsiveness to any of the treatments carried out in this study. Interestingly, the presence of particular cis-elements within the promoter regions of each gene was positively correlated with their expression profiles.
The grapevine DHN family comprises four divergent members. While it is likely that their functions overlap to some extent, it seems that DHN1 provides the main stress-responsive function. In addition, our results suggest a close relationship between expression patterns, physicochemical properties, and cis-regulatory elements in the promoter regions of the DHN genes.
Grapevine; Dehydrin; Stress-induced expression; Powdery mildew; Promoter
Dehydrins (DHNs) are a family of plant proteins typically induced in response to stress conditions that cause cellular dehydration, such as low temperatures, high salinity, and drought. Loquat (Eriobotrya japonica) is a perennial fruit crop that blossoms during winter. Loquat fruitlets are frequently injured by freezing. To evaluate the role of the EjDHNs in freezing resistance in loquat fruitlets, two cultivars of loquat, the freezing-sensitive ‘Ninghaibai’ (FS-NHB) and the freezing-tolerant ‘Jiajiao’ (FT-JJ), were analyzed under induced freezing stress. Freezing stress led to obvious accumulation of reactive oxygen species and considerable lipid peroxidation in membranes during the treatment period. Both these phenomena were more pronounced in ‘FS-NHB’ than in ‘FS-JJ.’ Immunogold labeling of dehydrin protein was performed. DHN proteins were found to be concentrated mainly in the vicinity of the plasma membrane, and the density of the immunogold labeling was significantly higher after freezing treatment, especially in the more freezing-tolerant cultivar ‘FT-JJ.’ Seven DHNs, showing four different structure types, were obtained from loquat fruitlets and used to study the characteristics of different EjDHN proteins. These DHN proteins are all highly hydrophilic, but they differ significantly in size, ranging from 188 to 475 amino acids, and in biochemical properties, such as theoretical pI, aliphatic index, and instability index. Freezing treatment resulted in up-regulation of the expression levels of all seven EjDHNs, regardless of structure type. The accumulation of the transcripts of these EjDHN genes was much more pronounced in ‘FT-JJ’ than in ‘FS-NHB.’ Altogether, this study provides evidence that EjDHNs are involved in the cryoprotection of the plasma membrane during freeze-induced dehydration in loquat fruitlets.
As a dehydrin belonging to group II late embryogenesis abundant protein (LEA) family, Arabidopsis Low Temperature-Induced 30 (LTI30)/XERO2 has been shown to be involved in plant freezing stress resistance. However, the other roles of AtLTI30 remain unknown. In this study, we found that the expression of AtLTI30 was largely induced by drought stress and abscisic acid (ABA) treatments. Thereafter, AtLTI30 knockout mutants and overexpressing plants were isolated to investigate the possible involvement of AtLTI30 in ABA and drought stress responses. AtLTI30 knockout mutants were less sensitive to ABA-mediated seed germination, while AtLTI30 overexpressing plants were more sensitive to ABA compared with wild type (WT). Consistently, the AtLTI30 knockout mutants displayed decreased drought stress resistance, while the AtLTI30 overexpressing plants showed improved drought stress resistance compared with WT, as evidenced by a higher survival rate and lower leaf water loss than WT after drought stress. Moreover, manipulation of AtLTI30 expression positively regulated the activities of catalases (CATs) and endogenous proline content, as a result, negatively regulated drought stress-triggered hydrogen peroxide (H2O2) accumulation. All these results indicate that AtLTI30 is a positive regulator of plant drought stress resistance, partially through the modulation of ABA sensitivity, H2O2 and proline accumulation.
Low Temperature-Induced 30; abscisic acid; hydrogen peroxide; drought stress; reactive oxygen species; Arabidopsis
The development of chilling and freezing injury symptoms in plants is known to frequently coincide with peroxidation of free fatty acids. Mitochondria are one of the major sources of reactive oxygen species during cold stress. Recently it has been suggested that uncoupling of oxidation and phosphorylation in mitochondria during oxidative stress can decrease ROS formation by mitochondrial respiratory chain generation. At the same time, it is known that plant uncoupling mitochondrial protein (PUMP) and other UCP-like proteins are not the only uncoupling system in plant mitochondria. All plants have cyanide-resistant oxidase (AOX) whose activation causes an uncoupling of respiration and oxidative phosphorylation. Recently it has been found that in cereals, cold stress protein CSP 310 exists, and that this causes uncoupling of oxidation and phosphorylation in mitochondria.
We studied the effects of CSP 310-like native cytoplasmic proteins from a number of cereal species (winter rye, winter wheat, Elymus and maize) on the energetic activity of winter wheat mitochondria. This showed that only CSP 310 (cold shock protein with molecular weight 310 kD) caused a significant increase of non-phosphorylative respiration. CSP 310-like proteins of other cereals studied did not have any significant influence on mitochondrial energetic activity. It was found that among CSP 310-like proteins only CSP 310 had prooxidant activity. At the same time, Elymus CSP 310-like proteins have antioxidant activity. The study of an influence of infiltration by different plant uncoupling system activators (pyruvate, which activates AOX, and linoleic acid which is a substrate and activator for PUMP and CSP 310) showed that all of these decreased lipid peroxidation during cold stress.
Different influence of CSP 310-like proteins on mitochondrial energetic activity and lipid peroxidation presumably depend on the various subunit combinations in their composition. All the plant cell systems that caused an uncoupling of oxidation and phosphorylation in plant mitochondria can participate in plant defence from oxidative damage during cold stress.
Dehydrins (DHNs), or group 2 LEA (Late Embryogenesis Abundant) proteins, play a fundamental role in plant response and adaptation to abiotic stresses. They accumulate typically in maturing seeds or are induced in vegetative tissues following salinity, dehydration, cold and freezing stress. The generally accepted classification of dehydrins is based on their structural features, such as the presence of conserved sequences, designated as Y, S and K segments. The K segment representing a highly conserved 15 amino acid motif forming amphiphilic a-helix is especially important since it has been found in all dehydrins. Since more than 20 y, they are thought to play an important protective role during cellular dehydration but their precise function remains unclear. This review outlines the current status of the progress made toward the structural, physico-chemical and functional characterization of plant dehydrins and how these features could be exploited in improving stress tolerance in plants.
abiotic stress; dehydration stress; drought; cold acclimation; freezing tolerance; LEA proteins; dehydrins
Dehydrins belongs to a large group of highly hydrophilic proteins known as Late Embryogenesis Abundant (LEA) proteins. It is well known that dehydrins are intrinsically disordered plant proteins that accumulate during the late stages of embryogenesis and in response to abiotic stresses; however, the molecular mechanisms by which their functions are carried out are still unclear. We have previously reported that transgenic Arabidopsis plants overexpressing an Opuntia streptacantha SK3 dehydrin (OpsDHN1) show enhanced tolerance to freezing stress. Herein, we show using a split-ubiquitin yeast two-hybrid system that OpsDHN1 dimerizes. We found that the deletion of regions containing K-segments and the histidine-rich region in the OpsDHN1 protein affects dimer formation. Not surprisingly, in silico protein sequence analysis suggests that OpsDHN1 is an intrinsically disordered protein, an observation that was confirmed by circular dichroism and gel filtration of the recombinantly expressed protein. The addition of zinc triggered the association of recombinantly expressed OpsDHN1 protein, likely through its histidine-rich motif. These data brings new insights about the molecular mechanism of the OpsDHN1 SK3-dehydrin.
yeast two-hybrid; SK3-dehydrin; K-segments; homodimer; histidine-rich region; intrinsically disordered proteins
Light and temperature are the key abiotic modulators of plant gene expression. In the present work the effect of light under low temperature treatment was analyzed by using microarrays. Specific attention was paid to the up and down regulated genes by using promoter analysis. This approach revealed putative regulatory networks of transcription factors behind the induction or repression of the genes.
Induction of a few oxidative stress related genes occurred only under the Cold/Light treatment including genes encoding iron superoxide dismutase (FeSOD) and glutathione-dependent hydrogen peroxide peroxidases (GPX). The ascorbate dependent water-water cycle genes showed no response to Cold/Light or Cold/Dark treatments. Cold/Light specifically induced genes encoding protective molecules like phenylpropanoids and photosynthesis-related carotenoids also involved in the biosynthesis of hormone abscisic acid (ABA) crucial for cold acclimation. The enhanced/repressed transcript levels were not always reflected on the respective protein levels as demonstrated by dehydrin proteins.
Cold/Light up regulated twice as many genes as the Cold/Dark treatment and only the combination of light and low temperature enhanced the expression of several genes earlier described as cold-responsive genes. Cold/Light-induced genes included both cold-responsive transcription factors and several novel ones containing zinc-finger, MYB, NAC and AP2 domains. These are likely to function in concert in enhancing gene expression. Similar response elements were found in the promoter regions of both the transcription factors and their target genes implying a possible parallel regulation or amplification of the environmental signals according to the metabolic/redox state in the cells.
Improvement of freezing tolerance of red clover (Trifolium pratense L.) would increase its persistence under cold climate. In this study, we assessed the freezing tolerance and compared the proteome composition of non-acclimated and cold-acclimated plants of two initial cultivars of red clover: Endure (E-TF0) and Christie (C-TF0) and of populations issued from these cultivars after three (TF3) and four (TF4) cycles of phenotypic recurrent selection for superior freezing tolerance. Through this approach, we wanted to identify proteins that are associated with the improvement of freezing tolerance in red clover.
Freezing tolerance expressed as the lethal temperature for 50 % of the plants (LT50) increased markedly from approximately −2 to −16 °C following cold acclimation. Recurrent selection allowed a significant 2 to 3 °C increase of the LT50 after four cycles of recurrent selection. Two-dimensional difference gel electrophoresis (2D-DIGE) was used to study variations in protein abundance. Principal component analysis based on 2D-DIGE revealed that the largest variability in the protein data set was attributable to the cold acclimation treatment and that the two genetic backgrounds had differential protein composition in the acclimated state only. Vegetative storage proteins (VSP), which are essential nitrogen reserves for plant regrowth, and dehydrins were among the most striking changes in proteome composition of cold acclimated crowns of red clovers. A subset of proteins varied in abundance in response to selection including a dehydrin that increased in abundance in TF3 and TF4 populations as compared to TF0 in the Endure background.
Recurrent selection performed indoor is an effective approach to improve the freezing tolerance of red clover. Significant improvement of freezing tolerance by recurrent selection was associated with differential accumulation of a small number of cold-regulated proteins that may play an important role in the determination of the level of freezing tolerance.
Electronic supplementary material
The online version of this article (doi:10.1186/s12870-016-0751-2) contains supplementary material, which is available to authorized users.
Red clover; Cold acclimation; Proteomic analysis; Recurrent selection; Freezing tolerance; Plant abiotic stress
Adverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields. The C-repeat binding factors (CBFs) are critical transcription factors constituting the gene regulatory network that mediates the acclimation process to low temperatures. They regulate a large number of cold-responsive genes, including COLD-REGULATED (COR) genes, via the CBF-COR regulon. Recent studies have shown that the CBF transcription factors also play a role in plant responses to drought and salt stresses. Putative CBF gene homologues and their downstream genes are also present in the genome of Brachypodium distachyon, which is perceived as a monocot model in recent years. However, they have not been functionally characterized at the molecular level.
Three CBF genes that are responsive to cold were identified from Brachypodium, designated BdCBF1, BdCBF2, and BdCBF3, and they were functionally characterized by molecular biological and transgenic approaches in Brachypodium and Arabidopsis thaliana. Our results demonstrate that the BdCBF genes contribute to the tolerance response of Brachypodium to cold, drought, and salt stresses by regulating downstream targets, such as DEHYDRIN5.1 (Dhn5.1) and COR genes. The BdCBF genes are induced under the environmental stress conditions. The BdCBF proteins possess transcriptional activation activity and bind directly to the promoters of the target genes. Transgenic Brachypodium plants overexpressing the BdCBF genes exhibited enhanced resistance to drought and salt stresses as well as low temperatures, and accordingly endogenous contents of proline and soluble sugars were significantly elevated in the transgenic plants. The BdCBF transcription factors are also functional in the heterologous system Arabidopsis. Transgenic Arabidopsis plants overexpressing the BdCBF genes were also tolerant to freezing, drought, and salt stresses, and a set of stress-responsive genes was upregulated in the transgenic Arabidopsis plants.
Taken together, our results strongly support that the BdCBF transcription factors are key regulators of cold stress responses in Brachypodium and the CBF-mediated cold stress signaling pathway is conserved in this plant species. We believe that this study would confer great impact on stress biology in monocot species and could be applied to engineer abiotic stress tolerance of bioenergy grass species.
Brachypodium distachyon; C-repeat binding factor (CBF); COLD-REGULATED (COR); Abiotic stress tolerance; Arabidopsis thaliana
The recently described complex nature of some dehydrin-coding sequences in Trifolium repens could explain the considerable variability among transcripts originating from a single gene.1 For some of the sequences the existence of natural antisense transcripts (NATs), which could form sense-antisense (SAS) pairs, was predicted. The present study demonstrates that cis-natural antisense transcripts of 2 dehydrin types (YnKn and YnSKn) accumulate in white clover plants subjected to treatments with polyethylene glycol (PEG), abscisic acid (ABA), and high salt concentration. The isolated YnKn
cis-NATs mapped to sequence site enriched in alternative start codons. Some of the sense-antisense pairs exhibited inverse expression with differing profiles which depended on the applied stress. A natural antisense transcript coding for an ABC F family protein (a trans-NAT) which shares short sequence homology with YnSKn dehydrin was identified in plants subjected to salt stress. Forthcoming experiments will evaluate the impact of NATs on transcript abundances, elucidating the role of transcriptional and post-transcriptional interferences in the regulation of dehydrin levels under various abiotic stresses.
Dehydrins; natural antisense transcripts; sense-antisense pairs; splice variants; Trifolium repens
Fall dormant/freezing tolerant plants often also exhibit superior tolerance to drought conditions compared to their non-fall dormant/freezing intolerant counterparts. This experiment aimed to investigate this phenomenon in an agriculturally important crop. Seven alfalfa cultivars with varying levels of fall dormancy/freezing tolerance were exposed to a water deficit. The more fall dormant cultivars had superior tolerance to a mild water deficit. Two genes, CAS18 (encodes for a dehydrin like protein) and CorF (encodes for a galactinol synthase), were up regulated in association with this drought tolerance. Both these genes are early response genes, providing clues to the stress signalling pathways involved.
The growth of fall dormant/freezing tolerant plants often surpasses the growth of non-fall dormant/non-freezing tolerant types of the same species under water-limited conditions, while under irrigated conditions non-fall dormant types exhibit superior yield performance. To investigate the mechanism behind this phenomenon, we exposed seven diverse alfalfa (Medicago sativa) cultivars to water-limited and fully watered conditions and measured their shoot growth, shoot water potential and gas exchange parameters and the relative abundance of taproot RNA transcripts associated with chilling stress/freezing tolerance. Fall dormant cultivars had greater shoot growth relative to the fully watered controls under a mild water deficit (a cumulative water deficit of 625 mL pot−1) and did not close their stomata until lower shoot water potentials compared with the more non-fall dormant cultivars. Several gene transcripts previously associated with freezing tolerance increased in abundance when plants were exposed to a mild water deficit. Two transcripts, corF (encodes galactinol synthase) and cas18 (encodes a dehydrin-like protein), increased in abundance in fall dormant cultivars only. Once water deficit stress became severe (a cumulative water deficit of 2530 mL pot−1), the difference between fall dormancy groups disappeared with the exception of the expression of a type 1 sucrose synthase gene, which decreased in fall dormant cultivars. The specific adaptation of fall dormant cultivars to mild water deficit conditions and the increase in abundance of specific genes typically associated with freezing tolerance in these cultivars is further evidence of a link between freezing tolerance/fall dormancy and adaption to drought conditions in this species.
Alfalfa; forage legumes; gene expression; lucerne; moisture stress.
Response to a high salinity treatment of 300 mM NaCl was studied in a cultivated barley Hordeum vulgare Syrian cultivar Tadmor and in a halophytic wild barley H. marinum. Differential salinity tolerance of H. marinum and H. vulgare is underlied by qualitative and quantitative differences in proteins involved in a variety of biological processes. The major aim was to identify proteins underlying differential salinity tolerance between the two barley species. Analyses of plant water content, osmotic potential and accumulation of proline and dehydrin proteins under high salinity revealed a relatively higher water saturation deficit in H. marinum than in H. vulgare while H. vulgare had lower osmotic potential corresponding with high levels of proline and dehydrins. Analysis of proteins soluble upon boiling isolated from control and salt-treated crown tissues revealed similarities as well as differences between H. marinum and H. vulgare. The similar salinity responses of both barley species lie in enhanced levels of stress-protective proteins such as defense-related proteins from late-embryogenesis abundant family, several chaperones from heat shock protein family, and others such as GrpE. However, there have also been found significant differences between H. marinum and H. vulgare salinity response indicating an active stress acclimation in H. marinum while stress damage in H. vulgare. An active acclimation to high salinity in H. marinum is underlined by enhanced levels of several stress-responsive transcription factors from basic leucine zipper and nascent polypeptide-associated complex families. In salt-treated H. marinum, enhanced levels of proteins involved in energy metabolism such as glycolysis, ATP metabolism, and photosynthesis-related proteins indicate an active acclimation to enhanced energy requirements during an establishment of novel plant homeostasis. In contrast, changes at proteome level in salt-treated H. vulgare indicate plant tissue damage as revealed by enhanced levels of proteins involved in proteasome-dependent protein degradation and proteins related to apoptosis. The results of proteomic analysis clearly indicate differential responses to high salinity and provide more profound insight into biological mechanisms underlying salinity response between two barley species with contrasting salinity tolerance.
glycophyte; halophyte; salinity; proteome; stress acclimation; stress damage; Hordeum marinum; Hordeum vulgare
The objective of this research was to analyse whether ameliorating drought stress through exogenously applied spermine (Spm) was related to carbohydrate metabolism, dehydrins accumulation and the transcription of genes encoding dehydrins in two white clovers (drought-susceptible cv. ‘Ladino’ and drought-resistant cv. ‘Haifa’) under controlled drying conditions for 10 days. The results show that the application of Spm effectively alleviates negative effects caused by drought stress in both cultivars. Exogenous Spm led to accumulation of more water-soluble carbohydrates (WSC), sucrose, fructose and sorbitol in both cultivars under drought stress, and also significantly elevated glucose content in leaves of drought-resistant cv. ‘Haifa’, but had no effect on drought-susceptible cv. ‘Ladino’. Accordingly, the key enzyme activities of sucrose and sorbitol metabolism changed along with the application of Spm under drought stress. Spm induced a significant increase in sucrose phosphate synthase (SPS) or sorbitol dehydrogenase (SDH) activity, but decrease in sucrose synthetase (SS) activity when two cultivars were subjected to drought. In addition, the improved accumulation of dehydrins induced by exogenous Spm coincided with three genes expression which was responsible for dehydrins synthesis. But Spm-induced transcript level of dehydrin genes increased earlier in cv. ‘Ladino’ than that in cv. ‘Haifa’. Thus, these results suggest that ameliorating drought stress through exogenously applied Spm may be associated with increased carbohydrate accumulation and dehydrins synthesis. There are differences between drought-susceptible and -resistant white clover cultivars related to Spm regulation of WSC metabolism and dehydrins expression.
As a widely used warm-season turfgrass in landscapes and golf courses, bermudagrass encounters multiple abiotic stresses during the growth and development. Physiology analysis indicated that abiotic stresses induced the accumulation of ROS and decline of photosynthesis, resulting in increased cell damage and inhibited growth. Proteomic and metabolomic approaches showed that antioxidant enzymes and osmoprotectant contents (sugar, sucrose, dehydrin, proline) were extensively changed under abiotic stress conditions. Exogenous application of small molecules, such as ABA, NO, CaCl2, H2S, polyamine and melatonin, could effectively alleviate damages caused by multiple abiotic stresses, including drought, salt, heat and cold. Based on high through-put RNA seq analysis, genes involved in ROS, transcription factors, hormones, and carbohydrate metabolisms were largely enriched. The data indicated that small molecules induced the accumulation of osmoprotectants and antioxidants, kept cell membrane integrity, increased photosynthesis and kept ion homeostasis, which protected bermudagrass from damages caused by abiotic stresses.
bermudagrass; abiotic stress; small molecule; melatonin
Stipa purpurea, an endemic forage species on the Tibetan Plateau, is highly resistant to cold and drought, but the mechanisms underlying its responses to drought stress remain elusive. An understanding of such mechanisms may be useful for developing cultivars that are adaptable to water deficit. In this study, we analyzed the physiological and proteomic responses of S. purpurea under increasing drought stress. Seedlings of S. purpurea were subjected to a drought gradient in a controlled experiment, and proteins showing changes in abundance under these conditions were identified by two-dimensional electrophoresis followed by mass spectrometry analysis. A western blotting analysis was conducted to confirm the increased abundance of a heat-shock protein, NCED2, and a dehydrin in S. purpurea seedlings under drought conditions. We detected carbonylated proteins to identify oxidation-sensitive proteins in S. purpurea seedlings, and found that ribulose-1, 5-bisphosphate carboxylase oxygenase (RuBisCO) was one of the oxidation-sensitive proteins under drought. Together, these results indicated drought stress might inhibit photosynthesis in S. purpurea by oxidizing RuBisCO, but the plants were able to maintain photosynthetic efficiency by a compensatory upregulation of unoxidized RuBisCO and other photosynthesis-related proteins. Further analyses confirmed that increased abundance of antioxidant enzymes could balance the redox status of the plants to mitigate drought-induced oxidative damage.
• Background and Aims Summer dormancy in perennial grasses has been studied inadequately, despite its potential to enhance plant survival and persistence in Mediterranean areas. The aim of the present work was to characterize summer dormancy and dehydration tolerance in two cultivars of Dactylis glomerata (dormant ‘Kasbah’, non-dormant ‘Oasis’) and their hybrid using physiological indicators associated with these traits.
• Methods Dehydration tolerance was assessed in a glasshouse experiment, while seasonal metabolic changes which produce putative protectants for drought, such as carbohydrates and dehydrins that might be associated with summer dormancy, were analysed in the field.
• Key Results The genotypes differed in their ability to survive increasing soil water deficit: lethal soil water potential (Ψs) was −3·4 MPa for ‘Kasbah’ (although non-dormant), −1·3 MPa for ‘Oasis’, and −1·6 MPa for their hybrid. In contrast, lethal water content of apices was similar for all genotypes (approx. 0·45 g H2O g d. wt−1), and hence the greater survival of ‘Kasbah’ can be ascribed to better drought avoidance rather than dehydration tolerance. In autumn-sown plants, ‘Kasbah’ had greatest dormancy, the hybrid was intermediate and ‘Oasis’ had none. The more dormant the genotype, the lower the metabolic activity during summer, and the earlier the activity declined in spring. Decreased monosaccharide content was an early indicator of dormancy induction. Accumulation of dehydrins did not correlate with stress tolerance, but dehydrin content was a function of the water status of the tissues, irrespective of the soil moisture. A protein of approx. 55 kDa occurred in leaf bases of the most dormant cultivar even in winter.
• Conclusions Drought avoidance and summer dormancy are correlated but can be independently expressed. These traits are heritable, allowing selection in breeding programmes.
Orchard grass; drought tolerance; avoidance; dehydration; dehydrins; carbohydrates; Dactylis glomerata, summer dormancy
Dehydrin is a plant disordered protein whose functions are not yet totally understood. Here it is reported that a KS-type dehydrin can reduce the formation of reactive oxygen species (ROS) from Cu. AtHIRD11, which is the Arabidopsis KS-type dehydrin, inhibited generation of hydrogen peroxide and hydroxyl radicals in the Cu–ascorbate system. The radical-reducing activity of AtHIRD11 was stronger than those of radical-silencing peptides such as glutathione and serum albumin. The addition of Cu2+ reduced the disordered state, decreased the trypsin susceptibility, and promoted the self-association of AtHIRD11. Domain analyses indicated that the five domains containing histidine showed ROS-reducing activities. Histidine/alanine substitutions indicated that histidine is a crucial residue for reducing ROS generation. Using the 27 peptides which are related to the KnS-type dehydrins of 14 plant species, it was found that the strengths of ROS-reducing activities can be determined by two factors, namely the histidine contents and the length of the peptides. The degree of ROS-reducing activities of a dehydrin can be predicted using these indices.
Circular dichroism; dehydrin; disordered protein; heavy metal; histidine; reactive oxygen species.
Salt stress is a major challenge for growth and development of plants. The mangrove tree Avicennia officinalis has evolved salt tolerance mechanisms such as salt secretion through specialized glands on its leaves. Although a number of structural studies on salt glands have been done, the molecular mechanism of salt secretion is not clearly understood. Also, studies to identify salt gland-specific genes in mangroves have been scarce.
By subtractive hybridization (SH) of cDNA from salt gland-rich cell layers (tester) with mesophyll tissues as the driver, several Expressed Sequence Tags (ESTs) were identified. The major classes of ESTs identified include those known to be involved in regulating metabolic processes (37%), stress response (17%), transcription (17%), signal transduction (17%) and transport functions (12%). A visual interactive map generated based on predicted functional gene interactions of the identified ESTs suggested altered activities of hydrolase, transmembrane transport and kinases. Quantitative Real-Time PCR (qRT-PCR) was carried out to validate the expression specificity of the ESTs identified by SH. A Dehydrin gene was chosen for further experimental analysis, because it is significantly highly expressed in salt gland cells, and dehydrins are known to be involved in stress remediation in other plants. Full-length Avicennia officinalis Dehydrin1 (AoDHN1) cDNA was obtained by Rapid Amplification of cDNA Ends. Phylogenetic analysis and further characterization of this gene suggested that AoDHN1 belongs to group II Late Embryogenesis Abundant proteins. qRT-PCR analysis of Avicennia showed up-regulation of AoDHN1 in response to salt and drought treatments. Furthermore, some functional insights were obtained by growing E. coli cells expressing AoDHN1. Growth of E. coli cells expressing AoDHN1 was significantly higher than that of the control cells without AoDHN1 under salinity and drought stresses, suggesting that the mangrove dehydrin protein helps to mitigate the abiotic stresses.
Thirty-four ESTs were identified to be enriched in salt gland-rich tissues of A. officinalis leaves. qRT-PCR analysis showed that 10 of these were specifically enriched in the salt gland-rich tissues. Our data suggest that one of the selected genes, namely, AoDHN1 plays an important role to mitigate salt and drought stress responses.
Electronic supplementary material
The online version of this article (doi:10.1186/s12870-014-0291-6) contains supplementary material, which is available to authorized users.
Avicennia officinalis; Salinity; Dehydrin; Subtractive hybridization; Leaf salt glands; Drought stress