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 are known as Group II late embryogenesis abundant proteins. Their high hydrophilicity and thermostability suggest that they may be structure stabilizers with detergent and chaperone-like properties. They are localised in the nucleus, cytoplasm, and plasma membrane. We have recently found putative dehydrins in the mitochondria of some cereals in response to cold. It is not known whether dehydrin-like proteins accumulate in plant mitochondria in response to stimuli other than cold stress.
We have found five putative dehydrins in the mitochondria of winter wheat, rye and maize seedlings. Two of these polypeptides had the same molecular masses in all three species (63 and 52 kD) and were thermostable. Drought, freezing, cold, and exogenous ABA treatment led to higher accumulation of dehydrin-like protein (dlp) 63 kD in the rye and wheat mitochondria. Protein 52 kD was induced by cold adaptation and ABA. Some accumulation of these proteins in the maize mitochondria was found after cold exposition only. The other three proteins appeared to be heat-sensitive and were either slightly induced or not induced at all by all treatments used.
We have found that, not only cold, but also drought, freezing and exogenous ABA treatment result in accumulation of the thermostable dehydrins in plant mitochondria. Most cryotolerant species such as wheat and rye accumulate more heat-stable dehydrins than cryosensitive species such as maize. It has been supposed that their function is to stabilize proteins in the membrane or in the matrix. Heat-sensitive putative dehydrins probably are not involved in the stress reaction and adaptation of plants.
In this study, the roles of fungal dehydrin-like proteins in pathogenicity and protection against environmental stresses were investigated in the necrotrophic seed-borne fungus Alternaria brassicicola. Three proteins (called AbDhn1, AbDhn2 and AbDhn3), harbouring the asparagine-proline-arginine (DPR) signature pattern and sharing the characteristic features of fungal dehydrin-like proteins, were identified in the A. brassicicola genome. The expression of these genes was induced in response to various stresses and found to be regulated by the AbHog1 mitogen-activated protein kinase (MAPK) pathway. A knock-out approach showed that dehydrin-like proteins have an impact mainly on oxidative stress tolerance and on conidial survival upon exposure to high and freezing temperatures. The subcellular localization revealed that AbDhn1 and AbDhn2 were associated with peroxisomes, which is consistent with a possible perturbation of protective mechanisms to counteract oxidative stress and maintain the redox balance in AbDhn mutants. Finally, we show that the double deletion mutant ΔΔabdhn1-abdhn2 was highly compromised in its pathogenicity. By comparison to the wild-type, this mutant exhibited lower aggressiveness on B. oleracea leaves and a reduced capacity to be transmitted to Arabidopsis seeds via siliques. The double mutant was also affected with respect to conidiation, another crucial step in the epidemiology of the disease.
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.
• 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
The genomes of three plants, Arabidopsis (Arabidopsis thaliana), rice (Oryza sativa), and soybean (Glycine max), have been sequenced, and their many genes and promoters have been predicted. In Arabidopsis, cis-acting promoter elements involved in cold- and dehydration-responsive gene expression have been extensively analysed; however, the characteristics of such cis-acting promoter sequences in cold- and dehydration-inducible genes of rice and soybean remain to be clarified. In this study, we performed microarray analyses using the three species, and compared characteristics of identified cold- and dehydration-inducible genes. Transcription profiles of the cold- and dehydration-responsive genes were similar among these three species, showing representative upregulated (dehydrin/LEA) and downregulated (photosynthesis-related) genes. All (46 = 4096) hexamer sequences in the promoters of the three species were investigated, revealing the frequency of conserved sequences in cold- and dehydration-inducible promoters. A core sequence of the abscisic acid-responsive element (ABRE) was the most conserved in dehydration-inducible promoters of all three species, suggesting that transcriptional regulation for dehydration-inducible genes is similar among these three species, with the ABRE-dependent transcriptional pathway. In contrast, for cold-inducible promoters, the conserved hexamer sequences were diversified among these three species, suggesting the existence of diverse transcriptional regulatory pathways for cold-inducible genes among the species.
plant genome; cis-acting promoter elements; cold; dehydration; microarray
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
The wild tomato species Solanum chilense and S. peruvianum are a valuable non-model system for studying plant adaptation since they grow in diverse environments facing many abiotic constraints. Here we investigate the sequence evolution of regulatory regions of drought and cold responsive genes and their expression regulation. The coding regions of these genes were previously shown to exhibit signatures of positive selection. Expression profiles and sequence evolution of regulatory regions of members of the Asr (ABA/water stress/ripening induced) gene family and the dehydrin gene pLC30-15 were analyzed in wild tomato populations from contrasting environments. For S. chilense, we found that Asr4 and pLC30-15 appear to respond much faster to drought conditions in accessions from very dry environments than accessions from more mesic locations. Sequence analysis suggests that the promoter of Asr2 and the downstream region of pLC30-15 are under positive selection in some local populations of S. chilense. By investigating gene expression differences at the population level we provide further support of our previous conclusions that Asr2, Asr4, and pLC30-15 are promising candidates for functional studies of adaptation. Our analysis also demonstrates the power of the candidate gene approach in evolutionary biology research and highlights the importance of wild Solanum species as a genetic resource for their cultivated relatives.
In contrast to orthodox seeds that acquire desiccation tolerance during maturation, recalcitrant seeds are unable to survive drying. These desiccation-sensitive seeds constitute an interesting model for comparative analysis with phylogenetically close species that are desiccation tolerant. Considering the importance of LEA (late embryogenesis abundant) proteins as protective molecules both in drought and in desiccation tolerance, the heat-stable proteome was characterized in cotyledons of the legume Castanospermum australe and it was compared with that of the orthodox model legume Medicago truncatula. RNA sequencing identified transcripts of 16 homologues out of 17 LEA genes for which polypeptides are detected in M. truncatula seeds. It is shown that for 12 LEA genes, polypeptides were either absent or strongly reduced in C. australe cotyledons compared with M. truncatula seeds. Instead, osmotically responsive, non-seed-specific dehydrins accumulated to high levels in the recalcitrant cotyledons compared with orthodox seeds. Next, M. truncatula mutants of the ABSCISIC ACID INSENSITIVE3 (ABI3) gene were characterized. Mature Mtabi3 seeds were found to be desiccation sensitive when dried below a critical water content of 0.4g H2O g DW–1. Characterization of the LEA proteome of the Mtabi3 seeds revealed a subset of LEA proteins with severely reduced abundance that were also found to be reduced or absent in C. australe cotyledons. Transcripts of these genes were indeed shown to be ABI3 responsive. The results highlight those LEA proteins that are critical to desiccation tolerance and suggest that comparable regulatory pathways responsible for their accumulation are missing in both desiccation-sensitive genotypes, revealing new insights into the mechanistic basis of the recalcitrant trait in seeds.
abi3; Castanospermum australe; desiccation tolerance; late embryogenesis abundant proteins; Medicago truncatula; proteomics; recalcitrant seed; RNAseq.
Rhizophora mucronata Lam. is a tropical mangrove with semi-viviparous (cotyledon body protrusion before shedding), non-quiescent and non-desiccating (recalcitrant) seeds. As recalcitrance has been thought to relate to the absence of desiccation-related proteins such as dehydrins, we for the first time systematically described and classified embryogenesis in R. mucronata and assessed the presence of dehydrin-like proteins. Embryogenesis largely follows the classic pattern till stage eight, the torpedo stage, with the formation of a cotyledonary body. Ovule and embryo express radical adaptations to semi-vivipary in the saline environment: (1) A large, highly vacuolated and persistent endosperm without noticeable food reserves that envelopes the developing embryo. (2) Absence of vascular tissue connections between embryo and maternal tissue, but, instead, transfer layers in between endosperm and integument and endosperm and embryo. Dehydrin-like proteins (55–65 kDa) were detected by the Western analysis, in the ovules till stage 10 when the integuments are dehisced. An additional 50 kDa band was detected at stages 6–8. Together these results suggest a continuous flow of water with nutrients from the integument via the endosperm to the embryo, circumventing the vascular route and probably suppressing the initially induced dehydrin expression.
Dehydrins; Embryo development; Mangroves; Rhizophora mucronata; Semi-vivipary
The expressed sequence tag M6G10 was originally isolated from a screening for differentially expressed transcripts during the reproductive stage of the white truffle Tuber borchii. mRNA levels for M6G10 increased dramatically during fruiting body maturation compared to the vegetative mycelial stage.
Bioinformatics tools, phylogenetic analysis and expression studies were used to support the hypothesis that this sequence, named TbDHN1, is the first dehydrin (DHN)-like coding gene isolated in fungi. Homologs of this gene, all defined as "coding for hypothetical proteins" in public databases, were exclusively found in ascomycetous fungi and in plants. Although complete (or almost complete) fungal genomes and EST collections of some Basidiomycota and Glomeromycota are already available, DHN-like proteins appear to be represented only in Ascomycota. A new and previously uncharacterized conserved signature pattern was identified and proposed to Uniprot database as the main distinguishing feature of this new group of DHNs. Expression studies provide experimental evidence of a transcript induction of TbDHN1 during cellular dehydration.
Expression pattern and sequence similarities to known plant DHNs indicate that TbDHN1 is the first characterized DHN-like protein in fungi. The high similarity of TbDHN1 with homolog coding sequences implies the existence of a novel fungal/plant group of LEA Class II proteins characterized by a previously undescribed signature pattern.
Plants are exposed to different external conditions that affect growth, development, and productivity. Water deficit is one of these adverse conditions caused by drought, salinity, and extreme temperatures. Plants have developed different responses to prevent, ameliorate or repair the damage inflicted by these stressful environments. One of these responses is the activation of a set of genes encoding a group of hydrophilic proteins that typically accumulate to high levels during seed dehydration, at the last stage of embryogenesis, hence named Late Embryogenesis Abundant (LEA) proteins. LEA proteins also accumulate in response to water limitation in vegetative tissues, and have been classified in seven groups based on their amino acid sequence similarity and on the presence of distinctive conserved motifs. These proteins are widely distributed in the plant kingdom, from ferns to angiosperms, suggesting a relevant role in the plant response to this unfavorable environmental condition. In this review, we analyzed the LEA proteins from those legumes whose complete genomes have been sequenced such as Phaseolus vulgaris, Glycine max, Medicago truncatula, Lotus japonicus, Cajanus cajan, and Cicer arietinum. Considering their distinctive motifs, LEA proteins from the different groups were identified, and their sequence analysis allowed the recognition of novel legume specific motifs. Moreover, we compile their transcript accumulation patterns based on publicly available data. In spite of the limited information on these proteins in legumes, the analysis and data compiled here confirm the high correlation between their accumulation and water deficit, reinforcing their functional relevance under this detrimental conditions.
legumes; common bean; soybean; Medicago; LEA proteins; water deficit; abiotic stress
LEA (late embryogenesis abundant) proteins have first been described about 25 years ago as accumulating late in plant seed development. They were later found in vegetative plant tissues following environmental stress and also in desiccation tolerant bacteria and invertebrates. Although they are widely assumed to play crucial roles in cellular dehydration tolerance, their physiological and biochemical functions are largely unknown.
We present a genome-wide analysis of LEA proteins and their encoding genes in Arabidopsis thaliana. We identified 51 LEA protein encoding genes in the Arabidopsis genome that could be classified into nine distinct groups. Expression studies were performed on all genes at different developmental stages, in different plant organs and under different stress and hormone treatments using quantitative RT-PCR. We found evidence of expression for all 51 genes. There was only little overlap between genes expressed in vegetative tissues and in seeds and expression levels were generally higher in seeds. Most genes encoding LEA proteins had abscisic acid response (ABRE) and/or low temperature response (LTRE) elements in their promoters and many genes containing the respective promoter elements were induced by abscisic acid, cold or drought. We also found that 33% of all Arabidopsis LEA protein encoding genes are arranged in tandem repeats and that 43% are part of homeologous pairs. The majority of LEA proteins were predicted to be highly hydrophilic and natively unstructured, but some were predicted to be folded.
The analyses indicate a wide range of sequence diversity, intracellular localizations, and expression patterns. The high fraction of retained duplicate genes and the inferred functional diversification indicate that they confer an evolutionary advantage for an organism under varying stressful environmental conditions. This comprehensive analysis will be an important starting point for future efforts to elucidate the functional role of these enigmatic proteins.
We report a series of microarray-based comparisons of gene expression in the leaf and crown of the winter barley cultivar Luxor, following the exposure of young plants to various periods of low (above and below zero) temperatures. A transcriptomic analysis identified genes which were either expressed in both the leaf and crown, or specifically in one or the other. Among the former were genes responsible for calcium and abscisic acid signalling, polyamine synthesis, late embryogenesis abundant proteins and dehydrins. In the crown, the key organ for cereal overwintering, cold treatment induced transient changes in the transcription of nucleosome assembly genes, and especially H2A and HTA11, which have been implicated in cold sensing in Arabidopsis thaliana. In the leaf, various heat-shock proteins were induced. Differences in expression pattern between the crown and leaf were frequent for genes involved in certain pathways responsible for osmolyte production (sucrose and starch, raffinose, γ-aminobutyric acid metabolism), sugar signalling (trehalose metabolism) and secondary metabolism (lignin synthesis). The action of proteins with antifreeze activity, which were markedly induced during hardening, was demonstrated by a depression in the ice nucleation temperature.
Electronic supplementary material
The online version of this article (doi:10.1007/s10142-011-0213-8) contains supplementary material, which is available to authorized users.
Barley; Differentially expressed genes; Cold acclimation; Crown; Leaf; Metabolic pathways
This article identifies novel stress-protective proteins that belong to the family of intrinsically unstructured proteins, DprA and DprB, which are associated with the cytosol and the peroxisomes in Aspergillus fumigatus.
During a search for genes controlling conidial dormancy in Aspergillus fumigatus, two dehydrin-like genes, DprA and DprB, were identified. The deduced proteins had repeated stretches of 23 amino acids that contained a conserved dehydrin-like protein (DPR) motif. Disrupted DprAΔ mutants were hypersensitive to oxidative stress and to phagocytic killing, whereas DprBΔ mutants were impaired in osmotic and pH stress responses. However, no effect was observed on their pathogenicity in our experimental models of invasive aspergillosis. Molecular dissection of the signaling pathways acting upstream showed that expression of DprA was dependent on the stress-activated kinase SakA and the cyclic AMP-protein kinase A (cAMP-PKA) pathways, which activate the bZIP transcription factor AtfA, while expression of DprB was dependent on the SakA mitogen-activated protein kinase (MAPK) pathway, and the zinc finger transcription factor PacC. Fluorescent protein fusions showed that both proteins were associated with peroxisomes and the cytosol. Accordingly, DprA and DprB were important for peroxisome function. Our findings reveal a novel family of stress-protective proteins in A. fumigatus and, potentially, in filamentous ascomycetes.
Jatropha curcas L. is a highly drought and salt tolerant plant species that is typically used as a traditional folk medicine and biofuel crop in many countries. Understanding the molecular mechanisms that underlie the response to various abiotic environmental stimuli, especially to drought and salt stresses, in J. curcas could be important to crop improvement efforts. In this study, we cloned and characterized the gene for a late embryogenesis abundant (LEA) protein from J. curcas that we designated JcLEA. Sequence analyses showed that the JcLEA protein belongs to group 5, a subgroup of the LEA protein family. In young seedlings, expression of JcLEA is significantly induced by abscisic acid (ABA), dehydration, and salt stress. Subcellular localization analysis shows that that JcLEA protein is distributed in both the nucleus and cytoplasm. Moreover, based on growth status and physiological indices, the overexpression of JcLEA in transgenic Arabidopsis plants conferred increased resistance to both drought and salt stresses compared to the WT. Our data suggests that the group 5 JcLEA protein contributes to drought and salt stress tolerance in plants. Thus, JcLEA is a potential candidate gene for plant genetic modification.
The moss, Physcomitrella patens is a non-seed land plant belonging to early diverging lineages of land plants following colonization of land in the Ordovician period in Earth’s history. Evidence suggests that mosses can be highly tolerant of abiotic stress. We showed previously that dehydration stress and abscisic acid treatments induced oscillations in steady-state levels of LEA (Late Embryogenesis Abundant) protein transcripts, and that removal of ABA resulted in rapid attenuation of oscillatory increases in transcript levels. Here, we show that other abiotic stresses like salt and osmotic stresses also induced oscillations in steady-state transcript levels and that the amplitudes of the oscillatory increases in steady-state transcript levels are reflective of the severity of the abiotic stress treatment. Together, our results suggest that oscillatory increases in transcript levels in response to abiotic stresses may be a general phenomenon in P. patens and that temporally dynamic increases in steady-state transcript levels may be important for adaptation to life in constantly fluctuating environmental conditions.
abiotic stress; salt stress; osmotic stress; oscillations; gene expression
Plants respond to abiotic stress through complex regulation of transcription, including both transcriptional activation and repression. Dehydration-responsive-element binding protein (DREB)-type transcription factors are well known to play important roles in adaptation to abiotic stress. The mechanisms by which DREB-type transcription factors activate stress-induced gene expression have been relatively well studied. However, little is known about how DREB-type transcriptional repressors modulate plant stress responses. In this study, we report the functional analysis of RAP2.1, a DREB-type transcriptional repressor.
RAP2.1 possesses an APETALA2 (AP2) domain that binds to dehydration-responsive elements (DREs) and an ERF-associated amphiphilic repression (EAR) motif, as the repression domain located at the C-terminus of the protein. Expression of RAP2.1 is strongly induced by drought and cold stress via an ABA-independent pathway. Arabidopsis plants overexpressing RAP2.1 show enhanced sensitivity to cold and drought stresses, while rap2.1-1 and rap2.1-2 T-DNA insertion alleles result in reduced sensitivity to these stresses. The reduced stress sensitivity of the plant containing the rap2.1 allele can be genetically complemented by the expression of RAP2.1, but not by the expression of EAR-motif-mutated RAP2.1. Furthermore, chromatin immunoprecipitation (ChIP) analysis has identified Responsive to desiccation/Cold-regulated (RD/COR) genes as downstream targets of RAP2.1 in vivo. Stress-induced expression of the RD/COR genes is repressed by overexpression of RAP2.1 and is increased in plants expressing the rap2.1 allele. In addition, RAP2.1 can negatively regulate its own expression by binding to DREs present in its own promoter. Our data suggest that RAP2.1 acts as a negative transcriptional regulator in defence responses to cold and drought stress in Arabidopsis.
A hypothetical model for the role of RAP2.1 in modulating plant responses to cold and drought is proposed in this study. It appears that RAP2.1 acts as a negative "subregulon" of DREB-type activators and is involved in the precise regulation of expression of stress-related genes, acting to keep stress responses under tight control.
Transcriptional activation of the VERNALIZATION1 gene mediates the acceleration of flowering by prolonged cold (vernalization) in temperate cereals. This study examined the earliest stages of the transcriptional response of VRN1 to low temperatures. Time-course analyses, using a sensitive quantitative PCR assay, showed that in sprouting barley seedlings VRN1 transcripts begin to accumulate within 24 hours of the onset of cold. The kinetics of the initial transcriptional response of VRN1 to cold was similar to the cold-induced genes DEHYDRIN5 (DHN5) and COLD REGULATED 14B (COR14B), but occurred at lower levels compared to cold acclimation genes or the response to longer cold treatments. Temperatures between 15 and –2 °C induced expression of VRN1 within 24 hours, with a maximal response observed between 2 and –2 °C. Transcriptional induction was also observed in undifferentiated callus cells. There were significant increases in histone acetylation levels at the VRN1 locus in response to 24-hour cold treatment. Sodium butyrate, a histone deacetylation inhibitor, triggered an increase in histone acetylation at VRN1 chromatin and elevated VRN1 transcript levels. The transcriptional response of VRN1 to short-term cold treatment was examined in near-isogenic lines that have different VRN1 genotypes, showing that an allele of the barley VRN1 gene with an insertion in the first intron and high basal expression levels has a reduced transcriptional response to short term cold treatment. This study suggests that low-temperature induction of VRN1 is a cellular response to cold triggered by the same mechanisms that mediate low-temperature induction of cold acclimation genes.
Chromatin; cereal; cold acclimation; MADS box; vernalization; VRN1.
Freezing tolerance is an important feature for plant survival during winter. In plants, extracellular freezing occurs at subzero temperatures, resulting in dehydration and mechanical stresses upon the plasma membrane. However, many plants can acquire enhanced freezing tolerance by exposure to non-freezing temperatures, which is referred to as cold acclimation. The plasma membrane is the primary site of freezing injury. During cold acclimation, the lipid composition in the plasma membrane changes, which may protect the plasma membrane from injuries caused by freeze-induced dehydration stress (e.g., phase transition). Recently, we have examined the behavior of the plasma membrane during the freezing process using protoplasts isolated from cold-acclimated Arabidopsis leaves. The observations indicate that the cryobehavior of the plasma membrane after cold acclimation may act to resist the mechanical stress caused by freezing.
freezing tolerance; cold acclimation; surface area regulation; plasma membrane; protoplast
Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance.
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.
LEA (late embryogenesis abundant) proteins are associated with tolerance to water stress resulting from desiccation and cold shock. Although various
functions have been proposed to LEA proteins, their precise role is not fully defined. In silico analysis of the amino acid sequence of two LEA proteins
(early methionine-labeled Vigna, EMV) from the tropical legume crop, Vigna radiata identified a 20 residues motif
‘GGQTRKQQLGSEGYHEMGRK’ characteristic to group 1 LEA proteins. Structural analyses hypothesize these proteins to function like DNA/RNA
binding proteins in protecting macromolecules/ membrane stabilization at the time of dehydration process.
LEA proteins; Vigna radiate; 20-mer motif; function assignments; DNA/RNA binding proteins
MYB-type transcription factors play a diverse role in plant development and response to abiotic stress. This study isolated a rice R2R3-type MYB gene, OsMYB2, and functionally characterized its role in tolerance to abiotic stress by generating transgenic rice plants with overexpressing and RNA interference OsMYB2. Expression of OsMYB2 was up-regulated by salt, cold, and dehydration stress. OsMYB2 was localized in the nucleus with transactivation activity. No difference in growth and development between the OsMYB2-overexpressing and wild-type plants was observed under normal growth conditions, but the OsMYB2-overexpressing plants were more tolerant to salt, cold, and dehydration stresses and more sensitive to abscisic acid than wild-type plants. The OsMYB2-overexpressing plants accumulated greater amounts of soluble sugars and proline than wild-type plants under salt stress. Overexpression of OsMYB2 enhanced up-regulation of genes encoding proline synthase and transporters. The OsMYB2-overexpressing plants accumulated less amounts of H2O2 and malondialdehyde. The enhanced activities of antioxidant enzymes, including peroxidase, superoxide dismutase, and catalase, may underlie the lower H2O2 contents in OsMYB2-overexpressing plants. There was greater up-regulation of stress-related genes, including OsLEA3, OsRab16A, and OsDREB2A, in the OsMYB2-overexpressing plants. Microarray analysis showed that expression of numerous genes involving diverse functions in stress response was altered in the OsMYB2-overexpressing plants. These findings suggest that OsMYB2 encodes a stress-responsive MYB transcription factor that plays a regulatory role in tolerance of rice to salt, cold, and dehydration stress.
Abiotic stress; MYB; OsMYB2; oxidative stress; proline; rice; soluble sugars
Expression of the wheat dehydrin gene Cor410b is induced several fold above its non-stressed levels upon exposure to stresses such as cold, drought and wounding. Deletion analysis of the TdCor410b promoter revealed a single functional C-repeat (CRT) element. Seven transcription factors (TFs) were shown to bind to this CRT element using yeast one-hybrid screens of wheat and barley cDNA libraries, of which only one belonged to the DREB class of TFs. The remaining six encoded ethylene response factors (ERFs) belong to three separate subfamilies. Analysis of binding selectivity of these TFs indicated that all seven could bind to the CRT element (GCCGAC), and that three of the six ERFs could bind both to the CRT element and the ethylene-responsive GCC-box (GCCGCC). The TaERF4 subfamily members specifically bound the CRT element, and did not bind either the GCC-box or DRE element (ACCGAC). Molecular modeling and site-directed mutagenesis identified a single residue Pro42 in the Apetala2 (AP2) domain of TaERF4-like proteins that is conserved in monocotyledonous plants and is responsible for the recognition selectivity of this subfamily. We suggest that both DREB and ERF proteins regulate expression of the Cor410b gene through a single, critical CRT element. Members of the TaERF4 subfamily are specific, positive regulators of Cor410b gene expression.