Accumulation of dehydrin-like proteins in the mitochondria of cereals in response to cold, freezing, drought and ABA treatment

Phosphatidic acid produced by phospholipase Dα1 and Dδ is incorporated into the internal membranes but not involved in the gene expression of RD29A in the abscisic acid signaling network in Arabidopsis thaliana

Core protein components of the abscisic acid (ABA) signaling network, pyrabactin resistance (PYR), protein phosphatases 2C (PP2C), and SNF1-related protein kinase 2 (SnRK2) are involved in the regulation of stomatal closure and gene expression downstream responses in Arabidopsis thaliana. Phosphatidic acid (PA) produced by the phospholipases Dα1 and Dδ (PLDs) in the plasma membrane has been identified as a necessary molecule in ABA-inducible stomatal closure. On the other hand, the involvement of PA in ABA-inducible gene expression has been suggested but remains a question. In this study, the involvement of PA in the ABA-inducible gene expression was examined in the model plant Arabidopsis thaliana and the canonical RD29A ABA-inducible gene that possesses a single ABA-responsive element (ABRE) in the promoter. The promoter activity and accumulation of the RD29A mRNA during ABA exposure to the plants were analyzed under conditions in which the production of PA by PLDs is abrogated through chemical and genetic modification. Changes in the subcellular localization of PA during the signal transduction were analyzed with confocal microscopy. The results obtained in this study suggest that inhibition of PA production by the PLDs does not affect the promoter activity of RD29A. PA produced by the PLDs and exogenously added PA in the plasma membrane are effectively incorporated into internal membranes to transduce the signal. However, exogenously added PA induces stomatal closure but not RD29A expression. This is because PA produced by the PLDs most likely inhibits the activity of not all but only the selected PP2C family members, the negative regulators of the RD29A promoter. This finding underscores the necessity for experimental verifications to adapt previous knowledge into a signaling network model before its construction.

Plant dehydrins and dehydrin-like proteins: characterization and participation in abiotic stress response

Abiotic stress has a significant impact on plant growth and development. It causes changes in the subcellular organelles, which, due to their stress sensitivity, can be affected. Cellular components involved in the abiotic stress response include dehydrins, widely distributed proteins forming a class II of late embryogenesis abundant protein family with characteristic properties including the presence of evolutionarily conserved sequence motifs (including lysine-rich K-segment, N-terminal Y-segment, and often phosphorylated S motif) and high hydrophilicity and disordered structure in the unbound state. Selected dehydrins and few poorly characterized dehydrin-like proteins participate in cellular stress acclimation and are also shown to interact with organelles. Through their functioning in stabilizing biological membranes and binding reactive oxygen species, dehydrins and dehydrin-like proteins contribute to the protection of fragile organellar structures under adverse conditions. Our review characterizes the participation of plant dehydrins and dehydrin-like proteins (including some organellar proteins) in plant acclimation to diverse abiotic stress conditions and summarizes recent updates on their structure (the identification of dehydrin less conserved motifs), classification (new proposed subclasses), tissue- and developmentally specific accumulation, and key cellular activities (including organellar protection under stress acclimation). Recent findings on the subcellular localization (with emphasis on the mitochondria and plastids) and prospective applications of dehydrins and dehydrin-like proteins in functional studies to alleviate the harmful stress consequences by means of plant genetic engineering and a genome editing strategy are also discussed.

Distinct Tomato Cultivars Are Characterized by a Differential Pattern of Biochemical Responses to Drought Stress

Future climate scenarios suggest that crop plants will experience environmental changes capable of affecting their productivity. Among the most harmful environmental stresses is drought, defined as a total or partial lack of water availability. It is essential to study and understand both the damage caused by drought on crop plants and the mechanisms implemented to tolerate the stress. In this study, we focused on four cultivars of tomato, an economically important crop in the Mediterranean basin. We investigated the biochemical mechanisms of plant defense against drought by focusing on proteins specifically involved in this stress, such as osmotin, dehydrin, and aquaporin, and on proteins involved in the general stress response, such as HSP70 and cyclophilins. Since sugars are also known to act as osmoprotectants in plant cells, proteins involved in sugar metabolism (such as RuBisCO and sucrose synthase) were also analyzed. The results show crucial differences in biochemical behavior among the selected cultivars and highlight that the most tolerant tomato cultivars adopt quite specific biochemical strategies such as different accumulations of aquaporins and osmotins. The data set also suggests that RuBisCO isoforms and aquaporins can be used as markers of tolerance/susceptibility to drought stress and be used to select tomato cultivars within breeding programs.

CaDHN3, a Pepper (Capsicum annuum L.) Dehydrin Gene Enhances the Tolerance against Salt and Drought Stresses by Reducing ROS Accumulation

Dehydrins (DHNs) play an important role in abiotic stress tolerance in a large number of plants, but very little is known about the function of DHNs in pepper plants. Here, we isolated a Y₁SK₂-type DHN gene “CaDHN3” from pepper. To authenticate the function of CaDHN3 in salt and drought stresses, it was overexpressed in Arabidopsis and silenced in pepper through virus-induced gene silencing (VIGS). Sub-cellular localization showed that CaDHN3 was located in the nucleus and cell membrane. It was found that CaDHN3-overexpressed (OE) in Arabidopsis plants showed salt and drought tolerance phenotypic characteristics, i.e., increased the initial rooting length and germination rate, enhanced chlorophyll content, lowered the relative electrolyte leakage (REL) and malondialdehyde (MDA) content than the wild-type (WT) plants. Moreover, a substantial increase in the activities of antioxidant enzymes; including the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and lower hydrogen peroxide (H₂O₂) contents and higher O₂^•− contents in the transgenic Arabidopsis plants. Silencing of CaDHN3 in pepper decreased the salt- and drought-stress tolerance, through a higher REL and MDA content, and there was more accumulation of reactive oxygen species (ROS) in the CaDHN3-silenced pepper plants than the control plants. Based on the yeast two-hybrid (Y2H) screening and Bimolecular Fluorescence Complementation (BiFC) results, we found that CaDHN3 interacts with CaHIRD11 protein in the plasma membrane. Correspondingly, the expressions of four osmotic-related genes were significantly up-regulated in the CaDHN3-overexpressed lines. In brief, our results manifested that CaDHN3 may play an important role in regulating the relative osmotic stress responses in plants through the ROS signaling pathway. The results of this study will provide a basis for further analyses of the function of DHN genes in pepper.

Plant survival under drought stress: Implications, adaptive responses, and integrated rhizosphere management strategy for stress mitigation

In many regions of the world, the incidence and extent of drought spells are predicted to increase which will create considerable pressure on global agricultural yields. Most likely among all the abiotic stresses, drought has the strongest effect on soil biota and plants along with complex environmental effects on other ecological systems. Plants being sessile appears the least resilient where drought creates osmotic stress, limits nutrient mobility due to soil heterogeneity, and reduces nutrient access to plant roots. Drought tolerance is a complex quantitative trait controlled by many genes and is one of the difficult traits to study and characterize. Nevertheless, existing studies on drought have indicated the mechanisms of drought resistance in plants on the morphological, physiological, and molecular basis and strategies have been devised to cope with the drought stress such as mass screening, breeding, marker-assisted selection, exogenous application of hormones or osmoprotectants and or engineering for drought resistance. These strategies have largely ignored the role of the rhizosphere in the plant's drought response. Studies have shown that soil microbes have a substantial role in modulation of plant response towards biotic and abiotic stress including drought. This response is complex and involves alteration in host root system architecture through hormones, osmoregulation, signaling through reactive oxygen species (ROS), induction of systemic tolerance (IST), production of large chain extracellular polysaccharides (EPS), and transcriptional regulation of host stress response genes. This review focuses on the integrated rhizosphere management strategy for drought stress mitigation in plants with a special focus on rhizosphere management. This combinatorial approach may include rhizosphere engineering by addition of drought-tolerant bacteria, nanoparticles, liquid nano clay (LNC), nutrients, organic matter, along with plant-modification with next-generation genome editing tool (e.g., CRISPR/Cas9) for quickly addressing emerging challenges in agriculture. Furthermore, large volumes of rainwater and wastewater generated daily can be smartly recycled and reused for agriculture. Farmers and other stakeholders will get a proper knowledge-exchange and an ideal road map to utilize available technologies effectively and to translate the measures into successful plant-water stress management. The proposed approach is cost-effective, eco-friendly, user-friendly, and will impart long-lasting benefits on agriculture and ecosystem and reduce vulnerability to climate change.

Cold-regulated gene LeCOR413PM2 confers cold stress tolerance in tomato plants

Tomato (Lycopersicon esculentum Mill) is an important food plant that has been used as a model plant in genetic evolution and molecular biology research. The plant is originated from the tropics; thus, it is sensitive to cold. Its growth and development can be easily affected by cold stress. In this study, cold-regulated gene LeCOR413PM2 was cloned from tomato leaves and then used to generate two types of transgenic tomato plants: LeCOR413PM2-overexpressing transgenic plants and RNA-interference-expressing transgenic plants. The functions and expression of LeCOR413PM2 gene in response to cold stress were subsequently assessed. The results showed that LeCOR413PM2 localized in the plasma membrane. Expression of LeCOR413PM2 gene in the leaf of transgenic tomato plant was highest compared to that in other organs (i.e., root, stem, flower and fruit); it was elevated when plants were treated with cold stress. Overexpression of LeCOR413PM2 gene was found to not only reduce damage to cell membrane, accumulation of ROS, and photoinhibition of PSII, but also maintain high activity of antioxidant enzymes and content of osmotic regulators. The results also reveal that high activities of antioxidant enzymes were caused by the up-regulation of their gene expressions. This study demonstrates that the overexpression of LeCOR413PM2 could increase cold tolerance of transgenic tomato plants, while the suppressed expression of LeCOR413PM2 by RNA interference could increase the sensitivity of plants to cold.

In-Cold Exposure to Z-3-Hexenal Provides Protection Against Ongoing Cold Stress in Zea mays

Green leaf volatiles (GLVs), which have mostly been described as providers of protection against insect herbivory and necrotrophic pathogen infections, were recently shown to provide significant fortification against cold stress damage. It was further demonstrated that cold-damaged maize seedlings released a significant amount of GLVs, in particular, Z-3-hexenal (Z-3-HAL). Here, we report that the in-cold treatment of maize seedlings with Z-3-HAL significantly improved cold stress resistance. The transcripts for cold-protective genes were also significantly increased in the Z-3-HAL treated maize seedlings over those found in only cold stressed plants. Consequently, the maize seedlings treated with HAL during cold showed a significantly increased structural integrity, significantly less damage, and increased growth after cold stress, relative to the non-HAL treated maize seedlings. Together, these results demonstrate the protective effect of in-cold treatment with HAL against cold damage, and suggest that the perception of these compounds during cold episodes significantly improves resistance against this abiotic stress.

Unigene-based RNA-seq provides insights on drought stress responses in Marsdenia tenacissima

Marsdenia tenacissima is a well-known anti-cancer medicinal plant used in traditional Chinese medicine, which often grows on the karst landform and the water conservation capacity of land is very poorly and drought occurrences frequently. We found M. tenacissima has strong drought resistance because of continuousdrought16 d, the leaves of M. tenacissima were fully curly and dying. But the leaves were fully almost recovering after re-watering 24h. The activity of SOD and POD were almost doubled under drought stress. The content of osmotic regulating substance proline and soluble sugar were three times than control group. But after re-watering, these indexes were declined rapidly. Three cDNA libraries of control, drought stress, and re-watering treatments were constructed. There were 43,129,228, 47,116,844, and 42,815,454 clean reads with Q20 values of 98.06, 98.04, and 97.88respectively.SRA accession number of raw data was PRJNA498187 on NCBI. A total of 8672, 6043, and 6537 differentially expressed genes (DEGs) were identified in control vs drought stress, control vs re-watering, and drought stress vs re-watering, respectively. In addition, 1039, 1016, and 980 transcription factors (TFs) were identified, respectively. Among them, 363, 267, and 299 TFs were identified as DEGs in drought stress, re-watering, and drought stress and re-watering, respectively. These differentially expressed TFs mainly belonged to the bHLH, bZIP, C2H2, ERF, MYB, MYB-related, and NAC families. A comparative analysis found that 1174 genes were up-regulated and 2344 were down-regulated under drought stress and this pattern was the opposite to that found after re-watering. Among the up-regulated genes, 64 genes were homologous to known functional genes that directly protect plants against drought stress. Furthermore, 44 protein kinases and 38 TFs with opposite expression patterns under drought stress and re-watering were identified, which are possibly candidate regulators for drought stress resistance in M. tenacissima. Our study is the first to characterize the M. tenacissima transcriptome in response to drought stress, and will serve as a useful resource for future studies on the functions of candidate protein kinases and TFs involved in M. tenacissima drought stress resistance.

Green leaf volatiles protect maize (Zea mays) seedlings against damage from cold stress

Although considerable evidence has accumulated on the defensive activity of plant volatile organic compounds against pathogens and insect herbivores, less is known about the significance of volatile organic compounds emitted by plants under abiotic stress. Here, we report that green leaf volatiles (GLVs), which were previously shown to prime plant defences against insect herbivore attack, also protect plants against cold stress (4 °C). We show that the expression levels of several cold stress-related genes are significantly up-regulated in maize (Zea mays) seedlings treated with physiological concentrations of the GLV, (Z)-3-hexen-1-yl acetate (Z-3-HAC), and that seedlings primed with Z-3-HAC exhibit increased growth and reduced damage after cold stress relative to unprimed seedlings. Together, these data demonstrate the protective and priming effect of GLVs against cold stress and suggest an activity of GLVs beyond the activation of typical plant defence responses against herbivores and pathogens.

Mitochondrial Biogenesis in Diverse Cauliflower Cultivars under Mild and Severe Drought. Impaired Coordination of Selected Transcript and Proteomic Responses, and Regulation of Various Multifunctional Proteins

Mitochondrial responses under drought within Brassica genus are poorly understood. The main goal of this study was to investigate mitochondrial biogenesis of three cauliflower (Brassica oleracea var. botrytis) cultivars with varying drought tolerance. Diverse quantitative changes (decreases in abundance mostly) in the mitochondrial proteome were assessed by two-dimensional gel electrophoresis (2D PAGE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Respiratory (e.g., complex II, IV (CII, CIV) and ATP synthase subunits), transporter (including diverse porin isoforms) and matrix multifunctional proteins (e.g., components of RNA editing machinery) were diversely affected in their abundance under two drought levels. Western immunoassays showed additional cultivar-specific responses of selected mitochondrial proteins. Dehydrin-related tryptic peptides (found in several 2D spots) immunopositive with dehydrin-specific antisera highlighted the relevance of mitochondrial dehydrin-like proteins for the drought response. The abundance of selected mRNAs participating in drought response was also determined. We conclude that mitochondrial biogenesis was strongly, but diversely affected in various cauliflower cultivars, and associated with drought tolerance at the proteomic and functional levels. However, discussed alternative oxidase (AOX) regulation at the RNA and protein level were largely uncoordinated due to the altered availability of transcripts for translation, mRNA/ribosome interactions, and/or miRNA impact on transcript abundance and translation.

Functional characterization of KS-type dehydrin ZmDHN13 and its related conserved domains under oxidative stress

Dehydrins belong to the group 2 family LEA (Late Embryogenesis Abundant) proteins, which are up-regulated in most plants during cold and drought stress. According to the number and order of the Y-, S- and K-segments, dehydrins are classified into five subclasses: YnSKn, YnKn, SKn, Kn and KnS. Here, the maize (Zea mays L.) KS-type dehydrin gene, ZmDHN13, was identified and later characterized. Expression profiling demonstrated that ZmDHN13 was constitutively expressed, but its expression was also altered by high osmosis, low temperature, oxidative stress and abscisic acid (ABA). Furthermore, the roles of the three conserved segments in phosphorylation, localization, binding metal ions and physiological functions were explored. ZmDHN13 was mainly localized in the nucleus, depending on phosphorylation status. Additional studies indicated that ZmDHN13 could be phosphorylated by CKII (casein kinase II), when the NLS (nuclear localization signal) segment and the S-segment were core sequences. The overexpression of ZmDHN13 enhanced transgenic tobacco tolerance to oxidative stress, and the three conserved segments exhibited a cooperative effect in response to environmental stresses in vivo.

Plant dehydrins: shedding light on structure and expression patterns of dehydrin gene family in barley

Dehydrins, an important group of late embryogenesis abundant proteins, accumulate in response to dehydration stresses and play protective roles under stress conditions. Herein, phylogenetic analysis of the dehydrin family was performed using the protein sequences of 108 dehydrins obtained from 14 plant species based on plant taxonomy and protein subclasses. Sub-cellular localization and phosphorylation sites of these proteins were also predicted. The protein features distinguishing these dehydrins categories were identified using various attribute weighting and decision tree analyses. The results revealed that the presence of the S motif preceding the K motif (Y_nSK_n, SK_n, and S_nKS) was more evident and the Y_nSK_n subclass was more frequent in monocots. In barley, as one of the most drought-tolerant crops, there are ten members of Y_nSK_n out of 13 HvDhns. In promoter regions, six types of abiotic stress-responsive elements were identified. Regulatory elements in UTR sequences of HvDhns were infrequent while only four miRNA targets were found. Furthermore, physiological parameters and gene expression levels of HvDhns were studied in tolerant (HV1) and susceptible (HV2) cultivars, and in an Iranian tolerant wild barley genotype (Spontaneum; HS) subjected to gradual water stress and after recovery duration at the vegetative stage. The results showed the significant impact of dehydration on dry matter, relative leaf water, chlorophyll contents, and oxidative damages in HV2 compared with the other studied genotypes, suggesting a poor dehydration tolerance, and incapability of recovering after re-watering in HV2. Under severe drought stress, among the 13 HvDhns genes, 5 and 10 were exclusively induced in HV1 and HS, respectively. The gene and protein structures and the expression patterns of HvDhns as well as the physiological data consistently support the role of dehydrins in survival and recovery of barley plants from drought particularly in HS. Overall, this information would be helpful for functional characterization of the Dhn family in plants.

Identification of vernalization responsive genes in the winter wheat cultivar Jing841 by transcriptome sequencing

This study aimed to identify vernalization responsive genes in the winter wheat cultivar Jing841 by comparing the transcriptome data with that of a spring wheat cultivar Liaochun10. For each cultivar, seedlings before and after the vernalization treatment were sequenced by Solexa/Illumina sequencing. Genes differentially expressed after and before vernalization were identified as differentially expressed genes (DEGs) using false discovery rate (FDR) ≤ 0.001 and |log2 (fold change)|>1 as cutoffs. The Jing841-specific DEGs were screened and subjected to functional annotation using gene ontology (GO) database. Vernalization responsive genes among the specific genes were selected for validation by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and the expression change over the time was investigated for the top 11 genes with the most significant expression differences. A total of 138,062 unigenes were obtained. Overall, 636 DEGs were identified as vernalization responsive genes including some known genes such as VRN-1 and COR14a, and some unknown contigs. The qRT-PCR validated changes in the expression of 18 DEGs that were detected by RNA-seq. Among them, 11 genes displayed four different types of expression patterns over time during the 30-day-long vernalization treatment. Genes or contigs such as VRN-A1, COR14a, IRIP, unigene1806 and Cl18953. Contig2 probably have critical roles in vernalization.

New Insights on Drought Stress Response by Global Investigation of Gene Expression Changes in Sheepgrass (Leymus chinensis)

Water is a critical environmental factor that restricts the geographic distribution of plants. Sheepgrass [Leymus chinensis, (Trin.) Tzvel] is an important forage grass in the Eurasia Steppe and a close germplasm for wheat and barley. This native grass adapts well to adverse environments such as cold, salinity, alkalinity and drought, and it can survive when the soil moisture may be less than 6% in dry seasons. However, little is known about how sheepgrass tolerates water stress at the molecular level. Here, drought stress experiment and RNA-sequencing (RNA-seq) was performed in three pools of RNA samples (control, drought stress, and rewatering). We found that sheepgrass seedlings could still survive when the soil water content (SWC) was reduced to 14.09%. Differentially expressed genes (DEGs) analysis showed that 7320 genes exhibited significant responses to drought stress. Of these DEGs, 2671 presented opposite expression trends before and after rewatering. Furthermore, ~680 putative sheepgrass-specific water responsive genes were revealed that can be studied deeply. Gene ontology (GO) annotation revealed that stress-associated genes were activated extensively by drought treatment. Interestingly, cold stress-related genes were up-regulated greatly after drought stress. The DEGs of MAPK and calcium signal pathways, plant hormone ABA, jasmonate, ethylene, brassinosteroid signal pathways, cold response CBF pathway participated coordinatively in sheepgrass drought stress response. In addition, we identified 288 putative transcription factors (TFs) involved in drought response, among them, the WRKY, NAC, AP2/ERF, bHLH, bZIP, and MYB families were enriched, and might play crucial and significant roles in drought stress response of sheepgrass. Our research provided new and valuable information for understanding the mechanism of drought tolerance in sheepgrass. Moreover, the identification of genes involved in drought response can facilitate the genetic improvement of crops by molecular breeding.

Biochemical Analyses of Sorghum Varieties Reveal Differential Responses to Drought

We have examined the biochemical responses of two sorghum cultivars of differing drought tolerance, Samsorg 17 (more drought tolerant) and Samsorg 40 (less drought tolerant), to sustained drought. Plants were exposed to different degrees of drought and then maintained at that level for five days. Responses were examined in terms of metabolic changes and the expression of drought induced proteins-Heat Shock Proteins (HSPs) and dehydrins (DHNs). Generalised phenotypic changes were studied using Fourier transform infrared (FT-IR) Spectroscopy and non-targeted Gas Chromatography Mass Spectrometry (GC-MS) was employed to detect changes in metabolites, while changes in protein expression were examined using Western blot analysis. Different response profiles of metabolites, HSPs and DHNs were observed in the two cultivars. Metabolic changes involved variation in amino acids, polysaccharides and their derivatives. A total of 188 compounds, with 142 known metabolites and 46 unknown small molecules, were detected in the two sorghum varieties. Under water deficit conditions, Samsorg 17 accumulated sugars and sugar alcohols, while in Samsorg 40 amino acids increased in concentration. This study suggest that the two Sorghum varieties adopt distinct approaches in response to drought, with Samsorg 17 being better able to maintain leaf function under severe drought conditions.

Deep sequencing revealed molecular signature of horizontal gene transfer of plant like transcripts in the mosquito Anopheles culicifacies: an evolutionary puzzle

In prokaryotes, horizontal gene transfer (HGT) has been regarded as an important evolutionary drive to acquire and retain beneficial genes for their survival in diverse ecologies. However, in eukaryotes, the functional role of HGTs remains questionable, although current genomic tools are providing increased evidence of acquisition of novel traits within non-mating metazoan species. Here, we provide another transcriptomic evidence for the acquisition of massive plant genes in the mosquito, Anopheles culicifacies. Our multiple experimental validations including genomic PCR, RT-PCR, real-time PCR, immuno-blotting and immuno-florescence microscopy, confirmed that plant like transcripts (PLTs) are of mosquito origin and may encode functional proteins. A comprehensive molecular analysis of the PLTs and ongoing metagenomic analysis of salivary microbiome provide initial clues that mosquitoes may have survival benefits through the acquisition of nuclear as well as chloroplast encoded plant genes. Our findings of PLTs further support the similar questionable observation of HGTs in other higher organisms, which is still a controversial and debatable issue in the community of evolutionists. We believe future understanding of the underlying mechanism of the feeding associated molecular responses may shed new insights in the functional role of PLTs in the mosquito.

Silencing of dehydrin CaDHN1 diminishes tolerance to multiple abiotic stresses in Capsicum annuum L

We cloned a dehydrins gene CaDHN1 from pepper and the expression of CaDHN1 was markedly upregulated by cold, salt, osmotic stresses and salicylic acid (SA) treatment. Dehydrins (DHNs) are a subfamily of group 2 late embryogenesis-abundant (LEA) proteins that are thought to play an important role in enhancing abiotic stress tolerance in plants. In this study, a DHN EST (Expressed Sequence Tag) was obtained from 6 to 8 true leaves seedlings of pepper cv P70 (Capsicum annuum L.) by our laboratory. However, the DHN gene in pepper was not well characterized. According to this EST sequence, we isolated a DHN gene, designated as CaDHN1, and investigated the response and expression of this gene under various stresses. Our results indicated that CaDHN1 has the DHN-specific and conserved K- and S- domain and encodes 219 amino acids. Phylogenetic analysis showed that CaDHN1 belonged to the SKn subgroup. Tissue expression profile analysis revealed that CaDH N1 was expressed predominantly in fruits and flowers. The expression of CaDHN1 was markedly upregulated in response to cold, salt, osmotic stresses and salicylic acid (SA) treatment, but no significant change by abscisic acid (ABA) and heavy metals treatment. Loss of function of CaDHN1 using the virus-induced gene silencing (VIGS) technique led to decreased tolerance to cold-, salt- and osmotic-induced stresses. Overall, these results suggest that CaDHN1 plays an important role in regulating the abiotic stress resistance in pepper plants.

The pepper late embryogenesis abundant protein CaLEA1 acts in regulating abscisic acid signaling, drought and salt stress response

As sessile organisms, plants are constantly challenged by environmental stresses, including drought and high salinity. Among the various abiotic stresses, osmotic stress is one of the most important factors for growth and significantly reduces crop productivity in agriculture. Here, we report a function of the CaLEA1 protein in the defense responses of plants to osmotic stress. Our analyses showed that the CaLEA1 gene was strongly induced in pepper leaves exposed to drought and increased salinity. Furthermore, we determined that the CaLEA1 protein has a late embryogenesis abundant (LEA)_3 homolog domain highly conserved among other known group 5 LEA proteins and is localized in the processing body. We generated CaLEA1-silenced peppers and CaLEA1-overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to dehydration and high salinity. Virus-induced gene silencing of CaLEA1 in pepper plants conferred enhanced sensitivity to drought and salt stresses, which was accompanied by high levels of lipid peroxidation in dehydrated and NaCl-treated leaves. CaLEA1-OX plants exhibited enhanced sensitivity to abscisic acid (ABA) during seed germination and in the seedling stage; furthermore, these plants were more tolerant to drought and salt stress than the wild-type plants because of enhanced stomatal closure and increased expression of stress-responsive genes. Collectively, our data suggest that CaLEA1 positively regulates drought and salinity tolerance through ABA-mediated cell signaling.

Quantification of expression of dehydrin isoforms in the desiccation tolerant plant Craterostigma plantagineum using specifically designed reference genes

Craterostigma plantagineum is a desiccation tolerant resurrection plant. Many genes are induced during desiccation. Dehydrins are a group of dehydration-induced genes present in all higher plants. The current study aims at classifying the most abundantly expressed dehydrin genes from vegetative tissues of C. plantagineum and quantifying their expression. To identify variations between dehydrin isoforms at different stages of desiccation and rehydration by RT-qPCR, the target mRNA requires an accurate and reliable normalization. Previously we reported that RNAs from leaves and roots of C. plantagineum are not degraded during desiccation and subsequent rehydration thus allowing the use of RT-qPCR to test the stability of reference genes. The expression stability of eight candidate reference genes was tested in leaves, roots and callus. These genes were ranked according to their stability of gene expression using GeNorm(PLUS) and RefFinder. The most consistently expressed reference genes in each tissue were identified and used to normalize gene expression data. Dehydrin isoforms were divided in three groups based on the expression level during the desiccation process in three different tissues (leaves, roots and callus).

Protein profiles reveal diverse responsive signaling pathways in kernels of two maize inbred lines with contrasting drought sensitivity

Drought stress is a major factor that contributes to disease susceptibility and yield loss in agricultural crops. To identify drought responsive proteins and explore metabolic pathways involved in maize tolerance to drought stress, two maize lines (B73 and Lo964) with contrasting drought sensitivity were examined. The treatments of drought and well water were applied at 14 days after pollination (DAP), and protein profiles were investigated in developing kernels (35 DAP) using iTRAQ (isobaric tags for relative and absolute quantitation). Proteomic analysis showed that 70 and 36 proteins were significantly altered in their expression under drought treatments in B73 and Lo964, respectively. The numbers and levels of differentially expressed proteins were generally higher in the sensitive genotype, B73, implying an increased sensitivity to drought given the function of the observed differentially expressed proteins, such as redox homeostasis, cell rescue/defense, hormone regulation and protein biosynthesis and degradation. Lo964 possessed a more stable status with fewer differentially expressed proteins. However, B73 seems to rapidly initiate signaling pathways in response to drought through adjusting diverse defense pathways. These changes in protein expression allow for the production of a drought stress-responsive network in maize kernels.

Perturbation of polyamine catabolism affects grape ripening of Vitis vinifera cv. Trincadeira

Grapes are economically the most important fruit worldwide. However, the complexity of biological events that lead to ripening of nonclimacteric fruits is not fully understood, particularly the role of polyamines' catabolism. The transcriptional and metabolic profilings complemented with biochemical data were studied during ripening of Trincadeira grapes submitted to guazatine treatment, a potent inhibitor of polyamine oxidase activity. The mRNA expression profiles of one time point (EL 38) corresponding to harvest stage was compared between mock and guazatine treatments using Affymetrix GrapeGen(®) genome array. A total of 2113 probesets (1880 unigenes) were differentially expressed between these samples. Quantitative RT-PCR validated microarrays results being carried out for EL 35 (véraison berries), EL 36 (ripe berries) and EL 38 (harvest stage berries). Metabolic profiling using HPLC and (1)H NMR spectroscopy showed increase of putrescine, proline, threonine and 1-O-ethyl-β-glucoside in guazatine treated samples. Genes involved in amino acid, carbohydrate and water transport were down-regulated in guazatine treated samples suggesting that the strong dehydrated phenotype obtained in guazatine treated samples may be due to impaired transport mechanisms. Genes involved in terpenes' metabolism were differentially expressed between guazatine and mock treated samples. Altogether, results support an important role of polyamine catabolism in grape ripening namely in cell expansion and aroma development.

JcLEA, a novel LEA-like protein from Jatropha curcas, confers a high level of tolerance to dehydration and salinity in Arabidopsis thaliana

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.

Immunoanalysis of dehydrins in Araucaria angustifolia embryos

The aim of this study was to describe the dehydrin content of mature Araucaria angustifolia embryos, a species of endangered and economically important conifers, native to southern Brazil, northeastern Argentina, and eastern Paraguay. The A. angustifolia seeds have been categorized as recalcitrant. Dehydrins were studied by western blot analysis and in situ immunolocalization microscopy using antibodies raised against the K segment, a highly conserved lysine-rich 15-amino acid sequence extensively used to recognize proteins immunologically related to the dehydrin family. Western blot analysis of the heat-stable protein fraction, as estimated by 15 % SDS-PAGE, revealed three main bands of approximately 20-, 26-, and 29-kDa; when 17.5 % SDS-PAGE was used, each band resolved into two other bands. Two thermosensitive dehydrin bands of around 16 and 35 kDa were common to the axis and cotyledons, and another thermosensitive band, with molecular mass of approximately 10 kDa, was present in the cotyledons only. Following alkaline phosphatase (AP) treatment, a gel mobility shift was detected for each one of the four main bands that can be due to phosphorylation. Dehydrins were detected in all axis and cotyledon tissues using in situ immunolocalization microscopy. At the subcellular level, dehydrins were immunolocalized in the nuclei, protein bodies, and microbodies. In the nucleus, dehydrins were found to be associated with chromatin. We concluded that the gel mobility shift for the four main bands (probably due to phosphorylation), the presence of thermosensitive bands, and the specific localizations in nuclei and protein bodies provide key starting points to understand the function of dehydrins in the embryo cells of this species.

Roles for blue light, jasmonate and nitric oxide in the regulation of dormancy and germination in wheat grain (Triticum aestivum L.)

Abscisic acid (ABA) plays a central role in seed dormancy and transcriptional regulation of genes coding for ABA biosynthetic and degradation enzymes is responsible for control of ABA content. However, little is known about signalling both before and after ABA regulation, in particular, how environmental signals are perceived and transduced. We are interested in these processes in cereal grains, particularly in relation to the development of strategies for controlling pre-harvest sprouting in barley and wheat. Our previous studies have indicated possible components of dormancy control and here we present evidence that blue light, nitric oxide (NO) and jasmonate are major controlling elements in wheat grain. Using microarray and pharmacological studies, we have found that blue light inhibits germination in dormant grain and that methyl jasmonate (MJ) and NO counteract this effect by reducing dormancy. We also present evidence that NO and jasmonate play roles in dormancy control in vivo. ABA was reduced by MJ and this was accompanied by reduced levels of expression of TaNCED1 and increased expression of TaABA8'OH-1 compared with dormant grain. Similar changes were caused by after-ripening. Analysis of global gene expression showed that although jasmonate and after-ripening caused important changes in gene expression, the changes were very different. While breaking dormancy, MJ had only a small number of target genes including gene(s) encoding beta-glucosidase. Our evidence indicates that NO and MJ act interdependently in controlling reduction of ABA and thus the demise of dormancy.

Induction of Drought Stress Resistance by Multi-Functional PGPR Bacillus licheniformis K11 in Pepper

Drought stress is one of the major yield affecting factor for pepper plant. The effects of PGPRs were analyzed in relation with drought resistance. The PGPRs inoculated pepper plants tolerate the drought stress and survived as compared to non-inoculated pepper plants that died after 15 days of drought stress. Variations in protein and RNA accumulation patterns of inoculated and non-inoculated pepper plants subjected to drought conditions for 10 days were confirmed by two dimensional polyacrylamide gel electrophoresis (2D-PAGE) and differential display PCR (DD-PCR), respectively. A total of six differentially expressed stress proteins were identified in the treated pepper plants by 2D-PAGE. Among the stress proteins, specific genes of Cadhn, VA, sHSP and CaPR-10 showed more than a 1.5-fold expressed in amount in B. licheniformis K11-treated drought pepper compared to untreated drought pepper. The changes in proteins and gene expression patterns were attributed to the B. licheniformis K11. Accordingly, auxin and ACC deaminase producing PGPR B. licheniformis K11 could reduce drought stress in drought affected regions without the need for overusing agrochemicals and chemical fertilizer. These results will contribute to the development of a microbial agent for organic farming by PGPR.

Water deficit modulates the response of Vitis vinifera to the Pierce's disease pathogen Xylella fastidiosa

Pierce's disease, caused by the bacterium Xylella fastidiosa, is one of the most devastating diseases of cultivated grape, currently restricted to the Americas. To test the long-standing hypothesis that Pierce's disease results from pathogen-induced drought stress, we used the Affymetrix Vitis GeneChip to compare the transcriptional response of Vitis vinifera to Xylella infection, water deficit, or a combination of the two stresses. The results reveal a redirection of gene transcription involving 822 genes with a minimum twofold change (P < 0.05), including the upregulation of transcripts for phenylpropanoid and flavonoid biosynthesis, pathogenesis-related proteins, abscisic acid- and jasmonic acid-responsive biosynthesis, and downregulation of transcripts related to photosynthesis, growth, and nutrition. Although the transcriptional response of plants to Xylella infection was largely distinct from the response of healthy plants to water stress, we find that 138 of the pathogen-induced genes exhibited a significantly stronger transcriptional response when plants were simultaneously exposed to infection and drought stress, suggesting a strong interaction between disease and water deficit. This interaction between drought stress and disease was mirrored in planta at the physiological level for aspects of water relations and photosynthesis and in terms of the severity of disease symptoms and the extent of pathogen colonization, providing a molecular correlate of the classical concept of the disease triangle in which environment impacts disease severity.

Proteomic changes associated with freeze-thaw injury and post-thaw recovery in onion (Allium cepa L.) scales

The ability of plants to recover from freeze-thaw injury is a critical component of freeze-thaw stress tolerance. To investigate the molecular basis of freeze-thaw recovery, here we compared the proteomes of onion scales from unfrozen control (UFC), freeze-thaw injured (INJ), and post-thaw recovered (REC) treatments. Injury-related proteins (IRPs) and recovery-related proteins (RRPs) were differentiated according to their accumulation patterns. Many IRPs decreased right after thaw without any significant re-accumulation during post-thaw recovery, while others were exclusively induced in INJ tissues. Most IRPs are antioxidants, stress proteins, molecular chaperones, those induced by physical injury or proteins involved in energy metabolism. Taken together, these observations suggest that while freeze-thaw compromises the constitutive stress protection and energy supply in onion scales, it might also recruit 'first-responders' (IRPs that were induced) to mitigate such injury. RRPs, on the other hand, are involved in the injury-repair program during post-thaw environment conducive for recovery. Some RRPs were restored in REC tissues after their first reduction right after thaw, while others exhibit higher abundance than their 'constitutive' levels. RRPs might facilitate new cellular homeostasis, potentially by re-establishing ion homeostasis and proteostasis, cell-wall remodelling, reactive oxygen species (ROS) scavenging, defence against possible post-thaw infection, and regulating the energy budget to sustain these processes.

Designing disorder: Tales of the unexpected tails

Protein tags of various sizes and shapes catalyze progress in biosciences. Well-folded tags can serve to solubilize proteins. Small, unfolded, peptide-like tags have become invaluable tools for protein purification as well as protein-protein interaction studies. Intrinsically Disordered Proteins (IDPs), which lack unique 3D structures, received exponentially increasing attention during the last decade. Recently, large ID tags have been developed to solubilize proteins and to engineer the pharmacological properties of protein and peptide pharmaceuticals. Here, we contrast the complementary benefits and applications of both folded and ID tags based on predictions of ID. Less structure often means more function in a shorter tag.

Cloning and characterization of dehydrin gene from Ammopiptanthus mongolicus

Based on the sequence of an expressed sequence tag, the full-length cDNA of 1,008 nucleotides was cloned from Ammopiptanthus mongolicus by rapid amplification of cDNA ends. It was designated as AmDHN, encoding a protein of 183 amino acids. The calculated molecular weight of the AmDHN protein is 18.4 k Da, and theoretical isoelectric point is 5.78. The AmDHN localized in nucleus. Under normal growth conditions, differential expression of AmDHN exhibited that the expression was the highest in seeds and the lowest in flowers. AmDHN could be induced by NaCl, PEG6000, ABA and drought treatments. Salt and drought resistances of transgenic plants with overexpression of AmDHN are improved. Taken together, these results demonstrated that AmDHN could regulate the expression of abiotic-responsive genes and plays important roles in modulating the tolerance of plants to abiotic stresses.

Accumulation pattern of dehydrins during sugarcane (var. SP80.3280) somatic embryogenesis

The objective of the present study was to determine dehydrin protein levels in sugarcane var. SP80-3280 during somatic embryogenesis. Dehydrins from embryogenic and non-embryogenic cell cultures were analyzed using western blot and in situ immunolocalization microscopy. Both techniques employ antibodies raised against a highly conserved lysine-rich 15-amino acid sequence termed the K-domain, which is extensively used to recognize proteins immunologically related to the dehydrin family. In embryogenic cultures, western blot analysis of the heat-stable protein fraction revealed eleven major bands ranging from 52 to 17 kDa. They were already visible on the first days, gradually increasing until reaching peak values around day 14, when organogenesis begins, to later decrease in concurrence with the appearance of green plantlets (around day 28). These fluctuations indicate that this pattern of accumulation is under developmental control. Dehydrins were mainly immunolocalized in the nuclei. A phosphatase treatment of protein extracts caused a mobility shift of the 52, 49, and 43 kDa dehydrin bands suggesting a putative modulation mechanism based on protein phosphorylation. In sugarcane embryogenic cultures, presence of dehydrins is a novel finding. Dehydrins were absent in non-embryogenic cultures. The novel findings regarding accumulation, nuclear localization, and phosphorylation of dehydrins provide a starting point for further research on the role of these proteins in the induction and/or maintenance of embryogenesis.

KEY MESSAGE

The novel findings regarding accumulation, nuclear localization, and phosphorylation of dehydrins provide a starting point for further research on the role of these proteins in the induction and/or maintenance of embryogenesis.

Genome-wide identification and analysis of late embryogenesis abundant (LEA) genes in Prunus mume

Late embryogenesis abundant (LEA) proteins play important roles in plant desiccation tolerance. In this study, 30 LEA genes were identified from Chinese plum (Prunus mume) through genome-wide analysis. The PmLEA genes are distributed on all Chinese plum chromosomes except chromosome 3. Twelve (40 %) and five PmLEA genes are arranged in tandem and segmental duplications, respectively. The PmLEA genes could be divided into eight groups (LEA_1, LEA_2, LEA_3, LEA_4, LEA_5, PvLEA18, dehydrin and seed maturation protein). Ten gene conversion events were observed and most of them (70 %) were identified in dehydrin group. Most PmLEA genes were highly expressed in flower (22/30) and up-regulated by ABA treatment (19/30).

Genome-wide identification and analysis of late embryogenesis abundant (LEA) genes in Prunus mume

Late embryogenesis abundant (LEA) proteins play important roles in plant desiccation tolerance. In this study, 30 LEA genes were identified from Chinese plum (Prunus mume) through genome-wide analysis. The PmLEA genes are distributed on all Chinese plum chromosomes except chromosome 3. Twelve (40 %) and five PmLEA genes are arranged in tandem and segmental duplications, respectively. The PmLEA genes could be divided into eight groups (LEA_1, LEA_2, LEA_3, LEA_4, LEA_5, PvLEA18, dehydrin and seed maturation protein). Ten gene conversion events were observed and most of them (70 %) were identified in dehydrin group. Most PmLEA genes were highly expressed in flower (22/30) and up-regulated by ABA treatment (19/30).

Characterization of a novel Y2K-type dehydrin VrDhn1 from Vigna radiata

A novel dehydrin gene (VrDhn1) was isolated from an embryo cDNA library of Vigna radiata (L.) Wilczek (mungbean) variety VC1973A. The intronless VrDhn1 gene encodes a protein belonging to the Y(2)K-type dehydrin family. VrDhn1 protein accumulated in embryos and cotyledons during seed maturation and disappeared 2 days after seed imbibition (DAI). The expression of VrDhn1 mRNA and accumulation of VrDhn1 protein were at high levels in mature seeds, but neither mRNA nor protein was detected in mungbean vegetative tissues under normal growth conditions. The VrDhn1 mRNA level was extremely high in mature seeds and decreased to ∼30% at 1 DAI, and was not detectable at ~7 DAI. Tissue dehydration, salinity and exogenous ABA markedly induced VrDhn1 transcripts in plants as measured by quantitative real-time reverse transcription-PCR (qRT-PCR). VrDhn1 protein was not detected using immunoblots in seedlings under stress treatments. In mature seeds or 1 DAI seedlings, VrDhn1 proteins were immunolocalized in the nucleus and cytoplasm. VrDhn1 exhibited low affinity for non-specific interaction with DNA using electrophoretic mobility shift assays (EMSAs), and the exogenous addition of Zn(2+) or Ni(2+) stimulated interaction. The His-tagged VrDhn1 (30.17 kDa) protein showed a molecular mass of 63.1 kDa on gel filtration, suggesting a dimer form. This is the first report showing that a Y(2)K-type VrDhn1 enters the nucleus and interacts with DNA during seed maturation.

Global changes in gene expression of grapefruit peel tissue in response to the yeast biocontrol agent Metschnikowia fructicola

To gain a better understanding of the molecular changes taking place in citrus fruit tissue following the application of the yeast biocontrol agent Metschnikowia fructicola, microarray analysis was performed on grapefruit surface wounds using an Affymetrix Citrus GeneChip. Using a cut-off of P < 0.05 and a 1.5-fold change difference as biologically significant, the data indicated that 1007 putative unigenes showed significant expression changes following wounding and yeast application relative to wounded controls. Microarray results of selected genes were validated by reverse transcription-quantitative real-time polymerase chain reaction (RT-qPCR). The data indicated that yeast application induced the expression of the genes encoding Respiratory burst oxidase (Rbo), mitogen-activated protein kinase (MAPK) and mitogen-activated protein kinase kinase (MAPKK), G-proteins, chitinase (CHI), phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and 4-coumarate-CoA ligase (4CL). In contrast, three genes, peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), were down-regulated in grapefruit peel tissue treated with yeast cells. Moreover, suppression was correlated with significantly higher levels of hydrogen peroxide, superoxide anion and hydroxyl radical production in yeast-treated surface wounds. Interestingly, large amounts of hydrogen peroxide were detected inside yeast cells recovered from wounded fruit tissue, indicating the ability of the yeast to activate reactive oxygen species when it is in contact with plant tissue. This study provides the first global picture of gene expression changes in grapefruit in response to the yeast antagonist M. fructicola.

Functional characterization of an acidic SK(3) dehydrin isolated from an Opuntia streptacantha cDNA library

Cactus pears are succulent plants of the Cactaceae family adapted to extremely arid, hot and cold environments, making them excellent models for the study of molecular mechanisms underlying abiotic stress tolerance. Herein, we report a directional cDNA library from 12-month-old cladodes of Opuntia streptacantha plants subjected to abiotic stresses. A total of 442 clones were sequenced, representing 329 cactus pear unigenes, classified into eleven functional categories. The most abundant EST (unigen 33) was characterized under abiotic stress. This cDNA of 905 bp encodes a SK(3)-type acidic dehydrin of 248 amino acids. The OpsDHN1 gene contains an intron inserted within the sequence encoding the S-motif. qRT-PCR analysis shows that the OpsDHN1 transcript is specifically accumulated in response to cold stress, and induced by abscisic acid. Over-expression of the OpsDHN1 gene in Arabidopsis thaliana leads to enhanced tolerance to freezing treatment, suggesting that OpsDHN1 participates in freezing stress responsiveness. Generation of the first EST collection for the characterization of cactus pear genes constitutes a useful platform for the understanding of molecular mechanisms of stress tolerance in Opuntia and other CAM plants.

Prediction of thermostability from amino acid attributes by combination of clustering with attribute weighting: a new vista in engineering enzymes

The engineering of thermostable enzymes is receiving increased attention. The paper, detergent, and biofuel industries, in particular, seek to use environmentally friendly enzymes instead of toxic chlorine chemicals. Enzymes typically function at temperatures below 60°C and denature if exposed to higher temperatures. In contrast, a small portion of enzymes can withstand higher temperatures as a result of various structural adaptations. Understanding the protein attributes that are involved in this adaptation is the first step toward engineering thermostable enzymes. We employed various supervised and unsupervised machine learning algorithms as well as attribute weighting approaches to find amino acid composition attributes that contribute to enzyme thermostability. Specifically, we compared two groups of enzymes: mesostable and thermostable enzymes. Furthermore, a combination of attribute weighting with supervised and unsupervised clustering algorithms was used for prediction and modelling of protein thermostability from amino acid composition properties. Mining a large number of protein sequences (2090) through a variety of machine learning algorithms, which were based on the analysis of more than 800 amino acid attributes, increased the accuracy of this study. Moreover, these models were successful in predicting thermostability from the primary structure of proteins. The results showed that expectation maximization clustering in combination with uncertainly and correlation attribute weighting algorithms can effectively (100%) classify thermostable and mesostable proteins. Seventy per cent of the weighting methods selected Gln content and frequency of hydrophilic residues as the most important protein attributes. On the dipeptide level, the frequency of Asn-Glu was the key factor in distinguishing mesostable from thermostable enzymes. This study demonstrates the feasibility of predicting thermostability irrespective of sequence similarity and will serve as a basis for engineering thermostable enzymes in the laboratory.

Diverse accumulation of several dehydrin-like proteins in cauliflower (Brassica oleracea var. botrytis), Arabidopsis thaliana and yellow lupin (Lupinus luteus) mitochondria under cold and heat stress

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.

Identification of differentially expressed genes under drought stress in perennial ryegrass

Perennial ryegrass (Lolium perenne L.) is a widely used cool-season forage and turf grass species. Drought stress can significantly affect the growth and development of grass plants. Identification of genes involved in drought tolerance facilitates genetic improvement of perennial ryegrass. A forward and a reverse cDNA library were constructed in drought-tolerant (PI 440474) and drought-susceptible (PI 204085) accessions by using suppression subtractive hybridization (SSH). A BLAST search revealed that 95 of 256 expressed sequence tags (ESTs) obtained from the two libraries showed significant sequence homologies to genes with known functions. They were classified into different putative functional groups including amino acid metabolism, lipid metabolism, carbohydrate metabolism, transcription, protein synthesis and destination, energy, photosynthesis, signal transduction, cellular transport and detoxification. Among them, 50 ESTs were from forward library (the drought tolerant over the susceptible accession). The expression patterns (reverse transcriptase polymerase chain reaction) of the selected genes encoding mitogen-activated protein kinase, superoxide dismutase and glutathione peroxidase (GPX) in additional accessions contrasting in drought tolerance were generally consistent with patterns of differentially expressed genes identified through SSH. The GPX fragment had a high degree of nucleotide diversity (pi = 0.0251) in the selected perennial ryegrass accessions. The results suggest that differentially expressed genes between drought tolerant and susceptible accessions may play an important role in the drought tolerance of perennial ryegrass. They can be used as candidate genes in examining nucleotide polymorphisms and conducting the association analysis of genes with drought tolerance.

Differential accumulation of dehydrins in response to water stress for hybrid and common bermudagrass genotypes differing in drought tolerance

Expression of dehydrin proteins may be induced or enhanced by environmental stresses that lead to cell dehydration. The objective of the this study was to investigate genetic variation in dehydrin protein accumulation in response to drought stress of whole-plants or dehydration of detached leaves and to identify dehydrins differentially expressed in bermudagrass (Cynodon spp.) genotypes differing in drought tolerance. Plants of four hybrid bermudagrass (Cynodondactylon L. xCynodontransvaalensis L.) ('Tifway', 'Tifdwarf', 'Tifeagle', 'Kan1') and four common bermudagrass (Cynodon dactylon) ('C299', 'Sportbermuda', 'H10', and 'H19') genotypes were subjected to 14d of drought stress and detached leaves of two genotypes were exposed to dehydration in growth chambers. Turf quality and leaf relative water content (RWC) decreased while electrolyte leakage (EL) increased during whole-plant drought stress for all genotypes, with more pronounced changes in each parameter for 'C299' and 'Tifeagle' than those for other genotypes ('Tifway', 'Kan 1', 'Sportbermuda', 'H10', and H19'), suggesting that the former two genotypes were more sensitive to drought stress than the other genotypes. During dehydration of detached leaves, relative water loss rate (RWL) was significantly lower in drought-tolerant 'Tifway' than in drought-sensitive 'C299'. Immunoblotting analysis indicated that no dehydrin polypeptides were detected in all genotypes under well-watered conditions. A 24-kDa polypeptide was detected in 'C299' at 6 d of drought, but not in the other genotypes. The dehydrin polypeptides of about 14-74kDa accumulated at 10d of drought stress and in a range of RWL for detached leaves, and two dehydrins (31 and 40kDa) exhibited differential accumulation in the drought-sensitive 'C299' and tolerant 'Tifway', as demonstrated by the whole-plant drought responses. The 31-kDa dehydrin polypeptide was present only in 'Tifway' and 'H19' at 10d of drought stress, and accumulated with the increasing RWL in detached leaves of 'Tifway'. The expression level of 40-kDa dehydrin polypeptides was greater in 'Tifway'' than in 'C299' at the same level of water deficit (from 10% to 65% RWL). These results indicated that the accumulation of 31- and 40-kDa dehydrins may contribute to drought or dehydration tolerance in warm-season bermudagrass.

Comparative expression and transcript initiation of three peach dehydrin genes

Dehydrin genes encode proteins with demonstrated cryoprotective and antifreeze activity, and they respond to a variety of abiotic stress conditions that have dehydration as a common component. Two dehydrins from peach (Prunus persica L. [Batsch.]) have been previously characterized; here, we describe the characterization of a third dehydrin from peach bark, PpDhn3, isolated by its response to low temperature. The expression of all three dehydrin genes was profiled by semi-quantitative reverse transcription PCR, and transcript initiation was mapped for all three genes using the RNA ligase-mediated 5' rapid amplification of cDNA ends technique. PpDhn3 transcripts from bark collected in December or July, as well as transcripts from developing fruit, initiated at a single site. Although most of the PpDhn1 transcripts initiated at a similar position, those from young fruit initiated much further upstream of the consensus TATA box. Bark and fruit transcripts encoding PpDhn2 initiated ca. 30 bases downstream of a consensus TATA box; however, transcripts from ripe fruit initiated further upstream. Ripe fruit transcripts of PpDhn2 contain a 5' leader intron which is predicted to add some 34 amino acids to the N-terminal methionine of the cognate protein when properly processed. Secondary structure prediction of sequences surrounding the TATA box suggests that conformational transitions associated with decreasing temperature contribute to the regulation of expression of the cold-responsive dehydrin genes. Taken together these results reveal new, unexpected levels of gene regulation contributing to the overall expression pattern of peach dehydrins.

Small heat-shock protein Hsp12 contributes to yeast tolerance to freezing stress

The HSP12 gene encodes one of the two major small heat-shock proteins of Saccharomyces cerevisiae and is induced under different conditions, such as low and high temperatures, osmotic or oxidative stress and high sugar or ethanol concentrations. However, few studies could demonstrate any correlation between HSP12 deletion or overexpression and a phenotype of sensitivity/resistance, making it difficult to attribute a role for Hsp12p under several of these stress conditions. We investigated the possible role of Hsp12p in yeast freezing tolerance. Contrary to what would be expected, the hsp12 null mutant when subjected to prolonged storage at −20 °C showed an increased resistance to freezing when compared with the isogenic wild-type strain. Because the mutant strain displayed a higher intracellular trehalose concentration than the wild-type, which could mask the effect of manipulating HSP12, we overexpressed the HSP12 gene in a trehalose-6-phosphate synthase (TPS1) null mutant. The tps1Δ strain overexpressing HSP12 showed an increase in resistance to freezing storage, indicating that Hsp12p plays a role in freezing tolerance in a way that seems to be interchangeable with trehalose. In addition, we show that overexpression of HSP12 in this tps1Δ strain also increased resistance to heat shock and that absence of HSP12 compromises the ability of yeast cells to accumulate high levels of trehalose in response to a mild heat stress.

DNA binding of citrus dehydrin promoted by zinc ion

Dehydrins are hydrophilic proteins that accumulate during embryogenesis and osmotic stress responses in plants. Here, we report an interaction between citrus dehydrin Citrus unshiu cold-regulated 15 kDa protein (CuCOR15) and DNA. Binding of CuCOR15 to DNA was detected by an electrophoretic mobility shift assay, a filter-binding assay and Southwestern blotting. The binding was stimulated by physiological concentrations of Zn2+, but little stimulation occurred when other divalent cations, such as Mg2+, Ca2+, Mn2+, Ni2+ and Cu2+, were substituted for Zn2+. Ethylenediaminetetraacetic acid cancelled the Zn2+-stimulated binding. A binding curve and competitor experiments suggested that the DNA binding of CuCOR15 exhibited low affinity and non-specificity. Moreover, tRNA competed with the DNA binding. Histidine-rich domains and a polylysine segment-containing domain participated in the DNA binding. These results suggest that CuCOR15 can interact with DNA, and also RNA, in the presence of Zn2+. Dehydrin may protect nucleic acids in plant cells during seed maturation and stress responses.