Isolation and characterization of the gene encoding glyceraldehyde-3-phosphate dehydrogenase

Identification of the GAPDH gene family in Citrullus lanatus and functional characteristics of ClGAPC2 in Arabidopsis thaliana

Members of the GAPDH family play important roles in plant growth and development, as well as in stress responses. Our aim was to identify stress resistance genes through systematic analysis of the GAPDH family in watermelon. This could not only provide genetic resources for stress resistance breeding, but also form a basis for the study of plant stress resistance mechanisms. Eight GAPDHs representing four types of plant GAPDH in watermelon were identified (ClGAPA/B, ClGAPC1-3, ClGAPCp1-2 and ClGAPN). A comprehensive analysis of physicochemical properties, chromosome distribution, evolutionary relationships, exon-intron structure and conserved motifs of watermelon GAPDHs was performed using bioinformatics. Expression characteristics were assessed by RT-qPCR. Based on RT-qPCR results, ClGAPC2 was screened as a candidate for subcellular localization analysis and functional verification in Arabidopsis thaliana. Eight GAPDHs were classified into four subfamilies. GAPDHs in each subgroup were generally conserved and shared similarities in structure and conserved motifs. ClGAPDHs had notable tissue specificity and different expression patterns in response to H₂ O₂ , chilling, salt, osmotic stress, heat, salicylic acid, gibberellin, brassinosterol, ethylene and abscisic acid treatments. Three ClGAPC genes, especially ClGAPC2, were markedly induced by several treatments. ClGAPC2 was located in the nucleus and cytoplasm of tabacum epidermal cells. The ClGAPC2 transgenic Arabidopsis showed enhanced tolerance to salinity at the germination stage. We suggest that ClGAPC2 plays important roles in the adaptation of watermelon to salinity. Our findings provided candidate genes for further improving the salt tolerance of watermelon.

Physiological Aspects of Germination and Early Seedling Establishment of Pleurotus sajor-caju Glyceraldehyde-3-Phosphate Dehydrogenase Expressing Transgenic Rice in Saline Environment

GPD encodes glyceraldehyde-3-phosphate dehydrogenase enzyme involved in sugar mobilization, particularly glycolysis and gluconeogenesis. The objective of this study was to determine physiological aspects of germination and early seedling establishment of PsGPD (Pleurotus sajor-caju glyceraldehyde-3-phosphate dehydrogenase) expressing transgenic rice (T5) against different salt concentrations. The T5 line that carried 2 copies of T-DNA and had the highest level of PsGPD expression was used in the investigation. Final germination percentage, amylase activity, reducing sugar accumulation, and chlorophyll biosynthesis were comparatively higher in PsGPD expressing transgenic rice against elevating saline conditions. A slow-paced conversion of porphyrin's precursors was seen through the matrix model and further elaborated by a graphical model. A sustained level of porphyrin was observed in PsGPD expressing transgenic rice. These data were concurrent with the relative gene expression and thermal imaging (thermography) of PsGPD expressing transgenic rice against salt stress. Morphological attributes also favored the salt tolerance exhibited by PsGPD-transformed rice.

Transcriptomic Analysis of Rice Plants Overexpressing PsGAPDH in Response to Salinity Stress

In plants, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a main enzyme in the glycolytic pathway. It plays an essential role in glycerolipid metabolism and response to various stresses. To examine the function of PsGAPDH (Pleurotus sajor-caju GAPDH) in response to abiotic stress, we generated transgenic rice plants with single-copy/intergenic/homozygous overexpression PsGAPDH (PsGAPDH-OX) and investigated their responses to salinity stress. Seedling growth and germination rates of PsGAPDH-OX were significantly increased under salt stress conditions compared to those of the wild type. To elucidate the role of PsGAPDH-OX in salt stress tolerance of rice, an Illumina HiSeq 2000 platform was used to analyze transcriptome profiles of leaves under salt stress. Analysis results of sequencing data showed that 1124 transcripts were differentially expressed. Using the list of differentially expressed genes (DEGs), functional enrichment analyses of DEGs such as Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were performed. KEGG pathway enrichment analysis revealed that unigenes exhibiting differential expression were involved in starch and sucrose metabolism. Interestingly, trehalose-6-phosphate synthase (TPS) genes, of which expression was enhanced by abiotic stress, showed a significant difference in PsGAPDH-OX. Findings of this study suggest that PsGAPDH plays a role in the adaptation of rice plants to salt stress.

Improving Azo Dye Decolorization Performance and Halotolerance of Pichia occidentalis A2 by Static Magnetic Field and Possible Mechanisms Through Comparative Transcriptome Analysis

A halotolerant yeast, Pichia occidentalis A2, was recently isolated that can decolorize various azo dyes. The azo dye decolorization performance of this strain was characterized, including the degradation pathway and detoxification effects of this yeast. Additionally, the effect of static magnetic field (SMF) on this decolorization process was investigated. Activities of key enzymes were analyzed to estimate the change of metabolic activity. Furthermore, possible mechanisms were analyzed through detecting differentially expressed genes between yeast A2 in the absence and presence of SMF. The results indicated that yeast A2 displayed the optimal decolorization performance when the concentrations (in g/L) of glucose, (NH4)2SO4, yeast extract, and NaCl were 4.0, 1.0, 0.1, and ≤30.0, respectively. Meanwhile, the optimal rotation speed, temperature, and pH were 160 rpm, 30°C, and 5.0, respectively. Acid Red B was decolorized and detoxified by yeast A2 through successive steps, including cleavage of the naphthalene-amidine bond, reductive deamination, oxidative deamination/desulfurization, open-loop of hydroxy-substituted naphthalene, and tricarboxylic acid cycle. The dye decolorization efficiency and halotolerance of yeast A2 were enhanced by 206.3 mT SMF. The activities of manganese peroxidase, and laccase were elevated 1.37- and 1.16-fold by 206.3 mT SMF, but lignin peroxidase activity showed little change. It was suggested from the transcriptome sequence that the enhanced halotolerance might be related to the upregulated genes encoding the enzymes or functional proteins related to intracellular synthesis and accumulation of glycerol.

Cytosolic glyceraldehyde-3-phosphate dehydrogenase 2/5/6 increase drought tolerance via stomatal movement and reactive oxygen species scavenging in wheat

Drought is a major threat to wheat growth and crop productivity. However, there has been only limited success in developing drought-hardy cultivars. This lack of progress is due, at least in part, to a lack of understanding of the molecular mechanisms of drought tolerance in wheat. Here, we evaluated the potential role of three cytosolic glyceraldehyde-3-phosphate dehydrogenases (TaGAPC2/5/6) under drought stress in wheat and Arabidopsis. We found that TaGAPC2/5/6 all positively responded to drought stress via reactive oxygen species (ROS) scavenging and stomatal movement. The results of yeast co-transformation and electrophoretic mobility shift assay showed that TaWRKY33 acted as a direct regulator of TaGAPC2/5/6 genes. The dual luciferase reporter assay indicated that TaWRKY33 positively activated the expression of TaGAPC2/5/6. The results of bimolecular fluorescence complementation and yeast two-hybrid system demonstrated that TaGAPC2/5/6 interacted with phospholipase Dδ (PLDδ). We then demonstrated that TaGAPC2/5/6 positively promoted the activity of TaPLDδ in vitro and in vivo. Furthermore, lower PLDδ activity in RNAi wheat could lead to less PA accumulation, causing higher stomatal aperture sizes under drought stress. In summary, our results establish a new positive regulatory mechanism of TaGAPCs which helps wheat fine-tune their drought responses.

Membrane Lipid Remodeling in Response to Salinity

Salinity is one of the most decisive environmental factors threatening the productivity of crop plants. Understanding the mechanisms of plant salt tolerance is critical to be able to maintain or improve crop yield under these adverse environmental conditions. Plant membranes act as biological barriers, protecting the contents of cells and organelles from biotic and abiotic stress, including salt stress. Alterations in membrane lipids in response to salinity have been observed in a number of plant species including both halophytes and glycophytes. Changes in membrane lipids can directly affect the properties of membrane proteins and activity of signaling molecules, adjusting the fluidity and permeability of membranes, and activating signal transduction pathways. In this review, we compile evidence on the salt stress responses of the major membrane lipids from different plant tissues, varieties, and species. The role of membrane lipids as signaling molecules in response to salinity is also discussed. Advances in mass spectrometry (MS)-based techniques have largely expanded our knowledge of salt-induced changes in lipids, however only a handful studies have investigated the underlying mechanisms of membrane lipidome regulation. This review provides a comprehensive overview of the recent works that have been carried out on lipid remodeling of plant membranes under salt treatment. Challenges and future perspectives in understanding the mechanisms of salt-induced changes to lipid metabolisms are proposed.

The difference of morphological characteristics and population structure in PAO and DPAOgranular sludges

We examined how long-term operation of anaerobic-oxic and anaerobic-anoxic sequencing batch reactors (SBRs) affects the enhanced biological phosphorus removal (EBPR) performance and sludge characteristics. The microbial characteristics of phosphorus accumulating organism (PAO) and denitrifying PAO (DPAO) sludge were also analyzed through a quantitative analysis of microbial community structure. Compared with the initial stage of operation characterized by unstable EBPR, both PAO and DPAO SBR produced a stable EBPR performance after about 100-day operation. From day 200 days (DPAO SBR) and 250 days (PAO SBR) onward, sludge granulation was observed, and the average granule size of DPAO SBR was approximately 5 times larger than that of PAO SBR. The DPAO granular sludge contained mainly rod-type microbes, whereas the PAO granular sludge contained coccus-type microbes. Fluorescence in situ hybridization analysis revealed that a high ratio of Accumulibacter clade I was found only in DPAO SBR, revealing the important role of this organism in the denitrifying EBPR system. A pyrosequencing analysis showed that Accumulibacter phosphatis was present in PAO sludge at a high proportion of 6%, whereas it rarely observed in DPAO sludge. Dechloromonas was observed in both PAO sludge (3.3%) and DPAO sludge (3.2%), confirming that this organism can use both O₂ and NO₃^- as electron acceptors. Further, Thauera spp. was identified to have a new possibility as denitrifier capable of phosphorous uptake under anoxic condition.

Analysis of the distribution of assimilation products and the characteristics of transcriptomes in rice by submergence during the ripening stage

Background

Research on the submergence stress of rice has concentrated on the quiescence strategy to survive in long-term flooding conditions based on Submergence-1A (SUB1A). In the case of the ripening period, it is important that submergence stress can affect the quality as well as the survival of rice. Therefore, it is essential to understand the changes in the distribution of assimilation products in grain and ripening characteristics in submergence stress conditions. However, such studies have been insufficient at the physiological and molecular biological levels.

Results

We confirmed that the distribution rate of assimilation products in grain was decreased by submergence treatment. These results were caused by an increase in the distribution rate of assimilation products to the stem according to escape strategy. To understand this phenomenon at the molecular level, we analyzed the relative expression levels of genes related to sucrose metabolism, and found that the sucrose phosphate synthase gene (OsSPS), which induces the accumulation of sucrose in tissues, was decreased in the seeds and leaves, but not in the stems. Furthermore, the sucrose transporter gene (OsSUT) related to sucrose transport decreased in the seeds and leaves, but increased in stems. We also analyzed the biological metabolic processes related to starch and sucrose synthesis, carbon fixation, and glycolysis using the KEGG mapper with selected differentially expressed genes (DEGs) in seeds, stems, and leaves caused by submergence treatment. We found that the expression of genes for each step related to starch and D-glucose synthesis was down-regulated in the seeds and leaves but up-regulated in the stem.

Conclusion

The results of this study provide basic data for the development of varieties and corresponding technologies adapted to submergence conditions, through understanding the action network of the elements that change in the submergence condition, as well as information regarding useful DEGs.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5320-7) contains supplementary material, which is available to authorized users.

Recurrent water deficit causes alterations in the profile of redox proteins in citrus plants

Plant acclimation to recurrent stress involves profound alterations in multiple genetic, metabolic and physiological processes. Stressful conditions usually implicate imbalance in reactive oxygen species (ROS) production and removal rates, which may lead to oxidative stress. However, the primary cellular targets of oxidative stress and their relevance in plant acclimation to abiotic stresses remains poorly characterized. By comparing redox proteomic and sugar profiles in citrus Valencia (VO) scions grafted onto two rootstocks with different soil water extraction capacities - Rangpur Lime (RL) and Sunki Maravilha (SM) - here we demonstrate that both ROS-mediated post-translational protein modification and changes in sugar composition are associated with acclimation to recurrent drought in citrus. The redox proteomic analysis of the distinct scion/rootstock combinations exposed to one (WD1), two (WD2) or three (WD3) water deficit episodes revealed a total of 32 and 55 redox protein spots present in VO/RL and VO/SM plants, respectively. Mass spectrometry analysis of these protein spots revealed essential targets of ROS-mediated posttranslational protein modification in citrus plants challenged by recurrent drought. The oxidation of cysteine thiol groups into glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was shown to increase in WD3 samples of the VO/RL combination, whereas the opposite was observed for the VO/SM combination. Similarly, recurrent drought promoted the oxidation of catalase thiol groups in VO/SM, but not in VO/RL. Carbohydrate profiling revealed that glucose, fructose and galactose may also contribute to the phenotypic differences observed between the citrus genotypes exposed to drought. These findings reveal for the first time that recurrent drought differentially affects the profile of redox proteomics of citrus, suggesting that this alteration may be part of the stress memory in perennial plants.

Metabolic Pathways Involved in Carbon Dioxide Enhanced Heat Tolerance in Bermudagrass

Global climate changes involve elevated temperature and CO2 concentration, imposing significant impact on plant growth of various plant species. Elevated temperature exacerbates heat damages, but elevated CO2 has positive effects on promoting plant growth and heat tolerance. The objective of this study was to identify metabolic pathways affected by elevated CO2 conferring the improvement of heat tolerance in a C4 perennial grass species, bermudagrass (Cynodon dactylon Pers.). Plants were planted under either ambient CO2 concentration (400 μmol⋅mol-1) or elevated CO2 concentration (800 μmol⋅mol-1) and subjected to ambient temperature (30/25°C, day/night) or heat stress (45/40°C, day/night). Elevated CO2 concentration suppressed heat-induced damages and improved heat tolerance in bermudagrass. The enhanced heat tolerance under elevated CO2 was attributed to some important metabolic pathways during which proteins and metabolites were up-regulated, including light reaction (ATP synthase subunit and photosystem I reaction center subunit) and carbon fixation [(glyceraldehyde-3-phosphate dehydrogenase, GAPDH), fructose-bisphosphate aldolase, phosphoglycerate kinase, sedoheptulose-1,7-bisphosphatase and sugars) of photosynthesis, glycolysis (GAPDH, glucose, fructose, and galactose) and TCA cycle (pyruvic acid, malic acid and malate dehydrogenase) of respiration, amino acid metabolism (aspartic acid, methionine, threonine, isoleucine, lysine, valine, alanine, and isoleucine) as well as the GABA shunt (GABA, glutamic acid, alanine, proline and 5-oxoproline). The up-regulation of those metabolic processes by elevated CO2 could at least partially contribute to the improvement of heat tolerance in perennial grass species.

Subtractive transcriptome analysis of leaf and rhizome reveals differentially expressed transcripts in Panax sokpayensis

In the present study, suppression subtractive hybridization (SSH) strategy was used to identify rare and differentially expressed transcripts in leaf and rhizome tissues of Panax sokpayensis. Out of 1102 randomly picked clones, 513 and 374 high quality expressed sequenced tags (ESTs) were generated from leaf and rhizome subtractive libraries, respectively. Out of them, 64.92 % ESTs from leaf and 69.26 % ESTs from rhizome SSH libraries were assembled into different functional categories, while others were of unknown function. In particular, ESTs encoding galactinol synthase 2, ribosomal RNA processing Brix domain protein, and cell division cycle protein 20.1, which are involved in plant growth and development, were most abundant in the leaf SSH library. Other ESTs encoding protein KIAA0664 homologue, ubiquitin-activating enzyme e11, and major latex protein, which are involved in plant immunity and defense response, were most abundant in the rhizome SSH library. Subtractive ESTs also showed similarity with genes involved in ginsenoside biosynthetic pathway, namely farnesyl pyrophosphate synthase, squalene synthase, and dammarenediol synthase. Expression profiles of selected ESTs validated the quality of libraries and confirmed their differential expression in the leaf, stem, and rhizome tissues. In silico comparative analyses revealed that around 13.75 % of unigenes from the leaf SSH library were not represented in the available leaf transcriptome of Panax ginseng. Similarly, around 18.12, 23.75, 25, and 6.25 % of unigenes from the rhizome SSH library were not represented in available root/rhizome transcriptomes of P. ginseng, Panax notoginseng, Panax quinquefolius, and Panax vietnamensis, respectively, indicating a major fraction of novel ESTs. Therefore, these subtractive transcriptomes provide valuable resources for gene discovery in P. sokpayensis and would complement the available transcriptomes from other Panax species.

A phloem-limited fijivirus induces the formation of neoplastic phloem tissues that house virus multiplication in the host plant

A number of phloem-limited viruses induce the development of tumours (enations) in the veins of host plants, but the relevance of tumour induction to the life cycle of those viruses is unclear. In this study, we performed molecular and structural analyses of tumours induced by rice black-streaked dwarf virus (RBSDV, genus Fijivirus) infection in maize plants. The transcript level of the maize cdc2 gene, which regulates the cell cycle, was highly elevated in tumour tissues. Two-dimensional electrophoresis identified 25 cellular proteins with altered accumulation in the tumour tissues. These proteins are involved in various metabolic pathways, including photosynthesis, redox, energy pathways and amino acid synthesis. Histological analysis indicated that the tumours predominantly originated from hyperplastic growth of phloem, but those neoplastic tissues have irregular structures and cell arrangements. Immunodetection assays and electron microscopy observations indicated that in the shoots, RBSDV is confined to phloem and tumour regions and that virus multiplication actively occurs in the tumour tissue, as indicated by the high accumulation of non-structural proteins and formation of viroplasms in the tumour cells. Thus, the induction of tumours by RBSDV infection provides a larger environment that is favourable for virus propagation in the host plant.

Ethrel-stimulated prolongation of latex flow in the rubber tree (Hevea brasiliensis Muell. Arg.): an Hev b 7-like protein acts as a universal antagonist of rubber particle aggregating factors from lutoids and C-serum

Ethrel is the most effective stimuli in prolonging the latex flow that consequently increases yield per tapping. This effect is largely ascribed to the enhanced lutoid stability, which is associated with the decreased release of initiators of rubber particle (RP) aggregation from lutoid bursting. However, the increase in both the bursting index of lutoids and the duration of latex flow after applying ethrel or ethylene gas in high concentrations suggests that a new mechanism needs to be introduced. In this study, a latex allergen Hev b 7-like protein in C-serum was identified by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI TOF MS). In vitro analysis showed that the protein acted as a universal antagonist of RP aggregating factors from lutoids and C-serum. Ethrel treatment obviously weakened the effect of C-serum on RP aggregation, which was closely associated with the increase in the level of the Hev b 7-like protein and the decrease in the level of the 37 kDa protein, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), western blotting analysis and antibody neutralization. Thus, the increase of the Hev b 7-like protein level or the ratio of the Hev b 7-like protein to the 37 kDa protein in C-serum should be primarily ascribed to the ethrel-stimulated prolongation of latex flow duration.

The beta subunit of glyceraldehyde 3-phosphate dehydrogenase is an important factor for maintaining photosynthesis and plant development under salt stress-Based on an integrative analysis of the structural, physiological and proteomic changes in chloroplasts in Thellungiella halophila

Thellungiella halophila, a new model halophyte, can survive under highly saline conditions. We performed comparative proteomics of chloroplasts from plants grown under different saline conditions. Seventy-five salt-responsive proteins were positively identified by mass spectrometry, which represented 43 unique ones. These proteins were categorized into 7 main pathways: light reaction, carbon fixation, energy metabolism, antenna proteins, cell structure, and protein degradation and folding. Saline conditions increased the abundance of proteins involved in photosynthesis, energy metabolism and cell structure. The results indicated that Thellungiella could withstand high salinity by maintaining normal or high photosynthetic capacity, reducing ROS production, as well as enhancing energy usage. Meanwhile, the ultrastructural and physiological data also agree with chloroplast proteomics results. Subsequently, the glyceraldehydes 3-phosphate dehydrogenase beta subunit (GAPB) involved in carbon fixation was selected and its role in salt tolerance was clarified by over-expressing it in Arabidopsis. ThGAPB-overexpressing plants had higher total chlorophyll contents, dry weights, water contents and survival rates than that of wild type plants. These results indicated that ThGAPB might improve plant salt tolerance by maintaining higher recycling rates of ADP and NADP(+) to decrease ROS production, helping to maintain photosynthetic efficiency and plant development under saline conditions.

Review of recent transgenic studies on abiotic stress tolerance and future molecular breeding in potato

Global warming has become a major issue within the last decade. Traditional breeding programs for potato have focused on increasing productivity and quality and disease resistance, thus, modern cultivars have limited tolerance of abiotic stresses. The introgression of abiotic stress tolerance into modern cultivars is essential work for the future. Recently, many studies have investigated abiotic stress using transgenic techniques. This manuscript focuses on the study of abiotic stress, in particular drought, salinity and low temperature, during this century. Dividing studies into these three stress categories for this review was difficult. Thus, based on the study title and the transgene property, transgenic studies were classified into five categories in this review; oxidative scavengers, transcriptional factors, and above three abiotic categories. The review focuses on studies that investigate confer of stress tolerance and the identification of responsible factors, including wild relatives. From a practical application perspective, further evaluation of transgenic potato with abiotic stress tolerance is required. Although potato plants, including wild species, have a large potential for abiotic stress tolerance, exploration of the factors responsible for conferring this tolerance is still developing. Molecular breeding, including genetic engineering and conventional breeding using DNA markers, is expected to develop in the future.

A heavy metal-associated protein (AcHMA1) from the halophyte, Atriplex canescens (Pursh) Nutt., confers tolerance to iron and other abiotic stresses when expressed in Saccharomyces cerevisiae

Many heavy metals are essential for metabolic processes, but are toxic at elevated levels. Metal tolerance proteins provide resistance to this toxicity. In this study, we identified and characterized a heavy metal-associated protein, AcHMA1, from the halophyte, Atriplex canescens. Sequence analysis has revealed that AcHMA1 contains two heavy metal binding domains. Treatments with metals (Fe, Cu, Ni, Cd or Pb), PEG6000 and NaHCO3 highly induced AcHMA1 expression in A. canescens, whereas NaCl and low temperature decreased its expression. The role of AcHMA1 in metal stress tolerance was examined using a yeast expression system. Expression of the AcHMA1 gene significantly increased the ability of yeast cells to adapt to and recover from exposure to excess iron. AcHMA1 expression also provided salt, alkaline, osmotic and oxidant stress tolerance in yeast cells. Finally, subcellular localization of an AcHMA1/GFP fusion protein expressed in tobacco cells showed that AcHMA1 was localized in the plasma membrane. Thus, our results suggest that AcHMA1 encodes a membrane-localized metal tolerance protein that mediates the detoxification of iron in eukaryotes. Furthermore, AcHMA1 also participates in the response to abiotic stress.

Over-expression of PsGPD, a mushroom glyceraldehyde-3-phosphate dehydrogenase gene, enhances salt tolerance in rice plants

Transgenic potatoes expressing glyceraldehyde-3-phosphate dehydrogenase (GPD), isolated from the oyster mushroom, Pleurotus sajor-caju, had increased tolerance to salt stress (Jeong et al. Biochem Biophys Res Commun 278:192-196, 2000). To examine the physiological mechanisms enhancing salt tolerance in GPD-transgenic rice plants, the salt tolerance of five GPD transgenic rice lines (T1-T5) derived from Dongjin rice cultivar were evaluated in a fixed 150 mM saline environment in comparison to two known wild-type rice cultivars, Dongjin (salt sensitive) and Pokali (salt tolerant). Transgenic lines, T2, T3, and T5, had a substantial increase in biomass and relative water content compared to Dongjin. Stomatal conductance and osmotic potential were higher in the GPD transgenic lines and were similar to those in Pokali. The results are discussed based on the comparative physiological response of GPD transgenic lines with those of the salt-sensitive and salt-tolerant rice cultivars.

Suppression Subtractive Hybridization Analysis of Genes Regulated by Application of Exogenous Abscisic Acid in Pepper Plant (Capsicum annuum L.) Leaves under Chilling Stress

Low temperature is one of the major factors limiting pepper (Capsicum annuum L.) production during winter and early spring in non-tropical regions. Application of exogenous abscisic acid (ABA) effectively alleviates the symptoms of chilling injury, such as wilting and formation of necrotic lesions on pepper leaves; however, the underlying molecular mechanism is not understood. The aim of this study was to identify genes that are differentially up- or downregulated in ABA-pretreated hot pepper seedlings incubated at 6°C for 48 h, using a suppression subtractive hybridization (SSH) method. A total of 235 high-quality ESTs were isolated, clustered and assembled into a collection of 73 unigenes including 18 contigs and 55 singletons. A total of 37 unigenes (50.68%) showed similarities to genes with known functions in the non-redundant database; the other 36 unigenes (49.32%) showed low similarities or unknown functions. Gene ontology analysis revealed that the 37 unigenes could be classified into nine functional categories. The expression profiles of 18 selected genes were analyzed using quantitative RT-PCR; the expression levels of 10 of these genes were at least two-fold higher in the ABA-pretreated seedlings under chilling stress than water-pretreated (control) plants under chilling stress. In contrast, the other eight genes were downregulated in ABA-pretreated seedlings under chilling stress, with expression levels that were one-third or less of the levels observed in control seedlings under chilling stress. These results suggest that ABA can positively and negatively regulate genes in pepper plants under chilling stress.

microRNAs associated with drought response in the bioenergy crop sugarcane (Saccharum spp.)

Sugarcane (Saccharum spp.) is one of the most important crops in the world. Drought stress is a major abiotic stress factor that significantly reduces sugarcane yields. However the gene network that mediates plant responses to water stress remains largely unknown in several crop species. Although several microRNAs that mediate post-transcriptional regulation during water stress have been described in other species, the role of the sugarcane microRNAs during drought stress has not been studied. The objective of this work was to identify sugarcane miRNAs that are differentially expressed under drought stress and to correlate this expression with the behavior of two sugarcane cultivars with different drought tolerances. The sugarcane cultivars RB867515 (higher drought tolerance) and RB855536 (lower drought tolerance) were cultivated in a greenhouse for three months and then subjected to drought for 2, 4, 6 or 8 days. By deep sequencing of small RNAs, we were able to identify 18 miRNA families. Among all of the miRNAs thus identified, seven were differentially expressed during drought. Six of these miRNAs were differentially expressed at two days of stress, and five miRNAs were differentially expressed at four days. The expression levels of five miRNAs (ssp-miR164, ssp-miR394, ssp-miR397, ssp-miR399-seq 1 and miR528) were validated by RT-qPCR (quantitative reverse transcriptase PCR). Six precursors and the targets of the differentially expressed miRNA were predicted using an in silico approach and validated by RT-qPCR; many of these targets may play important roles in drought tolerance. These findings constitute a significant increase in the number of identified miRNAs in sugarcane and contribute to the elucidation of the complex regulatory network that is activated by drought stress.

Identification of mRNA transcript and screening of amino acids in response to interaction of salinity and nitrate in aquatic fern Azolla caroliniana

The mechanisms by which Azolla caroliniana respond to salt stress in absence and presence of nitrate is investigated. Screening of amino acid and differential display is used to compare overall differences in gene expression between salinity-stressed and unstressed Azolla caroliniana by quantitative reverse transcriptase polymerase chain reaction (RT-PC R). Results showed that under saline conditions, aspartic acid, glutamic acid, alanine and leucine were the amino acids found to be abundant in Azolla caroliniana, accounting for 11.26%, 8.66%, 9.43%, and 12.36%, respectively. Following salinity stress, a decrease in free glutamate concomitant with a parallel decrease in free proline was indeed evident. Interaction between nitrate and salinity stress increased proline content significantly. By screening a cDNA library, we have identified protein products by homology with known proteins. The RNA transcripts encoding protein influencing secondary metabolites and vacuolar Na+/H+ antiporter that facilitate the transport system. The databasematched under interaction of nitrate and 50 mM NaCl were associated with wall biosynthesis, disease resistance, metabolite transport and protein regulator, other gene for metabolism of steroids and secondary transport. Results obtained from this research could represent a key step in understanding the molecular mechanism of salt tolerance of Azolla caroliniana in the presence and absence of nitrate.

Overexpression of a heat shock protein (ThHSP18.3) from Tamarix hispida confers stress tolerance to yeast

It is well known that plant heat shock proteins (HSPs) play important roles both in response to adverse environmental conditions and in various developmental processes. However, among plant HSPs, the functions of tree plant HSPs are poorly characterized. To improve our understanding of tree HSPs, we cloned and characterized an HSP gene (ThHSP18.3) from Tamarix hispida. Sequence alignment reveals that ThHSP18.3 belongs to the class I small heat shock protein family. A transient expression assay showed that ThHSP18.3 protein was targeted to the cell nucleus. Treatment of Tamarix hispida with cold and heat shock highly induced ThHSP18.3 expression in all studied leaves, roots and stems, whereas, treatment of T. hispida with NaCl, NaHCO(3), and PEG induced ThHSP18.3 expression in leaves and decreased its expression in roots and stems. Further, to study the role of ThHSP18.3 in stress tolerance under different stress conditions, we cloned ThHSP18.3 into the pYES2 vector, transformed and expressed the vector in yeast Saccharomyces cerevisiae. Yeast cells transformed with an empty pYES2 vector were employed as a control. Compared to the control, yeast cells expressing ThHSP18.3 showed greater tolerance to salt, drought, heavy metals, and both low and high temperatures, indicating that ThHSP18.3 confers tolerance to these stress conditions. These results suggested that ThHSP18.3 is involved in tolerance to a variety of stress conditions in T. hispida.

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

Water deficit arises as a result of low temperature, salinity and dehydration, thereby affecting plant growth adversely and making it imperative for plants to surmount such situations by acclimatizing/adapting at various levels. Water deficit stress results in significant changes in gene expression, mediated by interconnected signal transduction pathways that may be triggered by calcium, and regulated via ABA dependent and/or independent pathways. Hence, adaptation of plants to such stresses involves maintaining cellular homeostasis, detoxification of harmful elements and also growth alterations. Stress in general cause excess production of reactive oxygen species (ROS) and the plants overcome the same by either preventing the accumulation of ROS or by eliminating the ROS formed. Ion homeostasis includes processes such as cellular uptake, sequestration and export in conjunction with long distance transport. Requisite amounts of osmolytes are hence synthesized under stress to maintain turgor along with maintaining the macromolecular structures and also for scavenging ROS. Another noteworthy response is the accumulation of novel proteins, including enzymes involved in the biosynthesis of osmoprotectants, heat-shock proteins (HSPs), late embryogenesis abundant (LEA) proteins, antifreeze proteins, chaperones, detoxification enzymes, transcription factors, kinases and phosphatases. The LEAs belong to a redundant protein family and are highly hydrophilic, boiling-soluble, non-globular and therefore have been defined and classified accordingly. The precise function of LEAs is still unknown, but substantial evidence indicates their involvement in dessication tolerance as the expression of LEAs confers increased resistance to stress in heterologous yeast system and also significantly improves water deficit tolerance in transgenic plants. Genetic manipulation of plants towards conferring abiotic stress tolerance is a daunting task, as the abiotic stress tolerance mechanism is highly complex and various strategies have been exploited to address and evaluate the stress tolerance mechanism, and the molecular responses to water deficit via complex signaling networks. Genomic technologies have recently been useful in integrating the multigenicity of the plant stress responses through, transcriptomics, proteomics and metabolite profilling and their interactions. This review deals with the recent developments on genetic approaches for water stress tolerance in plants, with special emphasis on LEAs.

A heat shock protein gene (hsp22.4) from Chaetomium globosum confers heat and Na2CO3 tolerance to yeast

A small heat shock protein gene (hsp22.4) was cloned from Chaetomium globosum using rapid amplification of cDNA ends (RACE). The 986-bp full-length hsp22.4 cDNA contains a 609-bp open reading frame encoding a 202-amino-acid protein with an estimated molecular mass of 22.4 kDa. The hsp22.4 gene was amplified using specific primers in the 5' and 3' untranslated regions of the hsp22.4 cDNA. The temporal expression of hsp22.4 was measured in C. globosum by real-time reverse transcriptase-polymerase chain reaction after exposure to heat, cold, Na(2)CO(3), and NaCl. The expression of hsp22.4 was induced by heat and Na(2)CO(3) treatment and inhibited by cold and NaCl treatment. The hsp22.4 gene was inserted into pYES2 containing the inducible GAL1 promoter and transferred into yeast (Saccharomyces cerevisiae) for expression. The hsp22.4 transgenic yeast displayed significantly greater resistance to heat and Na(2)CO(3) stresses than control (yeast cells transformed with empty pYES2), suggesting that the expression of hsp22.4 gene confers not only heat tolerance but also significant alkali (Na(2)CO(3)) stress tolerance.

Cloning of the glyceraldehyde-3-phosphate dehydrogenase gene from Pseudozyma flocculosa and functionality of its promoter in two Pseudozyma species

Pseudozyma flocculosa is a yeast-like epiphyte recently classified as a basidiomycete related to the Ustilaginales. In this study, we report the cloning of its gene coding for a putative glyceraldehyde-3-phosphate dehydrogenase (GPD). This gene was selected on the premise that its transcripts are abundant during the growth phase of P. flocculosa. The complete sequence of this gene was found to contain two introns in the coding region and one in the 3'-untranslated region. This gene was present in a single copy in the genome of P. flocculosa. By comparing its deduced amino acid sequence with various sequences from basidiomycetous and ascomycetous fungi, we observed a stronger homology with the former group as predicted by the new classification of P. flocculosa. The promoter region lacked a typical TATA or CAAT box but contained a CT-rich region including the transcription start site. Although the GPD promoter showed a stronger affinity within P. flocculosa, it remained active across species as shown by expressing the green fluorescent protein in Pseudozyma antarctica. The cloning of this gene and its promoter brings new and versatile options to the limited genetic tools currently available for the study of the recently defined Pseudozyma genus.

Pleurotus sajor-caju HSP100 complements a thermotolerance defect inhsp104 mutantSaccharomyces cerevisiae

A putative Hsp100 gene was cloned from the fungus Pleurotus sajor-caju. mRNA expression studies demonstrated that this gene (designated PsHsp100) is highly induced by high temperature,induced less strongly by exposure to ethanol, and not induced by drought or salinity. Heat shock induction is detectable at 37 degrees C and reaches a maximum level at 42 degrees C. PsHsp100 mRNA levels sharply increased within 15 min of exposure to high temperature, and reached a maximum expression level at 2 h that was maintained for several hours. These results indicate that PsHsp100 could work at an early step in thermotolerance. To examine its function, PsHsp100 was transformed into a temperature-sensitive hsp104 deletion mutant Saccharomycetes cerivisiae strain to test the hypothesis that PsHSP100 is an protein that functions in thermotolerance. Overexpression of PsHSP100 complemented the thermotolerance defect of the hsp104 mutant yeast, allowing them being survive even at 50 degree C for 4 h. These results indicate that PsHSP100 protein is functional as an HSP100 in yeast and could play and important role in thermotolerance in P. sajor-caju.