Mechanisms Of Drought Stress Tolerance Research Articles

Transcriptional response of otsA, P5CR, glgX, nodC, and molecular chaperone genes under the PEG-induced drought stress in Mesorhizobium ciceri Ca181

Abstract This study was carried out to elucidate the mechanism of drought stress tolerance in bacterium Mesorhizobium ciceri Ca181, and further to correlate the finding with various salts impacts on the survival. Expression analysis of genes otsA, P5CR, glgX, major chaperone; groELS, dnaKJ, and nodulation protein-coding nodC genes were carried to reveal their roles in enhancing the PEG-induced drought tolerance. Yeast extract mannitol (YEM) broth supplemented with 47% polyethylene glycol (PEG-6000; w/v) was used to create the drought stress environment in the medium and strain Ca181 was able to tolerate PEG-induced drought stress for up to 5 days of incubation at 28 °C. PEG-induced desiccated cells showed variable expression patterns at the time interval of 5 min, 15 min, 1 h, 4 h, 8 h, 48 h, and 120 h. All the genes showed low levels of expression when the cells were grown until exponential growth phase in the presence of PEG-induced drought stress. However, when cells at the exponential phase of growth were incubated with PEG, maximum expression occurred after 5 min and 15 min, followed by a rapid decrease in the expression of otsA, P5CR, nodC, and molecular chaperone genes while the maximum expression of glgX was observed after 1 h of PEG-induced drought stress. The present study expands our information related to PEG-induced drought stress tolerance in strain Ca181, and impacts of salts additionally, expression analysis of these genes will contribute to our understanding of the molecular mechanism.

A U-box E3 ubiquitin ligase OsPUB67 is positively involved in drought tolerance in rice.

OsPUB67, a U-box E3 ubiquitin ligase, may interact with two drought tolerance negative regulators (OsRZFP34 and OsDIS1) and improve drought tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. E3 ubiquitin ligases are major components of the ubiquitination cascade and contribute to the biotic and abiotic stress response in plants. In the present study, we show that a rice drought responsive gene, OsPUB67, encoding the U-box E3 ubiquitin ligase was significantly induced by drought, salt, cold, JA, and ABA, and was expressed in nuclei, cytoplasm, and membrane systems. This distribution of expression suggests a significant role for OsPUB67 in a wide range of biological processes and abiotic stress response. Over-expression of OsPUB67 improved drought stress tolerance by enhancing the reactive oxygen scavenging ability and stomatal closure. Bimolecular fluorescence complementation assays revealed that a few E2s interacted with OsPUB67 with unique functional implications in different cell components. Further evidence showed that several E3 ubiquitin ligases interacted with OsPUB67, especially OsRZFP34 and OsDIS1, which are negative regulators of drought tolerance. This interaction on the stomata implied OsPUB67 might function as a heterodimeric ubiquitination complex in response to drought stress. Comprehensive transcriptome analysis revealed OsPUB67 participated in regulating genes involved in the abiotic stress response and transcriptional regulation in an ABA-dependent manner. Our findings revealed OsPUB67 mediated a multilayered complex drought stress tolerance mechanism.

Genome-wide identification of drought-responsive miRNAs in grass pea (Lathyrus sativus L.)

The grass pea (Lathyrus sativus L.) is an attractive legume which grows traditionally in drought-stricken, rain-fed and poor fertile soils. Globally drought is a major constraint for agriculture. Regulatory mechanism such as non-coding RNA is an important molecule to control gene expression in every domain of life. Therefore, identification and characterization of drought-responsive miRNAs of this plant can be very useful genomic resource to understand the molecular mechanisms of drought stress tolerance in plants. In this study we identified 143 and 128 conserved miRNAs by sequencing small RNA libraries from control (LC) and moisture-stressed (LD) leaf tissues. Additionally, 5 and 11 novel miRNAs were also found in LC and LD library respectively, among which 2 miRNAs were common. Further, we observed that 8 and 12 known miRNAs were up- and down- regulated under drought stress. Importantly, complementary miRNA (feeder) stands were also found for all the mature miRNAs. Expressions of few known and novel miRNAs were validated by qPCR in the tolerant genotype of grass pea under drought stress. The predicted target sequence of differentially expressed miRNAs were found to be either transcription factors such as F-box, U-Box or protein coding genes involved in proline, betain and osmolyte biosynthesis pathway indicating that these miRNAs may have specific role in imparting drought tolerance. These findings provide valuable information to understand the function of miRNAs in an inherently drought tolerant plant.

A leucine-rich repeat-receptor-like kinase gene SbER2\u20131 from sorghum (Sorghum bicolor L.) confers drought tolerance in maize

BackgroundERECTA (ER) is a leucine-rich repeat-receptor-like kinase gene (LRR-RLK) encoding a protein isolated from Arabidopsis. Although the regulatory functions of ER genes have been widely explored in plant development and disease resistance, their roles in drought stress responses remain to be clarified.ResultsIn this study, we cloned and characterized two ER genes, SbER1–1 and SbER2–1, from the drought-tolerant model plant sorghum (Sorghum bicolor L.). Under drought stress, the two genes were expressed in the leaves and stems but not in the roots, and SbER2–1 transcript accumulation in the stem was increased. SbER2–1 was localized both on the plasma membrane and in the chloroplast. Moreover, SbER2–1 expression in Arabidopsis and maize conferred increased drought tolerance, especially in regard to water-use efficiency, increasing the net photosynthetic rate in maize under drought stress. Based on RNA-Seq analysis together with the physiological data, we conclude that the transgenic maize plants have upregulated phenylpropanoid metabolism and increased lignin accumulation under drought stress.ConclusionsOur results demonstrate that SbER2–1 plays an important role in response to drought stress. Furthermore, photosynthetic systems and phenylpropanoid metabolism are implicated in SbER2–1-mediated drought stress tolerance mechanisms. The use of genetic engineering to regulate SbER2–1 expression in plants and to breed new varieties tolerant to drought is a research field full of potential.

Comparative Proteomic and Physiological Analyses of Two Divergent Maize Inbred Lines Provide More Insights into Drought-Stress Tolerance Mechanisms.

Drought stress is the major abiotic factor threatening maize (Zea mays L.) yield globally. Therefore, revealing the molecular mechanisms fundamental to drought tolerance in maize becomes imperative. Herein, we conducted a comprehensive comparative analysis of two maize inbred lines contrasting in drought stress tolerance based on their physiological and proteomic responses at the seedling stage. Our observations showed that divergent stress tolerance mechanisms exist between the two inbred-lines at physiological and proteomic levels, with YE8112 being comparatively more tolerant than MO17 owing to its maintenance of higher relative leaf water and proline contents, greater increase in peroxidase (POD) activity, along with decreased level of lipid peroxidation under stressed conditions. Using an iTRAQ (isobaric tags for relative and absolute quantification)-based method, we identified a total of 721 differentially abundant proteins (DAPs). Amongst these, we fished out five essential sets of drought responsive DAPs, including 13 DAPs specific to YE8112, 107 specific DAPs shared between drought-sensitive and drought-tolerant lines after drought treatment (SD_TD), three DAPs of YE8112 also regulated in SD_TD, 84 DAPs unique to MO17, and five overlapping DAPs between the two inbred lines. The most significantly enriched DAPs in YE8112 were associated with the photosynthesis antenna proteins pathway, whilst those in MO17 were related to C5-branched dibasic acid metabolism and RNA transport pathways. The changes in protein abundance were consistent with the observed physiological characterizations of the two inbred lines. Further, quantitative real-time polymerase chain reaction (qRT-PCR) analysis results confirmed the iTRAQ sequencing data. The higher drought tolerance of YE8112 was attributed to: activation of photosynthesis proteins involved in balancing light capture and utilization; enhanced lipid-metabolism; development of abiotic and biotic cross-tolerance mechanisms; increased cellular detoxification capacity; activation of chaperones that stabilize other proteins against drought-induced denaturation; and reduced synthesis of redundant proteins to help save energy to battle drought stress. These findings provide further insights into the molecular signatures underpinning maize drought stress tolerance.

Genetic identification and expression profiling of drought responsive genes in sorghum

Drought is the most important yield limiting abiotic stress worldwide and could have negative effects on food security. This study was conducted to map yield and yield-contributing trait QTLs under drought stress by association mapping, and to in silico identify drought responsive genes and assay their expression profile. Association analysis was conducted using 181 SSR markers and nine phenotypic traits collected from a structured sorghum population consisting of 96 accessions evaluated under optimum and drought stressed conditions at Assiut University Experimental Farm, Assiut, Egypt. Genomic regions associated with major drought tolerance QTLs were annotated with NCBI and sorghum databases to identify drought responsive genes, which were further transcriptionally analyzed. Significant differences between optimum irrigation and drought-stressed conditions were observed in all measured phenotypic traits. Association analysis revealed 93 marker-trait associations between 71 SSR markers and the nine phenotypic traits with an R2 value ranging from 6.56 to 42.64%. A high degree of linkage disequilibrium (>52%) was identified among markers on different chromosomes, suggesting epistatic interaction. BLASTP annotation of QTL genomic sequences identified 86 gene homologs, from which fifteen genes are drought responsive. All fifteen genes were differentially expressed in drought tolerant and susceptible accessions and their expression levels were highly induced in response to drought stress. The results provide a powerful approach coupling association and in silico analyses to identify gene clusters having a common expression profile with similar function, pointing to an evolutionary mechanism to initiate a quantitative drought stress tolerance mechanism.

Unveiling the molecular mechanisms of drought stress tolerance in rice (Oryza sativa L.) using computational approaches

Unveiling the molecular mechanisms of drought stress tolerance in rice (Oryza sativa L.) using computational approaches

Metabolic features involved in drought stress tolerance mechanisms in peanut nodules and their contribution to biological nitrogen fixation

Legumes belong to the most important crops worldwide. They increase soil fertility due their ability to establish symbiotic associations with soil microorganisms, known as rhizobia, capable of fixing nitrogen from the atmosphere. However, they are frequently exposed to abiotic stress conditions in particular drought. Such adverse conditions impair the biological nitrogen fixation (BNF) and depend largely on the legume. Therefore, two peanut cultivars with contrasting tolerance to drought, namely the more tolerant EC-98 and the sensitive Granoleico, were investigated to elucidate the relative contribution of BNF to the tolerance to drought. The tolerant cultivar EC-98 sustained growth and BNF similar to the control condition despite the reduced water potential and photosynthesis, suggesting the functioning of distinct metabolic pathways that contributed to enhance the tolerance. The biochemical and metabolomics approaches revealed that nodules from the tolerant cultivar accumulated trehalose, proline and gamma-aminobutyric acid (GABA), metabolites with known function in protecting against drought stress. The amide metabolism was severely affected in nodules from the sensitive cultivar Granoleico as revealed by the low content of asparagine and glutamine in the drought stressed plants. The sensitive cultivar upon rehydration was unable to re-establish a metabolism similar to well-watered plants. This was evidenced by the low level of metabolites and, transcripts and specific activities of enzymes from the carbon (sucrose synthase) and nitrogen (glutamine synthetase) metabolism which decreased below the values of control plants. Therefore, the increased content of metabolites with protective functions under drought stress likely is crucial for the full restoration upon rehydration. Smaller changes of drought stress-related metabolites in nodule are another trait that contributes to the effective control of BNF in the tolerant peanut cultivar (EC-98).

Impact of drought on photosynthesis: Molecular perspective

The reduction in the precipitation level and the occurrence of frequent drought will be among the top future worries for humans to tackle on this planet. Globally 80% of the agricultural land area is rainfed. According to current research and predictions of frequent drought in the future, there will be a substantial reduction in the economic yield of crop plants, a major threat to food security. Drought tolerance is a major economic consideration to yield. Various biological processes are getting affected by low water stress. Photosynthesis which is an essential biological process for the survival of plants is getting majorly influenced. However, plants have some inbuilt mechanisms to respond to drought stress to some extent. In this mini review, we have highlighted the impact of drought on crop plants, its impact on photosynthesis and responses of plants to drought stress. Understanding mechanism of drought stress tolerance will lead towards development of drought tolerance in crop plants.

Genome-Wide Investigation of WRKY Transcription Factors Involved in Terminal Drought Stress Response in Common Bean

WRKY transcription factor plays a key role in drought stress. However, the characteristics of the WRKY gene family in the common bean (Phaseolus vulgaris L.) are unknown. In this study, we identified 88 complete WRKY proteins from the draft genome sequence of the “G19833” common bean. The predicted genes were non-randomly distributed in all chromosomes. Basic information, amino acid motifs, phylogenetic tree and the expression patterns of PvWRKY genes were analyzed, and the proteins were classified into groups 1, 2, and 3. Group 2 was further divided into five subgroups: 2a, 2b, 2c, 2d, and 2e. Finally, we detected 19 WRKY genes that were responsive to drought stress using qRT-PCR; 11 were down-regulated, and 8 were up-regulated under drought stress. This study comprehensively examines WRKY proteins in the common bean, a model food legume, and it provides a foundation for the functional characterization of the WRKY family and opportunities for understanding the mechanisms of drought stress tolerance in this plant.

Global De Novo Protein-Protein Interactome Elucidates Interactions of Drought-Responsive Proteins in Horse Gram (Macrotyloma uniflorum).

Inspired by the availability of de novo transcriptome of horse gram (Macrotyloma uniflorum) and recent developments in systems biology studies, the first ever global protein-protein interactome (PPI) map was constructed for this highly drought-tolerant legume. Large-scale studies of PPIs and the constructed database would provide rationale behind the interplay at cascading translational levels for drought stress-adaptive mechanisms in horse gram. Using a bidirectional approach (interolog and domain-based), a high-confidence interactome map and database for horse gram was constructed. Available transcriptomic information for shoot and root tissues of a sensitive (M-191; genotype 1) and a drought-tolerant (M-249; genotype 2) genotype of horse gram was utilized to draw comparative PPI subnetworks under drought stress. High-confidence 6804 interactions were predicted among 1812 proteins covering about one-fourth of the horse gram proteome. The highest number of interactions (33.86%) in horse gram interactome matched with Arabidopsis PPI data. The top five hub nodes mostly included ubiquitin and heat-shock-related proteins. Higher numbers of PPIs were found to be responsive in shoot tissue (416) and root tissue (2228) of genotype 2 compared with shoot tissue (136) and root tissue (579) of genotype 1. Characterization of PPIs using gene ontology analysis revealed that kinase and transferase activities involved in signal transduction, cellular processes, nucleocytoplasmic transport, protein ubiquitination, and localization of molecules were most responsive to drought stress. Hence, these could be framed in stress adaptive mechanisms of horse gram. Being the first legume global PPI map, it would provide new insights into gene and protein regulatory networks for drought stress tolerance mechanisms in horse gram. Information compiled in the form of database (MauPIR) will provide the much needed high-confidence systems biology information for horse gram genes, proteins, and involved processes. This information would ease the effort and increase the efficacy for similar studies on other legumes. Public access is available at http://14.139.59.221/MauPIR/ .

Comprehensive tissue-specific proteome analysis of drought stress responses in Pennisetum glaucum (L.) R. Br. (Pearl millet)

Pearl millet is the fifth most important cereal crop worldwide and cultivated especially by small holder farmers in arid and semi-arid regions because of its drought and salt tolerance. The molecular mechanisms of drought stress tolerance in Pennisetum remain elusive. We have used a shotgun proteomics approach to investigate protein signatures from different tissues under drought and control conditions. Drought stressed plants showed significant changes in stomatal conductance and increased root growth compared to the control plants. Root, leaf and seed tissues were harvested and 2281 proteins were identified and quantified in total. Leaf tissue showed the largest number of significant changes (120), followed by roots (25) and seeds (10). Increased levels of root proteins involved in cell wall-, lipid-, secondary- and signaling metabolism and the concomitantly observed increased root length point to an impaired shoot–root communication under drought stress. The harvest index (HI) showed a significant reduction under drought stress. Proteins with a high correlation to the HI were identified using sparse partial least square (sPLS) analysis. Considering the importance of Pearl millet as a stress tolerant food crop, this study provides a first reference data set for future investigations of the underlying molecular mechanisms. Biological significanceDrought stress is the most limiting factor for plant growth and crop production worldwide. At the same time drought susceptible cereal crops are among the largest producers worldwide. In contrast, Pearl millet is a drought and salt tolerant cereal crop especially used in arid and semi-arid regions by small farmers. The multifactorial molecular mechanisms of this unique drought tolerance are not known. Here, we employ shotgun proteomics for a first characterization of the Pearl millet drought stress proteome. The experimental setup and the data set generated from this study reveal comprehensive physiological and proteomic responses of the drought stressed Pearl millet plants. Our study reveals statistically significant tissue-specific protein signatures during the adaptation to drought conditions. Thus, the work provides a first reference study of the drought stress proteome and related drought responsive proteins (DRP's) in Pearl millet.

RING Type E3 Ligase CaAIR1 in Pepper Acts in the Regulation of ABA Signaling and Drought Stress Response.

Several E3 ubiquitin ligases have been associated with the response to abiotic and biotic stresses in higher plants. Here, we report that the hot pepper (Capsicum annuum) ABA-Insensitive RING protein 1 gene (CaAIR1) is essential for a hypersensitive response to drought stress. CaAIR1 contains a C3HC4-type RING finger motif, which plays a role for attachment of ubiquitins to the target protein, and a putative transmembrane domain. The expression levels of CaAIR1 are up-regulated in pepper leaves by ABA treatments, drought and NaCl, suggesting its role in the response to abiotic stress. Our analysis showed that CaAIR1 displays self-ubiquitination and is localized in the nucleus. We generated CaAIR1-silenced peppers via virus-induced gene silencing (VIGS) and CaAIR1-overexpressing (OX) transgenic Arabidopsis plants to evaluate their responses to ABA and drought. VIGS of CaAIR1 in pepper plants conferred an enhanced tolerance to drought stress, which was accompanied by low levels of transpirational water loss in the drought-treated leaves. CaAIR1-OX plants displayed an impaired sensitivity to ABA during seed germination, seedling and adult stages. Moreover, these plants showed enhanced sensitivity to drought stress because of reduced stomatal closure and decreased expression of stress-responsive genes. Thus, our data indicate that CaAIR1 is a negative regulator of the ABA-mediated drought stress tolerance mechanism.

Multienvironment Quantitative Trait Loci Analysis for Photosynthate Acquisition, Accumulation, and Remobilization Traits in Common Bean Under Drought Stress

Many of the world’s common bean (Phaseolus vulgaris L.) growing regions are prone to either intermittent or terminal drought stress, making drought the primary cause of yield loss under farmers’ field conditions. Improved photosynthate acquisition, accumulation, and then remobilization have been observed as important mechanisms for adaptation to drought stress. The objective of this study was to tag quantitative trait loci (QTL) for photosynthate acquisition, accumulation, and remobilization to grain by using a recombinant inbred line population developed from the Mesoamerican intragenepool cross of drought-susceptible DOR364 and drought-tolerant BAT477 grown under eight environments differing in drought stress across two continents: Africa and South America. The recombinant inbred line population expressed quantitative variation and transgressive segregation for 11 traits associated with drought tolerance. QTL were detected by both a mixed multienvironment model and by composite interval mapping for each environment using a linkage map constructed with 165 genetic markers that covered 11 linkage groups of the common bean genome. In the multienvironment, mixed model, nine QTL were detected for 10 drought stress tolerance mechanism traits found on six of the 11 linkage groups. Significant QTL × environment interaction was observed for six of the nine QTL. QTL × environment interaction was of the cross-over type for three of the six significant QTL with contrasting effect of the parental alleles across different environments. In the composite interval mapping, we found 69 QTL in total. The majority of these were found for Palmira (47) or Awassa (18), with fewer in Malawi (4). Phenotypic variation explained by QTL in single environments ranged up to 37%, and the most consistent QTL were for Soil Plant Analysis Development (SPAD) leaf chlorophyll reading and pod partitioning traits. QTL alignment between the two detection methods showed that yield QTL on b08 and stem carbohydrate QTL on b05 were most consistent between the multilocation model and the single environment detection. Our results indicate the relevance of QTL detection in the sites in which bean breeding will be undertaken and the importance of photosynthate accumulation as a trait for common bean drought tolerance.

Construction and analysis of cotton (Gossypium arboreum L.) drought-related cDNA library

BackgroundDrought is one of the most important environmental factors causing water stress for cotton, and it greatly limits cotton growth and crop productivity. So far only a few drought-tolerance genes have been functionally characterized in details, and most efforts on this topic have been made in model organisms. Therefore, to identify more drought-related genes in cotton plays a crucial role in elucidating the underlying mechanisms of drought tolerance as well as utilizing bioengineering techniques to improve the tolerance in this organism.FindingsHere we constructed a subtractive drought-tolerance cDNA library using suppressive subtractive hybridization (SSH). Through differential screening and bioinformatics analysis, we identified 392 positive clones with differential expression, corresponding 265 unique genes. By BLAST search against Genbank, we found that more than half of these EST sequences were homologous to those previously known drought-related genes and that there were 57 sequences with unknown functions, suggesting that many more genes are involved in this complex trait. Moreover, using RT-PCR, we examined the expression of nine representative candidate genes and confirmed that their expression levels were increased at different levels under drought stress.ConclusionOur results show that drought tolerance is a complex trait in cotton, which involves the coordination of many genes and multiple metabolism pathways. The candidate EST sequences we identified here would facilitate further functional studies of drought-related genes and provide important insights into the molecular mechanisms of drought-stress tolerance and genetic breeding in cotton.