Over-expression of tobacco NtHSP70-1 contributes to drought-stress tolerance in plants

Transcriptome-wide identification of the Hsp70 gene family in Pugionium cornutum and functional analysis of PcHsp70-5 under drought stress

MAIN CONCLUSION

The PcHsp70-5 enhances drought stress tolerance in transgenic Arabidopsis thaliana by upregulating stress tolerance genes and antioxidant enzyme activities. Heat shock proteins (HSPs) constitute a class of evolutionarily conserved proteins synthesized by organisms in response to various adverse environmental stimuli such as elevated temperatures, drought, hormonal fluctuations, high salt concentrations, and mechanical stress. However, research on HSPs has predominantly focused on model plants and crops, whereas their functions in desert plants have not been well investigated. This study analyzed the transcriptome of Pugionium cornutum and identified the complete ORFs of 25 genes of the PcHsp70 family genes. Their expression levels under drought stress were investigated using existing RNA-seq data. PcHsp70-5 genes exhibited high expression levels in both roots and leaves under drought stress. Consequently, the PcHsp70-5 genes were cloned and transformed into Arabidopsis thaliana for further analysis of their roles in drought stress response. Real-time fluorescence quantitative PCR (qRT-PCR) analysis demonstrated that both, drought stress and ABA, induced PcHsp70-5 expression. Under drought conditions, transgenic Arabidopsis plants exhibited markedly enhanced growth compared to wild-type plants, as evidenced by improved survival rates, root length, fresh weight, chlorophyll content, and reduced levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in leaves, indicating that PcHsp70-5 overexpression mitigated growth inhibition and oxidative damage induced by drought stress. Subsequent research revealed that PcHsp70-5 overexpression significantly augmented the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and increased the proline content in transgenic Arabidopsis under drought conditions, alongside a significant increase in the expression levels of genes related to stress tolerance. This suggests that PcHsp70-5 enhances drought stress tolerance in transgenic Arabidopsis by upregulating stress tolerance genes and antioxidant enzyme activities.

Characteristics analysis of Early Responsive to Dehydration genes in Arabidopsis thaliana (AtERD)

Early Responsive to Dehydration (ERD) genes are rapidly induced in response to various biotic and abiotic stresses, such as bacteria, drought, light, temperature and high salt in Arabidopsis thaliana. Sixteen ERD of Arabidopsis thaliana (AtERD) genes have been previously identified. The lengths of the coding region of the genes are 504-2838 bp. They encode 137-745 amino acids. In this study, the AtERD genes structure and promoter are analyzed through bioinformatics, and a overall function is summarized and a systematic signal pathway involving AtERD genes is mapped. AtERD9, AtERD11 and AtERD13 have the GST domain. AtERD10 and AtERD14 have the Dehyd domain. The promoters regions contain 32 light responsive elements, 23 ABA responsive elements, 5 drought responsive elements, 5 meristem expression related elements and 132 core promoter elements. The study provides a theoretical guidance for subsequent studies of AtERD genes.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

Exogenous Abscisic Acid Affects the Heat Tolerance of Rice Seedlings by Influencing the Accumulation of ROS

Heat stress (HS) has become one of the major abiotic stresses that severely constrain rice growth. Abscisic acid (ABA) plays an important role in plant development and stress response. However, the effect of different concentrations of exogenous ABA on HS tolerance in rice still needs to be further elucidated. Here, we found that high concentrations of exogenous ABA increased HS damage in seedlings, whereas 10^-12 M ABA treatment increased fresh and dry weight under HS relative to mock seedlings. Our further data showed that, in response to HS, 10^-5 M, ABA-treated seedlings exhibited a lower chlorophyll content, as well as transcript levels of chlorophyll biosynthesis and antioxidant genes, and increased the accumulation of reactive oxygen species (ROS). In addition, the transcript abundance of some heat-, defense-, and ABA-related genes was downregulated on 10^-5 M ABA-treated seedlings under HS. In conclusion, high concentrations of exogenous ABA reduced the HS tolerance of rice seedlings, and this negative effect could be achieved by regulating the accumulation of ROS, chlorophyll biosynthesis, and the transcription levels of key genes in seedlings under HS.

Characterization of HSP70 family in watermelon (Citrullus lanatus): identification, structure, evolution, and potential function in response to ABA, cold and drought stress

Watermelon (Citrullus lanatus) as a crop with important economic value, is widely cultivated around the world. The heat shock protein 70 (HSP70) family in plant is indispensable under stress conditions. However, no comprehensive analysis of watermelon HSP70 family is reported to date. In this study, 12 ClHSP70 genes were identified from watermelon, which were unevenly located in 7 out of 11 chromosomes and divided into three subfamilies. ClHSP70 proteins were predicted to be localized primarily in cytoplasm, chloroplast, and endoplasmic reticulum. Two pairs of segmental repeats and 1 pair of tandem repeats existed in ClHSP70 genes, and ClHSP70s underwent strong purification selection. There were many abscisic acid (ABA) and abiotic stress response elements in ClHSP70 promoters. Additionally, the transcriptional levels of ClHSP70s in roots, stems, true leaves, and cotyledons were also analyzed. Some of ClHSP70 genes were also strongly induced by ABA. Furthermore, ClHSP70s also had different degrees of response to drought and cold stress. The above data indicate that ClHSP70s may be participated in growth and development, signal transduction and abiotic stress response, laying a foundation for further analysis of the function of ClHSP70s in biological processes.

Molecular and Physiological Mechanisms to Mitigate Abiotic Stress Conditions in Plants

Agriculture production faces many abiotic stresses, mainly drought, salinity, low and high temperature. These abiotic stresses inhibit plants' genetic potential, which is the cause of huge reduction in crop productivity, decrease potent yields for important crop plants by more than 50% and imbalance agriculture's sustainability. They lead to changes in the physio-morphological, molecular, and biochemical nature of the plants and change plants' regular metabolism, which makes them a leading cause of losses in crop productivity. These changes in plant systems also help to mitigate abiotic stress conditions. To initiate the signal during stress conditions, sensor molecules of the plant perceive the stress signal from the outside and commence a signaling cascade to send a message and stimulate nuclear transcription factors to provoke specific gene expression. To mitigate the abiotic stress, plants contain several methods of avoidance, adaption, and acclimation. In addition to these, to manage stress conditions, plants possess several tolerance mechanisms which involve ion transporters, osmoprotectants, proteins, and other factors associated with transcriptional control, and signaling cascades are stimulated to offset abiotic stress-associated biochemical and molecular changes. Plant growth and survival depends on the ability to respond to the stress stimulus, produce the signal, and start suitable biochemical and physiological changes. Various important factors, such as the biochemical, physiological, and molecular mechanisms of plants, including the use of microbiomes and nanotechnology to combat abiotic stresses, are highlighted in this article.

Comparative Transcriptome Analysis of Grafted Tomato with Drought Tolerance

Grafting is a method used in agriculture to improve crop production and tolerance to biotic and abiotic stress. This technique is widely used in tomato, Solanum lycopersicum L.; however, the effects of grafting on changes in gene expression associated with stress tolerance in shoot apical meristem cells are still under-discovered. To clarify the effect of grafting, we performed a transcriptomic analysis between non-grafted and grafted tomatoes using the tomato variety Momotaro-scion and rootstock varieties, TD1, GS, and GF. Drought tolerance was significantly improved not only by a combination of compatible resistant rootstock TD1 but also by self-grafted compared to non-grafted lines. Next, we found the differences in gene expression between grafted and non-grafted plants before and during drought stress treatment. These altered genes are involved in the regulation of plant hormones, stress response, and cell proliferation. Furthermore, when comparing compatible (Momo/TD1 and Momo/Momo) and incompatible (Momo/GF) grafted lines, the incompatible line reduced gene expression associated with phytohormones but increased in wounding and starvation stress-response genes. These results conclude that grafting generates drought stress tolerance through several gene expression changes in the apical meristem.

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.

The positive feedback regulatory loop of miR160-Auxin Response Factor 17-HYPONASTIC LEAVES 1 mediates drought tolerance in apple trees

Drought stress tolerance is a complex trait regulated by multiple factors. Here, we demonstrate that the miRNA160-Auxin Response Factor 17 (ARF17)-HYPONASTIC LEAVES 1 module is crucial for apple (Malus domestica) drought tolerance. Using stable transgenic plants, we found that drought tolerance was improved by higher levels of Mdm-miR160 or MdHYL1 and by decreased levels of MdARF17, whereas reductions in MdHYL1 or increases in MdARF17 led to greater drought sensitivity. Further study revealed that modulation of drought tolerance was achieved through regulation of drought-responsive miRNA levels by MdARF17 and MdHYL1; MdARF17 interacted with MdHYL1 and bound to the promoter of MdHYL1. Genetic analysis further suggested that MdHYL1 is a direct downstream target of MdARF17. Importantly, MdARF17 and MdHYL1 regulated the abundance of Mdm-miR160. In addition, the Mdm-miR160-MdARF17-MdHYL1 module regulated adventitious root development. We also found that Mdm-miR160 can move from the scion to the rootstock in apple and tomato (Solanum lycopersicum), thereby improving root development and drought tolerance of the rootstock. Our study revealed the mechanisms by which the positive feedback loop of Mdm-miR160-MdARF17-MdHYL1 influences apple drought tolerance.

Genome-Wide Identification and Expression Analysis of Heat Shock Protein 70 (HSP70) Gene Family in Pumpkin (Cucurbita moschata) Rootstock under Drought Stress Suggested the Potential Role of these Chaperones in Stress Tolerance

Heat shock protein 70s (HSP70s) are highly conserved proteins that are involved in stress responses. These chaperones play pivotal roles in protein folding, removing the extra amounts of oxidized proteins, preventing protein denaturation, and improving the antioxidant system activities. This conserved family has been characterized in several crops under drought stress conditions. However, there is no study on HSP70s in pumpkin (Cucurbita moschata). Therefore, we performed a comprehensive analysis of this gene family, including phylogenetic relationship, motif and gene structure analysis, gene duplication, collinearity, and promoter analysis. In this research, we found 21 HSP70s that were classified into five groups (from A to E). These genes were mostly localized in the cytoplasm, chloroplast, mitochondria, nucleus, and endoplasmic reticulum (ER). We could observe more similarity in closely linked subfamilies in terms of motifs, the number of introns/exons, and the corresponding cellular compartments. According to the collinearity analysis, gene duplication had occurred as a result of purifying selection. The results showed that the occurrence of gene duplication for all nine gene pairs was due to segmental duplication (SD). Synteny analysis revealed a closer relationship between pumpkin and cucumber than pumpkin and Arabidopsis. Promoter analysis showed the presence of various cis-regulatory elements in the up-stream region of the HSP70 genes, such as hormones and stress-responsive elements, indicating a potential role of this gene family in stress tolerance. We furtherly performed the gene expression analysis of the HSP70s in pumpkin under progressive drought stress. Pumpkin is widely used as a rootstock to improve stress tolerance, as well as fruit quality of cucumber scion. Since stress-responsive mobile molecules translocate through vascular tissue from roots to the whole plant body, we used the xylem of grafted materials to study the expression patterns of the HSP70 (potentially mobile) gene family. The results indicated that all CmoHSP70s had very low expression levels at 4 days after stress (DAS). However, the genes showed different expression patterns by progressing he drought period. For example, the expression of CmoHSP70-4 (in subgroup E) and CmoHSP70-14 (in subgroup C) sharply increased at 6 and 11 DAS, respectively. However, the expression of all genes belonging to subgroup A did not change significantly in response to drought stress. These findings indicated the diverse roles of this gene family under drought stress and provided valuable information for further investigation on the function of this gene family, especially under stressful conditions.

Profiling of N6-Methyladenosine (m6A) Modification Landscape in Response to Drought Stress in Apple (Malus prunifolia (Willd.) Borkh)

Drought stress is a significant environmental factor limiting crop growth worldwide. Malus prunifolia is an important apple species endemic to China and is used for apple cultivars and rootstocks with great drought tolerance. N⁶-methyladenosine (m⁶A) is a common epigenetic modification on messenger RNAs (mRNAs) in eukaryotes which is critical for various biological processes. However, there are no reports on m⁶A methylation in apple response to drought stress. Here, we assessed the m⁶A landscape of M. prunifolia seedlings in response to drought and analyzed the association between m⁶A modification and transcript expression. In total, we found 19,783 and 19,609 significant m⁶A peaks in the control and drought treatment groups, respectively, and discovered a UGUAH (H: A/U/C) motif. In M. prunifolia, under both control and drought conditions, peaks were highly enriched in the 3' untranslated region (UTR) and coding sequence (CDS). Among 4204 significant differential m⁶A peaks in drought-treated M. prunifolia compared to control-treated M. prunifolia, 4158 genes with m⁶A modification were identified. Interestingly, a large number of hypermethylated peaks (4069) were stimulated by drought treatment compared to hypomethylation. Among the hypermethylated peak-related genes, 972 and 1238 differentially expressed genes (DEGs) were up- and down-regulated in response to drought, respectively. Gene ontology (GO) analyses of differential m⁶A-modified genes revealed that GO slims related to RNA processing, epigenetic regulation, and stress tolerance were significantly enriched. The m⁶A modification landscape depicted in this study sheds light on the epigenetic regulation of M. prunifolia in response to drought stress and indicates new directions for the breeding of drought-tolerant apple trees.

Genome-Wide Identification and Characterization of HSP70 Gene Family in Aquilaria sinensis (Lour.) Gilg

The heat shock protein 70 (HSP70) gene family perform a fundamental role in protecting plants against biotic and abiotic stresses. Aquilaria sinensis is a classic stress-induced medicinal plant, producing a valuable dark resin in a wood matrix, known as agarwood, in response to environmental stresses. The HSP70 gene family has been systematic identified in many plants, but there is no comprehensive analysis at the genomic level in A. sinensis. In this study, 15 putative HSP70 genes were identified in A. sinensis through genome-wide bioinformatics analysis. Based on their phylogenetic relationships, the 15 AsHSP70 were grouped into six sub-families that with the conserved motifs and gene structures, and the genes were mapped onto six separate linkage groups. A qRT-PCR analysis showed that the relative expression levels of all the AsHSP70 genes were up-regulated by heat stress. Subcellular localization of all HSP70s was predicted, and three were verified by transiently expressed in Arabidopsis protoplasts. Based on the expression profiles in different tissues and different layers treated with Agar-Wit, we predict AsHSP70 genes are involved in different stages of agarwood formation. The systematic identification and expression analysis of HSP70s gene family imply some of them may play important roles in the formation of agarwood. Our findings not only provide a foundation for further study their biological function in the later research in A. sinensis, but also provides a reference for the analysis of HSPs in other species.

Genome-wide analysis of HSP70 gene superfamily in Pyropia yezoensis (Bangiales, Rhodophyta): identification, characterization and expression profiles in response to dehydration stress

BACKGROUND

Heat shock proteins (HSPs) perform a fundamental role in protecting plants against abiotic stresses. Individual family members have been analyzed in previous studies, but there has not yet been a comprehensive analysis of the HSP70 gene family in Pyropia yezoensis.

RESULTS

We investigated 15 putative HSP70 genes in Py. yezoensis. These genes were classified into two sub-families, denoted as DnaK and Hsp110. In each sub-family, there was relative conservation of the gene structure and motif. Synteny-based analysis indicated that seven and three PyyHSP70 genes were orthologous to HSP70 genes in Pyropia haitanensis and Porphyra umbilicalis, respectively. Most PyyHSP70s showed up-regulated expression under different degrees of dehydration stress. PyyHSP70-1 and PyyHSP70-3 were expressed in higher degrees compared with other PyyHSP70s in dehydration treatments, and then expression degrees somewhat decreased in rehydration treatment. Subcellular localization showed PyyHSP70-1-GFP and PyyHSP70-3-GFP were in the cytoplasm and nucleus/cytoplasm, respectively. Similar expression patterns of paired orthologs in Py. yezoensis and Py. haitanensis suggest important roles for HSP70s in intertidal environmental adaptation during evolution.

CONCLUSIONS

These findings provide insight into the evolution and modification of the PyyHSP70 gene family and will help to determine the functions of the HSP70 genes in Py. yezoensis growth and development.

Fulvic acid enhances drought resistance in tea plants by regulating the starch and sucrose metabolism and certain secondary metabolism

The aim of this work was to gain insight into the molecular mechanisms underlying the effect of fulvic acid on drought-exposed tea plants. We performed proteomic analysis of fulvic acid-treated tea leaves from the target plants using tandem mass tag quantitative labeling technology and compared the results with those of a previous transcriptomic analysis. We identified 48 and 611 differentially abundant proteins in the leaves of tea plants treated with fulvic acid compared with the control under mild and severe drought, respectively. Comparative analysis showed that, under severe drought, 55 genes had similar expression patterns at the transcriptome and proteome levels, such as PAL, GBE, GBSS and bAS. Bioinformatic analysis revealed that those genes were mainly related to the starch and sucrose metabolism, phenylpropanoid biosynthesis and triterpenoid biosynthesis. SIGNIFICANCE: This study broadens the understanding of the molecular mechanisms underlying the improved drought resistance seen in tea plants in the presence of fulvic acid and provides a basis for further research on the genomics of drought tolerance in these plants. In addition, these findings could be used to develop new guidance strategies for improved drought management systems in tea plantation.

Transcriptional regulation and stress-defensive key genes induced by γ-aminobutyric acid in association with tolerance to water stress in creeping bentgrass

γ-Aminobutyric acid (GABA) acts as an important regulator involved in the mediation of cell signal transduction and stress tolerance in plants. However, the function of GABA in transcriptional regulation is not fully understood in plants under water stress. The creeping bentgrass (Agrostis stolonifera) was pretreated with or without GABA (0.5 mM) for 24 hours before being exposed to 5 days of water stress. Physiological analysis showed that GABA-treated plants maintained significantly higher endogenous GABA content, leaf relative water content, net photosynthetic rate, and lower osmotic potential than untreated plants under water stress. The GABA application also significantly alleviated stress-induced increases in superoxide anion (O2.-) content, hydrogen peroxide (H2O2) content, and electrolyte leakage through enhancing total antioxidant capacity, superoxide dismutase (SOD) activity, and peroxidase (POD) activity in response to water stress. The transcriptomic analysis demonstrated that the GABA-induced changes in differentially expressed genes (DEGs) involved in carbohydrates, amino acids, and secondary metabolism helped to maintain better osmotic adjustment, energy supply, and metabolic homeostasis when creeping bentgrass suffers from water stress. The GABA triggered Ca2+-dependent protein kinase (CDPK) signaling and improved transcript levels of DREB1/2 and WRKY1/24/41 that could be associated with the upregulation of stress-related functional genes such as POD, DHNs, and HSP70 largely contributing to improved tolerance to water stress in relation to the antioxidant, prevention of cell dehydration, and protein protection in leaves.

Drought Stress Impacts on Plants and Different Approaches to Alleviate Its Adverse Effects

Drought stress, being the inevitable factor that exists in various environments without recognizing borders and no clear warning thereby hampering plant biomass production, quality, and energy. It is the key important environmental stress that occurs due to temperature dynamics, light intensity, and low rainfall. Despite this, its cumulative, not obvious impact and multidimensional nature severely affects the plant morphological, physiological, biochemical and molecular attributes with adverse impact on photosynthetic capacity. Coping with water scarcity, plants evolve various complex resistance and adaptation mechanisms including physiological and biochemical responses, which differ with species level. The sophisticated adaptation mechanisms and regularity network that improves the water stress tolerance and adaptation in plants are briefly discussed. Growth pattern and structural dynamics, reduction in transpiration loss through altering stomatal conductance and distribution, leaf rolling, root to shoot ratio dynamics, root length increment, accumulation of compatible solutes, enhancement in transpiration efficiency, osmotic and hormonal regulation, and delayed senescence are the strategies that are adopted by plants under water deficit. Approaches for drought stress alleviations are breeding strategies, molecular and genomics perspectives with special emphasis on the omics technology alteration i.e., metabolomics, proteomics, genomics, transcriptomics, glyomics and phenomics that improve the stress tolerance in plants. For drought stress induction, seed priming, growth hormones, osmoprotectants, silicon (Si), selenium (Se) and potassium application are worth using under drought stress conditions in plants. In addition, drought adaptation through microbes, hydrogel, nanoparticles applications and metabolic engineering techniques that regulate the antioxidant enzymes activity for adaptation to drought stress in plants, enhancing plant tolerance through maintenance in cell homeostasis and ameliorates the adverse effects of water stress are of great potential in agriculture.

Genome-Wide Identification and Expression Profile of the SNAT Gene Family in Tobacco (Nicotiana tabacum)

Melatonin plays key roles in development and confers stress tolerance to plants. Serotonin N-acetyltransferase (SNAT) is either the enzyme involved in the last step or the penultimate enzyme of phytomelatonin biosynthesis. To date, SNAT genes have not been characterized in tobacco (Nicotiana tabacum), an economically important plant species. The sequence of the Acetyltransf_7 conserved domain was used as a query sequence, and 12 NtSNAT candidate genes were in turn identified in the genome of tobacco. These NtSNATs could be divided into two groups based on the phylogenetic tree. NtSNAT1 and NtSNAT2 clustered together with the other typical SNATs, but the other 10 NtSNATs separately clustered outside of the typical SNATs. These 10 NtSNATs have only motif 1, whereas representative SNATs, such as NtSNAT1 and NtSNAT2 or a SNAT from cyanobacteria, have five motifs. In addition, NtSNAT1 and NtSNAT2 are highly homologous to the characterized OsSNAT1, 62.95 and 71.36%, respectively; however, the homology between the other 10 NtSNAT genes and OsSNAT1 is low. Concomitantly, it is hypothesized that NtSNAT1 and NtSNAT2 are the homolog of SNATs, whereas the other 10 candidates could be considered NtSNAT-like genes. Furthermore, both Nicotiana tomentosiformis and Nicotiana sylvestris, two diploid ancestor species of N. tabacum, have two SNAT candidates; therefore, it is speculated that gene rearrangement or deletion during the process of genomic stabilization after whole-genome duplication or polyploidization led to the preservation of NtSNAT1 and NtSNAT2 during the evolution of tobacco from the ancestral diploid to the allotetraploid. NtSNAT and NtSNAT-like genes were differentially expressed in all organs under different stress conditions, indicating that these genes potentially associated with plant growth and development and stress resistance. Under different stress conditions, the expression of NtSNAT1 was significantly upregulated upon high-temperature and cadmium stresses, while the expression of NtSNAT2 did not significantly increase under any of the tested stress treatments. These results provide valuable information for elucidating the evolutionary relationship of SNAT genes in tobacco and genetic resources for improving tobacco production in the future.

Genome-wide transcriptional changes triggered by water deficit on a drought-tolerant common bean cultivar

BACKGROUND

Common bean (Phaseolus vulgaris L.) is a relevant crop cultivated over the world, largely in water insufficiency vulnerable areas. Since drought is the main environmental factor restraining worldwide crop production, efforts have been invested to amend drought tolerance in commercial common bean varieties. However, scarce molecular data are available for those cultivars of P. vulgaris with drought tolerance attributes.

RESULTS

As a first approach, Pinto Saltillo (PS), Azufrado Higuera (AH), and Negro Jamapa Plus (NP) were assessed phenotypically and physiologically to determine the outcome in response to drought on these common bean cultivars. Based on this, a Next-generation sequencing approach was applied to PS, which was the most drought-tolerant cultivar to determine the molecular changes at the transcriptional level. The RNA-Seq analysis revealed that numerous PS genes are dynamically modulated by drought. In brief, 1005 differentially expressed genes (DEGs) were identified, from which 645 genes were up-regulated by drought stress, whereas 360 genes were down-regulated. Further analysis showed that the enriched categories of the up-regulated genes in response to drought fit to processes related to carbohydrate metabolism (polysaccharide metabolic processes), particularly genes encoding proteins located within the cell periphery (cell wall dynamics). In the case of down-regulated genes, heat shock-responsive genes, mainly associated with protein folding, chloroplast, and oxidation-reduction processes were identified.

CONCLUSIONS

Our findings suggest that secondary cell wall (SCW) properties contribute to P. vulgaris L. drought tolerance through alleviation or mitigation of drought-induced osmotic disturbances, making cultivars more adaptable to such stress. Altogether, the knowledge derived from this study is significant for a forthcoming understanding of the molecular mechanisms involved in drought tolerance on common bean, especially for drought-tolerant cultivars such as PS.

Proteomic profiling of developing wheat heads under water-stress

A replicated iTRAQ (isobaric tags for relative and absolute quantification) study on developing wheat heads from two doubled haploid (DH) lines identified from a cross between cv Westonia x cv Kauz characterized the proteome changes influenced by reproductive stage water-stress. All lines were exposed to 10 days of water-stress from early booting (Zadok 40), with sample sets taken from five head developmental stages. Two sample groups (water-stressed and control) account for 120 samples that required 18 eight-plex iTRAQ runs. Based on the IWGSC RefSeq v1 wheat assembly, among the 4592 identified proteins, a total of 132 proteins showed a significant response to water-stress, including the down-regulation of a mitochondrial Rho GTPase, a regulator of intercellular fundamental biological processes (7.5 fold) and cell division protein FtsZ at anthesis (6.0 fold). Up-regulated proteins included inosine-5'-monophosphate dehydrogenase (3.83 fold) and glycerophosphodiester phosphodiesterase (4.05 fold). The Pre-FHE and FHE stages (full head emerged) of head development were differentiated by 391 proteins and 270 proteins differentiated the FHE and Post-FHE stages. Water-stress during meiosis affected seed setting with 27% and 6% reduction in the progeny DH105 and DH299 respectively. Among the 77 proteins that differentiated between the two DH lines, 7 proteins were significantly influenced by water-stress and correlated with the seed set phenotype response of the DH lines to water-stress (e.g. the up-regulation of a subtilisin-like protease in DH 299 relative to DH 105). This study provided unique insights into the biological changes in developing wheat head that occur during water-stress.

Knockdown of CaHSP60-6 confers enhanced sensitivity to heat stress in pepper (Capsicum annuum L.)

HSP60 gene family in pepper was analyzed through bioinformatics along with transcriptional regulation against multiple abiotic and hormonal stresses. Furthermore, the knockdown of CaHSP60-6 increased sensitivity to heat stress. The 60 kDa heat shock protein (HSP60) also known as chaperonin (cpn60) is encoded by multi-gene family that plays an important role in plant growth, development and in stress response as a molecular chaperone. However, little is known about the HSP60 gene family in pepper (Capsicum annuum L.). In this study, 16 putative pepper HSP60 genes were identified through bioinformatic tools. The phylogenetic tree revealed that eight of the pepper HSP60 genes (50%) clustered into group I, three (19%) into group II, and five (31%) into group III. Twelve (75%) CaHSP60 genes have more than 10 introns, while only a single gene contained no introns. Chromosomal mapping revealed that the tandem and segmental duplication events occurred in the process of evolution. Gene ontology enrichment analysis predicted that CaHSP60 genes were responsible for protein folding and refolding in an ATP-dependent manner in response to various stresses in the biological processes category. Multiple stress-related cis-regulatory elements were found in the promoter region of these CaHSP60 genes, which indicated that these genes were regulated in response to multiple stresses. Tissue-specific expression was studied under normal conditions and induced under 2 h of heat stress measured by RNA-Seq data and qRT-PCR in different tissues (roots, stems, leaves, and flowers). The data implied that HSP60 genes play a crucial role in pepper growth, development, and stress responses. Fifteen (93%) CaHSP60 genes were induced in both, thermo-sensitive B6 and thermo-tolerant R9 lines under heat treatment. The relative expression of nine representative CaHSP60 genes in response to other abiotic stresses (cold, NaCl, and mannitol) and hormonal applications [ABA, methyl jasmonate (MeJA), and salicylic acid (SA)] was also evaluated. Knockdown of CaHSP60-6 increased the sensitivity to heat shock treatment as documented by a higher relative electrolyte leakage, lipid peroxidation, and reactive oxygen species accumulation in silenced pepper plants along with a substantial lower chlorophyll content and antioxidant enzyme activity. These results suggested that HSP60 might act as a positive regulator in pepper defense against heat and other abiotic stresses. Our results provide a basis for further functional analysis of HSP60 genes in pepper.

Transgenic crops for the agricultural improvement in Pakistan: a perspective of environmental stresses and the current status of genetically modified crops

Transgenic technologies have emerged as a powerful tool for crop improvement in terms of yield, quality, and quantity in many countries of the world. However, concerns also exist about the possible risks involved in transgenic crop cultivation. In this review, literature is analyzed to gauge the real intensity of the issues caused by environmental stresses in Pakistan. In addition, the research work on genetically modified organisms (GMOs) development and their performance is analyzed to serve as a guide for the scientists to help them select useful genes for crop transformation in Pakistan. The funding of GMOs research in Pakistan shows that it does not follow the global trend. We also present socio-economic impact of GM crops and political dimensions in the seed sector and the policies of the government. We envisage that this review provides guidelines for public and private sectors as well as the policy makers in Pakistan and in other countries that face similar environmental threats posed by the changing climate.

Transcriptomic and metabolomic profiling of drought-tolerant and susceptible sesame genotypes in response to drought stress

BACKGROUND

Sesame is an important oil crop due to its high oil, antioxidant, and protein content. Drought stress is a major abiotic stress that affects sesame production as well as the quality of sesame seed. To reveal the adaptive mechanism of sesame in response to water deficient conditions, transcriptomic and metabolomics were applied in drought-tolerant (DT) and drought-susceptible (DS) sesame genotypes.

RESULTS

Transcriptomic analysis reveals a set of core drought-responsive genes (684 up-regulated and 1346 down-regulated) in sesame that was robustly differently expressed in both genotypes. Most enriched drought-responsive genes are mainly involved in protein processing in endoplasmic reticulum, plant hormone signal transduction photosynthesis, lipid metabolism, and amino acid metabolism. Drought-susceptible genotype was more disturbed by drought stress at both transcriptional and metabolic levels, since more drought-responsive genes/metabolites were identified in DS. Drought-responsive genes associated with stress response, amino acid metabolism, and reactive oxygen species scavenging were more enriched or activated in DT. According to the partial least-squares discriminate analysis, the most important metabolites which were accumulated under drought stress in both genotypes includes ABA, amino acids, and organic acids. Especially, higher levels of ABA, proline, arginine, lysine, aromatic and branched chain amino acids, GABA, saccharopine, 2-aminoadipate, and allantoin were found in DT under stress condition. Combination of transcriptomic and metabolomic analysis highlights the important role of amino acid metabolism (especially saccharopine pathway) and ABA metabolism and signaling pathway for drought tolerance in sesame.

CONCLUSION

The results of the present study provide valuable information for better understanding the molecular mechanism underlying drought tolerance of sesame, and also provide useful clues for the genetic improvement of drought tolerance in sesame.

The Hsp70 Gene Family in Solanum tuberosum: Genome-Wide Identification, Phylogeny, and Expression Patterns

Heat shock protein 70 (Hsp70) family members play important roles in protecting plants against abiotic stresses, including salt, drought, heat, and cold. In this study, 20 putative StHsp70 genes were identified in potato (Solanum tuberosum L.) through the integration of the gene structures, chromosome locations, phylogenetic relationships, and expression profiles. These StHsp70 genes were classified into five sub-families based on phylogenetic analysis. Chromosome mapping revealed that they were unevenly and unequally distributed on 10 of the 12 chromosomes. Furthermore, segmental and tandem duplication events contributed to the expansion of the StHsp70 genes. Phylogenetic tree of the HSP70 genes from potato and other plant species revealed multiple sub-families. These findings indicated a common ancestor which had generated diverse sub-families prior to a mono-dicot split. In addition, expression analysis using RNA-seq revealed that the majority of these genes were expressed in at least one of the tested tissue, and were induced by Phytophthora infestans. Then, based on qRT-PCR analysis, the results showed that the transcript levels of some of the StHsp70 genes could be remarkably induced by such abiotic and hormone stresses, which indicated their potential roles in mediating the responses of potato plants to both abiotic and biotic stress conditions.

Combinations of Small RNA, RNA, and Degradome Sequencing Uncovers the Expression Pattern of microRNA⁻mRNA Pairs Adapting to Drought Stress in Leaf and Root of Dactylis glomerata L

Drought stress is a global problem, and the lack of water is a key factor that leads to agricultural shortages. MicroRNAs play a crucial role in the plant drought stress response; however, the microRNAs and their targets involved in drought response have not been well elucidated. In the present study, we used Illumina platform (https://www.illumina.com/) and combined data from miRNA, RNA, and degradome sequencing to explore the drought- and organ-specific miRNAs in orchardgrass (Dactylis glomerata L.) leaf and root. We aimed to find potential miRNA⁻mRNA regulation patterns responding to drought conditions. In total, 519 (486 conserved and 33 novel) miRNAs were identified, of which, 41 miRNAs had significant differential expression among the comparisons (p < 0.05). We also identified 55,366 unigenes by RNA-Seq, where 12,535 unigenes were differently expressed. Finally, our degradome analysis revealed that 5950 transcripts were targeted by 487 miRNAs. A correlation analysis identified that miRNA ata-miR164c-3p and its target heat shock protein family A (HSP70) member 5 gene comp59407_c0 (BIPE3) may be essential in organ-specific plant drought stress response and/or adaptation in orchardgrass. Additionally, Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) analyses found that "antigen processing and presentation" was the most enriched downregulated pathway in adaptation to drought conditions. Taken together, we explored the genes and miRNAs that may be involved in drought adaptation of orchardgrass and identified how they may be regulated. These results serve as a valuable genetic resource for future studies focusing on how plants adapted to drought conditions.

Identification of differentially accumulated proteins involved in regulating independent and combined osmosis and cadmium stress response in Brachypodium seedling roots

In this study, we aimed to identify differentially accumulated proteins (DAPs) involved in PEG mock osmotic stress, cadmium (Cd²⁺) stress, and their combined stress responses in Brachypodium distachyon seedling roots. The results showed that combined PEG and Cd²⁺ stresses had more significant effects on Brachypodium seedling root growth, physiological traits, and ultrastructures when compared with each individual stress. Totally, 106 DAPs were identified that are responsive to individual and combined stresses in roots. These DAPs were mainly involved in energy metabolism, detoxification and stress defense and protein metabolism. Principal component analysis revealed that DAPs from Cd²⁺ and combined stress treatments were grouped closer than those from osmotic stress treatment, indicating that Cd²⁺ and combined stresses had more severe influences on the root proteome than osmotic stress alone. Protein-protein interaction analyses highlighted a 14-3-3 centered sub-network that synergistically responded to osmotic and Cd²⁺ stresses and their combined stresses. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis of 14 key DAP genes revealed that most genes showed consistency between transcriptional and translational expression patterns. A putative pathway of proteome metabolic changes in Brachypodium seedling roots under different stresses was proposed, which revealed a complicated synergetic responsive network of plant roots to adverse environments.

An Alcohol Dehydrogenase Gene from Synechocystis sp. Confers Salt Tolerance in Transgenic Tobacco

Synechocystis salt-responsive gene 1 (sysr1) was engineered for expression in higher plants, and gene construction was stably incorporated into tobacco plants. We investigated the role of Sysr1 [a member of the alcohol dehydrogenase (ADH) superfamily] by examining the salt tolerance of sysr1-overexpressing (sysr1-OX) tobacco plants using quantitative real-time polymerase chain reactions, gas chromatography-mass spectrometry, and bioassays. The sysr1-OX plants exhibited considerably increased ADH activity and tolerance to salt stress conditions. Additionally, the expression levels of several stress-responsive genes were upregulated. Moreover, airborne signals from salt-stressed sysr1-OX plants triggered salinity tolerance in neighboring wild-type (WT) plants. Therefore, Sysr1 enhanced the interconversion of aldehydes to alcohols, and this occurrence might affect the quality of green leaf volatiles (GLVs) in sysr1-OX plants. Actually, the Z-3-hexenol level was approximately twofold higher in sysr1-OX plants than in WT plants within 1-2 h of wounding. Furthermore, analyses of WT plants treated with vaporized GLVs indicated that Z-3-hexenol was a stronger inducer of stress-related gene expression and salt tolerance than E-2-hexenal. The results of the study suggested that increased C6 alcohol (Z-3-hexenol) induced the expression of resistance genes, thereby enhancing salt tolerance of transgenic plants. Our results revealed a role for ADH in salinity stress responses, and the results provided a genetic engineering strategy that could improve the salt tolerance of crops.

Comparative Physiological and Molecular Analyses of Two Contrasting Flue-Cured Tobacco Genotypes under Progressive Drought Stress

Drought is a major environmental factor that limits crop growth and productivity. Flue-cured tobacco (Nicotiana tabacum) is one of the most important commercial crops worldwide and its productivity is vulnerable to drought. However, comparative analyses of physiological, biochemical and gene expression changes in flue-cured tobacco varieties differing in drought tolerance under long-term drought stress are scarce. In this study, drought stress responses of two flue-cured tobacco varieties, LJ851 and JX6007, were comparatively studied at the physiological and transcriptional levels. After exposing to progressive drought stress, the drought-tolerant LJ851 showed less growth inhibition and chlorophyll reduction than the drought-sensitive JX6007. Moreover, higher antioxidant enzyme activities and lower levels of H2O2, Malondialdehyde (MDA), and electrolyte leakage after drought stress were found in LJ851 when compared with JX6007. Further analysis showed that LJ851 plants had much less reductions than the JX6007 in the net photosynthesis rate and stomatal conductance during drought stress; indicating that LJ851 had better photosynthetic performance than JX6007 during drought. In addition, transcriptional expression analysis revealed that LJ851 exhibited significantly increased transcripts of several categories of drought-responsive genes in leaves and roots under drought conditions. Together, these results indicated that LJ851 was more drought-tolerant than JX6007 as evidenced by better photosynthetic performance, more powerful antioxidant system, and higher expression of stress defense genes during drought stress. This study will be valuable for the development of novel flue-cured tobacco varieties with improved drought tolerance by exploitation of natural genetic variations in the future.

Molecular cloning and functional analysis of the drought tolerance gene MsHSP70 from alfalfa (Medicago sativa L.)

Heat shock proteins (HSPs) are a ubiquitously expressed class of protective proteins that play a key role in plant response to stressful conditions. This study aimed to characterize and investigate the function of an HSP gene in alfalfa (Medicago sativa). MsHSP70, which contains a 2028-bp open reading frame, was identified through homology cloning. MsHSP70 shares high sequence identity (94.47%) with HSP70 from Medicago truncatula. Expression analysis of MsHSP70 in alfalfa organs revealed a relatively higher expression level in aerial organs such as flowers, stems and leaves than in roots. MsHSP70 was induced by heat shock, abscisic acid (ABA) and hydrogen peroxide. Transgenic Arabidopsis seedlings overexpressing MsHSP70 were hyposensitive to polyethylene glycol (PEG) and ABA treatments, suggesting that exogenous expression of MsHSP70 enhanced Arabidopsis tolerance to these stresses. Examination of physiological indexes related to drought and ABA stress demonstrated that in comparison with non-transgenic plants, T3 transgenic Arabidopsis plants had an increased proline content, higher superoxide dismutase (SOD) activity, and decreased malondialdehyde (MDA) content. Furthermore, higher relative water content (RWC) was detected in transgenic plants compared with non-transgenic plants under drought stress. These findings clearly indicate that molecular manipulation of MsHSP70 in plants can have substantial effects on stress tolerance.

OsASR5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H2 O2 signalling in rice

Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid, stress and ripening (ASR) genes from upland rice variety, IRAT109 (Oryza sativa L. ssp. japonica), and demonstrated that overexpression of OsASR5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of OsASR5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H₂ O₂ , a second messenger for the induction of stomatal closure in response to ABA, was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss-of-function mutant, osasr5, showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that OsASR5 functioned as chaperone-like protein and interacted with stress-related HSP40 and 2OG-Fe (II) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that OsASR5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone-like protein that possibly prevents drought stress-related proteins from inactivation.

Global Scale Transcriptional Profiling of Two Contrasting Barley Genotypes Exposed to Moderate Drought Conditions: Contribution of Leaves and Crowns to Water Shortage Coping Strategies

Drought is a serious threat for sustainable agriculture. Barley represents a species well adapted to environmental stresses including drought. To elucidate the adaptive mechanism of barley on transcriptional level we evaluated transcriptomic changes of two contrasting barley cultivars upon drought using the microarray technique on the level of leaves and crowns. Using bioinformatic tools, differentially expressed genes in treated vs. non-treated plants were identified. Both genotypes revealed tissue dehydration under drought conditions as shown at water saturation deficit and osmotic potential data; however, dehydration was more severe in Amulet than in drought-resistant Tadmor under the same ambient conditions. Performed analysis showed that Amulet enhanced expression of genes related to active plant growth and development, while Tadmor regarding the stimulated genes revealed conservative, water saving strategy. Common reactions of both genotypes and tissues included an induction of genes encoding several stress-responsive signaling proteins, transcription factors as well as effector genes encoding proteins directly involved in stress acclimation. In leaf, tolerant cultivar effectively stimulated mainly the expression of genes encoding proteins and enzymes involved in protein folding, sulfur metabolism, ROS detoxification or lipid biosynthesis and transport. The crown specific reaction of tolerant cultivar was an enhanced expression of genes encoding proteins and enzymes involved in cell wall lignification, ABRE-dependent abscisic acid (ABA) signaling, nucleosome remodeling, along with genes for numerous jasmonate induced proteins.

Heterologous expression of the Hsp24 from Trichoderma asperellum improves antifungal ability of Populus transformant Pdpap-Hsp24 s to Cytospora chrysosperma and Alternaria alternate

The tolerance of plants to biotic and abiotic stresses could be improved by transforming with fungal resistance-related genes. In this study, the cDNA sequence (GenBank Acc. No. KP337939) of the resistance-related gene Hsp24 encoding the 24 kD heat shock protein was obtained from the biocontrol fungus Trichoderma asperellum ACCC30536. The promoter region of Hsp24 contained many cis-regulators related to stresses response, such as "GCN4" and "GCR1" etc. Hsp24 transcription in T. asperellum was up-regulated under six different environmental stresses, compared with the control. Furthermore, following heterologous transformation into Populus davidiana × P. alba var. Pyramidalis (Pdpap), Hsp24 was successfully transcribed in transformant Pdpap-Hsp24s. Pathogen-related genes (PRs) in four Pdpap-Hsp24s were up-regulated compared with those in the control Pdpap (Pdpap-Con). After co-culture of Pdpap-Hsp24s with the weak parasite Cytospora chrysosperma, the transcription of genes related to hormone signal pathway (JA and SA) were up-regulated in Pdpap-Hsp24s, and ethidium bromide (EtBr) and Nitro-blue tetrazolium (NBT) staining assays indicated that the cell membrane permeability and the active oxygen content of Pdpap-Hsp24s leaves were lower than that of the control Pdpap-Con. And when the Pdpap-Hsp24s were under the Alternaria alternate stress, the activities of superoxide dismutase (SOD) and peroxidase (POD) got higher in Pdpap-Hsp24s than that in Pdpap-Con, and the disease spots in Pdpap-Con leaves were obviously larger than those in Pdpap-Hsp24s leaves. In summary, Hsp24 of T. asperellum ACCC30536 is an important defense response gene, and its heterologous expression improved the resistance of transformant Pdpap-Hsp24s to C. chrysosperma and A. alternate.

Genome-wide identification of salinity responsive HSP70s in common bean

The present study is aimed to identify and characterize HSP70 (PvHSP70) genes in two different common bean cultivars under salt stress. For this purpose various in silico methods such as RNAseq data and qRT-PCR analysis were used. A total of 24 candidate PvHSP70 gene were identified. Except for chromosome 4 and 7, these candidate PvHSP70 genes were distributed on the remaining chromosomes. While the lowest number of PvHSP70 genes was determined on chromosomes 1, 3, 5, 7, 9, 10 and 11 (one HSP70 gene), the highest number of PvHSP70s was on chromosomes 6 and 8 (seven HSP70 genes each). Three genes; PvHSP70-5, -9, and -10 were found to have no-introns. In addition, four tandemly and six segmentally duplicated gene couples were detected. A total of 13 PvHSP70 genes were targeted by miRNAs of 44 plant species and the most targeted genes were PvHSP70-5 and -23. The expression profile of PvHSP70 genes based on publicly available RNA-seq data was identified and salt treated leaf tissue was found to have more gene expression levels compared to the root. qRT-PCR analysis showed that the transcript concentrations of upregulated PvHSP70 genes in leaves of Zulbiye (sensitive) were mostly higher than those of Yakutiye (resistant). The present study revealed that PvHSP70 genes might play an important role in salt stress response for common bean cultivars and variability between cultivars also suggests that these genes could be used as functional markers for salt tolerance in common bean.

Microarray and genetic analysis reveals that csa-miR159b plays a critical role in abscisic acid-mediated heat tolerance in grafted cucumber plants

Root-shoot communication plays a vital role in plant growth, development and adaptation to environmental stimuli. Grafting-induced stress tolerance is associated with the induction of plentiful stress-related genes and proteins; the mechanism involved, however, remains obscure. Here, we show that the enhanced tolerance against heat stress in cucumber plants with luffa as rootstock was accompanied with an increased accumulation of abscisic acid (ABA), down-regulation of a subset of microRNAs (miRNAs) but up-regulation of their target genes and CsHSP70 accumulation in the shoots. Significantly, luffa rootstock and foliar application of ABA both down-regulated csa-miR159b and up-regulated its target mRNAs CsGAMYB1 and CsMYB29-like and CsHSP70 accumulation in cucumber, while ectopic expression of csa-miR159b led to decreased heat tolerance, AtMYB33 transcript and AtHSP70 accumulation in Arabidopsis plants. Taken together, our results suggest that root-originated signals such as ABA could alter miRNAs in the shoots, which have a major role in the post-transcriptional regulation of the stress-responsive genes.

Overexpression of MuHSP70 gene from Macrotyloma uniflorum confers multiple abiotic stress tolerance in transgenic Arabidopsis thaliana

A 70-KD heat shock protein (HSP70) is one of the most conserved chaperones. It is involved in de novo protein folding and prevents the aggregation of unfolded proteins under lethal environmental factors. The purpose of this study is to characterise a MuHSP70 from horsegram (Macrotyloma uniflorum) and elucidating its role in stress tolerance of plants. A MuHSP70 was cloned and characterised from a natural drought stress tolerant HPK4 variety of horsegram (M. uniflorum). For functional characterization, MuHSP70 was overexpressed in transgenic Arabidopsis. Overexpression of MuHSP70 was found to provide tolerance to the transgenic Arabidopsis against various stresses such as heat, cold, drought, salinity and oxidative stress. MuHSP70 transgenics were observed to maintain the shoot biomass, root length, relative water content, and chlorophyll content during exposure to multi-stresses relative to non-transgenic control. Transgenic lines have further shown the reduced levels of MDA, H2O2, and proteolytic activity. Together, these findings suggest that overexpression of MuHSP70 plays an important role in improving abiotic stress tolerance and could be a crucial candidate gene for exploration in crop improvement program.

Erianthus arundinaceus HSP70 (EaHSP70) Acts as a Key Regulator in the Formation of Anisotropic Interdigitation in Sugarcane (Saccharum spp. hybrid) in Response to Drought Stress

Plant growth during abiotic stress is a long sought-after trait especially in crop plants in the context of global warming and climate change. Previous studies on leaf epidermal cells have revealed that during normal growth and development, adjacent cells interdigitate anisotropically to form cell morphological patterns known as interlocking marginal lobes (IMLs), involving the cell wall-cell membrane-cortical actin continuum. IMLs are growth-associated cell morphological changes in which auxin-binding protein (ABP), Rho GTPases and actin are known to play important roles. In the present study, we investigated the formation of IMLs under drought stress and found that Erianthus arundinaceus, a drought-tolerant wild relative of sugarcane, develops such growth-related cell morphological patterns under drought stress. Using confocal microscopy, we showed an increasing trend in cortical F-actin intensity in drought-tolerant plants with increasing soil moisture stress. In order to check the role of drought tolerance-related genes in IML formation under soil moisture stress, we adopted a structural data mining strategy and identified indirect connections between the ABPs and heat shock proteins (HSPs). Initial experimental evidence for this connection comes from the high transcript levels of HSP70 observed in drought-stressed Erianthus, which developed anisotropic interdigitation, i.e. IMLs. Subsequently, by overexpressing the E. arundinaceus HSP70 gene (EaHSP70) in sugarcane (Saccharum spp. hybrid), we confirm the role of HSP70 in the formation of anisotropic interdigitation under drought stress. Taken together, our results suggest that EaHSP70 acts as a key regulator in the formation of anisotropic interdigitation in drought-tolerant plants (Erianthus and HSP70 transgenic sugarcane) under moisture stress in an actin-mediated pathway. The possible biological significance of the formation of drought-associated interlocking marginal lobes (DaIMLs) in sugarcane plants upon drought stress is discussed.

Genome-wide identification and analysis of drought-responsive genes and microRNAs in tobacco

Drought stress response is a complex trait regulated at transcriptional and post-transcriptional levels in tobacco. Since the 1990s, many studies have shown that miRNAs act in many ways to regulate target expression in plant growth, development and stress response. The recent draft genome sequence of Nicotiana benthamiana has provided a framework for Digital Gene Expression (DGE) and small RNA sequencing to understand patterns of transcription in the context of plant response to environmental stress. We sequenced and analyzed three Digital Gene Expression (DGE) libraries from roots of normal and drought-stressed tobacco plants, and four small RNA populations from roots, stems and leaves of control or drought-treated tobacco plants, respectively. We identified 276 candidate drought responsive genes (DRGs) with sequence similarities to 64 known DRGs from other model plant crops, 82 were transcription factors (TFs) including WRKY, NAC, ERF and bZIP families. Of these tobacco DRGs, 54 differentially expressed DRGs included 21 TFs, which belonged to 4 TF families such as NAC (6), MYB (4), ERF (10), and bZIP (1). Additionally, we confirmed expression of 39 known miRNA families (122 members) and five conserved miRNA families, which showed differential regulation under drought stress. Targets of miRNAs were further surveyed based on a recently published study, of which ten targets were DRGs. An integrated gene regulatory network is proposed for the molecular mechanisms of tobacco root response to drought stress using differentially expressed DRGs, the changed expression profiles of miRNAs and their target transcripts. This network analysis serves as a reference for future studies on tobacco response stresses such as drought, cold and heavy metals.

Erianthus arundinaceus HSP70 (EaHSP70) overexpression increases drought and salinity tolerance in sugarcane (Saccharum spp. hybrid)

Heat shock proteins (HSPs) have a major role in stress tolerance mechanisms in plants. Our studies have shown that the expression of HSP70 is enhanced under water stress in Erianthus arundinaceus. In this paper, we evaluate the effects of overexpression of EaHSP70 driven by Port Ubi 2.3 promoter in sugarcane. The transgenic events exhibit significantly higher gene expression, cell membrane thermostability, relative water content, gas exchange parameters, chlorophyll content and photosynthetic efficiency. The overexpression of EaHSP70 transgenic sugarcane led to the upregulation of stress-related genes. The transformed sugarcane plants had better chlorophyll retention and higher germination ability than control plants under salinity stress. Our results suggest that EaHSP70 plays an important role in sugarcane acclimation to drought and salinity stresses and its potential for genetic engineering of sugarcane for drought and salt tolerance.

Hydrogen peroxide mediates abscisic acid-induced HSP70 accumulation and heat tolerance in grafted cucumber plants

Root-shoot communications play important roles in plant stress responses. Here, we examined the roles of root-sourced signals in the shoot response to heat in cucumber plants. Cucumber plants grafted onto their own roots and luffa roots were exposed to aerial and root-zone heat to examine their tolerance by assessing the levels of oxidative stress, PSII photoinhibition, accumulation of abscisic acid (ABA), H2 O2 and heat shock protein (HSP) 70 using immunoblotting, chlorophyll fluorescence, immunoassay, CeCl3 staining and Western blotting, respectively. Grafting onto the luffa rootstock enhanced the shoot tolerance to the heat. This enhanced tolerance was associated with increased accumulation of ABA and apoplastic H2 O2 , RBOH transcripts and HSP70 expression and a decrease in oxidative stress in the shoots. The increases in the ABA and H2 O2 concentrations in the shoots were attributed to an increase in ABA transport from roots and an increase in ABA biosynthesis in the shoots when the root-zone and shoots were heat stressed, respectively. Inhibition of H2 O2 accumulation compromised luffa rootstock-induced HSP70 expression and heat tolerance. These results suggest that, under heat stress, ABA triggers the expression of HSP70 in an apoplastic H2 O2 -dependent manner, implicating the role of an ABA-dependent H2 O2 -driven mechanism in a systemic response involving root-shoot communication.

Transcriptome-wide profiling and expression analysis of diploid and autotetraploid Paulownia tomentosa × Paulownia fortunei under drought stress

Paulownia is a fast-growing deciduous hardwood species native to China, which has high ecological and economic value. In an earlier study, we reported ploidy-dependent differences in Paulownia drought tolerance by the microscopic observations of the leaves. Autotetraploid Paulownia has a higher resistance to drought stress than their diploid relatives. In order to obtain genetic information on molecular mechanisms responses of Paulownia plants to drought, Illumina/Solexa Genome sequencing platform was used to de novo assemble the transcriptomes of leaves from diploid and autotetraploid Paulownia tomentosa × Paulownia fortunei seedlings (PTF2 and PTF4 respectively) grown under control conditions and under drought stress and obtained 98,671 nonredundant unigenes. A comparative transcriptome analysis revealed that hundreds of unigenes were predicted to be involved mainly in ROS-scavenging system, amino acid and carbohydrate metabolism, plant hormone biosynthesis and signal transduction, while these unigenes exhibited differential transcript alteration of the two accessions. This study provides a comprehensive map of how P. tomentosa × P. fortunei responds to drought stress at physiological and molecular levels, which may help in understanding the mechanisms involve in water-deficit response and will be useful for further study of drought tolerance in woody plants.

Comparative proteomic responses of two bermudagrass (Cynodon dactylon (L). Pers.) varieties contrasting in drought stress resistance

Drought (water-deficit) stress is a serious environmental problem in plant growth and cultivation. As one of widely cultivated warm-season turfgrass, bermudagrass (Cynodon dactylon (L). Pers.) exhibits drastic natural variation in the drought stress resistance in leaves and stems of different varieties. In this study, proteomic analysis was performed to identify drought-responsive proteins in both leaves and stems of two bermudagrass varieties contrasting in drought stress resistance, including drought sensitive variety (Yukon) and drought tolerant variety (Tifgreen). Through comparative proteomic analysis, 39 proteins with significantly changed abundance were identified, including 3 commonly increased and 2 decreased proteins by drought stress in leaves and stems of Yukon and Tifgreen varieties, 2 differentially regulated proteins in leaves and stems of two varieties after drought treatment, 23 proteins increased by drought stress in Yukon variety and constitutively expressed in Tifgreen variety, and other 3 differentially expressed proteins under control and drought stress conditions. Among them, proteins involved in photosynthesis (PS), glycolysis, N-metabolism, tricarboxylicacid (TCA) and redox pathways were largely enriched, which might be contributed to the natural variation of drought resistance between Yukon and Tifgreen varieties. These studies provide new insights to understand the molecular mechanism underlying bermudagrass response to drought stress.

Evidence for selection on gene expression in cultivated rice (Oryza sativa)

Artificial selection has been used throughout plant domestication and breeding to develop crops that are adapted to diverse environments. Here, we investigate whether gene regulatory changes have been widespread targets of lineage-specific selection in cultivated lines Minghui 63 and Zhenshan 97 of rice, Oryza sativa. A line experiencing positive selection for either an increase or a decrease in genes' transcript abundances is expected to have an overabundance of expression quantitative trait locus (eQTL) alleles that increase or decrease those genes' expression, respectively. Results indicate that several genes that share Gene Ontology terms or are members of the same coexpression module have eQTL alleles from one parent that consistently increase gene expression relative to the second parent. A second line of evidence for lineage-specific selection is an overabundance of cis-trans pairs of eQTL alleles that affect gene expression in the same direction (are reinforcing). Across all cis-trans pairs of eQTL, including pairs that both weakly and strongly affect gene expression, there is no evidence for selection. However, the frequency of genes with reinforcing eQTL increases with eQTL strength. Therefore, there is evidence that eQTL with strong effects were positively selected during rice cultivation. Among 41 cis-trans pairs with strong trans eQTL, 31 have reinforcing eQTL. Several of the candidate genes under positive selection accurately predict phenotypic differences between Minghui 63 and Zhenshan 97. Overall, our results suggest that positive selection for regulatory alleles may be a key factor in plant improvement.

A chrysanthemum heat shock protein confers tolerance to abiotic stress

Heat shock proteins are associated with protection against various abiotic stresses. Here, the isolation of a chrysanthemum cDNA belonging to the HSP70 family is reported. The cDNA, designated CgHSP70, encodes a 647-residue polypeptide, of estimated molecular mass 70.90 kDa and pI 5.12. A sub-cellular localization assay indicated that the cDNA product is deposited in the cytoplasm and nucleus. The performance of Arabidopsis thaliana plants constitutively expressing CgHSP70 demonstrated that the gene enhances tolerance to heat, drought and salinity. When CgHSP70 was stably over-expressed in chrysanthemum, the plants showed an increased peroxidase (POD) activity, higher proline content and inhibited malondialdehyde (MDA) content. After heat stress, drought or salinity the transgenic plants were better able to recover, demonstrating CgHSP70 positive effect.

Expression analysis of nine small heat shock protein genes from Tamarix hispida in response to different abiotic stresses and abscisic acid treatment

Heat shock proteins (HSPs) play important roles in protecting plants against environmental stresses. Furthermore, small heat shock proteins (sHSPs) are the most ubiquitous HSP subgroup with molecular weights ranging from 15 to 42 kDa. In this study, nine sHSP genes (designated as ThsHSP1-9) were cloned from Tamarix hispida. Their expression patterns in response to cold, heat shock, NaCl, PEG and abscisic acid (ABA) treatments were investigated in the roots and leaves of T. hispida by real-time RT-PCR analysis. The results showed that most of the nine ThsHSP genes were expressed at higher levels in roots than in leaves under normal growth condition. All of ThsHSP genes were highly induced under conditions of cold (4 °C) and different heat shocks (36, 40, 44, 48 and 52 °C). Under NaCl stress, all nine ThsHSPs genes were up-regulated at least one stress time-point in both roots and leaves. Under PEG and ABA treatments, the nine ThsHSPs showed various expression patterns, indicating a complex regulation pathway among these genes. This study represents an important basis for the elucidation of ThsHSP gene function and provides essential information that can be used for stress tolerance genetic engineering in future studies.

Proteomic profiling of γ-ECS overexpressed transgenic Nicotiana in response to drought stress

The contribution of Glutathione (GSH) in drought stress tolerance is an established fact. However, the proteins which are directly or indirectly related to the increased level of GSH in response to drought stress are yet to be known. To explore this, here, transgenic tobacco plants (NtGp11) overexpressing gamma-glutamylcysteine synthetase (γ-ECS) was tested for tolerance against drought stress. NtGp11 conferred tolerance to drought stress by increased germination rate, water retention, water recovery, chlorophyll, and proline content compared with wild-type plants. Semi-quantitative RT-PCR analysis revealed that the transcript levels of stress-responsive genes were higher in NtGp11 compared with wild-type in response to drought stress. Two-dimensional gel electrophoresis (2-DE) coupled with MALDI TOF-TOF MS/MS analysis has been used to identify 43 differentially expressed proteins in response to drought in wild-type and NtGp11 plants. The results demonstrated the up-accumulation of 58.1% of proteins among which 36%, 24%, and 20% of them were related to stress and defense, carbon metabolism and energy metabolism categories, respectively. Taken together, our results demonstrated that GSH plays an important role in combating drought stress in plants by inducing stress related genes and proteins like HSP70, chalcone synthase, glutathione peroxidase, thioredoxin peroxidase, ACC oxidase, and heme oxygenase I.

Drought tolerance in wheat

Drought is one of the most important phenomena which limit crops' production and yield. Crops demonstrate various morphological, physiological, biochemical, and molecular responses to tackle drought stress. Plants' vegetative and reproductive stages are intensively influenced by drought stress. Drought tolerance is a complicated trait which is controlled by polygenes and their expressions are influenced by various environmental elements. This means that breeding for this trait is so difficult and new molecular methods such as molecular markers, quantitative trait loci (QTL) mapping strategies, and expression patterns of genes should be applied to produce drought tolerant genotypes. In wheat, there are several genes which are responsible for drought stress tolerance and produce different types of enzymes and proteins for instance, late embryogenesis abundant (lea), responsive to abscisic acid (Rab), rubisco, helicase, proline, glutathione-S-transferase (GST), and carbohydrates during drought stress. This review paper has concentrated on the study of water limitation and its effects on morphological, physiological, biochemical, and molecular responses of wheat with the possible losses caused by drought stress.

Heat-shock protein 70 binds microtubules and interacts with kinesin in tobacco pollen tubes

The heat-shock proteins of 70 kDa are a family of ubiquitously expressed proteins important for protein folding. Heat-shock protein 70 assists other nascent proteins to achieve the spatial structure and ultimately helps the cell to protect against stress factors, such as heat. These proteins are localized in different cellular compartments and are associated with the cytoskeleton. We identified a heat-shock protein 70 isoform in the pollen tube of tobacco that binds to microtubules in an ATP-dependent manner. The heat-shock protein 70 was identified as part of the so-called ATP-MAP (ATP-dependent microtubule-associated protein) fraction, which also includes the 90-kDa kinesin, a mitochondria-associated motor protein. The identity of heat-shock protein 70 was validated by immunological assays and mass spectrometry. Sequence analysis showed that this heat-shock protein 70 is more similar to specific heat-shock proteins of Arabidopsis than to corresponding proteins of tobacco. Two-dimensional electrophoresis indicated that this heat-shock protein 70 isoform only is part of the ATP-MAP fraction and that is associated with the mitochondria of pollen tubes. Sedimentation assays showed that the binding of heat-shock protein 70 to microtubules is not affected by AMPPNP but it increases in the presence of the 90-kDa kinesin. Binding of heat-shock protein 70 to microtubules occurs only partially in the presence of ATP but it does not occur if, in addition to ATP, the 90-kDa kinesin is also present. Data suggest that the binding (but not the release) of heat-shock protein 70 to microtubules is facilitated by the 90-kDa kinesin.