Physiological performance and differential expression profiling of genes associated with drought tolerance in contrasting varieties of two Gossypium species

Screening cotton genotypes for their drought tolerance ability based on the expression level of dehydration-responsive element-binding protein and proline biosynthesis-related genes and morpho-physio-biochemical responses

Drought stress adversely affects growth, development, productivity, and fiber quality of cotton (Gossypium hirsutum L). Breeding strategies to enhance drought tolerance require an improved knowledge of plant drought responses necessitating proper identification of drought-tolerant genotypes of crops, including cotton. The objective of this study was to classify the selected cotton genotypes for their drought tolerance ability based on morpho-physio-biochemical traits using Hierarchical Ward's cluster analysis. Five genotypes of cotton (Takfa 3, Takfa 6, Takfa 7, Takfa 84-4, and Takfa 86-5) were selected as plant materials, and were grown under well-watered (WW; 98 ± 2% field capacity) and water-deficit (WD; 50 ± 2% field capacity) conditions for 16 days during the flower initiation stage. Data on morpho-physio-biochemical parameters and gene expression levels for these parameters were collected, and subsequently genotypes were classified either as a drought tolerant or drought susceptible one. Upregulation of GhPRP (proline-rich protein), GhP5CS (Δ1-pyrroline-5-carboxylate synthetase), and GhP5CR (Δ1-pyrroline-5-carboxylate reductase) in relation to free proline enrichment was observed in Takfa 3 genotype under WD condition. An accumulation of free proline, total soluble sugar, and potassium in plants under WD conditions was detected, which played a key role as major osmolytes controlling cellular osmotic potential. Magnesium and calcium concentrations were also enriched in leaves under WD conditions, functioning as essential elements and regulating photosynthetic abilities. Leaf greenness, net photosynthetic rate, stomatal conductance, and transpiration rate were also declined under WD conditions, leading to growth retardation, especially aboveground traits of Takfa 6, Takfa 7, Takfa 84-4, and Takfa 86-5 genotypes. An increase in leaf temperature (1.1 - 4.0 °C) and crop water stress index (CWSI > 0.75) in relation to stomatal closure and reduced transpiration rate was recorded in cotton genotypes under WD conditions compared with WW conditions. Based on the increase of free proline, soluble sugar, leaf temperature, and CWSI, as well as the decrease of aboveground growth traits and physiological attributes, five genotypes were categorized into two cluster groups: drought tolerant (Takfa 3) and drought susceptible (Takfa 6, Takfa 7, Takfa 84-4, and Takfa 86-5). The identified drought-tolerant cotton genotype, namely, Takfa 3, may be grown in areas experiencing drought conditions. It is recommended to further validate the yield traits of Takfa 3 under rainfed field conditions in drought-prone environments.

Distinctive physiological and molecular responses of foxtail millet and maize to nicosulfuron

Introduction

Nicosulfuron is the leading acetolactate synthase inhibitor herbicide product, and widely used to control gramineous weeds. Here, we investigated the metabolic process of nicosulfuron into foxtail millet and maize, in order to clarify the mechanism of the difference in sensitivity of foxtail millet and maize to nicosulfuron from the perspective of physiological metabolism and provide a theoretical basis for the breeding of nicosulfuron-resistant foxtail millet varieties.

Methods

We treated foxtail millet (Zhangzagu 10, Jingu 21) and maize (Nongda 108, Ditian 8) with various doses of nicosulfuron in both pot and field experiments. The malonaldehyde (MDA) content, target enzymes, detoxification enzymes, and antioxidant enzymes, as well as related gene expression levels in the leaf tissues of foxtail millet and maize were measured, and the yield was determined after maturity.

Results

The results showed that the recommended dose of nicosulfuron caused Zhangzagu 10 and Jingu 21 to fail to harvest; the yield of the sensitive maize variety (Ditian 8) decreased by 37.09%, whereas that of the resistant maize variety (Nongda 108) did not decrease. Nicosulfuron stress increased the CYP450 enzyme activity, MDA content, and antioxidant enzyme activity of foxtail millet and maize, reduced the acetolactate synthase (ALS) activity and ALS gene expression of foxtail millet and Ditian 8, and reduced the glutathione S-transferase (GST) activity and GST gene expression of foxtail millet. In conclusion, target enzymes, detoxification enzymes, and antioxidant enzymes were involved in the detoxification metabolism of nicosulfuron in plants. ALS and GST are the main factors responsible for the metabolic differences among foxtail millet, sensitive maize varieties, and resistant maize varieties.

Discussion

These findings offer valuable insights for exploring the target resistance (TSR) and non-target resistance (NTSR) mechanisms in foxtail millet under herbicide stress and provides theoretical basis for future research of develop foxtail millet germplasm with diverse herbicide resistance traits.

Spectral reflectance and fluorescence is a rapid, non-destructive tool for drought tolerance monitoring in Withania somnifera (L.) Dunal

Withania somnifera plants were exposed to drought stress for 23 days. Relative water content (RWC), gaseous exchange, fluorescence parameters, and spectral reflectance changes were monitored under drought stress. Assimilation rate and RWC decreased by 81% and 65%, respectively, during drought exposure of 23 days. Photosynthetic reflectance index (PRI) and water index (WI) showed a decreasing pattern under drought stress and correlated with Amax and RWC. Anthocyanin reflectance index and anthocyanin content increased with drought stress. Similarly, rational among R727, R696, R770, and R731 reflects chlorophyll content and Chl a/b ratio and copes with actual chlorophyll content. Fluorescence changes showed the opening and closing of PSII reaction centers, while absorbance change at 830/875 nm showed activity and energy balance of PSI. Non-photochemical quenching increased under drought, which showed depoxydation of xanthine cycle pigment. Energy balance at the acceptor and donor side of PSI adjusted under drought stress by increasing electron carrying limitation at donor side. Energy balance between PSI and PSII is maintained by increasing cyclic electron flux under mild drought stress. Both protective mechanism depoxydation of xanthine cycle pigment and enhancement of cyclic electron flux reduced or diminished under severe drought stress. Decrease in leaf area and stomatal closure may cause a reduction in transpiration that results into loss of RWC and altered physiological processes. Since fluorescence, absorbance change and spectral reflectance are non-invasive measurements that may be used as indicators for assessing drought tolerance in medicinal plants.

Growth, Physiological, and Biochemical Responses of Ethiopian Red Pepper (Capsicum annum L.) Cultivars to Drought Stress

Red pepper (Capsicum annum L.) is an increasingly important economic crop in the world. Thus, this study aimed to investigate the growth, physiological, and biochemical responses of red pepper cultivars under drought stress conditions. A pot culture experiment was conducted in a completely randomized design with three replications, four treatments, and three cultivars. Totally, 36 pots and six seeds per pot were used to grow the seeds. After five weeks, the cultivars were exposed to different drought stress conditions (100% FC or control, 80% FC or low stress, 60% FC or moderate stress, and 40% FC or severe stress). All the collected data were subjected to an analysis of variance (ANOVA). Shoot length was reduced significantly (p < 0.05) in the Hagerew cultivar under severe drought stress. The photosynthesis rate was reduced by 21.11% (p < 0.05) in the Mitmita cultivar under severe drought stress. The highest percentage reduction of chlorophyll content (77.28%) was recorded in the Hagerew cultivar. Both Markofana and Mitmita responded to drought stress by increasing the accumulation of proline and phenolic compounds. The root-to-shoot ratio was increased significantly in both Markofana and Mitmita cultivars (27.91% and 50.92%), respectively, under drought-stress conditions. This study depicted that the cultivar Mitmita was the most drought-tolerant cultivar among the three cultivars.

Comparison of selenite and selenate in alleviation of drought stress in Nicotiana tabacum L

Exogenous selenium (Se) improves the tolerance of plants to abiotic stress. However, the effects and mechanisms of different Se species on drought stress alleviation are poorly understood. This study aims to evaluate and compare the different effects and mechanisms of sodium selenate (Na2SeO4) and sodium selenite (Na2SeO3) on the growth, photosynthesis, antioxidant system, osmotic substances and stress-responsive gene expression of Nicotiana tabacum L. under drought stress. The results revealed that drought stress could significantly inhibit growth, whereas both Na2SeO4 and Na2SeO3 could significantly facilitate the growth of N. tabacum under drought stress. However, compared to Na2SeO3, Se application as Na2SeO4 induced a significant increase in the root tip number and number of bifurcations under drought stress. Furthermore, both Na2SeO4 and Na2SeO3 displayed higher levels of photosynthetic pigments, better photosynthesis, and higher concentrations of osmotic substances, antioxidant enzymes, and stress-responsive gene (NtCDPK2, NtP5CS, NtAREB and NtLEA5) expression than drought stress alone. However, the application of Na2SeO4 showed higher expression levels of the NtP5CS and NtAREB genes than Na2SeO3. Both Na2SeO4 and Na2SeO3 alleviated many of the deleterious effects of drought in leaves, which was achieved by reducing stress-induced lipid peroxidation (MDA) and H2O2 content by enhancing the activity of antioxidant enzymes, while Na2SeO4 application showed lower H2O2 and MDA content than Na2SeO3 application. Overall, the results confirm the positive effects of Se application, especially Na2SeO4 application, which is markedly superior to Na2SeO3 in the role of resistance towards abiotic stress in N. tabacum.

A type-2C protein phosphatase (GhDRP1) participates in cotton (Gossypium hirsutum) response to drought stress

GhDRP1 acts as a negatively regulator to participate in response to drought stress possibly by modulating ABA signaling pathway and flavonoid biosynthesis pathway which affects stomata movement and thus water loss, ROS scavenging enzymes, and proline accumulation in cotton. Type-2C protein phosphatases (PP2C) may play important roles in plant stress signal transduction. Here, we show the evidence that a cotton PP2C protein GhDRP1 participates in plant response to drought stress. GhDRP1 gene encodes an active type-2C protein phosphatase (PP2C) and its expression is significantly induced in cotton by drought stress. Compared with wild type, the GhDRP1 overexpression (OE) transgenic cotton and Arabidopsis displayed reduced drought tolerance, whereas GhDRP1-silenced (RNAi) cotton showed enhanced drought tolerance. Under drought stress, malondialdehyde content was lower, whereas superoxide dismutase and peroxidase activities, proline content, stomata closure and relative water content were higher in GhDRP1 RNAi plants compared with those in wild type. In contrast, GhDRP1 OE plants showed the opposite phenotype under the same conditions. Expression levels of some stress-related and flavonoid biosynthesis-related genes were altered in GhDRP1 transgenic plants under drought stress. Additionally, GhDRP1 protein could interact with other proteins such as PYLs, SNF1-related protein kinase and GLK1-like protein. Collectively, these data suggest that GhDRP1 participates in plant response to drought stress possibly by modulating ABA signaling pathway and flavonoid biosynthesis pathway which affects stomata movement and thus water loss, ROS scavenging enzymes, and proline accumulation in cotton.

Overexpression of WssgtL3.1 gene from Withania somnifera confers salt stress tolerance in Arabidopsis

Overexpression of Withania somnifera SGT gene (WssgtL3.1) in transgenic Arabidopsis improves various agronomic and physiological traits and alters conjugated sterol levels to mitigate the effect of salt stress. Sterols are essential constituents of cell membranes that are involved in several biological functions, including response to various biotic and abiotic stresses by altering membrane permeability and signaling pathways. Sterol glycosyltransferases (SGTs) are enzymes that are involved in sterol modification by converting sterols into sterol-conjugates to play essential roles in adaptive responses. However, their roles under abiotic stresses are lesser-known. Among abiotic stresses, salinity imposes serious threat to crop yield worldwide, hence the present study intends to investigate the role of WssgtL3.1-overexpressed Arabidopsis plants under salt stress indicating the crosstalk between SGT gene and salinity to develop improved crop varieties with better stress tolerance ability. The findings revealed that overexpression of WssgtL3.1 gene in A. thaliana improved the resistance against salt stress in the overexpressing lines. Transgenic lines showed significantly higher germination rate, increased plant growth with less chlorophyll damage compared to wild-type (WT) control plants. Moreover, better tolerance also correlated with enhanced osmolytes (proline and soluble sugar), better membrane integrity, decreased H₂O₂ production and lesser MDA accumulation and Na⁺/K⁺ ratio with more negative osmotic potential in overexpressed lines. Additionally, in sterol profiling, significant enhancement in stigmasterol was also observed in transgenic lines than WT plants. Furthermore, in expression profiling, salt responsive genes LEA 4-5, sucrose synthase, and transporter of monosaccharide (ERD) significantly upregulated in overexpressing lines as compared to WT. Thus our data strongly support the defensive role of Withania somnifera SGT gene (WssgtL3.1) against salt stress and contribute to improved salinity tolerance in plants through sterol modulation.

Mutant Gossypium universal stress protein-2 (GUSP-2) gene confers resistance to various abiotic stresses in E. coli BL-21 and CIM-496-Gossypium hirsutum

Gossypium arboreum is considered a rich source of stress-responsive genes and the EST database revealed that most of its genes are uncharacterized. The full-length Gossypium universal stress protein-2 (GUSP-2) gene (510 bp) was cloned in E. coli and Gossypium hirsutum, characterized and point mutated at three positions, 352–354, Lysine to proline (M1-usp-2) & 214–216, aspartic acid to serine (M2-usp-2) & 145–147, Lysine to Threonine (M3-usp-2) to study its role in abiotic stress tolerance. It was found that heterologous expression of one mutant (M1-usp-2) provided enhanced tolerance against salt and osmotic stresses, recombinant cells have higher growth up to 10-5dilution in spot assay as compared to cells expressing W-usp-2 (wild type GUSP-2), M2-usp-2 and M3-usp-2 genes. M1-usp-2 gene transcript profiling exhibited significant expression (8.7 fold) in CIM-496-Gossypium hirsutum transgenic plants and enhance drought tolerance. However, little tolerance against heat and cold stresses in bacterial cells was observed. The results from our study concluded that the activity of GUSP-2 was enhanced in M1-usp-2 but wipe out in M2-usp-2 and M3-usp-2 response remained almost parallel to W-usp-2. Further, it was predicted through in silico analysis that M1-usp-2, W-usp-2 and M3-usp-2 may be directly involved in stress tolerance or function as a signaling molecule to activate the stress adaptive mechanism. However, further investigation will be required to ascertain its role in the adaptive mechanism of stress tolerance.

Expression Characterization of Flavonoid Biosynthetic Pathway Genes and Transcription Factors in Peanut Under Water Deficit Conditions

Drought is one of the hostile environmental stresses that limit the yield production of crop plants by modulating their growth and development. Peanut (Arachis hypogaea) has a wide range of adaptations to arid and semi-arid climates, but its yield is prone to loss due to drought. Other than beneficial fatty acids and micronutrients, peanut harbors various bioactive compounds including flavonoids that hold a prominent position as antioxidants in plants and protect them from oxidative stress. In this study, understanding of the biosynthesis of flavonoids in peanut under water deficit conditions was developed through expression analysis and correlational analysis and determining the accumulation pattern of phenols, flavonols, and anthocyanins. Six peanut varieties (BARD479, BARI2011, BARI2000, GOLDEN, PG1102, and PG1265) having variable responses against drought stress have been selected. Higher water retention and flavonoid accumulation have been observed in BARI2011 but downregulation has been observed in the expression of genes and transcription factors (TFs) which indicated the maintenance of normal homeostasis. ANOVA revealed that the expression of flavonoid genes and TFs is highly dependent upon the genotype of peanut in a spatiotemporal manner. Correlation analysis between expression of flavonoid biosynthetic genes and TFs indicated the role of AhMYB111 and AhMYB7 as an inhibitor for AhF3H and AhFLS, respectively, and AhMYB7, AhTTG1, and AhCSU2 as a positive regulator for the expression of Ah4CL, AhCHS, and AhF3H, respectively. However, AhbHLH and AhGL3 revealed nil-to-little relation with the expression of flavonoid biosynthetic pathway genes. Correlational analysis between the expression of TFs related to the biosynthesis of flavonoids and the accumulation of phenolics, flavonols, and anthocyanins indicated coregulation of flavonoid synthesis by TFs under water deficit conditions in peanut. This study would provide insight into the role of flavonoid biosynthetic pathway in drought response in peanut and would aid to develop drought-tolerant varieties of peanut.

Pre treatment with Bacillus subtilis mitigates drought induced photo-oxidative damages in okra by modulating antioxidant system and photochemical activity

Growth promoting potential of Bacillus subtilis (BS) in drought stressed Abelmoschus esculentus (L.) Moench (okra) was assessed by measuring the chlorophyll stability index (CSI), chlorophyll a (Chl-a) fluorescence, leaf osmotic potential and lipid peroxidation by malondialdehyde content, emission of reactive oxygen species (ROS), osmolyte content and the activity of non-enzyme and enzyme antioxidants. BS treatment significantly increased the leaf osmotic potential, osmolyte production and the activity of non-enzyme and enzyme antioxidants under drought stress. BS treatment mitigated the drought-induced reduction in Chl a fluorescence and CSI. Concomitant increase in total sugar, proline, non-enzyme antioxidants [glutathione and ascorbate] and enzyme antioxidants like superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase and dehydroascorbate reductase modulate the intracellular ROS concentration in okra to resist the stress induced oxidative damage in BS treated plants led to fast recovery and less photodamage.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00982-8.

Metabolomics of Withania somnifera (L.) Dunal: Advances and applications

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera L. (Solanaceae), commonly known as Ashwagandha or Indian ginseng, is used in Ayurveda (Indian system of traditional medicine) for vitality, cardio-protection and treating other ailments, such as neurological disorders, gout, and skin diseases.

AIM OF THE REVIEW

We present a critical overview of the information on the metabolomics of W. somnifera and highlight the significance of the technique for use in quality control of medicinal products. We have also pointed out the use of metabolomics to distinguish varieties and to identify best methods of cultivation, collection, as well as extraction.

MATERIAL AND METHODS

The relevant information on medicinal value, phytochemical studies, metabolomics of W. somnifera, and their applications were collected from a rigorous electronic search through scientific databases, including Scopus, PubMed, Web of Science and Google Scholar. Structures of selected metabolites were from the PubChem.

RESULTS

The pharmacological activities of W. somnifera were well documented. Roots are the most important parts of the plant used in Ayurvedic preparations. Stem and leaves also have a rich content of bioactive phytochemicals like steroidal lactones, alkaloids, and phenolic acids. Metabolomic studies revealed that metabolite profiles of W. somnifera depended on plant parts collected and the developmental stage of the plant, besides the season of sample collection and geographical location. The levels of withanolides were variable, depending on the morpho/chemotypes within the species of W. somnifera. Although studies on W. somnifera were initiated several years ago, the complexity of secondary metabolites was not realized due to the lack of adequate and fool-proof technology for phytochemical fingerprinting. Sophistications in chromatography coupled to mass spectrometry facilitated the discovery of several new metabolites. Mutually complementary techniques like LC-MS, GC-MS, HPTLC, and NMR were employed to obtain a comprehensive metabolomic profile. Subsequent data analyses and searches against spectral databases enabled the annotation of signals and dereplication of metabolites in several numbers without isolating them individually.

CONCLUSIONS

The present review provides a critical update of metabolomic data and the diverse application of the technique. The identification of parameters for standardization and quality control of herbal products is essential to facilitate mandatory checks for the purity of formulation. Such studies would enable us to identify the best geographical location of plants and the time of collection. We recommend the use of metabolomic analysis of herbal products based on W. somnifera for quality control as well as the discovery of novel bioactive compounds.

Drought Exacerbates Botryosphaeria Dieback Symptoms in Grapevines and Confounds Host-based Molecular Markers of Infection by Neofusicoccum parvum

Neofusicoccum parvum, causal fungus of the grapevine trunk disease Botryosphaeria dieback, attacks the wood of Vitis vinifera. Because lesions are internal, using putative host-based markers of infection from leaves for diagnosis is a nondestructive option. However, their specificity under drought stress is unknown. Potted 'Cabernet-Sauvignon' were inoculated with N. parvum in the greenhouse after wounding (IW), and with wounded and nonwounded noninoculated controls. At 2 weeks postinoculation (WPI), half of the plants were severely stressed (SS), receiving 30% water volume of the well-watered (WW) plants. Larger lesions at 12 WPI among IW-SS plants, compared with all other treatments, revealed an interactive effect of inoculation and drought on lesion length. Expression of eight putative marker genes was analyzed in leaves by qPCR at the onset of drought stress, and at 8 and 12 WPI. One marker showed consistent over-expression at 8 WPI in IW plants, regardless of water treatment, suggesting specificity to infection. By 12 WPI, higher expression of seven genes in all SS plants (across inoculation treatments) revealed specificity to drought. Cross-reactivity of markers to drought, therefore, limits their utility for disease diagnosis in the field, where drought induced by climate and deficit irrigation is common.

Differential activity of the antioxidant defence system and alterations in the accumulation of osmolyte and reactive oxygen species under drought stress and recovery in rice (Oryza sativa L.) tillering

The objective of this study was to investigate the effects of drought stress on the activity of antioxidant enzymes and osmotic adjustment substance content in the tillering period of drought-sensitive and drought-tolerant rice cultivars. The results showed that the superoxide dismutase (SOD), peroxidase (POD), catalase activity (CAT), hydrogen peroxide content, soluble protein content and soluble sugar content increased with the accumulation of time and intensity of drought stress. Compared with the drought-sensitive cultivar, drought-resistant cultivar had a smaller photosynthetic affected area, longer CAT enzyme activity duration, and lower H2O2 accumulation. Unlike POD and CAT enzymes, which maintain the ability to scavenge hydrogen peroxide under long drought conditions, ascorbate peroxidase (APX) enzymes seem to be a rapid response mechanism to scavenge hydrogen peroxide under drought stress. Under a -10 kPa water potential, using soluble sugars on the osmotic adjustment ability of the drought-resistant cultivars was more efficient; under -40 kPa water potential, drought-resistant cultivars can maintain relative high levels of ascorbate (ASA) content in the short term. After the restoration of irrigation, the indices gradually returned to control levels. The ASA content showed faster accumulation ability in drought-resistant cultivars and faster recovery. The soluble protein content recovered more slowly in drought-sensitive cultivars under the -40 kPa treatment. Drought-resistant cultivars showed stronger resistance to drought in the -10 kPa treatment and obtained similar yield to the control, while the drought-sensitive cultivars were more obviously affected by the drought stress.

Molecular and Physio-Biochemical Characterization of Cotton Species for Assessing Drought Stress Tolerance

Drought stress significantly limits cotton growth and production due to the necessity of water at every stage of crop growth. Hence, it is essential to identify tolerant genetic resources and understand the mechanisms of drought tolerance in economically and socially important plants such as cotton. In this study, molecular and physio-biochemical investigations were conducted by analyzing different parameters by following standard protocols in three different cotton species, namely TM-1 (Gossypium hirsutum), Zhongmian-16 (Gossypium arboreum), and Pima4-S (Gossypium barbadense). Drought stress significantly decreased plant growth, chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), maximum photochemical efficiency of PSII (Fv/Fm), and relative water content. TM-1 resulted in more tolerance than the other two species. The accumulation of proline, soluble proteins, soluble sugars, hydrogen peroxide (H₂O₂), and superoxide radicals (O₂•-) increased significantly in TM-1. In addition, TM-1 maintained the integrity of the chloroplast structure under drought conditions. The relative expression level of drought-responsive genes including coding for transcription factors and other regulatory proteins or enzymes controlling genes (ERF, ERFB, DREB, WRKY6, ZFP1, FeSOD, CuZnSOD, MAPKKK17, P5CR, and PRP5) were higher in TM-1 under drought, conferring a more tolerant status than in Zhongmian-16 and Pima4-S. The findings of this research could be utilized for predicting a tolerant cotton genotype as well as evaluating prospective cotton species in the variety development program.

Modulations in primary and secondary metabolic pathways and adjustment in physiological behaviour of Withania somnifera under drought stress

In general medicinal plants grown under water limiting conditions show much higher concentrations of secondary metabolites in comparison to control plants. In the present study, Withania somnifera plants were subjected to water stress and data related to drought tolerance phenomenon was collected and a putative mechanistic concept considering growth responses, physiological behaviour, and metabolite content and gene expression aspects is presented. Drought induced metabolic and physiological responses as well as drastic decrease in CO₂ uptake due to stomatal limitations. As a result, the consumption of reduction equivalents (NADPH²⁺) for CO₂ assimilation via the calvin cycle declines significantly resulting in the generation of a large oxidative stress and an oversupply of antioxidant enzymes. Drought also results in the shifting of metabolic processes towards biosynthetic activities that consume reduction equivalents. Thus, biosynthesis of reduced compounds (isoprenoids, phenols and alkaloids) is enhanced. The dynamics of various metabolites have been discussed in the light of gene expression analysis of control and drought treated leaves. Gene encoding enzymes of pathways leading to glucose, fructose and fructan production, conversion of triose phosphates to hexoses and hexose phosphorylation were up-regulated in the drought stressed leaves. The down-regulated Calvin cycle genes were co-ordinately regulated with the down-regulation of chloroplast triosephosphate/phosphate translocator, cytoplasmic fructose-1,6-bisphosphate aldolase and fructose bisphosphatase. Expression of gene encoding Squalene Synthase (SQS) was highly upregulated under drought stress which is responsible for the diversion of carbon flux towards withanolides biosynthesis from isoprenoid pathway.

Comparative Study of Withanolide Biosynthesis-Related miRNAs in Root and Leaf Tissues of Withania somnifera

Withania somnifera, popularly known as Indian ginseng, is one of the most important medicinal plants. The plant is well studied in terms of its pharmaceutical activities and genes involved in biosynthetic pathways. However, not much is known about the regulatory mechanism of genes responsible for the production of secondary metabolites. The idea was to identify miRNA transcriptome responsible for the regulation of withanolide biosynthesis, specifically of root and leaf tissues individually. The transcriptome data of in vitro culture of root and leaf tissues of the plant was considered for miRNA identification. A total of 24 and 39 miRNA families were identified in root and leaf tissues, respectively. Out of these, 15 and 27 miRNA families have shown their involvement in different biological functions in root and leaf tissues, respectively. We report here, specific miRNAs and their corresponding target genes for corresponding root and leaf tissues. The target genes have also been analyzed for their role in withanolide metabolism. Endogenous root-miR5140, root-miR159, leaf-miR477, and leaf-miR530 were reported for regulation of withanolide biosynthesis.

Transcript profiling and gene expression analysis under drought stress in Ziziphus nummularia (Burm.f.) Wright & Arn

Drought is one of the prime abiotic stresses responsible for limiting agricultural productivity. A number of drought responsive genes have been isolated and functionally characterized but these studies have been restricted to a few model plant systems. Very few drought responsive genes have been reported till date from non model drought tolerant plants. The present study aimed at identifying differentially expressed genes from a drought tolerant, non-model plant, Ziziphus nummularia (Burm.f.) Wight & Arn. One month old seedlings of Z. nummularia were subjected to drought stress by 30% Polyethylene glycol (PEG 6000) treatment for 6, 12, 24, 48 and 72 h. A significant reduction in RWC and increase in proline was observed at 24 h and 48 h of treatment. Suppression subtractive hybridization (SSH) library was constructed with drought stressed seedlings after 24 h and 48 h of PEG 6000 treatment. A total of 142 and 530 unigenes from 24 h and 48 h library were identified respectively. Gene ontology studies revealed that about 9.78% and 15.07% unigenes from 24 h and 48 h SSH libraries were expressed in "response to stress". Fifteen putative drought responsive genes identified in SSH library were validated for drought responsive differential expression by RT-qPCR. Significant changes in fold expressions were observed with time in the treated samples compared to the control. A heat map revealing the expression profile of genes was constructed by hierarchical clustering. Various genes identified in SSH libraries can serve as a resource for marker discovery and selection of candidate genes to improve drought tolerance in other susceptible crops.

Characterization of glutathione S-transferases in the detoxification of metolachlor in two maize cultivars of differing herbicide tolerance

Glutathione S-transferases (GSTs) have been widely studied in relation to their role in herbicide tolerance and detoxification. However, a detailed characterization of GSTs from herbicide tolerant and sensitive maize cultivars is still lacking. In this study, we determined the mechanism of differential tolerance between two maize cultivars which had 4-fold difference tolerance to metolachlor. The metabolism rate of metolachlor was more rapid in the tolerant cultivar (Zea mays L. cv Nongda86) than the susceptible one (Zea mays L. cv Zhengda958). Addition of the GST inhibitor ethacrynic acid reduced the metabolism of metolachlor indicating the involvement of GSTs in the differential detoxification of metolachlor. The expression profiles of 32 GST isozymes were measured using quantitative RT-PCR. The results showed the expression of GST genes were slightly up-regulated in Nongda86, but severely inhibited in Zhengdan958 24h after metolachlor treatment. The genes GSTI, GSTIII, GSTIV, GST5, GST6 and GST7, which can detoxify chloroacetanilide herbicides, were all expressed higher in Nongda86 compared to Zhendgan958. The result of GST activity was consistent with the gene expression profiles. Collectively, higher-level expression of GST genes, leading to higher GST activity and faster herbicide detoxification, appears to be responsible for the difference in tolerance to metolachlor in two maize cultivars.

Dehydration induced transcriptomic responses in two Tibetan hulless barley (Hordeum vulgare var. nudum) accessions distinguished by drought tolerance

Background

The harsh environment on the Qinghai-Tibetan Plateau gives Tibetan hulless barley (Hordeum vulgare var. nudum) great ability to resist adversities such as drought, salinity, and low temperature, and makes it a good subject for the analysis of drought tolerance mechanism. To elucidate the specific gene networks and pathways that contribute to its drought tolerance, and for identifying new candidate genes for breeding purposes, we performed a transcriptomic analysis using two accessions of Tibetan hulless barley, namely Z772 (drought-tolerant) and Z013 (drought-sensitive).

Results

There were more up-regulated genes of Z772 than Z013 under both mild (5439-VS-2604) and severe (7203-VS-3359) dehydration treatments. Under mild dehydration stress, the pathways exclusively enriched in drought-tolerance genotype Z772 included Protein processing in endoplasmic reticulum, tricarboxylic acid (TCA) cycle, Wax biosynthesis, and Spliceosome. Under severe dehydration stress, the pathways that were mainly enriched in Z772 included Carbon fixation in photosynthetic organisms, Pyruvate metabolism, Porphyrin and chlorophyll metabolism. The main differentially expressed genes (DEGs) in response to dehydration stress and genes whose expression was different between tolerant and sensitive genotypes were presented in this study, respectively. The candidate genes for drought tolerance were selected based on their expression patterns.

Conclusions

The RNA-Seq data obtained in this study provided an initial overview on global gene expression patterns and networks that related to dehydration shock in Tibetan hulless barley. Furthermore, these data provided pathways and a targeted set of candidate genes that might be essential for deep analyzing the molecular mechanisms of plant tolerance to drought stress.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4152-1) contains supplementary material, which is available to authorized users.

Physiological performance of two contrasting rice varieties under water stress

Two rice varieties PR-115 and Super-7 were imposed to water stress and different physiological traits were monitored to evaluate the performance of these varieties under drought. Under water stress condition although the relative water content, osmotic potential, chlorophyll content, photosynthesis rate, carbon discrimination and biomass decreased in both the varieties however, the reduction was more pronounced in Super-7 variety. Oryzanol a trans-ester of ferulic acid functions as antioxidant and it increased along with total phenolic and anthocyanin content in both the varieties under drought stress. However, gallic acid, 4 hydroxy benzoic acid, syringic acid and chlorogenic acid showed differential pattern in both of the varieties under water limiting conditions. Under drought, grain yield was penalized by 17 and 54% in PR-115 and Super-7 varieties, respectively in comparison to watered plants. Super-7 variety showed pronounced electrolyte leakage and MDA enhancement under water stress condition. High non photochemical quenching and reduction in Y(NO) and Y(II) indicated balanced energy management in tolerant PR-115 variety. The studies showed that PR-115 is a drought tolerant variety while Super-7 is drought sensitive in nature.

Drought Induced Changes in Growth, Osmolyte Accumulation and Antioxidant Metabolism of Three Maize Hybrids

Consequences of drought stress in crop production systems are perhaps more deleterious than other abiotic stresses under changing climatic scenarios. Regulations of physio-biochemical responses of plants under drought stress can be used as markers for drought stress tolerance in selection and breeding. The present study was conducted to appraise the performance of three different maize hybrids (Dong Dan 80, Wan Dan 13, and Run Nong 35) under well-watered, low, moderate and SD conditions maintained at 100, 80, 60, and 40% of field capacity, respectively. Compared with well-watered conditions, drought stress caused oxidative stress by excessive production of reactive oxygen species (ROS) which led to reduced growth and yield formation in all maize hybrids; nevertheless, negative effects of drought stress were more prominent in Run Nong 35. Drought-induced osmolyte accumulation and strong enzymatic and non-enzymatic defense systems prevented the severe damage in Dong Dan 80. Overall performance of all maize hybrids under drought stress was recorded as: Dong Dan 80 > Wan Dan 13 > Run Nong 35 with 6.39, 7.35, and 16.55% yield reductions. Consequently, these biochemical traits and differential physiological responses might be helpful to develop drought tolerance genotypes that can withstand water-deficit conditions with minimum yield losses.

Physiological performance and differential expression profiling of genes associated with drought tolerance in root tissue of four contrasting varieties of two Gossypium species

Root growth in drying soil is generally limited by a combination of mechanical impedance and water stress. As the major function of root tissue is water and nutrient uptake, so it imparts an important role in plant growth and stress management. Previously, we have studied physiological performance and expression profiling of gene associated with drought tolerance in leaf tissue of four cotton varieties. Here, we have further continued our studies with the root tissue of these varieties. The Gossypium hirsutum species JKC-770 is drought-tolerant and KC-2 is drought-sensitive, while Gossypium herbaceum species JKC-717 is drought-tolerant and RAHS-187 is drought-sensitive. JKC-770 and JKC-717 the drought-tolerant varieties showed a comparatively high glutathione-S-transferase, superoxide dismutase, proline along with their gene expression, and low malondialdehyde content indicating low membrane damage and better antioxidative defense under drought condition. The expression levels of cellulose synthase, xyloglucan:xyloglucosyl transferase, and glycosyl hydrolases suggest modulation in cell wall structure and partitioning of sugars towards osmoprotectants instead of cell wall biosynthesis in tolerant varieties. Heat shock proteins and serine/threonine protein phosphotases show upregulation under drought condition, which are responsible for temperature tolerance and protein phosphorylation, respectively. These effects many metabolic processes and may be playing a key role in drought tolerance and adaptability of JKC-770 towards drought tolerance. The long-term water use efficiency (WUE) estimated in terms of carbon isotope discrimination (∆(13)C) in the root tissues showed maximum depletion in the ∆(13)C values in JKC-770 variety, while minimum in RAHS-187 under drought stress with reference to their respective control, suggesting a high WUE in JKC-770 variety.

Membrane transporters and drought resistance - a complex issue

Land plants have evolved complex adaptation strategies to survive changes in water status in the environment. Understanding the molecular nature of such adaptive changes allows the development of rapid innovations to improve crop performance. Plant membrane transport systems play a significant role when adjusting to water scarcity. Here we put proteins participating in transmembrane allocations of various molecules in the context of stomatal, cuticular, and root responses, representing a part of the drought resistance strategy. Their role in the transport of signaling molecules, ions or osmolytes is summarized and the challenge of the forthcoming research, resulting from the recent discoveries, is highlighted.