Mechanisms Of Drought Tolerance Research Articles

Peculiarities of soybean-rhizobial systems subject to different levels of water supply fol-lowing treatment with succinic acid and epibrassinolide

All around the world, one of the leading – according to area of cultivated fields – oleic crops is soybean, which has a high demand for moisture. Given the significance of this crop and negative impact of drought on its yield, integrated research of the influence of insufficient water supply on the intensity of physiological-biochemical processes in those plants is necessary for identifying and understanding the drought-tolerance mechanisms of soybean, as well as symbiotic systems created with its participation, and also for search for ways to adapt it to this stressor. Therefore, our objective was determining the specifics of formation and functioning of the symbiotic systems of soybean and Bradyrhizobium japonicum, following treatment with succinic acid (0.01 g/L) and 24-epibrassinolide (0.00001 g/L), subject to different levels of watering. Our studies revealed that pre-sowing treatment of the seeds with a solution of 24-epibrassinolide with their subsequent inoculation with B. japonicum Т21-2 resulted in the most pronounced stimulation of formation and functioning of the symbiotic systems of soybean in the optimal growing conditions. At the same time, during water shortage, the intensity of nitrogen fixation was the highest in the plants grown from seeds that had been successively treated with the acid and the inoculant. We confirmed that water deficit led to significant increase in the overall content of phytohormones of cytokinin nature in the soybean root nodules, depending on the way the seeds were treated. However, the largest pool of cytokinins was seen in the plants that had been treated with succinic acid against the background of both optimal and insufficient water supply. Treatment of the seeds with 24-epibrassinolide caused significant excess of content of zeatin riboside over the content of zeatin during the flowering stage, whereas in the stage of pods formation it led to an opposite effect – excess of zeatin over zeatin riboside. Fourteen days-long water deficit decreased the content of chlorophylls in the leaves and grain productivity of the plants of all variants of the experiment. The use of growth regulators managed to alleviate the negative impact of stress and protect the pigment complex from ruination. Treatment of the seeds with solutions of succinic acid and 24-epibrassinolide provided the growth of soybean grain productivity regardless on water-supply level. The most efficient was 24-epibrassinolide. Therefore, use of 24-epibrassinolide for pre-sowing treatment of the soybean seeds provided formation of effective symbiotic systems with high nitrogen-fixing activity and caused a number of specific changes in the pattern of accumulation of free and complex forms of cytokinins in the root nodules of those plants. At the same time, the treatment provided the highest concentration of photosynthesis pigments in the soybean leaves, and as a result produced the greatest increase in grain productivity of plants of all the variants, regardless of levels of water supply. In turn, use of succinic acid produced the highest level of nitrogen-fixing activity in the case of the lowest number of root nodules in the conditions of insufficient water supply, and also caused significant accumulation of cytokinins in the nodules, compared with other studied variants against the background of both optimal and insufficient water supply. Therefore, it did result in increase in soybean grain productivity, but this was lower than in the plants treated with 24-epibrassinolide.

Calcium-Dependent Protein Kinase 5 (OsCPK5) Overexpression in Upland Rice (Oryza sativa L.) under Water Deficit.

Water deficit significantly affects global crop growth and productivity, particularly in water-limited environments, such as upland rice cultivation, reducing grain yield. Plants activate various defense mechanisms during water deficit, involving numerous genes and complex metabolic pathways. Exploring homologous genes that are linked to enhanced drought tolerance through the use of genomic data from model organisms can aid in the functional validation of target species. We evaluated the upland rice OsCPK5 gene, an A. thaliana AtCPK6 homolog, by overexpressing it in the BRSMG Curinga cultivar. Transformants were assessed using a semi-automated phenotyping platform under two irrigation conditions: regular watering, and water deficit applied 79 days after seeding, lasting 14 days, followed by irrigation at 80% field capacity. The physiological data and leaf samples were collected at reproductive stages R3, R6, and R8. The genetically modified (GM) plants consistently exhibited higher OsCPK5 gene expression levels across stages, peaking during grain filling, and displayed reduced stomatal conductance and photosynthetic rate and increased water-use efficiency compared to non-GM (NGM) plants under drought. The GM plants also exhibited a higher filled grain percentage under both irrigation conditions. Their drought susceptibility index was 0.9 times lower than that of NGM plants, and they maintained a higher chlorophyll a/b index, indicating sustained photosynthesis. The NGM plants under water deficit exhibited more leaf senescence, while the OsCPK5-overexpressing plants retained their green leaves. Overall, OsCPK5 overexpression induced diverse drought tolerance mechanisms, indicating the potential for future development of more drought-tolerant rice cultivars.

Trehalose alleviates the inhibition of adventitious root formation caused by drought stress in cucumber through regulating ROS metabolism and activating trehalose and plant hormone biosynthesis

Trehalose (Tre) plays a vital role in response to drought stress in plants but its regulatory mechanism remains unclear. Here, this study explores the mechanism of re-regulated drought tolerance during cucumber adventitious root formation. Our results indicate that 2 mM Tre displays remarkable drought alleviation in the aspect of root number, root length, fresh weight, and dry weight. Under drought stress, Tre could inhibit greatly the MDA, H2O2, and O2− accumulation, enhance obviously the activities of SOD, POD, and CAT enzymes and up-regulate significantly the transcript levels of SOD, POD, and CAT genes. Furthermore, Tre treatment also promotes Tre metabolism during drought stress: significantly increases starch and Tre contents and decreases glucose content, the biosynthesis enzymatic activity of the Tre metabolic pathway including TPS and TPP are enhanced and the activity of degradation enzyme THL is decreased, and corresponding genes TPS1, TPS2, TPPA, and TPPB are up-regulated. Tre significantly reversed the decrease caused by PEG in IAA, ethylene, ABA, and BR contents and the increase caused by PEG in GA3 and KT contents. Collectively, Tre appears to be the effective treatment in counteracting the negative effects of drought stress during adventitious root formation by regulating ROS, Tre metabolisms and plant hormones.

Effect of Acclimation to High Temperatures on the Mechanisms of Drought Tolerance in Species with Different Types of Photosynthesis: Sedobassia sedoides (C3–C4) and Bassia prostrata (C4-NADP)

The effect of drought on the morphophysiological, biochemical, and molecular genetic parameters of plants Sedobassia sedoides (Pall.) Freitag G. Kadereit with an intermediate C3–C4-type of photosynthesis and Bassia prostrata (L.) A.J. Scott with a C4-NADP type of photosynthesis grown at different temperatures (25 and 30°C) was studied. A decrease in the biomass, water content, and effective quantum yield (ΦPSII) of PSII, as well as an increase in the expression of the psbA gene encoding the PSII D1 protein under the action of drought, was observed in both species regardless of the growing temperature. Both species showed a decrease in the content of photosynthetic enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) under drought conditions at 25°С, which was accompanied by a significant increase in the expression of the rbcL and PPDK genes in S. sedoides. Acclimation of S. sedoides plants to elevated temperatures led to an increase in the activity of cyclic electron transport around PSI, to mitigation of the negative effect of drought on the light reactions of photosynthesis (reduction in NPQ) and the content of the PEPC enzyme, as well as to a shift in the ionic balance caused by a decrease in the potassium content. B. prostrata showed greater drought resistance and was characterized by greater thermolability of photosynthetic enzymes, changes in the content and ratio of which allowed this species to maintain growth in drought conditions at different temperatures.

MdbHLH160 is stabilized via reduced MdBT2-mediated degradation to promote MdSOD1 and MdDREB2A-like expression for apple drought tolerance.

Drought stress is a key environmental factor limiting the productivity, quality, and geographic distribution of crops worldwide. Abscisic acid (ABA) plays an important role in plant drought stress responses, but the molecular mechanisms remain unclear. Here, we report an ABA-responsive bHLH transcription factor, MdbHLH160, which promotes drought tolerance in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica). Under drought conditions, MdbHLH160 is directly bound to the MdSOD1 (superoxide dismutase 1) promoter and activated its transcription, thereby triggering reactive oxygen species (ROS) scavenging and enhancing apple drought tolerance. MdbHLH160 also promoted MdSOD1 enzyme activity and accumulation in the nucleus through direct protein interactions, thus inhibiting excessive nuclear ROS levels. Moreover, MdbHLH160 directly upregulated the expression of MdDREB2A-like, a DREB (dehydration-responsive element binding factor) family gene that promotes apple drought tolerance. Protein degradation and ubiquitination assays showed that drought and ABA treatment stabilized MdbHLH160. The BTB protein MdBT2 was identified as an MdbHLH160-interacting protein that promoted MdbHLH160 ubiquitination and degradation, and ABA treatment substantially inhibited this process. Overall, our findings provide insights into the molecular mechanisms of ABA-modulated drought tolerance at both the transcriptional and post-translational levels via the ABA-MdBT2-MdbHLH160-MdSOD1/MdDREB2A-like cascade.

Water stress and increased ploidy level enhance antioxidant enzymes, phytohormones, phytochemicals and polyphenol accumulation of tetraploid induced wallflower

Wallflower (Erysimum cheiri (L.) Crantz) is a profitable plant in the food, cosmetic, and pharmaceutical industries, as it produces valuable phenolic compounds. It is also an important flower in the floriculture industry cultivated mainly in the gardens and pots. Nonetheless, water scarcity as a worldwide phenomenon has deteriorated its growth and productivity. A main mechanism for drought tolerance is genome duplication and increased ploidy level, where more metabolites are produced. In this regard, diploid and tetraploid-induced plants of E. cheiri were subjected to well-watered (100% field capacity) and water deficit (50% field capacity) conditions for 30 days. Under water deficit conditions, the tetraploid wallflowers conserved their relative water content (RWC) at 85%, while the RWC of diploid plants was reduced to 68%. The chromosome-doubled plants showed advantages under water stress due to their higher osmotic adjustment by increased total soluble sugar and proline content, stronger antioxidant enzymes’ activity of SOD, CAT, APX, and POD, and enhanced non-enzymatic defense systems (i.e., total phenolic and flavonoid contents), compared with their control diploids. Also, stress hormones such as abscisic acid, salicylic acid, jasmonic acid, and auxins were increased in tetraploid plants under low water conditions, though cytokinin and gibberellin phytohormones were decreased as an adaptive strategy in the stress condition. Furthermore, chlorogenic acid and gallic acid were identified as the main phenolic compounds in 4x Erysimum leaves. The superiority of tetraploids over the diploid plants under water stress might be attributed to the extensive reprogramming of genes involved in hormonal signaling, reactive oxygen species detoxification, osmotic adjustment, and enhanced antioxidant defense system. The polyploidization technique combined with water scarcity, have proved fruitful for the production of excess secondary metabolites for various industrial uses.

Effect of Different Biochemical Parameters and Antioxidant Enzymes Activities on Drought Indices in Chickpea (Cicer arietinum L.)

Background: Drought is the foremost environmental restraint that effects the growth and yield of chickpea. The mechanism of response to drought differs with genotype and growth stages of individual crop species. The activation of antioxidant enzymes is an alternate defensive system against oxidative stress that ultimately decide development of putative drought tolerant mechanism. Methods: Eighty-three chickpea genotypes were grown under normal and drought stress conditions and leaf samples were used to estimate different biochemical parameters including total sugar, lipid peroxidation (MDA), chlorophyll, proline and protein along with estimation of activities of different antioxidant enzymes viz., catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APX) (EC 1.11.1.11), superoxide dismutase (SOD) and peroxidase (POX). Result: Positively significant correlation was found among proline under control with proline underwent stress (r=0.441), MDA under stress with proline under control (r=0.365) and MDA under control (r=0.336) at 1% level of significance. Positively significant correlation was also investigated between SOD under stressed condition with SOD under control (r=0.665), POX (0.449) and APX under stress (0.423), CAT under control (0.471) and CAT under stress condition (0.374) at 1% probability level. Heatmaps along with dendrograms represented expression levels of different antioxidant enzymes activities that showed variations among different genotypes. In conclusion. total sugar, proline and Malondialdehyde, have been increased under drought stressed condition whilst total chlorophyll and protein were decreased. While antioxidant enzymes viz., POX, APX, CAT and SOD levels increased under drought stressed conditions.

Sophora tonkinensis: response and adaptation of physiological characteristics, functional traits, and secondary metabolites to drought stress.

The medicinal plant Sophora tonkinensis is a characteristic Chinese shrub of karst areas. The arid climate in karst areas produces high-quality S. tonkinensis; however, the mechanisms of drought tolerance are not clear, which restricts sustainable plantings of S. tonkinensis. This study involved a 20-day drought stress experiment with potted S. tonkinensis and threee soil water regimes: control (CK), mild drought (MDT), and severe drought (SDT). Plant morphology, biomass, physiological indicators, alkaloid content, and other changes under drought stress were monitored. The content of soluble sugars and proteins, and activity of antioxidant enzymes in leaves and roots were higher under drought than CK, indicating that S. tonkinensis is tolerant to osmotic stress in early drought stages. Content of matrine and oxymatrine increased gradually with increasing drought duration in the short term. The epidermis of S. tonkinensis leaves have characteristics of desert plants, including upper epidermalwaxy layer, lower epidermal villi, and relatively sunken stomata, suggesting that S. tonkinensis has strong drought tolerance. In conclusion, drought stress changed the cell structure of S. tonkinensis, induced antioxidant enzyme activity and increased its resistance to drought.

The miRNA-mRNA Regulatory Modules of Pinus massoniana Lamb. in Response to Drought Stress.

Masson pine (Pinus massoniana Lamb.) is a major fast-growing woody tree species and pioneer species for afforestation in barren sites in southern China. However, the regulatory mechanism of gene expression in P. massoniana under drought remains unclear. To uncover candidate microRNAs, their expression profiles, and microRNA-mRNA interactions, small RNA-seq was used to investigate the transcriptome from seedling roots under drought and rewatering in P. massoniana. A total of 421 plant microRNAs were identified. Pairwise differential expression analysis between treatment and control groups unveiled 134, 156, and 96 differential expressed microRNAs at three stages. These constitute 248 unique microRNAs, which were subsequently categorized into six clusters based on their expression profiles. Degradome sequencing revealed that these 248 differentially expressed microRNAs targeted 2069 genes. Gene Ontology enrichment analysis suggested that these target genes were related to translational and posttranslational regulation, cell wall modification, and reactive oxygen species scavenging. miRNAs such as miR482, miR398, miR11571, miR396, miR166, miRN88, and miRN74, along with their target genes annotated as F-box/kelch-repeat protein, 60S ribosomal protein, copper-zinc superoxide dismutase, luminal-binding protein, S-adenosylmethionine synthase, and Early Responsive to Dehydration Stress may play critical roles in drought response. This study provides insights into microRNA responsive to drought and rewatering in Masson pine and advances the understanding of drought tolerance mechanisms in Pinus.

Exploring Drought Tolerance in Wheat: Insights from Biochemical, Morphological, and Physiological Responses

This review paper delves into the intricate biochemical foundations underlying drought tolerance mechanisms in wheat plants. This exploration encompasses multifaceted aspects, ranging from physiological adaptations to gene expression modulation. Plants like wheat employ repertoire of biochemical strategies to bolster their resilience against drought stress. It involves coordinating antioxidant enzymes, osmotic regulators, polyamines, and hormones to combat drought stress. The antioxidant system is crucial, countering reactive oxygen species produced during drought. Enzymes like SOD, CAT, and POD are activated to protect cells. Osmolytes like sugars and polyamines maintain cell integrity and water retention, while hormones like ABA control stomatal closure and water conservation. Gene expression highlights the plant's drought adaptability. AP2/ERF factors boost drought tolerance when overexpressed. Gene repression uses motifs like EAR to reduce expression for environmental adaptation. Gene expression shows the plant's drought adaptability. Overexpressed AP2/ERF factors enhance tolerance. Repression, like the EAR motif, aids variation. The morphological basis study examines how water scarcity affects different growth stages of wheat, such as germination, tillering, flowering, and grain filling. It identifies physio-morphological traits that could serve as the indicators of drought resilience, providing a new way to breed stress resistance. Furthermore, this article also explains plant characteristics important for adapting to drought, including photosynthesis, water relations, nutrient uptake, oxidative state, osmotic balance, and hormonal consequences. Each facet contributes to the intricate web of physiological adaptations that allow wheat plants to withstand and thrive under drought conditions. Comprehending these mechanisms aids breeding for drought-tolerant wheat, ensuring food security amid climate change.

Integration of the metabolome and transcriptome reveals the molecular mechanism of drought tolerance in Plumeria rubra.

Plumeria rubra L. cv. Acutifolia is an ornamental tree that displays a good drought-tolerance level. However, the molecular mechanisms of P. rubra adaptation to drought stress remains unclear. Here, drought-simulating pot experiments were conducted to explore drought stress response mechanism of P. rubra. Transcriptome analysis revealed 10,967 differentially expressed genes (DEGs), 6,498 of which were increased and 4,469 decreased. Gene Ontology (GO) analysis revealed that the DEGs were enriched in binding category, in metabolic process category, and in catalytic activities category. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that 9 pathways were significantly enriched, including biosynthesis of secondary metabolites (ko01110), plant hormone signal transduction (ko04075) and so on. In addition, the transcription factor families of AP2/ERFs, bZIP, and C2H2 were significantly upregulated while the families of bHLH, MYB-related, and NAC were significantly downregulated. Moreover, the results of metabolomics analysis indicated that some compounds were accumulated under drought stress, especially flavonoids. Overall, it was speculated that under drought stress, P. rubra first activates the plant hormone signal transduction pathway to regulate hormone contents. Then osmotic regulating substances such as organic acids and amino acids are accumulated to maintain osmotic balance. Finally, flavonoid levels are increased to scavenge reactive oxygen species. These results preliminarily revealed the molecular mechanisms adopted by P. rubra in response to drought stress.

Drought-Induced miRNA Expression Correlated with Heavy Metal, Phenolic Acid, and Protein and Nitrogen Levels in Five Chickpea Genotypes.

Drought is a prime stress, drastically affecting plant growth, development, and yield. Plants have evolved various physiological, molecular, and biochemical mechanisms to cope with drought. Investigating specific biochemical pathways related to drought tolerance mechanisms of plants through biotechnology approaches is one of the quickest and most effective strategies for enhancing crop production. Among them, microRNAs (miRNAs) are the principal post-transcriptional regulators of gene expression in plants during plant growth under biotic and abiotic stresses. In this study, five different chickpea genotypes (İnci, Hasan bey, Arda, Seçkin, and Diyar 95) were grown under normal and drought stress. We recorded the expression levels of microRNAs in these genotypes and found differential expression (miRNA396, miR408, miRNA414, miRNA528, and miRNA1533) under contrasting conditions. Results revealed that miRNA414 and miRNA528 considerably increased in all genotypes under drought stress, and expression levels of miRNA418, miRNA1533, and miRNA396 (except for the Seçkin genotype) were found to be higher under the watered conditions. These genotypes were also investigated for heavy metal, phenolic acid, protein, and nitrogen concentrations under normal and drought stress conditions. The Arda genotype showed a significant increase in nitrogen (5.46%) and protein contents (28.3%), while protein contents were decreased in the Hasan bey and Seçkin genotypes subjected to drought stress. In the case of metals, iron was the most abundant element in all genotypes (İnci = 15.4 ppm, Hasan bey = 29.6 ppm, Seçkin = 37.8 ppm, Arda = 26.3 ppm, and Diyar 95 = 40.8 ppm) under normal conditions. Interestingly, these results were related to miRNA expression in the chickpea genotypes and hint at the regulation of multiple pathways under drought conditions. Overall, the present study will help us to understand the miRNA-mediated regulation of various pathways in chickpea genotypes.

Integrated transcriptomics and metabolomics reveals that regulating biosynthesis and metabolism of HCN and GABA plays a key role in drought resistance of wild soybean

Wild soybeans [Glycine soja (Siebold & Zucc.)] grown in arid areas develop adaptive traits and they are important wild plant resources. In order to reveal the drought-tolerance mechanism in wild soybean, we studied the changes of growth parameters, photosynthetic physiology, and ion physiology of two wild soybean ecotypes under drought stress, and integratedly analyzed the transcriptome and metabolome changes in their leaves. Drought-tolerant wild soybean had greater root/shoot ratio, water use efficiency, and K+ and Ca2+ contents than common wild soybean. In drought-tolerant wild soybean, the gene encoding (R)-mandelonitrile lyase in the pathway of hydrogen cyanide (HCN) biosynthesis and metabolism and the genes encoding serine O-acetyltransferase and aminocyclopropanecarboxylate oxidase in the pathway of 1-aminocyclopropane-1-carboxylate oxidation to produce HCN were down-regulated. In HCN biosynthesis and metabolic pathways of drought-tolerant wild soybean, the content of cysteine as a raw material was significantly reduced, while the content of 3-cyanoalanine as a product was significantly increased. In addition, drought-tolerant wild soybeans up-regulated genes for glutamate synthase and glutamate decarboxylase during synthesis of 4-aminobutyric acid (GABA), accumulating aspartic acid, asparagine, glutamic acid, and GABA; and down-regulated the gene for 4-aminobutyrate-pyruvate transaminase in GABA metabolism. Integrated analysis showed that drought-resistant wild soybean weakened the production of HCN and enhanced the utilization of HCN to avoid HCN toxicity under drought stress. At the same time, it also accumulated GABA to maintain carbon/nitrogen balance and amino acid metabolism. This study provides insights into the genetic mechanism of adaptation to drought by wild soybean, which will be helpful for screening of excellent wild plant resources.

Drought stress in maize: stress perception to molecular response and strategies for its improvement.

Given the future demand for food crops, increasing crop productivity in drought-prone rainfed areas has become essential. Drought-tolerant varieties are warranted to solve this problem in major crops, with drought tolerance as a high-priority trait for future research. Maize is one such crop affected by drought stress, which limits production, resulting in substantial economic losses. It became a more serious issue due to global climate change. The most drought sensitive among all stages of maize is the reproductive stages and the most important for overall maize production. The exact molecular basis of reproductive drought sensitivity remains unclear due to genes' complex regulation of drought stress. Understanding the molecular biology and signaling of the unexplored area of reproductive drought tolerance will provide an opportunity to develop climate-smart drought-tolerant next-generation maize cultivars. In recent decades, significant progress has been made in maize to understand the drought tolerance mechanism. However, improving maize drought tolerance through breeding is ineffective due to the complex nature and multigenic control of drought traits. With the help of advanced breeding techniques, molecular genetics, and a precision genome editing approach like CRISPR-Cas, candidate genes for drought-tolerant maize can be identified and targeted. This review summarizes the effects of drought stress on each growth stage of maize, potential genes, and transcription factors that determine drought tolerance. In addition, we discussed drought stress sensing, its molecular mechanisms, different approaches to developing drought-resistant maize varieties, and how molecular breeding and genome editing will help with the current unpredictable climate change.

ABA-dependent suberization and aquaporin activity in rice (Oryza sativa L.) root under different water potentials.

Drought is one of the most stressful environments limiting crop growth and yield throughout the world. Therefore, most efforts have been made to document drought-derived genetic and physiological responses and to find better ways to improve drought tolerance. The interaction among them is unclear and/or less investigated. Therefore, the current study is to find a clue of metabolic connectivity among them in rice root experiencing different levels of drought condition. We selected 19 genes directly involved in abscisic acid (ABA) metabolism (6), suberization (6), and aquaporins (AQPs) activity (7) and analyzed the relatively quantitative gene expression using qRT-PCR from rice roots. In addition, we also analyzed proline, chlorophyll, and fatty acids and observed cross-sectional root structure (aerenchyma) and suberin lamella deposition in the endodermis. All drought conditions resulted in an obvious development of aerenchyma and two- to fourfold greater accumulation of proline. The limited water supply (-1.0 and -1.5 MPa) significantly increased gene expression (ABA metabolism, suberization, and AQPs) and developed greater layer of suberin lamella in root endodermis. In addition, the ratio of the unsaturated to the saturated fatty acids was increased, which could be considered as an adjusted cell permeability. Interestingly, these metabolic adaptations were an exception with a severe drought condition (hygroscopic coefficient, -3.1 MPa). Accordingly, we concluded that the drought-tolerant mechanism in rice roots is sophisticatedly regulated until permanent wilting point (-1.5 MPa), and ABA metabolism, suberization, and AQPs activity might be independent and/or concurrent process as a survival strategy against drought.

Drought tolerance mechanisms in chickpea (Cicer arietinum L.) investigated by physiological and transcriptomic analysis

Chickpea is a grain legume that enhances soil fertility and represents an important source of green proteins for human health. It is typically cultivated in marginal areas with limited water availability. The aim of this study was to shed light into the molecular mechanisms of drought tolerance of this legume. First, the physiological response of nine stable genotype lines in control and drought-stress conditions was assessed. Two of these genotypes (Desi PI5980808 and Kabuli Flip07 318 C) showed opposite physiological responses to drought stress. Desi PI5980808 displayed a reduced chlorophyll content and an unaltered concentration of osmolytes (proline and soluble sugars) under drought stress. Kabuli Flip07 318 C did not show any reduction in photosynthesis and chlorophyll content, but a significant increase of proline and soluble sugars was observed under the drought stress. To identify genes and molecular mechanisms involved in drought tolerance, RNA-seq was performed in control conditions and after one week of drought stress in these two contrasting genotypes. The genotype with higher drought sensitivity showed more intense changes in gene expression than the genotype with less sensitivity, up-regulating genes involved in photophosphorylation process (transferases, oxygen lyases and oxidoreductases), hormones (brassinosteroids, abscisic acid and gibberellin response), solute transporters, nutrient uptake, and cell wall properties (cellulose synthases, hemicellulose synthases, poligalacturonases, pectate lyases). Small number of up-regulated genes in the genotype with lower drought sensitivity included those involved in chromatin modifications. These results will be helpful for further studies aiming at identifying genes and molecular markers to be used in breeding strategies to develop chickpea cultivars more resilient to water stress.

RootBot: High-throughput root stress phenotyping robot.

Higher temperatures across the globe are causing an increase in the frequency and severity of droughts. In agricultural crops, this results in reduced yields, financial losses, and increased food costs at the supermarket. Root growth maintenance in drying soils plays a major role in a plant's ability to survive and perform under drought, but phenotyping root growth is extremely difficult due to roots being under the soil. RootBot is an automated high-throughput phenotyping robot that eliminates many of the difficulties and reduces the time required for performing drought-stress studies on primary roots. RootBot simulates root growth conditions using transparent plates to create a gap that is filled with soil and polyethylene glycol (PEG) to simulate low soil moisture. RootBot has a gantry system with vertical slots to hold the transparent plates, which theoretically allows for evaluating more than 50 plates at a time. Software pipelines were also co-opted, developed, tested, and extensively refined for running the RootBot imaging process, storing and organizing the images, and analyzing and extracting data. The RootBot platform and the lessons learned from its design and testing represent a valuable resource for better understanding drought tolerance mechanisms in roots, as well as for identifying breeding and genetic engineering targets for crop plants.

Functional traits of field-droughted contrasting rice genotypes reveal multiple independent genomic adaptations and metabolic responses

Drought is the most critical environmental stress limiting crop productivity and yield. Rice is one of the top leading food crops worldwide and modern rice varieties are notably drought-sensitive due to their high-water requirements. Generating drought-resilient varieties and fine-tuning their yield performance are time-consuming tasks that could be achieved by exploiting the genetic diversity expressed by the wild ancestors of current-day crop species. We conducted a large-scale field experiment, imposing pre-flowering and post-flowering water shortages on 20 Oryza genotypes. Using detailed agro-physiological, isotopomics, and metabolite characterization of different Asian and African rice accessions, we shed light on the evolutionary biases that have evolved into the spectrum of strategies used to adapt to drought and have added to the rice knowledge base. We find that relevant decreases in photosynthetic rates (linked with stomatal opening) that differed between genotypes. We also identified genotypic differences in core C and N metabolism, and central metabolic pathways, highlighting the possible mechanisms of drought tolerance. Additionally, data suggest strong genetic associations of several amino acids that are significantly enriched during drought. We provide strong evidence of the distinctiveness of agro-physiological and metabolic pathway behaviors to drought across the use of diverse germplasm resources. Also, the resulting data provide insight into the wide variety of germplasm responses triggered by drought.

ZFP37, C3H, NAC94, and bHLH148 transcription factors regulate cultivar-specific drought response by modulating r40C1 gene expression in rice

Lectins are gradually gaining importance in regulating abiotic stress response in plants. Among them, the R40 family plays pivotal role in regulating drought response. The expression of the Osr40C1 positively correlates with the degree of drought tolerance in indica rice cultivars. Although the mechanism of Osr40C1-mediated drought tolerance is well characterized, the gene's regulation under drought remains obscure. Here, we demonstrate that the Osr40C1 promoter is activated under drought to induce its transcription. A number of single nucleotide variations in the Osr40C1 promoter of the drought-tolerant IR36 and sensitive MTU1010 cultivar are detected. However, promoter swapping analysis reveals that these variations in the promoter sequence do not explain the cultivar-specific expression pattern of this gene. Next, we identified the transcription factors that interact with the Osr40C1 promoter. Among these transcription factors, OsZFP37, OsC3H, OsNAC94, and OsbHLH148 display significantly higher transcript abundance in IR36 compared with MTU1010. Furthermore, overexpression of each of these transcription factors confers drought tolerance, whereas their silencing leads to drought sensitivity. Interestingly, the Osr40C1 expression is significantly up-regulated in the transcription factor overexpression lines, while its expression is undetectable in the silencing lines. Together our study highlights how different transcription factors regulate the cultivar-specific expression pattern of Osr40C1 in rice.

Effect of Acclimation to High Temperatures on the Mechanisms of Drought Tolerance in Species with Different Types of Photosynthesis: Sedobassia sedoides (C3–C4) and Bassia prostrata (C4-NADP)

Effect of Acclimation to High Temperatures on the Mechanisms of Drought Tolerance in Species with Different Types of Photosynthesis: Sedobassia sedoides (C3–C4) and Bassia prostrata (C4-NADP)