Drought Tolerance Of Seedlings Research Articles

Functions of exogenous strigolactone application and strigolactone biosynthesis genes GhMAX3/GhMAX4b in response to drought tolerance in cotton (Gossypium hirsutum L.)

BackgroundDrought stress markedly constrains plant growth and diminishes crop productivity. Strigolactones (SLs) exert a beneficial influence on plant resilience to drought conditions. Nevertheless, the specific function of SLs in modulating cotton’s response to drought stress remains to be elucidated.ResultsIn this study, we assess the impact of exogenous SL (rac-GR24) administration at various concentrations (0, 1, 5, 10, 20 µM) on cotton growth during drought stress. The findings reveal that cotton seedlings treated with 5 µM exogenous SL exhibit optimal mitigation of growth suppression induced by drought stress. Treatment with 5 µM exogenous SL under drought stress conditions enhances drought tolerance in cotton seedlings by augmenting photosynthetic efficiency, facilitating stomatal closure, diminishing reactive oxygen species (ROS) generation, alleviating membrane lipid peroxidation, enhancing the activity of antioxidant enzymes, elevating the levels of osmoregulatory compounds, and upregulating the expression of drought-responsive genes. The suppression of cotton SL biosynthesis genes, MORE AXILLARY GROWTH 3 (GhMAX3) and GhMAX4b, impairs the drought tolerance of cotton. Conversely, overexpression of GhMAX3 and GhMAX4b in respective Arabidopsis mutants ameliorates the drought-sensitive phenotype in these mutants.ConclusionThese observations underscore that SLs significantly bolster cotton’s resistance to drought stress.

Metabolic pathways regulated by strigolactones foliar spraying enhance osmoregulation and antioxidant defense in drought-prone soybean

BackgroundDrought stress is a significant abiotic stressor that hinders growth, development, and crop yield in soybeans. Strigolactones (SLs) positively regulate plant resistance to drought stress. However, the impact of foliar application of SLs having different concentrations on soybean growth and metabolic pathways related to osmoregulation remains unknown. Therefore, to clarify the impact of SLs on soybean root growth and cellular osmoregulation under drought stress, we initially identified optimal concentrations and assessed key leaf and root indices. Furthermore, we conducted transcriptomic and metabolic analyses to identify differential metabolites and up-regulated genes.ResultsThe results demonstrated that drought stress had a significant impact on soybean biomass, root length, root surface area, water content and photosynthetic parameters. However, when SLs were applied through foliar application at appropriate concentrations, the accumulation of ABA and soluble protein increased, which enhanced drought tolerance of soybean seedlings by regulating osmotic balance, protecting membrane integrity, photosynthesis and activating ROS scavenging system. This also led to an increase in soybean root length, lateral root number and root surface area. Furthermore, the effects of different concentrations of SLs on soybean leaves and roots were found to be time-sensitive. However, the application of 0.5 µM SLs had the greatest beneficial impact on soybean growth and root morphogenesis under drought stress. A total of 368 differential metabolites were screened in drought and drought plus SLs treatments. The up-regulated genes were mainly involved in nitrogen compound utilization, and the down-regulated metabolic pathways were mainly involved in maintaining cellular osmoregulation and antioxidant defenses.ConclusionsSLs enhance osmoregulation in soybean plants under drought stress by regulating key metabolic pathways including Arachidonic acid metabolism, Glycerophospholipid metabolism, Linoleic acid metabolism, and Flavone and flavonol biosynthesis. This study contributes to the theoretical understanding of improving soybean adaptability and survival in response to drought stress.

Alleviation of Drought Stress in Zea Mays Seeding by Extracellular Polysaccharides Produced by Azotobacter

Azotobacter bacteria are Gram-negative, rod-shaped soil bacteria that can fix atmospheric nitrogen and promote plant growth. They are known to produce exopolysaccharides (EPS), which can help plants to retain water and tolerate drought stress. In this study, 20 Azotobacter isolates were isolated from dry and semi-dry soil samples. The isolates were characterized morphologically and microscopically and tested for their tolerance to drought using PEG6000 at concentrations of 0%, 5%, 10%, 15%, 20%, and 25%. They were also tested for their ability to produce EPS. The isolates that were most tolerant to drought and produced the most EPS were used as biofertilizers to improve the drought tolerance of maize seedlings. The seedlings were irrigated every 24, 48, or 72 hours. The results showed that the biofertilizers containing the two most drought-tolerant and EPS-producing Azotobacter isolates (Azotobacter 1 and Azotobacter 2) significantly improved the germination rate, dry weight, stress tolerance index, chlorophyll stability, and membrane damage index of the maize seedlings.

Anatomical traits explain drought response of seedlings from wet tropical forests.

Water availability regulates plant community dynamics but the drought response of seedlings remains poorly known, despite their vulnerability, especially for the Asian tropics. In particular, discerning how functional traits of seedlings mediate drought response can aid generalizable predictions of tree responses to global environmental change. We assessed interspecific variation in drought response explained by above- and below-ground seedling traits. We conducted a dry-down experiment in the greenhouse using 16 tree species from the humid forests of Western Ghats in southern India, chosen to represent differences in affinity to conditions of high and low seasonal drought (seasonality affiliation). We compared survival, growth, and photosynthetic performance under drought and well-watered conditions and assessed the extent to which species' responses were explained by seasonality affiliation and 12 traits of root, stem and leaf. We found that the species from seasonally dry forest reduced photosynthetic rate in drought compared with well-watered conditions, but seasonality affiliation did not explain differences in growth and survival. Performance in drought vs well-watered conditions were best explained by anatomical traits of xylem, veins and stomata. Species with larger xylem reduced their growth and photosynthesis to tolerate desiccation. In drought, species with smaller stomata correlated with lower survival even though photosynthetic activity decreased by a larger extent with larger stomata. Overall, anatomical traits of xylem and stomata, directly related to water transport and gas-exchange, played a more prominent role than commonly used traits (e.g., specific leaf area, leaf dry matter content) in explaining species response to drought, and may offer a good proxy for physiological traits related to drought tolerance of seedlings.

Evaluation technologies for assessing drought tolerance of Kimchi cabbage seedlings using hyperspectral imaging and principal component analysis

Conventionally, methods for evaluating the tolerance of kimchi cabbage have primarily relied on visual inspection. The development of evaluation criteria based on hyperspectral imaging may help address the problem of decision-making errors arising from visual inspection. However, to evaluate the tolerance of kimchi cabbage using hyperspectral imaging, not only are hyperspectral big data processing and sophisticated exponential model development required, but also real-time evaluation technology with high field usability. This study presents an evaluation method for extracting vegetation information from hyperspectral data, logically analyzing the extracted data, validating the developed model, and ensuring field utility. The red-edge band between 680 and 700 nm is for evaluating the drought tolerance of Kimchi cabbage. The proposed method allows for assessing the drought tolerance of Kimchi cabbage seedlings within a range of 1 to 30, using a robust index with a variance of approximately 2.25 and a sensitivity index with a variance of around 8.4. Since the proposed nonlinear drought tolerance evaluation method must strongly correlate with the chlorophyll index, its performance was verified using the newly proposed cross-point analyzer. While nonlinear drought evaluation technology can serve as a robust analysis method based on extensive data, it has the disadvantage of requiring a long evaluation time. However, the additionally developed cross-point analyzer can improve the real-time capability of testing. Proper utilization of these two analytical technologies enhances the performance of robust and rapid drought tolerance evaluation for Kimchi cabbage seedlings. Therefore, this study introduces two techniques for non-destructively and quantitatively explaining plant water stress.

A novel growth-promoting dark septate endophytic fungus improved drought tolerance in blueberries by modulating phytohormones and non-structural carbohydrates.

Drought is a significant global issue affecting agricultural production, and the utilization of beneficial rhizosphere microorganisms is one of the effective ways to increase the productivity of crops and forest under drought. In this study, we characterized a novel growth-promoting dark septate endophytes (DSE) fungus R16 derived from the blueberry roots. Hyphae or microsclerotia were visible within the epidermal or cortical cells of R16-colonized blueberry roots, which was consistent with the typical characteristics of DSE fungi. Inoculation with R16 promoted the growth of blueberry seedlings and the advantage over the control group was more significant under PEG-induced drought. Comparison of physiological indicators related to drought resistance between the inoculated and control groups was performed on the potted blueberry plants, including the chlorophyll content, net photosynthetic rate, root activities, MDA and H2O2 content, which indicated that R16 colonization mitigated drought injury in blueberry plants. We further analyzed the effects of R16 on phytohormones and non-structural carbohydrates (NSCs) to explore the mechanism of increased drought tolerance by R16 in blueberry seedlings. The results showed that except for the GA content, IAA, ZT and ABA varied significantly between the inoculated and control groups. SPS and S6PDH activities in mature leaves, the key enzymes responsible for sucrose and sorbitol synthesis, respectively, as well as SDH, SuSy, CWINV, HXK and FRK in roots, the key enzymes involved in the NSCs metabolism, showed significant differences between the inoculated and control groups before and after drought treatment. These results suggested that the positive effects of R16 colonization on the drought tolerance of blueberry seedlings are partially attributable to the regulation of phytohormone and sugar metabolism. This study provided valuable information for the research on the interaction between DSE fungi and host plants as well as the application of DSE preparations in agriculture.

Effect of Green Light Replacing Some Red and Blue Light on Cucumis melo under Drought Stress.

Light quality not only directly affects the photosynthesis of green plants but also plays an important role in regulating the development and movement of leaf stomata, which is one of the key links for plants to be able to carry out normal growth and photosynthesis. By sensing changes in the light environment, plants actively regulate the expansion pressure of defense cells to change stomatal morphology and regulate the rate of CO2 and water vapor exchange inside and outside the leaf. In this study, Cucumis melo was used as a test material to investigate the mitigation effect of different red, blue, and green light treatments on short-term drought and to analyze its drought-resistant mechanism through transcriptome and metabolome analysis, so as to provide theoretical references for the regulation of stomata in the light environment to improve the water use efficiency. The results of the experiment showed that after 9 days of drought treatment, increasing the percentage of green light in the light quality significantly increased the plant height and fresh weight of the treatment compared to the control (no green light added). The addition of green light resulted in a decrease in leaf stomatal conductance and a decrease in reactive oxygen species (ROS) content, malondialdehyde MDA content, and electrolyte osmolality in the leaves of melon seedlings. It indicated that the addition of green light promoted drought tolerance in melon seedlings. Transcriptome and metabolome measurements of the control group (CK) and the addition of green light treatment (T3) showed that the addition of green light treatment not only effectively regulated the synthesis of abscisic acid (ABA) but also significantly regulated the hormonal pathway in the hormones such as jasmonic acid (JA) and salicylic acid (SA). This study provides a new idea to improve plant drought resistance through light quality regulation.

Melatonin mitigates drought stress by increasing sucrose synthesis and suppressing abscisic acid biosynthesis in tomato seedlings.

The increasing prevalence of drought events poses a major challenge for upcoming crop production. Melatonin is a tiny indolic tonic substance with fascinating regulatory functions in plants. While plants can respond in several ways to alleviate drought stress, the processes underpinning stress sensing and signaling are poorly understood. Hereafter, the objectives of this investigation were to explore the putative functions of melatonin in the regulation of sugar metabolism and abscisic acid biosynthesis in drought-stressed tomato seedlings. Melatonin (100 μM) and/or water were foliar sprayed, followed by the plants being imposed to drought stress for 14 days. Drought stress significantly decreased biomass accumulation, inhibited photosynthetic activity, and stimulated senescence-associated gene 12 (SAG12) expression. Melatonin treatment effectively reversed drought-induced growth retardation as evidenced by increased leaf pigment and water balance and restricted abscisic acid (ABA) accumulation. Sugar accumulation, particularly sucrose content, was higher in drought-imposed seedlings, possibly owing to higher transcription levels of sucrose non-fermenting 1-related protein kinase 2 (SnKR2.2) and ABA-responsive element binding factors 2 (AREB2). Melatonin addition further uplifted the sucrose content, which coincided with increased activity of sucrose synthase (SS, 130%), sucrose phosphate synthase (SPS, 137%), starch degradation encoding enzyme β-amylase (BAM, 40%) and α-amylase (AMY, 59%) activity and upregulated their encoding BAM1(10.3 folds) and AMY3 (8.1 folds) genes expression at day 14 relative to the control. Under water deficit conditions, melatonin supplementation decreased the ABA content (24%) and its biosynthesis gene expressions. Additionally, sugar transporter subfamily genes SUT1 and SUT4 expression were upregulated by the addition of melatonin. Collectively, our findings illustrate that melatonin enhances drought tolerance in tomato seedlings by stimulating sugar metabolism and negatively regulating ABA synthesis.

Overexpression of the peroxidase gene ZmPRX1 increases maize seedling drought tolerance by promoting root development and lignification

Drought is a main abiotic stress factor hindering plant growth, development, and crop productivity. Therefore, it is crucial to understand the mechanisms by which plants cope with drought stress. Here, the function of the maize peroxidase gene ZmPRX1 in drought stress tolerance was investigated by measurement of its expression in response to drought treatment both in a ZmPRX1 overexpression line and a mutant line. The higher root lignin accumulation and seedling survival rate of the overexpression line than that of the wild type or mutant support a role for ZmPRX1 in maize drought tolerance by regulating root development and lignification. Additionally, yeast one-hybrid, Dule luciferase and ChIP-qPCR assays showed that ZmPRX1 is negatively regulated by a nuclear-localized ZmWRKY86 transcription factor. The gene could potentially be used for breeding of drought-tolerant cultivars.

Abscisic acid and glycine betaine-mediated seed and root priming enhance seedling growth and antioxidative defense in wheat under drought

The extent of drought tolerance in the seedlings of three wheat cultivars (WMRI-1, BARI GOM-33 and BARI GOM-21) was investigated by seed and root priming using abscisic acid (ABA) and glycine betaine (GB). The seeds were primed with ABA (10 and 20 μM) and GB (50 and 100 mM) and grown in pots maintaining control (0 % PEG) and drought (10 % PEG) conditions. Under drought, the root and shoot length, root and shoot biomass were significantly increased in ABA and GB primed seedlings than non-primed seedlings in all cultivars. Among the priming agents, either 20 μM ABA or 50 mM GB triggered better seedling growth in all wheat cultivars. These two levels were then applied with the nutrient solution in the hydroponics following four treatments: Control, Drought, Drought + ABA and Drought + GB. The seedling growth significantly declined in drought, while an improved seedling growth was observed in ABA and GB-treated plants in all cultivars. A considerable increase in lipid peroxidation, proline content, total antioxidant capacity and total flavonoid content in roots and leaves were recorded in all drought conditions, while these values were considerably reduced in ABA and GB treatments. Hierarchical clustering heatmap using stress tolerance index (STI) values showed that Drought + ABA and Drought + GB secured higher STI scores suggesting a greater degree of drought tolerance in all cultivars. In conclusion, seed and root priming of ABA and GB enhanced drought tolerance in the wheat seedlings by improving seedling growth and antioxidative defense suggesting a declined state of oxidative damage.

Legacy effects of early cotyledon removal on the growth, carbon and nitrogen storage, and drought response of Quercus variabilis seedlings

Predation of cotyledons can reduce short-term survival and growth in emerging oak seedlings, potentially affecting species recruitment. However, the physiological basis of reduced seedling performance after early cotyledon predation and the mid-term consequences of cotyledon predation on seedling drought tolerance remain poorly understood. We performed an experiment where we simulated predation by systematically removing cotyledons from Quercus variabilis seedlings at seven growth stages during emergence in the first growing season. We assessed survival, growth, and nitrogen (N) and non-structural carbohydrate (NSC) storage. Subsequently, in the second growing season, we assessed drought tolerance in seedlings with cotyledons removed at four growth stages in the previous season, and subjected seedlings to two drought levels to assess overall performance. During the first growing season, seedling survival showed less sensitivity to cotyledon removal compared to growth, N and NSC storage, which were significantly reduced when cotyledons were removed within the first 4 days after emergence. Early cotyledon removal (4 days after emergence) in the first growing season enhanced drought tolerance in the second growing season by reducing leaf embolism vulnerability, but it did not affect leaf drought tolerance traits such as the osmotic potential or the modulus of elasticity. Early cotyledon removal had a lasting effect on seedling growth and N and NSC storage building in the second growing season. Additionally, it exacerbated the negative consequences of drought on seedlings growth and N storage building, but it did not influence survival or NSC storage. Our findings evidence that early cotyledon removal in emerging oak seedlings has significant short- and medium-term repercussions on growth and capacity to store N and NSC, and it hinders the capacity of seedlings to respond to drought despite early cotyledon removal increases leaf drought tolerance. These functional legacies can influence oak seedling recruitment.

Determination of germination characteristics and salinity and drought tolerances of Mountain Swan (Atriplex nitens Schkuhr)

In this study, it was aimed to determine the appropriate seed germination temperature, salt tolerance, salinity and drought tolerance of seedlings in Mountain swan (Atriplex nitens). For this purpose, an experiment was established in 2021 in laboratory conditions according to the factorial experiment design in random plots and in greenhouse conditions according to the random plots experiment design with three replications. Firstly, 4 constant (10, 15, 20, 25, 30°C) and 2 variable (20/15, 25/15°C) temperatures were used in the refrigerated incubator. Total germination rates and average germination times of seeds with and without pericarp were determined. Secondly, 6 different salt concentrations (0, 100, 200, 300, 400 and 500 mM NaCl) were studied considering the optimum germination temperatures (25°C and 20/15°C). At the end of the study, germination rates (%), average germination times (days) and sensitivity indices (SI) were determined. In the last two stages, seedlings were subjected to 4 different salinity (0, 100, 200, 300, 400 and 500 mM NaCl) and 5 different drought (control, low, moderate, high and severe) tests under greenhouse conditions. At this stage, plant and root length, stem thickness, leaf area index (LAI), plant and root dry weight, root/plant ratio and tolerance percentage values were measured. As a result of the laboratory study, it was determined that seeds without pericarp had a better germination percentage than seeds with pericarp. The highest total and normal germination rates were obtained from 200 mM NaCl treatment at 20/15°C. Germination rate was determined from 0, 100 and 200 mM salt treatments at 25°C. These results showed that Atriplex nitens seeds could germinate in high salt concentrations and that their seedlings had high tolerance to drought and salinity.

The Quest for Reliable Drought Stress Screening in Tetraploid Wheat (Triticum turgidum spp.) Seedlings: Why MDA Quantification after Treatment with 10% PEG-6000 Falls Short.

Drought stress poses significant productivity challenges to wheat. Several studies suggest that lower malondialdehyde (MDA) content may be a promising trait to identify drought-tolerant wheat genotypes. However, the optimal polyethylene glycol (PEG-6000) concentration for screening seedlings for drought tolerance based on MDA quantification is not clear. The aim of this study was to verify whether a 10% (w/v) PEG-6000 concentration-induced water stress was reliable for discriminating between twenty-two drought-susceptible and drought-tolerant tetraploid wheat (Triticum turgidum spp. durum, turanicum, and carthlicum) accessions based on MDA quantification. To do so, its correlation with morpho-physiological traits, notoriously related to seedling drought tolerance, i.e., Seedling Vigour Index and Seedling Water Content, was evaluated. Results showed that MDA content was not a reliable biomarker for drought tolerance, as it did not correlate significantly with the aforementioned morpho-physiological traits, which showed, on the contrary, high positive correlation with each other. Combining our study with the cited literature, it clearly emerges that different wheat genotypes have different "water stress thresholds", highlighting that using a 10% PEG-6000 concentration for screening wheat seedlings for drought tolerance based on MDA quantification is not reliable. Given the conflicting results in the literature, this study provides important insights for selecting appropriate methods for evaluating wheat seedling drought tolerance.

The Identification of Drought Tolerance Candidate Genes in Oryza sativa L. ssp. Japonica Seedlings through Genome-Wide Association Study and Linkage Mapping

Drought stress poses a significant threat to rice production, necessitating the identification of genes associated with drought tolerance. This study employed a combination of genome-wide association study (GWAS) and linkage mapping to pinpoint seedling drought tolerance genes in Japonica rice. Using the leaf rolling scale (LRS) as the phenotypic index, we assessed rice drought tolerance under polyethylene glycol-induced drought during the seedling stage. A lead SNP C8_28933410 by GWAS was identified, which was located within qLRS-8-1 identified by linkage mapping on chromosome 8. Combing the LD block analyses and QTL interval, a 138.6 kb overlap interval was considered as the candidate region. Haplotype analysis, qRT-PCR, sequence analysis, and mutant phenotype verification led to the speculation that LOC_Os08g05520 is a candidate gene associated with drought tolerance. Our findings provide a valuable reference for breeders aiming to enhance rice drought tolerance.

Genome-wide identification of the CNGC gene family and negative regulation of drought tolerance by HvCNGC3 and HvCNGC16 in transgenic Arabidopsis thaliana

Cyclic nucleotide-gated ion channels (CNGCs), as non-selective cation channels, play essential roles in plant growth and stress responses. However, they have not been identified in Qingke (Hordeum vulgare L.). Here, we performed a comprehensive genome-wide identification and function analysis of the HvCNGC gene family to determine its role in drought tolerance. Phylogenetic analysis showed that 27 HvCNGC genes were divided into four groups and unevenly located on seven chromosomes. Transcription analysis revealed that two closely related members of HvCNGC3 and HvCNGC16 were highly induced and the expression of both genes were distinctly different in two extremely drought-tolerant materials. Transient expression revealed that the HvCNGC3 and HvCNGC16 proteins both localized to the plasma membrane and karyotheca. Overexpression of HvCNGC3 and HvCNGC16 in Arabidopsis thaliana led to impaired seed germination and seedling drought tolerance, which was accompanied by higher hydrogen peroxide (H2O2), malondialdehyde (MDA), proline accumulation and increased cell damage. In addition, HvCNGC3 and HvCNGC16-overexpression lines reduced ABA sensitivity, as well as lower expression levels of some ABA biosynthesis and stress-related gene in transgenic lines. Furthermore, Yeast two hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays revealed that HvCNGC3 and HvCNGC16 interacted with calmodulin/calmodulin-like proteins (CaM/CML), which, as calcium sensors, participate in the perception and decoding of intracellular calcium signaling. Thus, this study provides information on the CNGC gene family and provides insight into the function and potential regulatory mechanism of HvCNGC3 and HvCNGC16 in drought tolerance in Qingke.

Exogenous 24-Epibrassinolide Enhanced Drought Tolerance and Promoted BRASSINOSTEROID-INSENSITIVE2 Expression of Quinoa.

Brassinosteroids (BRs) are involved in the regulation of biotic and abiotic stresses in plants. The molecular mechanisms of BRs that alleviate the drought stress in quinoa have rarely been reported. Here, quinoa seedlings were treated with 24-epibrassinolide (EBR) and we transiently transferred CqBIN2 to the quinoa seedlings' leaves using VIGS technology to analyze the molecular mechanism of the BR mitigation drought stress. The results showed that EBR treatment significantly increased the root growth parameters, the antioxidant enzyme activities, and the osmolyte content, resulting in a decrease in the H2O2, O2∙-, and malondialdehyde content in quinoa. A transcriptome analysis identified 8124, 2761, and 5448 differentially expressed genes (DEGs) among CK and Drought, CK and EBR + Drought, and Drought and EBR + Drought groups. WGCNA divided these DEGs into 19 modules in which these characterized genes collectively contributed significantly to drought stress. In addition, the EBR application also up-regulated the transcript levels of CqBIN2 and proline biosynthesis genes. Silenced CqBIN2 by VIGS could reduce the drought tolerance, survival rate, and proline content in quinoa seedlings. These findings not only revealed that exogenous BRs enhance drought tolerance, but also provided insight into the novel functions of CqBIN2 involved in regulating drought tolerance in plants.

Colonization of root endophytic fungus Serendipita indica improves drought tolerance of Pinus taeda seedlings by regulating metabolome and proteome.

Pinus taeda is an important forest tree species for plantations because of its rapid growth and high yield of oleoresins. Although P. taeda plantations distribute in warm and wet southern China, drought, sometime serious and long time, often occurs in the region. To explore drought tolerance of P. taeda and usage of beneficial microorganisms, P. taeda seedlings were planted in pots and were inoculated with root endophytic fungus Serendipita indica and finally were treated with drought stress for 53 d. Metabolome and proteome of their needles were analyzed. The results showed that S. indica inoculation of P. taeda seedlings under drought stress caused great changes in levels of some metabolites in their needles, especially some flavonoids and organic acids. Among them, the levels of eriocitrin, trans-aconitic acid, vitamin C, uric acid, alpha-ketoglutaric acid, vitamin A, stachydrine, coumalic acid, itaconic acid, calceolarioside B, 2-oxoglutaric acid, and citric acid were upregulated more than three times in inoculated seedlings under drought stress, compared to those of non-inoculated seedlings under drought stress. KEGG analysis showed that some pathways were enriched in inoculated seedlings under drought stress, such as flavonoid biosynthesis, ascorbate and aldarate metabolism, C5-branched dibasic acid metabolism. Proteome analysis revealed some specific differential proteins. Two proteins, namely, H9X056 and H9VDW5, only appeared in the needles of inoculated seedlings under drought stress. The protein H9VNE7 was upregulated more than 11.0 times as that of non-inoculated seedlings under drought stress. In addition, S. indica inoculation increased enrichment of water deficient-inducible proteins (such as LP3-1, LP3-2, LP3-3, and dehydrins) and those involved in ribosomal structures (such as A0A385JF23). Meanwhile, under drought stress, the inoculation caused great changes in biosynthesis and metabolism pathways, mainly including phenylpropanoid biosynthesis, cutin, suberine and wax biosynthesis, and 2-oxocarboxylic acid metabolism. In addition, there were positive relationships between accumulation of some metabolites and enrichment of proteins in P. taeda under drought stress. Altogether, our results showed great changes in metabolome and proteome in inoculated seedlings under drought stress and provided a guideline to further study functions of metabolites and proteins, especially those related to drought stress.

Genome-wide scanning to identify and validate single nucleotide polymorphism markers associated with drought tolerance in spring wheat seedlings.

Unlike other growth stages of wheat, very few studies on drought tolerance have been done at the seedling stage, and this is due to the complexity and sensitivity of this stage to drought stress resulting from climate change. As a result, the drought tolerance of wheat seedlings is poorly understood and very few genes associated with drought tolerance at this stage were identified. To address this challenge, a set of 172 spring wheat genotypes representing 20 different countries was evaluated under drought stress at the seedling stage. Drought stress was applied on all tested genotypes by water withholding for 13 days. Two types of traits, namely morphological and physiological traits were scored on the leaves of all tested genotypes. Genome-wide association study (GWAS) is one of the effective genetic analysis methods that was used to identify target single nucleotide polymorphism (SNP) markers and candidate genes for later use in marker-assisted selection. The tested plant materials were genotyped using 25k Infinium iSelect array (25K) (herein after it will be identified as 25K) (for 172 genotypes) and genotyping-by-sequencing (GBS) (for 103 genotypes), respectively. The results of genotyping revealed 21,093 25K and 11,362 GBS-SNPs, which were used to perform GWAS analysis for all scored traits. The results of GWAS revealed that 131 and 55 significant SNPs were controlling morphological and physiological traits, respectively. Moreover, a total of eight and seven SNP markers were found to be associated with more than one morphological and physiological trait under drought stress, respectively. Remarkably, 10 significant SNPs found in this study were previously reported for their association with drought tolerance in wheat. Out of the 10 validated SNP markers, four SNPs were associated with drought at the seedling stage, while the remaining six SNPs were associated with drought stress at the reproductive stage. Moreover, the results of gene enrichment revealed 18 and six pathways as highly significant biological and molecular pathways, respectively. The selection based on drought-tolerant alleles revealed 15 genotypes with the highest number of different drought-tolerant alleles. These genotypes can be used as candidate parents in future breeding programs to produce highly drought-tolerant genotypes with high genetic diversity. Our findings in this study provide novel markers and useful information on the genetic basis of drought tolerance at early growth stages.

The effect of ectomycorrhizal fungal exposure on nursery-raised Pinus sylvestris seedlings: plant transpiration under short-term drought, root morphology and plant biomass.

Drought is a major environmental stressor that limits seedling growth. Several studies have found that some ectomycorrhizal fungi may increase the drought tolerance of nursery-raised seedlings. However, the precise role that different ectomycorrhizal fungi species play in drought tolerance remains unclear. We evaluated the transpiration rate of Pinus sylvestris seedlings under drought stress in greenhouse conditions by exposing seedlings to 10 ectomycorrhizal fungi species, with different functional traits (exploration type and hydrophobicity), and to 3 natural soil inoculums. We measured the transpiration and water potential of the seedlings during a 10-day drought period and a 14-day recovery period. We then analyzed their root morphology, stem, needle, root biomass and needle chlorophyll fluorescence. We showed that exposing seedlings to ectomycorrhizal fungi or soil inoculum had a positive effect on their transpiration rate during the driest period and through the recovery phase, leading to 2- to 3-fold higher transpiration rates compared with the nonexposed control seedlings. Seedlings exposed to medium-distance ectomycorrhizal fungi performed better than other exploration types under drought conditions, but ectomycorrhizal fungi hydrophobicity did not seem to affect the seedlings response to drought. No significant differences were observed in biomass accumulation and root morphology between the seedlings exposed to different ectomycorrhizal fungi species and the control. Our results highlight the positive and species-specific effect of ectomycorrhizal fungi exposure on drought tolerance in nursery-raised Scots pine seedlings. The studied ectomycorrhizal fungi functional traits may not be sufficient to predict the seedling response to drought stress, thus physiological studies across multiple species are needed to draw the correct conclusion. Our findings have potential practical implications for enhancing seedling drought tolerance in nursery plant production.

SbMYC2 mediates jasmonic acid signaling to improve drought tolerance via directly activating SbGR1 in sorghum.

SbMYC2 functions as a key regulator under JA signaling in enhancing drought tolerance of sorghum through direct activating SbGR1. Drought stress is one of the major threats to crop yield. In response to drought stress, functions of basic helix-loop-helix (bHLH) transcription factors (TFs) have been reported in Arabidopsis and rice, but little is known for sorghum. Here, we characterized the function of SbMYC2, a bHLH TF in sorghum, and found that SbMYC2 responded most significantly to PEG-simulated drought stress and JA treatments. Overexpression of SbMYC2 significantly enhanced drought tolerance in Arabidopsis, rice and sorghum. In addition, it reduced reactive oxygen species (ROS) accumulation and increased chlorophyll content in sorghum leaves. While silencing SbMYC2 by virus-induced gene silencing (VIGS) resulted in compromised drought tolerance of sorghum seedlings. Moreover, SbMYC2 can directly activate the expression of GLUTATHIONE-DISULFIDE REDUCTASE gene SbGR1. SbGR1 silencing led to significantly weakened drought tolerance of sorghum, and higher ROS accumulation and lower chlorophyll content in sorghum leaves were detected. In addition, SbMYC2 can interact with SbJAZs, suppressors of JA signaling, and thus can mediate JA signaling to activate SbGR1, thereby regulating sorghum's tolerance to drought stress. Overall, our findings demonstrate that bHLH TF SbMYC2 plays an important role in sorghum's response to drought stress, thus providing one theoretical basis for genetic enhancement of sorghum and even rice.