Drought Tolerance Of Seedlings Research Articles

Seed priming upregulates antioxidant defense and glyoxalase systems to conferring simulated drought tolerance in wheat seedlings

This experiment was conducted to understand the protective effect of different priming agents [50 µM salicylic acid (SA), 4 mM ascorbic acid (AsA), and 2.5 mM NaCl] under simulated drought [15% (m/v) polyethylene glycol (PEG-6000)] in wheat. Drought caused higher proline accumulation, lower relative water content, chlorosis, and growth inhibition. Enhanced levels of the malondialdehyde and hydrogen peroxide were evident with higher reactive oxygen species (ROS) generation that disrupted the plant antioxidant defense system. The activities of antioxidant enzymes were also significantly declined under PEG-induced drought stress. Drought also increased methylglyoxal (MG) formation, which aggravated oxidative damage to the next folds. However, priming wheat seeds with SA, AsA and NaCl decreased ROS production by decreasing AsA, increasing glutathione content, and upregulating the antioxidant defense system. Additionally, increased activities of glyoxalase system enzymes (glyoxalase I and glyoxalase II) controlled the overproduction of MG in drought-stressed wheat seedlings. Indeed, seed priming helps to alleviate drought-induced oxidative damage by modulating the antioxidant defense system. However, AsA provided a better defense to plants against drought stress. Therefore, it can be concluded that priming wheat seeds with SA, AsA, and NaCl confers drought stress tolerance by upregulating antioxidant defense and glyoxalase systems, thus ensuring better seedling establishment.

Seedling establishment and early growth in Calobota sericea subjected to moisture stress

The South African perennial legume Calobota sericea (Thunb.) Boatwr. & B-E van Wyk has been shown to be drought tolerant as mature plants, but information on drought tolerance of seedlings is lacking. This study evaluated the impact of moisture stress on seedling emergence, survival and growth in C. sericea. In the first trial, pre-germinated seeds were planted at 100, 70, 50 and 40% of soil moisture holding capacity without additional watering. Seedling emergence and mortality was recorded daily for 14 days. In the second trial, seeds were allowed to grow under well-watered conditions for one month, after which moisture stress was imposed for 15 and 30 days. Thereafter, the seedlings were uprooted, for shoot and root measurements. Results from these trials show that C. sericea seedlings will establish even at severely reduced water-availabilities, but without subsequent watering, significant seedling mortality will occur. Calobota sericea seedlings displayed a range of morphological adaptive strategies to moisture stress including the minimisation of water loss and optimisation of water uptake. Further research into the impacts of regular cycles of moisture stress is needed to determine if changes in morphology due to prior moisture stress will result in improved adaptation to subsequent moisture stress.

Heterologous Overexpression of ZmHDZIV13 Enhanced Drought and Salt Tolerance in Arabidopsis and Tobacco

The homeodomain leucine zipper (HD-Zip) IV transcription factor is indispensable in the response of plants to abiotic stress. Systematic studies have been carried out in Arabidopsis, rice and other species from which a series of stress resistance-related genes have been isolated. However, the function of the HD-Zip IV protein in maize is not clear. In this study, we cloned the HD-Zip IV gene ZmHDZIV13 and identified its function in the stress response. Our phylogenetic analysis showed that ZmHDZIV13 and AtHDG11 had high homology and might have similar functions. The heterologous overexpression of ZmHDZIV13 in Arabidopsis resulted in sensitivity to abscisic acid (ABA), salt tolerance during germination and drought tolerance in seedlings. Under drought stress, the transgenic Arabidopsis showed stronger drought resistance than the wild-type (control). The malondialdehyde content of ZmHDZIV13 transgenic plants was lower than that of the control, and the relative water content and proline content were significantly higher than those of the control. After the drought was relieved, the expression levels of stress-related genes were up-regulated in transgenic Arabidopsis. These results show that ZmHDZIV13, as a stress-responsive transcription factor, plays a role in the positive regulation of abiotic stress tolerance and can regulate an ABA-dependent signaling pathway to regulate drought response in plants.

Silicon enhances the drought resistance of peach seedlings by regulating hormone, amino acid, and sugar metabolism

BackgroundDrought is one of the main concerns worldwide and restricts the development of agriculture. Silicon improves the drought resistance of plants, but the underlying mechanism remains unclear.ResultsWe sequenced the transcriptomes of both control and silicon-treated peach seedlings under drought stress to identify genes or gene networks that could be managed to increase the drought tolerance of peach seedlings. Peach (Prunus persica) seedlings were used to analyse the effects of silicon on plant growth and physiological indexes related to drought resistance under drought stress. The results showed that silicon addition improved the water use efficiency, antioxidant capacity, and net photosynthetic rate, inhibition of stomatal closure, promoted the development of roots, and further regulated the synthesis of hormones, amino acids and sugars in peach seedlings. A comparative transcriptome analysis identified a total of 2275 genes that respond to silicon under drought stress. These genes were mainly involved in ion transport, hormone and signal transduction, biosynthetic and metabolic processes, stress and defence responses and other processes. We analysed the effects of silicon on the modulation of stress-related hormonal crosstalk and amino acid and sugar metabolism. The results showed that silicon promotes zeatin, gibberellin, and auxin biosynthesis, inhibits the synthesis of abscisic acid, then promote lateral root development and inhibit stomatal closure, and regulates the signal transduction of auxin, cytokinin, gibberellin and salicylic acid. Silicon also regulates the metabolism of various amino acids and promotes the accumulation of sucrose and glucose to improve drought resistance of peach seedlings.ConclusionsSilicon enhanced the drought resistance of peach seedlings by regulating stress-related hormone synthesis and signal transduction, and regulating amino acid and sugar metabolism.

A gain-of-function allele of a DREB transcription factor gene ameliorates drought tolerance in wheat.

Drought is a major environmental factor limiting wheat production worldwide. However, the genetic components underlying wheat drought tolerance are largely unknown. Here, we identify a DREB transcription factor gene (TaDTG6-B) by genome-wide association study that is tightly associated with drought tolerance in wheat. Candidate gene association analysis revealed that a 26-bp deletion in the TaDTG6-B coding region induces a gain-of-function for TaDTG6-BDel574, which exhibits stronger transcriptional activation, protein interactions, and binding activity to dehydration-responsive elements (DRE)/CRT cis-elements than the TaDTG6-BIn574 encoded by the allele lacking the deletion, thus conferring greater drought tolerance in wheat seedlings harboring this variant. Knockdown of TaDTG6-BDel574 transcripts attenuated drought tolerance in transgenic wheat, whereas its overexpression resulted in enhanced drought tolerance without accompanying phenotypic abnormalities. Furthermore, the introgression of the TaDTG6-BDel574 elite allele into drought-sensitive cultivars improved their drought tolerance, thus providing a valuable genetic resource for wheat breeding. We also identified 268 putative target genes that are directly bound and transcriptionally regulated by TaDTG6-BDel574. Further analysis showed that TaDTG6-BDel574 positively regulates TaPIF1 transcription to enhance wheat drought tolerance. These results describe the genetic basis and accompanying mechanism driving phenotypic variation in wheat drought tolerance, and provide a novel genetic resource for crop breeding programs.

The miR164-TaNAC14 module regulates root development and abiotic-stress tolerance in wheat seedlings

Previous studies have revealed the miR164 family and the miR164-targeted NAC transcription factor genes in rice (Oryza sativa) and Arabidopsis that play versatile roles in developmental processes and stress responses. In wheat (Triticum aestivum L.), we found nine genetic loci of tae-miR164 (tae-MIR164 a to i) producing two mature sequences that down-regulate the expression of three newly identified target genes of TaNACs (TaNAC1, TaNAC11, and TaNAC14) by the cleavage of the respective mRNAs. Overexpression of tae-miR164 or one of its target genes (TaNAC14) demonstrated that the miR164-TaNAC14 module greatly affects root growth and development and stress (drought and salinity) tolerance in wheat seedlings, and TaNAC14 promotes root growth and development in wheat seedlings and enhances drought tolerance, while tae-miR164 inhibits root development and reduces drought and salinity tolerance by down-regulating the expression of TaNAC14. These findings identify the miR164-TaNAC14 module as well as other tae-miR164-regulated genes which can serve as new genetic resources for stress-resistance wheat breeding.

CqZF-HD14 enhances drought tolerance in quinoa seedlings through interaction with CqHIPP34 and CqNAC79

Drought stress is a key agricultural problem that restricts plant development and crop yield. Research on quinoa (Chenopodium quinoa), a nutrient-rich crop with strong stress resistance, has been limited in terms of the molecular regulation of its adaptation to drought stress. This study identified the zinc finger–homeodomain (ZF-HD) family in quinoa and a drought-responsive Chenopodium quinoa ZF-HD14 (CqZF-HD14) through expression profiles. Transient overexpression of CqZF-HD14 promotes photosynthetic pigment accumulation under drought stress, strengthens the antioxidant system, and in turn enhances drought tolerance. Comprehensive genome-wide family analysis and expression profiling identified CqNAC79 and CqHIPP34 regulated by CqZF-HD14, and their interactions were further determined by bimolecular fluorescence complementation (BIFC). Moreover, physiological and biochemical analyses and transient overexpression also revealed that CqNAC79 and CqHIPP34 resist drought by promoting the accumulation of photosynthetic pigments and maintaining antioxidant capacity under drought stress. The synergistic effect of CqZF-HD14 with CqNAC79 or CqHIPP34 further enhanced the drought tolerance of quinoa seedlings. Taken together, the results indicate that CqZF-HD14, CqNAC79 and CqHIPP34 may be important contributors to the drought tolerance regulatory network in quinoa, and these findings add new members to the drought tolerance gene pool.

Effects of a Dark Septate Fungal Endophyte on the Growth and Physiological Response of Seedlings to Drought in an Epiphytic Orchid.

Dark septate endophytes (DSE) are a group of facultative biotrophic root-colonizing fungi that live within a plant for a part of their life cycle without causing any apparent, overt negative effects. These fungi have been found in >600 different plant species, including orchids. Although the precise ecological functions of dark septate fungal endophytes are not yet well understood, there is increasing evidence that they enhance host growth and nutrient acquisition, and improve the plant’s ability to tolerate biotic and abiotic stresses. In this research, we tested the effects of a DSE isolated from the roots of the epiphytic orchid Coelogyne viscosa on the growth and drought tolerance of orchid seedlings. Our results showed that addition of DSE inoculum significantly enhanced biomass of seedlings and increased the activities of drought resistance related enzymes and the accumulation of osmoregulatory substances. These results suggest that DSE can fulfill important ecological functions in stressful environments and potentially play an important role in the life cycle of epiphytic orchids.

Arbuscular mycorrhizal fungi improve the growth and drought tolerance of Cinnamomum migao by enhancing physio-biochemical responses.

Drought is the main limiting factor for plant growth in karst areas with a fragile ecological environment. Cinnamomum migao H.W. Li is an endemic medicinal woody plant present in the karst areas of southwestern China, and it is endangered due to poor drought tolerance. Arbuscular mycorrhizal fungi (AMF) are known to enhance the drought tolerance of plants. However, few studies have examined the contribution of AMF in improving the drought tolerance of C. migao seedlings. Therefore, we conducted a series of experiments to determine whether a single inoculation and coinoculation of AMF (Claroideoglomus lamellosum and Claroideoglomus etunicatum) enhanced the drought tolerance of C. migao. Furthermore, we compared the effects of single inoculation and coinoculation with different inoculum sizes (20, 40, 60, and 100 g; four replicates per treatment) on mycorrhizal colonization rate, plant growth, photosynthetic parameters, antioxidant enzyme activity, and malondialdehyde (MDA) and osmoregulatory substance contents. The results showed that compared with nonmycorrhizal plants, AMF colonization significantly improved plant growing status; net photosynthetic rate; superoxide dismutase, catalase, and peroxidase activities; and soluble sugar, soluble protein, and proline contents. Furthermore, AMF colonization increased relative water content and reduced MDA content in cells. These combined cumulative effects of AMF symbiosis ultimately enhanced the drought tolerance of seedlings and were closely related to the inoculum size. With an increase in inoculum size, the growth rate and drought tolerance of plants first increased and then decreased. The damage caused by drought stress could be reduced by inoculating 40–60 g of AMF, and the effect of coinoculation was significantly better than that of single inoculation at 60 g of AMF, while the effect was opposite at 40 g of AMF. Additionally, the interaction between AMF and inoculum sizes had a significant effect on drought tolerance. In conclusion, the inoculation of the AMF (Cl. lamellosum and Cl. etunicatum) improved photosynthesis, activated antioxidant enzymes, regulated cell osmotic state, and enhanced the drought tolerance of C. migao, enabling its growth in fragile ecological environments.

Comparative transcriptomics reveals new insights into melatonin-enhanced drought tolerance in naked oat seedlings.

The growth and development of naked oat (Avena nuda L.) seedlings, a grain recognized as nutritious and healthy, is limited by drought. Melatonin plays a positive role in plants under drought stress. However, its function is unclear in naked oats. This study demonstrated that melatonin enhances drought stress tolerance in oat seedlings. Melatonin application alleviated the declining growth parameters of two naked oat varieties, Huazao No.2 (H2) and Jizhangyou No.15 (J15), under drought stress by increasing the chlorophyll content and photosynthetic rate of leaves. Melatonin pretreatment induced differential gene expression in H2 and J15 under drought stress. Subsequently, the differential gene expression responses to melatonin in the two varieties were further analyzed. The key drought response transcription factors and the regulatory effect of melatonin on drought-related transcription factors were assessed, focusing on genes encoding proteins in the ABA signal transduction pathway, including PYL, PP2C, ABF, SNRK2, and IAA. Taken together, this study provides new insights into the effect and underlying mechanism of melatonin in alleviating drought stress in naked oat seedlings.

Biopriming of Maize Seeds with a Novel Bacterial Strain SH-6 to Enhance Drought Tolerance in South Korea

Maize is the third most common cereal crop worldwide, after rice and wheat, and plays a vital role in preventing global hunger crises. Approximately 50% of global crop yields are reduced by drought stress. Bacteria as biostimulants for biopriming can improve yield and enhance sustainable food production. Further, seed biopriming stimulates plant defense mechanisms. In this study, we isolated bacteria from the rhizosphere of Artemisia plants from Pohang beach, Daegu, South Korea. Twenty-three isolates were isolated and screened for growth promoting potential. Among them, bacterial isolate SH-6 was selected based on maximum induced tolerance to polyethylene glycol-simulated drought. SH-6 showed ABA concentration = 1.06 ± 0.04 ng/mL, phosphate solubilizing index = 3.7, and sucrose concentration = 0.51 ± 0.13 mg/mL. The novel isolate SH-6 markedly enhanced maize seedling tolerance to oxidative stress owing to the presence of superoxide dismutase, catalase, and ascorbate peroxidase activities in the culture media. Additionally, we quantified and standardized the biopriming effect of SH-6 on maize seeds. SH-6 significantly increased maize seedling drought tolerance by up to 20%, resulting in 80% germination potential. We concluded that the novel bacterium isolate SH-6 (gene accession number (OM757882) is a biostimulant that can improve germination performance under drought stress.

Improved drought tolerance in soybean by protein elicitor AMEP412 induced ROS accumulation and scavenging

Drought stress is a major limiting factor for soybean production. In this study, protein elicitor AMEP412 was applied on soybean seedlings to promote drought tolerance, and its correlation with alterations in the reactive oxygen species (ROS) in leaves was studied. The plants of soybean cv. Suinong 26 were sprayed with AMEP412 at the V1 stage and then treated with drought stress and rehydration. The alterations in phenotypes, physiological indices, ROS levels and antioxidant system as well as lipid peroxidation were monitored. The results showed that spraying AMEP412 significantly promoted the drought tolerance of soybean seedlings. Soybean seedlings pre-treated with AMEP412 performed better in phenotypes and physiological indexes, like leaf relative water content (RWC), leaf relative conductivity (RC) and osmolytes (free proline, soluble sugar and protein). In addition, the in situ and quantification detection of ROS revealed that AMEP412 pretreatment led to higher accumulation of ROS at the early stage and faster scavenging of ROS at the late stage. Moreover, AMEP412 pretreatment increased the activity of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), and the levels of ascorbate (AsA) and glutathione (GSH), but decreased the level of malondialdehyde (MDA) as compared with only drought treatment. Overall, the results indicated that AMEP412 was effective in alleviating the adverse effects of drought stress, which was partially attributable to the ROS accumulation and scavenging triggered by AMEP412.

Phenotyping cowpea accessions at the seedling stage for drought tolerance in controlled environments

Abstract One of the most important screening techniques used in cowpea selection for drought tolerance is screening at the seedling stage. The objective of this study was to phenotype 60 cowpea genotypes for seedling drought tolerance in screen houses (glasshouse and greenhouse). Principal component analysis revealed that of the 14 variables, the first 4 expressed more than 1 eigenvalue. Data showed that PC1, PC2, and PC3 contributed 39.3, 15.2, and 10%, respectively, with 64.68% total variation. A PCA plot and biplot showed that the number of pods (NP), seeds per pod (SP), survival count (SC), pod weight (PWT), and stem wilting in week 1 (WWK1) had the most significant contributions to genetic variability to drought tolerance and to yield after stress imposition based on the PCA, biplot, and cluster plot, the accessions IT 07-292-10, IT 07-274-2-9, IT90K-59, 835-911, RV 343, and IT 95K-2017-15 had the maximum variability in terms of NP, SP, SC, PWT, and WWK1 after drought imposition. Cowpea accessions 835-911, IT 07-292-10, RV 344, Kangorongondo, and IT 90K-59 were the major individuals that contributed mainly to domain information model (DIM) 1 and 2. The accessions that contributed the least were IT 89KD288, Chibundi mavara, and TVU12746. Thirty-six cowpea accessions from both screen houses were tolerant to drought, 15 were moderately tolerant, while 23 were susceptible. The findings of the study provided a useful tool for screening and determining drought-tolerant and susceptible accessions at the seedling stage.

Green Light Partial Replacement of Red and Blue Light Improved Drought Tolerance by Regulating Water Use Efficiency in Cucumber Seedlings

Light is one of the most important environmental signals in plant growth, development, and stress response. Green light has been proved to enhance plant defense against biotic and/or abiotic stress. To illustrate the effects of green light partially replaced red light and blue light on the plant under drought condition, cucumber (Cucumis sativus L. cv. Xinchun No. 4) seedlings were treated with short-term drought stress and were concomitantly exposed to four treatments, which were set up by adjusting the relative amount of green light as 0 (RB), 25 (RBG25), 50 (RBG50), and 75 (RBG75) μmol m−2 s−1, respectively, with a total photosynthetic photon flux density of 250 μmol m−2 s−1 and a fixed red-to-blue ratio of 4:1. The results showed that compared with RB, RBG50 significantly increased shoot fresh weight (FW) and dry weight (DW), root DW, plant height, stem diameter, leaf area, and leaf dry mass per unit area (LMA) by 10.61, 7.69, 66.13, 6.22, 10.02, 4.10, and 12.41%, respectively. Also, the addition of green light significantly increased the root volume and root tip number. Moreover, green light partial replacement of red light and blue light increased total water content, especially free water content, improved leaf water status, and alleviated water loss in plants caused by drought stress. Also, the addition of green light increased net photosynthetic rate (Pn), reduced both stomata conductance (gs) and transpiration rate (E), enhanced the intrinsic water-use efficiency (WUE) and instantaneous water-use efficiency (iWUE) of leaves, and increased the content of chlorophylls a and b. Green light substituting a proportion of blue and red light regulated stomatal aperture by significantly increasing abscisic acid (ABA) and γ-aminobutyric acid (GABA) content. In addition, the increase of GABA was resulted from the upregulation of Glutamate Decarboxylase 2 (CsGAD2). However, the relative electrolytic leakage and contents of malondialdehyde (MDA), superoxide anion (), and hydrogen peroxide (H2O2) vigorously decreased as the intensity of green light was added to the spectrum under drought. Conclusively, green light partially replaced red light and blue light and improved drought tolerance of cucumber seedlings by upregulating the expression of CsGAD2 gene and promoting the synthesis of GABA. The increase in GABA content further downregulated the expression of aluminum-activated malate transporter 9 (CsALMT9) gene, induced stomata to close, improved water utilization, and alleviated damage caused by drought. This study highlights a role of green light in plant physiological processes. Moreover, analyzing the function of green light on improving drought tolerance of plants could open alternative avenues for improving plant stress resilience.

Exogenous Applications of Spermidine Improve Drought Tolerance in Seedlings of the Ornamental Grass Hordeum jubatum in Northeast China

Hordeum jubatum L. is a potential ornamental grass species. Spermidine (Spd) plays a regulatory role in plant stress. This study measured seedling growth, photosynthesis, chlorophyll fluorescence, osmotic regulatory substance contents, and antioxidant enzyme activities in H. jubatum seedlings pretreated with Spd (0–1.5 mM at 0.5 mM intervals) in drought treatments simulating natural water loss. The results indicated that the water content, photosynthetic parameters maximal quantum yield of PSII photochemistry (Fv/Fm), actual quantum yield of photochemical energy conversion in PSII (ϕPSII), and photochemical quenching coefficient (qp) values of H. jubatum shoots decreased significantly with increasing drought intensity. Simultaneously, the contents of malondialdehyde (MDA) and the nonphotochemical quenching coefficient (NPQ) value increased. Spd improved growth and photosynthesis under drought stress. Spd also increased osmotic regulatory substance contents and antioxidant enzyme activities. These results suggest that the drought stress inhibited the growth of H. jubatum and damaged the photosynthetic systems, triggering a range of protective responses. Exogenous Spd mitigated the damage by promoting a variety of responses and adaptive mechanisms, such as adjusting stomatal conductance, promoting photosynthetic capacity, accelerating the synthesis of osmoregulatory molecules, and activating antioxidant enzyme systems. Additionally, 1.5 mM Spd-treated H. jubatum had the best drought tolerance. This study will help to develop an understanding of the effects of exogenous Spd on improving drought resistance and provide a strategy for the H. jubatum landscape effect to be achieved under water-limited conditions.

Overexpression of CgbHLH001, a Positive Regulator to Adversity, Enhances the Photosynthetic Capacity of Maize Seedlings under Drought Stress

Drought is a major environmental factor limiting crop productivity. Photosynthesis is very sensitive to drought. Basic helix-loop-helix (bHLH) transcription factors (TFs) are important in response to abiotic stress. However, their functions remain unclear. Herein, we generated CgbHLH001 (a TF gene from halophyte Chenopodium glaucum)-overexpressed (OE) and ZmbHLH-RNA interference (Ri) maize lines to investigate their photosynthesis-associated indexes under drought conditions. The photosynthetic capacity was increased in OE lines under drought stress compared with that in non-transgenic (NT) and Ri plants. A greater root biomass, higher root/shoot ratio, and a relatively lower leaf area reduction ratio was also observed in OE plants. Compared to NT and Ri plants, OE lines showed a higher chlorophyll content and net photosynthetic rate and better chlorophyll fluorescence parameters under drought conditions. Fructose and glucose contents were also significantly elevated in OE lines. Moreover, under stressful conditions, CgbHLH001 overexpression increased the expression of genes related to photosynthesis. Transcriptomic data showed that many differentially expressed genes were enriched in the photosynthetic system in OE and Ri plants under drought conditions and were prone to being upregulated under drought stress in OE plants. Therefore, our results suggest that CgbHLH001 improves photosynthetic efficiency under drought stress and confers drought tolerance in maize seedlings.

Brassinolide can improve drought tolerance of maize seedlings under drought stress: By inducing the photosynthetic performance, antioxidant capacity and ZmMYB gene expression of maize seedlings

Brassinolide can improve drought tolerance of maize seedlings under drought stress: By inducing the photosynthetic performance, antioxidant capacity and ZmMYB gene expression of maize seedlings

Overexpression of a Gene Encoding Trigonelline Synthase from Areca catechu L. Promotes Drought Resilience in Transgenic Arabidopsis.

Areca catechu L. is a commercially important palm tree widely cultured in tropical and subtropical areas. Its growth and production are severely hindered by the increasing threat of drought. In the present study, we investigated the physiological responses of areca seedlings to drought stress. The results showed that prolonged drought-induced yellowing on the overall area of most leaves significantly altered the chlorophyll fluorescence parameters, including maximum chemical efficiency (Fv/Fm), photochemical efficiency of PSII (Y(II)), photochemical chlorophyll fluorescence quenching (qP) and non-photochemical chlorophyll fluorescence quenching (NPQ). On the 10th day of drought treatment, the contents of proline in the areca leaves and roots increased, respectively, by 12.2 times and 8.4 times compared to normal watering. The trigonelline levels in the leaves rose from 695.35 µg/g to 1125.21 µg/g under 10 days of water shortage, while no significant changes were detected in the content of trigonelline in the roots. We determined the gene encoding areca trigonelline synthase (AcTS) by conducting a bioinformatic search of the areca genome database. Sequence analysis revealed that AcTS is highly homologous to the trigonelline synthases in Coffea arabica (CaTS 1 and CaTS 2) and all possess a conserved S-adenosyl- L-methionine binding motif. The overexpression of AcTS in Arabidopsis thaliana demonstrated that AcTS is responsible for the generation of trigonelline in transgenic Arabidopsis, which in turn improves the drought resilience of transgenic Arabidopsis. This finding enriches our understanding of the molecular regulatory mechanism of the response of areca to water shortage and provides a foundation for improving the drought tolerance of areca seedlings.

Identification of genes involved in drought tolerance in seedlings of the desert grass, Psammochloa villosa (Poaceae), based on full-length isoform sequencing and de novo assembly from short reads

Psammochloa villosa is a perennial herbaceous plant that is dominant within arid regions of the Inner Mongolian Plateau and the Qinghai-Tibet Plateau in China, where it is an endemic species and exhibits strong drought tolerance and wind resistance. To study drought tolerance in P. villosa and determine its molecular basis, we simulated high and moderate drought stress in a controlled environment and then analyzed transcriptome sequences by combining long-read sequences from a representative, wild-grown individual with short reads from the treatment groups. We obtained 184,076 high-quality isoforms as a reference and 168,650 genes (91.6%), which we were able to annotate according to public databases. Ultimately, we obtained 119,005 unigenes representing the transcriptome of P. villosa under drought stress and, among these, we identified 3089 differentially expressed genes and 1484 transcription factors. Physiologically, P. villosa that was exposed to high and moderate drought stress had reduced germination rates and shorter buds but generated more chlorophyll, which is atypical under drought stress and possibly reflects an adaptation of these plants to their arid environment. We inferred that significantly upregulated genes were annotated as ‘Chlorophyll a-b binding protein’ and ‘Light-harvesting chlorophyll-protein’ among drought and control groups. Broadly, our analyses revealed that drought stress triggered many genome-level responses, especially related to mitigation of radical oxygen species (ROS), which increase in concentration under drought stress. In particular, in the high drought stress group compared with the control, GO enrichment analysis revealed a significant enrichment of upregulated genes (n = 10) involved in mitigation of oxidative stress. Similarly, using KEGG we found significant enrichment of genes in the phenylpropanoid biosynthesis pathway (11 genes), which yields phenols that scavenge ROS. We also inferred that many genes involved in metabolism of arginine and proline, which may serve as both scavengers of ROS and osmoprotectants that interact with stress response genes based on our protein–protein interaction network analysis. We verified the relative expression levels of eight genes associated with mitigation of ROS, DNA repair, and transmembrane transporter activity using qRT-PCR, and the results were consistent with our inferences from transcriptomes. This study provides insights into the genomic and physiological basis of drought tolerance in P. villosa and represents a resource for development of the species as a forage crop via molecular breeding within arid lands.

24-Epibrassinolide and nitric oxide combined to improve the drought tolerance in kiwifruit seedlings by proline pathway and nitrogen metabolism

24-Epibrassinolide (EBR) and nitric oxide (NO) are redox signaling molecules that participate in plant stress response, but their combined role in drought stress response remains unclear. In this study, potted kiwifruit seedlings grown under drought stress were treated with sodium nitroprusside, a NO donor (SNP, 100 μM), 24-epibrassinolide (EBR, 0.01 mg·L−1), and their combination (S+E), as well as well-watered (CK) and drought treatments (DCK). Results revealed that plant biomass, leaf relative water content, photosynthetic pigment content, and photosynthetic capacity of leaves decreased, whereas MDA, H2O2, relative electrolyte leakage, endogenous NO, proline, and soluble sugar content increased in response to drought stress. The application of SNP and EBR alleviated the above adverse effects caused by drought stress and improved the enzyme activities of glutamine synthetase (GS), reduced the glutamate dehydrogenase (GDH) involved in nitrogen metabolism to maintain plant growth, and regulated the expression of aquaporin genes PIP1;1 and PIP2;2–1 to maintain normal water metabolism. The up-regulation of proline synthesis gene P5CR1 expression and the down-regulation of proline degradation gene ProDH expression caused proline accumulation under drought stress. Overall, the combination of SNP and EBR was more effective than independent SNP or EBR in mitigating drought stress in kiwifruit seedlings.