Molecular and genetic aspects of plant responses to osmotic stress

Transcriptome profiling of Gerbera hybrida reveals that stem bending is caused by water stress and regulation of abscisic acid

Background

Gerbera hybrida is one of the most popular cut flowers in the world; however, stem bending, which always happens when gerbera flower harvested from the field, greatly limits its vase life. To date the molecular mechanisms underlying stem bending remain poorly understood.

Results

In this study, we performed high-throughput transcriptome sequencing of gerbera during stem bending using the Illumina sequencing technology. Three cDNA libraries constructed from mRNAs of gerbera stem at stem bending stage 0, 2 and 4 were sequenced. More than 300 million high-quality reads were generated and assembled into 96,492 unigenes. Among them, 34,166 unigenes were functionally annotated based on similarity search with known protein. Sequences derived from plants at different stem bending stages were mapped to the assembled transcriptome, and 9,406 differentially expressed genes (DEGs) were identified. Through Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, specific pathways were identified during the stem bending process, such as phenylpropanoid biosynthesis pathway, phenylalanine metabolism pathway, starch and sucrose metabolism pathway, and plant hormone signal transduction pathway. A total of 211 transcription factors (TFs), including TF families involved in plant senescence, such as NAC, MYB, WRKY, and AP2/ERF members, as well as TFs related to water stress tolerance, were shown to be regulated during stem bending. Gene Onotology (GO) functional enrichment analysis indicated that key genes involved in responses to osmotic and oxidative stresses were also varied in expression during this process. Furthermore, analysis of DEGs involved in the hormone signaling pathways and determination of endogenous abscisic acid (ABA) content showed that stem bending may be an ethylene-independent process, but regulated by ABA. In short, our findings suggested that the stem bending of cut gerbera may be caused by the involvement of water stress and regulation of ABA during the postharvest life.

Conclusions

The transcriptome sequences provide a valuable resource in revealing the molecular mechanism underlying stem bending of cut flower and offer novel genes that can be used to guide future studies for ornamental plant breeding.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5961-1) contains supplementary material, which is available to authorized users.

Characterization and Expression Analysis of Heme Oxygenase Genes from Sorghum bicolor

Heme oxygenases (HOs) have a major role in phytochrome chromophore biosynthesis, and chromophores in turn have anti-oxidant properties. Plant heme oxygenases are divided into the HO1 sub-family comprising HO1, HO3, and HO4, and the HO2 sub-family, which consists of 1 member, HO2. This study identified and characterized 4 heme oxygenase members from Sorghum bicolor. Multiple sequence alignments showed that the heme oxygenase signature motif (QAFICHFYNI/V) is conserved across all SbHO proteins and that they share above 90% sequence identity with other cereals. Quantitative real-time polymerase chain reaction revealed that SbHO genes were expressed in leaves, stems, and roots, but most importantly their transcript level was induced by osmotic stress, indicating that they might play a role in stress responses. These findings will strengthen our understanding of the role of heme oxygenases in plant stress responses and may contribute to the development of stress tolerant crops.

SlNAC2 overexpression in Arabidopsis results in enhanced abiotic stress tolerance with alteration in glutathione metabolism

Plant NAC (NAM, ATAF, and CUC) transcription factors (TF) have important roles to play in abiotic stress responses through activation of a battery of functional genes/transcriptional regulators responsible for stress tolerance. Here we report the cloning of a novel Solanum lycopersicum L., NAC2 TF having 960 nucleotides long CDS (GenBank: KT740994.1). Phylogenetic analysis depicted the similarity of SlNAC2 to other orthologs. SlNAC2 was overexpressed in Arabidopsis thaliana to assess and characterize its role in plant abiotic stress responses. The transgenic events were first confirmed by genomic DNA PCR and qRT PCR; then the T3 generation plants were used for stress assays. Soil stress assay depicted better survivability of the transgenic plants under both salt (NaCl) and drought (PEG) stress. The transgenic plants showed enhanced endurance; with better antioxidative response, reduced accumulation of reactive oxygen species (ROS) molecules and better retention of water in tissue. This study for the very first time analyzed the different stakeholders of the glutathione metabolism in SlNAC2 overexpressing transgenic lines on exposure to both salinity and PEG stress. The expression of the two genes (ɤ-ECS, GS) responsible for glutathione biosynthesis increased with SlNAC2 overexpression. Further glutathione reductase responsible for reduction of glutathione disulfide (GSSG) to glutathione (GSH) also increased significantly which suggested the regulation of glutathione metabolism as a mechanism for the osmotic stress tolerance conferred to plants upon NAC overexpression.

Understanding the Impacts of Crude Oil and its Induced Abiotic Stresses on Agrifood Production: A Review

In many parts of the world, the agricultural sector is faced with a number of challenges including those arising from abiotic environmental stresses which are the key factors responsible for most reductions in agrifood production. Crude oil contamination, an abiotic stress factor and a common environmental contaminant, at toxic levels has negative impacts on plants. Although various attempts have been made to demonstrate the impact of abiotic stresses on crops, the underlying factors responsible for the effects of crude oil and its induced abiotic stresses on the composition of the stressed plants are poorly understood. Hence, this review provides an in-depth examination of the: (1) effect of petroleum hydrocarbons on plants; (2) impact of abiotic environmental stresses on crop quality; (3) mechanistic link between crude oil stress and its induced abiotic stresses; as well as (4) mode of action/plant response mechanism to these induced stresses. The paper clearly reveals the implications of crude oil-induced abiotic stresses arising from the soil-root-plant route and from direct application on plant leaves.

The up-regulation of proline synthesis in the meristematic tissues of wheat seedlings upon short-term exposure to osmotic stress

An increase in the cellular concentration of free proline is a common response of many plants to various types of environmental stress. In this study, we monitored the accumulation of proline and the activities of Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and Δ¹-pyrroline-5-carboxylate reductase (P5CR), the key enzymes of proline biosynthesis, in different parts of 4-day-old seedlings of wheat (Triticum aestivum L. cv. Josef) in the course of the first 8 h after the application of osmotic stress to determine the primary sites of proline production under water deficit conditions. Our results show that proline accumulated rapidly over this stress period in the root tips (cell division and elongation zone) and the basal region of the leaves in a time-dependent manner. Parallel to the rise in proline content, the activities of P5CS and P5CR increased markedly in these growing tissues under osmotic stress. Dissection of the root tip and the leaf base demonstrated that after 8 h of water shortage the accumulation of proline and the activities of P5CS and P5CR were highest in the regions where active cell division takes place. In the mature parts of the root and the leaf, there was virtually no enhancement of proline metabolism during the early phase of water deprivation investigated here. These data indicate that at the initial stage of water stress proline production is primarily required for the protection of the meristematic tissues in the roots and leaves. Furthermore, a transient rise in nitric oxide (NO) production was detected in the root tips and the leaf base in response to osmotic stress just before proline synthesis was enhanced. Treatment with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) reduced considerably the increase in the activities of P5CS and P5CR and suppressed the accumulation of proline by more than 85% in the stressed root tips and the leaf base. These results suggest that NO is involved as a signalling molecule in the up-regulation of proline synthesis in the growing tissues of young wheat seedlings in response to short-term water deprivation.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

The defense system for Bidens pilosa root exudate treatments in Pteris multifida gametophyte

According to the novel weapons hypothesis, root exudates are the inhibition factors for native species growth and development through invasive plants. It is hypothesized that antioxidant system (AOS) presents an effective role in plant defense system. The allelopathy indexes of P. multifida gametophyte biomass and sporogonium conversions rates turn negative with the dose and time effects, and the synthetical allelopathic effect index was -55.07% at 100% treatments under root exudates treatments. Under transmission electron microscopy, the cell structures turn burry. Next, AOS and programmed cell death (PCD) were tested in this study. In AOS, strong activities of superoxide dismutase, catalase, glutathione reductase and glutathione S-transferase (GST) were identified in gametophyte cells under the treatments, as well as the contents of glutathione, ascorbic acid and reduced ascorbate, while GPX activity decreased. Based on the input (SOD activity) and the output (GST activity) of antioxidant system, and the decreasing system control would be a reason leading gametophyte death under root exudates. At day 10, PCD would get its peak of 46.93% at 100% root exudates. We found a dynamic balance of PCD and AOS under the exudates treatments. We detected hexadecanoic acid, ethylene glycol and undecane are three major chemicals in root exudates. Our results provide a reference of AOS and PCD working under root exudates treatments in plants and offer novel strategy for the native species protection and invasion plants control in environment science.

Physiological mechanisms of exogenous calcium on alleviating salinity-induced stress in rice (Oryza sativa L.)

Being more sensitive to salt stress among the cereals, growth of rice (Oryza sativa L.) has been habitually affected by salinity. Although, several practices have evolved to sustain the growth of rice under salinity, the enormous role of calcium (Ca²⁺) as a signalling molecule in salt stress mitigation is still arcane. Considering this fact, an experiment was performed aiming to explicate the mechanism of salt-induced growth inhibition in rice and its alleviation by exogenous Ca²⁺. At germination stage, 10 mM and 15 mM CaCl₂ primed rice (cv. Binadhan-10 & Binadhan-7) seeds were grown in petri dishes for 9 days under 100 mM NaCl stress. At seedling stage, 9-day-old rice seedlings grown on sand were exposed to 100 mM NaCl alone and combined with 10 mM and 15 mM CaCl₂ for 15 days. This research revealed that salinity radically slowed down growth of rice seedlings and Ca²⁺ treatment noticeably improved growth performances. At germination stage, 10 mM CaCl₂ treatment significantly increased the final germination percentage, germination rate index (in Binadhan-7), shoot, root length (89.20, 67.58% in Bindhan-10 & 84.72, 31.15% in Bindhan-7) and biomass production under salinity. Similarly, at seedling stage, 10 mM CaCl₂ supplementation in salt-stressed plants enhanced shoot length (42.17, 28.76%) and shoot dry weight (339.52, 396.20%) significantly in Binadhan-10 & Binadhan-7, respectively, but enhanced root dry weight (36.76%) only in Binadhan-10. In addition, 10 mM CaCl₂ supplementation on salt-stressed seedlings increased the chlorophyll and proline content, and oppressed the accretion of reactive oxygen species thus protecting from oxidative damage more pronouncedly in Binadhan-10 than Binadhan-7 as reflected by the elevated levels of catalase and ascorbate peroxidase activity. The 15 mM CaCl₂ somehow also enhanced some growth parameters but overall was less effective than 10 mM CaCl₂ to alleviate salt stress, and sometimes showed negative effect. Therefore, supplementary application of calcium-rich fertilizers in saline prone soils can be an effective approach to acclimatize salt stress and cultivate rice successfully.

Detecting Salt Tolerance in Doubled Haploid Wheat Lines

Improving salt tolerance of genotypes requires a source of genetic variation and multiple accurate selection criteria for discriminating their salt tolerance. A combination of morpho-physiological and biochemical parameters and multivariate analysis was used to detect salt tolerance variation in 15 wheat lines developed by doubled haploid (DHL) technique. They were then compared with the salt-tolerant check cultivar Sakha 93. Salinity stress was investigated at three salinity levels (0, 100, and 200 mM NaCl) for 25 days. Considerable genetic variation was observed for all traits, as was high heritability (>60%) and genetic gain (>20%). Principal component analysis indicated the ability of nine traits (root number, root length, root dry weight, shoot length, shoot dry weight, specific root length, relative water content, membrane stability index, and catalase) to identify differences in salinity tolerance among lines. Three traits (shoot length, shoot dry weight, and catalase) were indicative of salt-tolerance, indicating their importance in improving and evaluating salt tolerant genotypes for breeding programs. The salinity tolerance membership index based on these three traits classified one new line (DHL21) and the check cultivar (Sakha 93) as highly salt-tolerant, DHL25, DHL26, DHL2, DHL11, and DHL5 as tolerant, and DHL23 and DHL12 as intermediate. Discriminant function analysis and MANOVA suggested differences among the five groups of tolerance. Among the donor genotypes, Sakha 93 remained the donor of choice for improving salinity tolerance during the seedling stage. The tolerated lines (DHL21, DHL25, DHL26, DHL2, DHL11, and DHL5) could be also recommended as useful and novel genetic resources for improving salinity tolerance of wheat in breeding programs.

Genome-scale identification, classification, and tissue specific expression analysis of late embryogenesis abundant (LEA) genes under abiotic stress conditions in Sorghum bicolor L

Late embryogenesis abundant (LEA) proteins, the space fillers or molecular shields, are the hydrophilic protective proteins which play an important role during plant development and abiotic stress. The systematic survey and characterization revealed a total of 68 LEA genes, belonging to 8 families in Sorghum bicolor. The LEA-2, a typical hydrophobic family is the most abundant family. All of them are evenly distributed on all 10 chromosomes and chromosomes 1, 2, and 3 appear to be the hot spots. Majority of the S. bicolor LEA (SbLEA) genes are intron less or have fewer introns. A total of 22 paralogous events were observed and majority of them appear to be segmental duplications. Segmental duplication played an important role in SbLEA-2 family expansion. A total of 12 orthologs were observed with Arabidopsis and 13 with Oryza sativa. Majority of them are basic in nature, and targeted by chloroplast subcellular localization. Fifteen miRNAs targeted to 25 SbLEAs appear to participate in development, as well as in abiotic stress tolerance. Promoter analysis revealed the presence of abiotic stress-responsive DRE, MYB, MYC, and GT1, biotic stress-responsive W-Box, hormone-responsive ABA, ERE, and TGA, and development-responsive SKn cis-elements. This reveals that LEA proteins play a vital role during stress tolerance and developmental processes. Using microarray data, 65 SbLEA genes were analyzed in different tissues (roots, pith, rind, internode, shoot, and leaf) which show clear tissue specific expression. qRT-PCR analysis of 23 SbLEA genes revealed their abundant expression in various tissues like roots, stems and leaves. Higher expression was noticed in stems compared to roots and leaves. Majority of the SbLEA family members were up-regulated at least in one tissue under different stress conditions. The SbLEA3-2 is the regulator, which showed abundant expression under diverse stress conditions. Present study provides new insights into the formation of LEAs in S. bicolor and to understand their role in developmental processes under stress conditions, which may be a valuable source for future research.

Response of Mediterranean Ornamental Plants to Drought Stress

Ornamental plants use unique adaptive mechanisms to overcome the negative effects of drought stress. A large number of species grown in the Mediterranean area offer the opportunity to select some for ornamental purposes with the ability to adapt to drought conditions. The plants tolerant to drought stress show different adaptation mechanisms to overcome drought stress, including morphological, physiological, and biochemical modifications. These responses include increasing root/shoot ratio, growth reduction, leaf anatomy change, and reduction of leaf size and total leaf area to limit water loss and guarantee photosynthesis. In this review, the effect of drought stress on photosynthesis and chlorophyll a fluorescence is discussed. Recent information on the mechanisms of signal transduction and the development of drought tolerance in ornamental plants is provided. Finally, drought-induced oxidative stress is analyzed and discussed. The purpose of this review is to deepen our knowledge of how drought may modify the morphological and physiological characteristics of plants and reduce their aesthetic value—that is, the key parameter of assessment of ornamental plants.

Enriched networks 'nucleoside/nucleotide and ribonucleoside/ribonucleotide metabolic processes' and 'response to stimulus' potentially conferred to drought adaptation of the epiphytic orchid Dendrobium wangliangii

Dendrobium wangliangii is an endangered and epiphytic orchid with tolerance to seasonally extreme arid conditions and occurs exclusively in the hot-dry valley area of southwestern China. To reveal its molecular basis responsible for ecological adaptation, large-scale transcriptome sequencing was performed using Illumina sequencing with pooled mRNA extracted from whole plants and pseudobulbs during drought and rainy seasons. Based on the target transcript selection, the differentially expressed genes were related to 8 well-known drought-tolerant categories, and to morphological traits in resistance to water stress including pseudobulbs and roots. Further gene ontology enrichment analysis revealed that 'nucleoside/nucleotide and ribonucleoside/ribonucleotide metabolic processes' and 'response to stimulus' were the two most important aspects in resistance to drought stress with respect to the whole plant. In addition, the difference in the number and category of differentially expressed genes in whole plant and stem suggested the involvement of genes specifically localized in the stem, such as GTP-binding protein, lipases, signaling related transcripts and those involved in the ATP metabolic process. The comprehensive analysis of the epiphytic orchid in response to water deprivation indicates that integral tactics lead to active adaptation as a basal defense response to drought stress by the endangered epiphyte, including the collaboration of metabolic processes, responses to a various stimulus and other candidate genes contribute to its extreme drought tolerance. Insights from this study can be further utilized to understand stress-responsive genes in other medicinally important species and to improve the drought tolerance of food crops.

Exogenous Melatonin Alleviates Oxidative Damages and Protects Photosystem II in Maize Seedlings Under Drought Stress

The protective role of melatonin in plants against various abiotic stresses have been widely demonstrated, but poorly explored in organ-specific responses and the transmission of melatonin signals across organs. In this study, the effects of melatonin with the root-irrigation method and the leaf-spraying method on the antioxidant system and photosynthetic machinery in maize seedlings under drought stress were investigated. The results showed that drought stress led to the rise in reactive oxygen species (ROS), severe cell death, and degradation of D1 protein, which were mitigated by the melatonin application. The application of melatonin improved the photosynthetic activities and alleviated the oxidative damages of maize seedlings under the drought stress. Compared with the leaf-spraying method, the root-irrigation method was more effective on enhancing drought tolerance. Moreover, maize seedlings made organ-specific physiological responses to the drought stress, and the physiological effects of melatonin varied with the dosage, application methods and plant organs. The signals of exogenous melatonin received by roots could affect the stress responses of leaves, and the melatonin signals perceived by leaves also led to changes in physiological metabolisms in roots under the stress. Consequently, the whole seedlings coordinated the different parts and made a systemic acclimation against the drought stress. Melatonin as a protective agent against abiotic stresses has a potential application prospect in the agricultural industry.

ANAC019 is required for recovery of reproductive development under drought stress in Arabidopsis

Morphological and transcriptomic evidences provide us strong support for the function of ANAC019 in reproductive development under drought stress. Plants are sensitive to drought conditions, particularly at the reproductive stage. Several studies have reported drought effects on crop reproductive development, but the molecular mechanism underlying drought response during reproduction is still unclear. A recent study showed that drought induces in Arabidopsis inflorescence increased expression of many genes, including ANAC019. However, the function of ANAC019 in drought response during reproductive development has not been characterized. Here, we report an investigation of the ANAC019 function in the response to drought during reproduction. ANAC019 is preferentially expressed in the inflorescence compared with the leaf, suggesting possible roles in regulating both stress response and flower development. The anac019 mutant was more sensitive to drought than WT plant, and exhibited a delay in recovery of floral organ development under prolonged drought stress. Moreover, many fewer genes were differentially expressed in the anac019 inflorescence under drought than that of WT, suggesting that the mutant was impaired in drought-induced gene expression. The genes affected by ANAC019 were associated with stress and hormone responses as well as floral development. In particular, the expression levels of several key drought-induced genes, DREB2A, DREB2B, ARF2, MYB21 and MYB24, were dramatically reduced in the absence of ANAC019, suggesting that ANAC019 is an upstream regulator these genes for drought response and flower development. These results provide strong support for the potential function of ANAC019 in reproductive development under drought stress.

Coping with drought: stress and adaptive mechanisms, and management through cultural and molecular alternatives in cotton as vital constituents for plant stress resilience and fitness

Increased levels of greenhouse gases in the atmosphere and associated climatic variability is primarily responsible for inducing heat waves, flooding and drought stress. Among these, water scarcity is a major limitation to crop productivity. Water stress can severely reduce crop yield and both the severity and duration of the stress are critical. Water availability is a key driver for sustainable cotton production and its limitations can adversely affect physiological and biochemical processes of plants, leading towards lint yield reduction. Adaptation of crop husbandry techniques suitable for cotton crop requires a sound understanding of environmental factors, influencing cotton lint yield and fiber quality. Various defense mechanisms e.g. maintenance of membrane stability, carbon fixation rate, hormone regulation, generation of antioxidants and induction of stress proteins have been found play a vital role in plant survival under moisture stress. Plant molecular breeding plays a functional role to ascertain superior genes for important traits and can offer breeder ready markers for developing ideotypes. This review highlights drought-induced damage to cotton plants at structural, physiological and molecular levels. It also discusses the opportunities for increasing drought tolerance in cotton either through modern gene editing technology like clustered regularly interspaced short palindromic repeat (CRISPR/Cas9), zinc finger nuclease, molecular breeding as well as through crop management, such as use of appropriate fertilization, growth regulator application and soil amendments.

Response of Salt-Stressed Common Bean Plant Performances to Foliar Application of Phosphorus (MAP)

The study objective is to evaluate the effect of mono-ammonuim phosphate (MAP; 0, 10, and 20 mM) applied as foliar application on the growth traits, green and dry yields characteristics, leaf photosynthetic pigments, chlorophyll fluorescence, and leaf contents of nutrients of common bean (Phaseolus vulgaris L., cv. “Bronco”) plants grown under saline soil conditions. To perform this objective, two field trials were conducted at the Experimental Farm of Faculty of Agriculture, Fayoum University during the 2016 and 2017 summer seasons. The obtained results showed that, Na+ content was significantly declined, while the all other tested parameters such as growth characteristics (i.e., shoot length, number of leaves per plant, area of leaves per plant, and shoot fresh and dry weights), yield characteristics of green pods and dry seeds (i.e., average pod weight, number of pods per plant, pods weight per plant, dry seed weight per plant and 100-seed weight), leaf photosynthetic pigments (i.e., total chlorophylls, total carotenoids) contents and leaf chlorophyll fluorescence (i.e., Fv/Fm and PI), leaf contents of N, P, K+, and Ca2+, and the ratios of K+/Na+, Ca2+/Na+ and K++Ca2+/Na+ were significantly increased by the two levels (i.e., 10 and 20 mM) of MAP compared to the controls (without MAP). The two MAP levels conferred the same results for most of the all tested parameters; particularly growth and yields characteristics, with some exceptions. Therefore, results of this study recommend using 10 mM MAP as foliar application to optimize the common bean performances in saline soils. Keywords: Common beans, Salinity, Phosphorus, Plant performance, Antioxidant defense systems, Photosynthesis, Water relations.

Functional Identification of Salt-Stress-Related Genes Using the FOX Hunting System from Ipomoea pes-caprae

Ipomoea pes-caprae is a seashore halophytic plant and is therefore a good model for studying the molecular mechanisms underlying salt and stress tolerance in plant research. Here, we performed Full-length cDNA Over-eXpressor (FOX) gene hunting with a functional screening of a cDNA library using a salt-sensitive yeast mutant strain to isolate the salt-stress-related genes of I. pes-caprae (IpSR genes). The library was screened for genes that complemented the salt defect of yeast mutant AXT3 and could grow in the presence of 75 mM NaCl. We obtained 38 candidate salt-stress-related full-length cDNA clones from the I. pes-caprae cDNA library. The genes are predicted to encode proteins involved in water deficit, reactive oxygen species (ROS) scavenging, cellular vesicle trafficking, metabolic enzymes, and signal transduction factors. When combined with the quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analyses, several potential functional salt-tolerance-related genes were emphasized. This approach provides a rapid assay system for the large-scale screening of I. pes-caprae genes involved in the salt stress response and supports the identification of genes responsible for the molecular mechanisms of salt tolerance.

Glycinebetaine Biosynthesis in Response to Osmotic Stress Depends on Jasmonate Signaling in Watermelon Suspension Cells

Glycinebetaine is an important non-toxic osmoprotectant, which is accumulated in higher plants under various stresses. The biosynthesis of glycinebetaine achieved via is a two-step oxidation from choline and betaine aldehyde, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Up-regulated gene expression of BADH and CMO induced by stress is clearly observed, but the signal transduction is poorly understood. Here, glycinebetaine accumulation in response to osmotic stress and growth recovery induced by exogenous glycinebetaine were observed in a watermelon cell line. When tracing back to the genome sequence of watermelon, it shows that there exists only one member of ClCMO or ClBADH corresponding to glycinebetaine biosynthesis. Both genes harbor a CGTCA-motif in their promoter region which is involved in methyl jasmonate (MeJA)-responsiveness. Amongst MeJA, Ethephon, abscisic acid (ABA), and salicylic acid (SA), MeJA was most effective in gene inducing the expression of ClCMO and ClBADH, and the accumulation of glycinebetaine could also reach an amount comparable to that after osmotic stress by mannitol. Moreover, when ibuprofen (IBU), a JA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, glycinebetaine accumulation was suppressed significantly. Interestingly, newly grown cells can keep a high content of glycinebetaine when they are sub-cultured from osmotic stressed cells. This study suggests that osmotic stress induced glycinebetaine biosynthesis occurs via JA signal transduction and not only plays a key role in osmotic stress resistance but also contributes to osmotic stress hardening.

Expression analysis of lncRNA AK370814 involved in the barley vitamin B6 salvage pathway under salinity

Long non-coding RNAs (lncRNAs), which are longer than > 200 nt, perform various functions in a variety of important biological processes. The aim of this study is the investigation of relative expression levels of AK372815 putative pyridoxal reductase (PLR) gene and sense lncRNA AK370814 on four barley genotypes (Hasat, Beysehir 99, Konevi 98 and Tarm 92) in response to 150 mM salinity application during 3 days post-germination. Seeds were placed randomly in petri dishes containing (a) only H₂O (control), (b) 150 mM NaCl, for 72 h. RNA isolation was carried out using TriPure® reagent from 150 mM salt-treated root and shoot samples. Relative expression levels of AK372815 PLR and sense lncRNA AK370814 were determined by qPCR. Results demonstrated that salinity affected the expression levels of both AK372815 PLR gene and sense lncRNA AK370814 during germination. Although expression levels of AK372815 PLR tended to be down-regulated under salinity, expression levels of sense lncRNA AK370814 were up-regulated. Another goal of this study is improvement of alternative approach to NGS technologies for determination of relative expression levels of sense lncRNAs under particular circumstances. This is the first report that demonstrates a relationship between lncRNA and vitamin B6 salvage pathway.

Transcriptome Analyses in Different Cucumber Cultivars Provide Novel Insights into Drought Stress Responses

Drought stress is one of the most serious threats to cucumber quality and yield. To gain a good understanding of the molecular mechanism upon water deficiency, we compared and analyzed the RNA sequencing-based transcriptomic responses of two contrasting cucumber genotypes, L-9 (drought-tolerant) and A-16 (drought-sensitive). In our present study, combining the analysis of phenotype, twelve samples of cucumber were carried out a transcriptomic profile by RNA-Seq under normal and water-deficiency conditions, respectively. A total of 1008 transcripts were differentially expressed under normal conditions (466 up-regulated and 542 down-regulated) and 2265 transcripts under drought stress (979 up-regulated and 1286 down-regulated). The significant positive correlation between RNA sequencing data and a qRT-PCR analysis supported the results found. Differentially expressed genes (DEGs) involved in metabolic pathway and biosynthesis of secondary metabolism were significantly changed after drought stress. Several genes, which were related to sucrose biosynthesis (Csa3G784370 and Csa3G149890) and abscisic acid (ABA) signal transduction (Csa4M361820 and Csa6M382950), were specifically induced after 4 days of drought stress. DEGs between the two contrasting cultivars identified in our study provide a novel insight into isolating helpful candidate genes for drought tolerance in cucumber.

Elucidating the role of osmotic, ionic and major salt responsive transcript components towards salinity tolerance in contrasting chickpea (Cicer arietinum L.) genotypes

The growth of chickpea (Cicer arietinum L.) is extremely hampered by salt stress. Understanding of physio-biochemical and molecular attributes along with morphological traits contributing to the salinity tolerance is important for developing salt tolerant chickpea varieties. To explore these facts, two genotypes CSG8962 and HC5 with contrasting salt tolerance were evaluated in the salinity stress (Control and 120 mM NaCl) conditions. CSG8962 maintained lower Na/K ratio in root and shoot, trammeled Na translocation to the shoots from roots compared to HC5 which ascribed to better exclusion of salt from its roots and compartmentation in the shoot. In chickpea, salt stress specifically induced genes/sequences involved at several levels in the salt stress signaling pathway. Higher induction of trehalose 6 phosphate synthase and protein kinase genes pertaining to the osmotic and signaling modules, respectively, were evident in CSG8962 compared to HC5. Further transcripts of late embryogenesis abundant, non-specific lipid transfer protein, HI and 219 genes/sequences were also highly induced in CSG8962 compared to HC5 which emphasizes the better protection of cellular membranous network and membrane-bound macromolecules under salt stress. This further suppressed the stress enhanced electrolyte leakage, loss of turgidity, promoted the higher compatible solute accumulation and maintained better cellular ion homoeostasis in CSG8962 compared to HC5. Our study further adds to the importance of these genes in salt tolerance by comparing their behavior in contrasting chickpea genotypes.

An Overview of the Genetics of Plant Response to Salt Stress: Present Status and the Way Forward

Salinity is one of the major threats faced by the modern agriculture today. It causes multidimensional effects on plants. These effects depend upon the plant growth stage, intensity, and duration of the stress. All these lead to stunted growth and reduced yield, ultimately inducing economic loss to the farming community in particular and to the country in general. The soil conditions of agricultural land are deteriorating at an alarming rate. Plants assess the stress conditions, transmit the specific stress signals, and then initiate the response against that stress. A more complete understanding of plant response mechanisms and their practical incorporation in crop improvement is an essential step towards achieving the goal of sustainable agricultural development. Literature survey shows that investigations of plant stresses response mechanism are the focus area of research for plant scientists. Although these efforts lead to reveal different plant response mechanisms against salt stress, yet many questions still need to be answered to get a clear picture of plant strategy to cope with salt stress. Moreover, these studies have indicated the presence of a complicated network of different integrated pathways. In order to work in a progressive way, a review of current knowledge is critical. Therefore, this review aims to provide an overview of our understanding of plant response to salt stress and to indicate some important yet unexplored dynamics to improve our knowledge that could ultimately lead towards crop improvement.

Trithorax-group proteins ARABIDOPSIS TRITHORAX4 (ATX4) and ATX5 function in abscisic acid and dehydration stress responses

Trithorax-group proteins (TrxGs) play essential regulatory roles in chromatin modification to activate transcription. Although TrxGs have been shown to be extensively involved in the activation of developmental genes, how the specific TrxGs function in the dehydration and abscisic acid (ABA)-mediated modulation of downstream gene expression remains unknown. Here, we report that two evolutionarily conserved Arabidopsis thaliana TrxGs, ARABIDOPSIS TRITHORAX4 (ATX4) and ATX5, play essential roles in the drought stress response. atx4 and atx5 single loss-of-function mutants showed drought stress-tolerant and ABA-hypersensitive phenotypes during seed germination and seedling development, while the atx4 atx5 double mutant displayed further exacerbation of the phenotypes. Genome-wide RNA-sequencing analyses showed that ATX4 and ATX5 regulate the expression of genes functioning in dehydration stress. Intriguingly, ABA-HYPERSENSITIVE GERMINATION 3 (AHG3), an essential negative regulator of ABA signaling, acts genetically downstream of ATX4 and ATX5 in response to ABA. ATX4 and ATX5 directly bind to the AHG3 locus and trimethylate histone H3 of Lys 4 (H3K4). Moreover, ATX4 and ATX5 occupancies at AHG3 are dramatically increased under ABA treatment, and are also essential for RNA polymerase II (RNAPII) occupancies. Our findings reveal novel molecular functions of A. thaliana TrxGs in dehydration stress and ABA responses.

Overexpression of SDH confers tolerance to salt and osmotic stress, but decreases ABA sensitivity in Arabidopsis

Sorbitol dehydrogenase (SDH) catalyses the reversible oxidation of sorbitol, xylitol and ribitol to their corresponding ketoses. In this study, we investigated the expression and role of Arabidopsis SDH in salt and osmotic stress tolerance, and abscisic acid (ABA) response. The expression patterns of SDH were investigated using transgenic Arabidopsis plants expressing beta-glucuronidase (GUS) under control of the promoter with the first intron of SDH. qRT-PCR and histochemical assay of GUS activity were used to study SDH expression regulation by ABA, salt and osmotic stress. SDH-overexpression lines of Arabidopsis were used to investigate the role of SDH in salt and osmotic stress, and ABA response. Arabidopsis SDH was predominantly expressed in source organs such as green cotyledons, fully expanded leaves and sepals, especially in vascular tissues of theses organs. SDH expression was inhibited by NaCl and mannitol treatments. Seed germination and post-germination growth of SDH-overexpressing lines exhibited decreased sensitivity to salt and osmotic stress compared to WT plants. The transcript of SDH was induced by ABA. Overexpression of SDH decreased sensitivity to ABA during seed germination and post-germination growth. Expression of AAO3 increased but ABI5 and MYB2 decreased in SDH-overexpressing lines after ABA treatment. This study demonstrates that expression of SDH is regulated by ABA, salt and osmotic stress. SDH functions in plant tolerance to salt and osmotic stress, and ABA response via specific regulating gene expression of ABA synthesis and signalling in Arabidopsis.

Differential expression of leaf proteins in four cultivars of peanut (Arachis hypogaea L.) under water stress

Drought is a major constraint to the productivity of many crops affecting various physiological and biochemical processes. Seventy percent of the peanuts are grown in semiarid tropics that are frequently prone to drought stress. So, we analyzed its effect in 4 cultivars of peanut, with different degrees of drought tolerance, under 10 and 20 days of water stress using two-dimensional gel electrophoresis and mass spectrometry. A total of 189 differentially expressed protein spots were identified in the leaf proteome of all the 4 cultivars using PD Quest Basic software; 74 in ICGV 91114, 41 in ICGS 76, 44 in J 11 and 30 in JL 24. Of these, 30 protein spots were subjected to in-gel trypsin digestion followed by MALDI-TOF that are functionally categorized into 5 groups: molecular chaperones, signal transducers, photosynthetic proteins, defense proteins and detoxification proteins. Of these, 12 proteins were sequenced. Late embryogenesis abundant protein, calcium ion binding protein, sucrose synthase isoform-1, 17.3 kDa heat shock protein and structural maintenance of chromosome proteins were overexpressed only in the 15 and 20 days stressed plants of ICGV 91114 cultivar while cytosolic ascorbate peroxidase was expressed with varying levels in the 10 and 20 days stressed plants of all the 4 cultivars. Signaling protein like 14-3-3 and defense proteins like alpha-methyl-mannoside-specific lectin and mannose/glucose-binding lectins were differentially expressed in the 4 cultivars. Photosynthetic protein like Rubisco was down-regulated in the stressed plants of all 4 cultivars while Photosystem-I reaction center subunit-II of chloroplast precursor protein was overexpressed in only 20 days stressed plants of ICGV 91114, ICGS 76 and J11 cultivars. These differentially expressed proteins could potentially be used as protein markers for screening the peanut germplasm and further crop improvement.

Integrative Potassium Humate and Biochar Application Reduces Salinity Effects and Contaminants, And Improves Growth and Yield of Eggplant Grown Under Saline Conditions

In agriculture sector, soil salinity is one of the major problems that limit plant performance, particularly in arid and semiarid regions, including Egypt. The effect of potassium humate (KH) and casuarina biochar (Bch), applied singly or in integration, on plant performance, physio-biochemical attributes and antioxidant, and contents of contaminants of Solanum melongena plants grown under salt stress (EC = 6.96 – 7.08 dS m?1 ) was investigated. Results showed that, soil treatment with KH significantly improved plant growth and productivity, physio-biochemical attributes, and contents of K+ , osmoprotectants and antioxidants (soluble sugars, proline and ascorbic acid), and significantly lowered plant contents of contaminants (NO3 ? , NO2 ? and Cd2+) and Na+ ion compared to the untreated controls. The same results trend was obtained with soil treatment with Bch. Integrative application of KH + Bch was most effective compared to the single KH or Bch treatment. The above results recommended benefits of the integrative treatment KH+TOC to soil for the possibility of sustainable agronomic performance of eggplant grown on saline soils.

Plant growth promoting bacteria as an alternative strategy for salt tolerance in plants: A review

Approximately 5.2 billion hectare agriculture land are affected by erosion, salinity and soil degradation. Salinity stress has significantly affecting the fertile lands, and therefore possesses a huge impact on the agriculture and economy of a country. Salt stress has severe effects on the growth and development of plants as well as reducing its yield. Plants are inherently equipped with stress tolerance ability to responds the specific type of stress. Plants retained specific mechanisms for salt stress mitigation, such as hormonal stimulation, ion exchange, antioxidant enzymes and activation of signaling cascades on their metabolic and genetic frontiers that sooth the stressed condition. Additional to the plant inherent mechanisms, certain plant growth promoting bacteria (PGPB) also have specialized mechanism that play key role for salt stress tolerance and plant growth promotion. These bacteria triggers plants to produce different plant growth hormones like auxin, cytokinine and gibberellin as well as volatile organic compounds. These bacteria also produces growth regulators like siderophore, which fix nitrogen, solubilize organic and inorganic phosphate. Considering the importance of PGPB in compensation of salt tolerance in plants, the present study has reviewed the different aspect and mechanism of bacteria that play key role in promoting plants growth and yield. It can be concluded that PGPB can be used as a cost effective and economical tool for salinity tolerance and growth promotion in plants.

An osmotin from the resurrection plant Tripogon loliiformis (TlOsm) confers tolerance to multiple abiotic stresses in transgenic rice

Osmotin is a key protein associated with abiotic and biotic stress response in plants. In this study, an osmotin from the resurrection plant Tripogon loliiformis (TlOsm) was characterized and functionally analyzed under abiotic stress conditions in T. loliiformis as well as in transgenic Nicotiana tabacum (tobacco) and Oryza sativa (rice) plants. Real-time PCR analysis on mixed elicitor cDNA libraries from T. loliiformis showed that TlOsm was upregulated a 1000-fold during the early stages of osmotic stresses (cold, drought, and salinity) in both shoots and roots but downregulated in shoots during heat stress. There was no change in TlOsm gene expression in roots of heat-stressed plants and during plant development. The plasma membrane localization of TlOsm was showed in fluorescent-tagged TlOsm tobacco plants using confocal laser scanning microscopic analysis. Transgenic rice plants expressing TlOsm were assessed for enhanced tolerance to salinity, drought and cold stresses. Constitutively expressed TlOsm in transgenic rice plants showed increased tolerance to cold, drought and salinity stress when compared with the wild-type and vector control counterparts. This was evidenced by maintained growth, retained higher water content and membrane integrity, and improved survival rate of TlOsm-expressing plants. The results thus indicate the involvement of TlOsm in plant response to multiple abiotic stresses, possibly through the signaling pathway, and highlight its potential applications for engineering crops with improved tolerance to cold, drought and salinity stress.

TaSnRK2.9, a Sucrose Non-fermenting 1-Related Protein Kinase Gene, Positively Regulates Plant Response to Drought and Salt Stress in Transgenic Tobacco

Sucrose non-fermenting 1-related protein kinase 2 (SnRK2) family members play crucial roles in plant abiotic stress response. However, the precise mechanism underlying the function of SnRKs has not been thoroughly elucidated in plants. In this research, a novel SnRK2 gene, TaSnRK2.9 was cloned and characterized from common wheat. The expression of TaSnRK2.9 was upregulated by polyethylene glycol (PEG), NaCl, H₂O₂, abscisic acid (ABA), methyl jasmonate (MeJA), and ethrel treatments. TaSnRK2.9 was mainly expressed in wheat young root, stamen, pistil, and lemma. Overexpressing TaSnRK2.9 in transgenic tobacco enhanced plants' tolerance to drought and salt stresses both in young seedlings and mature plants with improved survival rate, seed germination rate, and root length. Physiological analyses suggest that TaSnRK2.9 improved antioxidant system such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione (GSH) to reduce the H₂O₂ content under drought or salt stress. Additionally, TaSnRK2.9 overexpression plants had elevated ABA content, implying that the function of TaSnRK2.9 may be ABA-dependent. Moreover, TaSnRK2.9 increased the expression of some ROS-related, ABA-related, and stress-response genes under osmotic or salt treatment. TaSnRK2.9 could interact with NtABF2 in yeast two-hybrid assay, and increased the expression of NtABF2 under mannitol or NaCl treatment in transgenic tobacco plants. In conclusion, overexpression of TaSnRK2.9 in tobacco conferred plants tolerance to drought and salt stresses through enhanced ROS scavenging ability, ABA-dependent signal transduction, and specific SnRK-ABF interaction.

Physiological and Biochemical Responses of Lavandula angustifolia to Salinity Under Mineral Foliar Application

Saline water has been proposed as a solution to partially cover plant water demands due to scarcity of irrigation water in hot arid areas. Lavender (Lavandula angustifolia Mill.) plants were grown hydroponically under salinity (0-25-50-100 mM NaCl). The overcome of salinity stress was examined by K, Zn, and Si foliar application for the plant physiological and biochemical characteristics. The present study indicated that high (100 mM NaCl) salinity decreased plant growth, content of phenolics and antioxidant status and essential oil (EO) yield, while low-moderate salinity levels maintained the volatile oil profile in lavender. The integrated foliar application of K and Zn lighten the presumable detrimental effects of salinity in terms of fresh biomass, antioxidant capacity, and EO yield. Moderate salinity stress along with balanced concentration of K though foliar application changed the primary metabolites pathways in favor of major volatile oil constituents biosynthesis and therefore lavender plant has the potential for cultivation under prevalent semi-saline conditions. Zn and Si application, had lesser effects on the content of EO constituents, even though altered salinity induced changings. Our results have demonstrated that lavender growth/development and EO production may be affected by saline levels, whereas mechanisms for alteration of induced stress are of great significance considering the importance of the oil composition, as well.

Response of soil physicochemical properties and enzyme activities to long-term reclamation of coastal saline soil, Eastern China

Soil enzyme activity during different years of reclamation and land use patterns could indicate changes in soil quality. The objective of this research is to explore the dynamics of 5 soil enzyme activities (dehydrogenase, amylase, urease, acid phosphatase and alkaline phosphatase) involved in C, N, and P cycling and their responses to changes in soil physicochemical properties resulting from long-term reclamation of coastal saline soil. Soil samples from a total of 55 sites were collected from a coastal reclamation area with different years of reclamation (0, 7, 32, 40, 63a) in this study. The results showed that both long-term reclamation and land use patterns have significant effects on soil physicochemical properties and enzyme activities. Compared with the bare flat, soil water content, soil bulk density, pH and electrical conductivity showed a decreasing trend after reclamation, whereas soil organic carbon, total nitrogen and total phosphorus tended to increase. Dehydrogenase, amylase and acid phosphatase activities initially increased and then decreased with increasing years of reclamation, whereas urease and alkaline phosphatase activities were characterized by an increase-decrease-increase trend. Moreover, urease, acid phosphatase and alkaline phosphatase activities exhibited significant differences between coastal saline soil with 63years of reclamation and bare flat, whereas dehydrogenase and amylase activities remained unchanged. Aquaculture ponds showed higher soil water content, pH and EC but lower soil organic carbon, total nitrogen and total phosphorus than rapeseed, broad bean and wheat fields. Rapeseed, broad bean and wheat fields displayed higher urease and alkaline phosphatase activities and lower dehydrogenase, amylase and acid phosphatase activities compared with aquaculture ponds. Redundancy analysis revealed that the soil physicochemical properties explained 74.5% of the variation in soil enzyme activities and that an obvious relationship existed between soil nutrients and soil enzyme activities. These results will assist governmental evaluation of the quality of reclaimed coastal soil.

The maize WRKY transcription factor ZmWRKY17 negatively regulates salt stress tolerance in transgenic Arabidopsis plants

We cloned and characterized the ZmWRKY17 gene from maize. Overexpression of ZmWRKY17 in Arabidopsis led to increased sensitivity to salt stress and decreased ABA sensitivity through regulating the expression of some ABA- and stress-responsive genes. The WRKY transcription factors have been reported to function as positive or negative regulators in many different biological processes including plant development, defense regulation and stress response. This study isolated a maize WRKY gene, ZmWRKY17, and characterized its role in tolerance to salt stress by generating transgenic Arabidopsis plants. Expression of the ZmWRKY17 was up-regulated by drought, salt and abscisic acid (ABA) treatments. ZmWRKY17 was localized in the nucleus with no transcriptional activation in yeast. Yeast one-hybrid assay showed that ZmWRKY17 can specifically bind to W-box, and it can activate W-box-dependent transcription in planta. Heterologous overexpression of ZmWRKY17 in Arabidopsis remarkably reduced plant tolerance to salt stress, as determined through physiological analyses of the cotyledons greening rate, root growth, relative electrical leakage and malondialdehyde content. Additionally, ZmWRKY17 transgenic plants showed decreased sensitivity to ABA during seed germination and early seedling growth. Transgenic plants accumulated higher content of ABA than wild-type (WT) plants under NaCl condition. Transcriptome and quantitative real-time PCR analyses revealed that some stress-related genes in transgenic seedlings showed lower expression level than that in the WT when treated with NaCl. Taken together, these results suggest that ZmWRKY17 may act as a negative regulator involved in the salt stress responses through ABA signalling.

OsHAK1, a High-Affinity Potassium Transporter, Positively Regulates Responses to Drought Stress in Rice

Drought is one of the environmental factors that severely restrict plant distribution and crop production. Recently, we reported that the high-affinity potassium transporter OsHAK1 plays important roles in K acquisition and translocation in rice over low and high K concentration ranges, however, knowledge on the regulatory roles of OsHAK1 in osmotic/drought stress is limited. Here, transcript levels of OsHAK1 were found transiently elevated by water deficit in roots and shoots, consistent with the enhanced GUS activity in transgenic plants under stress. Under drought conditions, OsHAK1 knockout mutants (KO) presented lower tolerance to the stress and displayed stunted growth at both the vegetative and reproductive stages. Phenotypic analysis of OsHAK1 overexpression seedlings (Ox) demonstrated that they present better tolerance to drought stress than wild-type (WT). Compared to WT seedlings, OsHAK1 overexpressors had lower level of lipid peroxidation, higher activities of antioxidant enzymes (POX and CAT) and higher proline accumulation. Furthermore, qPCR analysis revealed that OsHAK1 act as a positive regulator of the expression of stress-responsive genes as well as of two well-known rice channel genes (OsTPKb and OsAKT1) involved in K homeostasis and stress responses in transgenic plants under dehydration. Most important, OsHAK1-Ox plants displayed enhanced drought tolerance at the reproductive stage, resulting in 35% more grain yield than WT under drought conditions, and without exhibiting significant differences under normal growth conditions. Consequently, OsHAK1 can be considered to be used in molecular breeding for improvement of drought tolerance in rice.

Transcriptome profiling of fully open flowers in a frost-tolerant almond genotype in response to freezing stress

Spring frost is a major limiting abiotic stress for the cultivation of almonds [Prunus dulcis (Mill.)] in Mediterranean areas or the Middle East. Spring frost, in particular, damages almond fully open flowers, resulting to significant reduction in yield. Little is known about the genetic factors expressed after frost stress in Prunus spp. as well as in almond fully open flowers. Here, we provide the molecular signature of pistils of fully open flowers from a frost-tolerant almond genotype. The level of frost tolerance in this genotype was determined for all three flowering stages and was confirmed by comparing it to two other cultivars using several physiological analyses. Afterwards, comprehensive expression profiling of genes expressed in fully open flowers was performed after being exposed to frost temperatures (during post-thaw period). Clean reads, 27,104,070 and 32,730,772, were obtained for non-frost-treated and frost-treated (FT) libraries, respectively. A total of 62.24 Mb was assembled, generating 50,896 unigenes and 66,906 transcripts. Therefore, 863 upregulated genes and 555 downregulated genes were identified in the FT library. Functional annotation showed that most of the upregulated genes were related to various biological processes involved in responding to abiotic stress. For the first time, a highly expressed cold-shock protein was identified in the reproductive organ of fruit trees. The expression of six genes was validated by RT-PCR. As the first comprehensive analysis of open flowers in a frost-tolerant almond genotype, this study represents a key step toward the molecular breeding of fruit tree species for frost tolerance.

SlCOR413IM1: A novel cold-regulation gene from tomato, enhances drought stress tolerance in tobacco

Drought stress adversely affects plant growth, development, and productivity. Genes functioning in plant response to drought stress are essential for drought tolerance. In this study, SlCOR413IM1, a cold-regulated gene isolated from Solanum lycopersium, was transferred to Nicotiana tabacum to investigate its function under drought stress. The subcellular localisation of SlCOR413IM1-GFP fusion protein in Arabidopsis protoplasts suggested that SlCOR413IM1 is a chloroplast protein. Expression analyses revealed that SlCOR413IM1 responded to drought and cold stresses. Under drought stress, transgenic plants maintained the high maximum photochemical efficiency, net photosynthetic rate (Pn) and D1 protein content of photosystem II (PSII). Compared with wild-type (WT) plants, transgenic plants showed higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and proline and soluble sugar content, which reduced reactive oxygen species (ROS) generation. However, the high SOD and APX activities in transgenic plants were independent of their transcription levels. Moreover, the transgenic plants exhibited better seed germination, water status and survival, as well as lower malondialdehyde (MDA) content and relative electrical conductivity (REC) than WT plants under drought stress. Taken together, these data demonstrated that overexpression of SlCOR413IM1 enhanced drought stress tolerance in transgenic tobacco.

Wheat TaPUB1 modulates plant drought stress resistance by improving antioxidant capability

E3 ligases play significant roles in plant stress tolerance by targeting specific substrate proteins for post-translational modification. In a previous study, we cloned TaPUB1 from Triticum aestivum L., which encodes a U-box E3 ligase. Real-time polymerase chain reaction revealed that the gene was up-regulated under drought stress. To investigate the function of TaPUB1 in the response of plants to drought, we generated transgenic Nicotiana benthamiana (N. benthamiana) plants constitutively expressing TaPUB1 under the CaMV35S promoter. Compared to wild type (WT), the transgenic plants had higher germination and seedling survival rates as well as higher photosynthetic rate and water retention, suggesting that the overexpression of TaPUB1 enhanced the drought tolerance of the TaPUB1 overexpressing (OE) plants. Moreover, less accumulation of reactive oxygen species (ROS) and stronger antioxidant capacity were detected in the OE plants than in the WT plants. To characterize the mechanisms involved, methyl viologen (MV) was used to induce oxidative stress conditions and we identified the functions of this gene in the plant tolerance to oxidative stress. Our results suggest that TaPUB1 positively modulates plant drought stress resistance potential by improving their antioxidant capacity.

The Reaumuria trigyna transcription factor RtWRKY1 confers tolerance to salt stress in transgenic Arabidopsis

Reaumuria trigyna (R. trigyna) is an endangered small shrub endemic to the Eastern Alxa-Western Ordos area in Inner Mongolia, China. Based on R. trigyna transcriptome data, the Group I WRKY transcription factor gene RtWRKY1 was cloned from R. trigyna. The full-length RtWRKY1 gene was 2100bp, including a 1261-bp open reading frame (ORF) encoding 573 amino acids. RtWRKY1 was mainly expressed in the stem and was induced by salt, cold stress, and ABA treatment. Overexpression of RtWRKY1 in Arabidopsis significantly enhanced the chlorophyll content, root length, and fresh weight of the transgenic lines under salt stress. RtWRKY1 transgenic Arabidopsis exhibited higher proline content, GSH-PX, POD, SOD, and CAT activities, and lower MDA content, Na⁺ content, and Na⁺/K⁺ ratio than wild-type Arabidopsis under salt stress conditions. Salt stress affected the expression of ion transport, proline biosynthesis, and antioxidant related genes, including AtAPX1, AtCAT1, AtSOD1, AtP5CS1, AtP5CS2, AtPRODH1, AtPRODH2, and AtSOS1 in transgenic lines. RtWRKY1 confers tolerance to salt stress in transgenic Arabidopsis by regulating plant growth, osmotic balance, Na⁺/K⁺ homeostasis, and the antioxidant system.

Arabidopsis thaliana sucrose phosphate synthase (sps) genes are expressed differentially in organs and tissues, and their transcription is regulated by osmotic stress

Sucrose is synthesized from UDP-Glc and Fru-6-phosphate via the activity of sucrose-phosphate synthase (SPS) enzymes, which produce Suc-6-phosphate. Suc-6-phosphate is rapidly dephosphorylated by phosphatases to produce Suc and inorganic phosphate. Arabidopsis has four sps genes encoding SPS enzymes. Of these enzymes, AtSPS1F and AtSPS2F have been grouped with other dicotyledonous SPS enzymes, while AtSPS3F and AtSPS4F are included in groups with both dicotyledonous and monocotyledonous SPS enzymes. In this work, we generated Arabidopsis thaliana transformants containing the promoter region of each sps gene fused to gfp::uidA reporter genes. A detailed characterization of expression conferred by the sps promoters in organs and tissues was performed. We observed expression of AtSPS1F, AtSPS2F and AtSPS3F in the columella roots of the plants that support sucrose synthesis. Hence, these findings support the idea that sucrose synthesis occurs in the columella cells, and suggests that sucrose has a role in this tissue. In addition, the expression of AtSPS4F was identified in embryos and suggests its participation in this developmental stage. Quantitative transcriptional analysis of A. thaliana plants grown in media with different osmotic potential showed that AtSPS2F and AtSPS4F respond to osmotic stress.

Whole-Genome Identification and Expression Pattern of the Vicinal Oxygen Chelate Family in Rapeseed (Brassica napus L.)

Vicinal oxygen chelate proteins (VOC) are members of the metalloenzyme superfamily, which plays roles in many biological reactions. Some members of the VOC superfamily have been systematically characterized but not in Brassica napus. In this study, 38 VOC genes were identified based on their conserved domains. The present results revealed that most of the BnaVOC genes have few introns, and all contained the typical VOC structure of βαβββ modules. The BnaVOC genes are distributed unevenly across 15 chromosomes in B. napus and occur as gene clusters on chromosomes C5 and A6. The synteny and phylogenetic analyses revealed that the VOC gene family is a consequence of mesopolyploidy events that occurred in Brassica evolution, and whole-genome duplication and segmental duplication played a major role in the expansion of the BnaVOC gene family. The expression profile analysis indicated that the expression of most BnaVOCs was increased in the leaves and late stage seeds. Further results indicated that seeds of B. napus with a high oil content show higher expression levels under drought stress conditions, suggesting that BnaVOCs not only respond to abiotic stress but may also affect lipid metabolism in drought stress. This present study provides a comprehensive overview of the VOC gene family and provides new insights into their biological function in B. napus evolution.

Alternative oxidase (AOX) constitutes a small family of proteins in Citrus clementina and Citrus sinensis L. Osb

The alternative oxidase (AOX) protein is present in plants, fungi, protozoa and some invertebrates. It is involved in the mitochondrial respiratory chain, providing an alternative route for the transport of electrons, leading to the reduction of oxygen to form water. The present study aimed to characterize the family of AOX genes in mandarin (Citrus clementina) and sweet orange (Citrus sinensis) at nucleotide and protein levels, including promoter analysis, phylogenetic analysis and C. sinensis gene expression. This study also aimed to do the homology modeling of one AOX isoform (CcAOXd). Moreover, the molecular docking of the CcAOXd protein with the ubiquinone (UQ) was performed. Four AOX genes were identified in each citrus species. These genes have an open reading frame (ORF) ranging from 852 bp to 1150 bp and a number of exons ranging from 4 to 9. The 1500 bp-upstream region of each AOX gene contained regulatory cis-elements related to internal and external response factors. CsAOX genes showed a differential expression in citrus tissues. All AOX proteins were predicted to be located in mitochondria. They contained the conserved motifs LET, NERMHL, LEEEA and RADE-H as well as several putative post-translational modification sites. The CcAOXd protein was modeled by homology to the AOX of Trypanosona brucei (45% of identity). The 3-D structure of CcAOXd showed the presence of two hydrophobic helices that could be involved in the anchoring of the protein in the inner mitochondrial membrane. The active site of the protein is located in a hydrophobic environment deep inside the AOX structure and contains a diiron center. The molecular docking of CcAOXd with UQ showed that the binding site is a recessed pocket formed by the helices and submerged in the membrane. These data are important for future functional studies of citrus AOX genes and/or proteins, as well as for biotechnological approaches leading to AOX inhibition using UQ homologs.

Aldo-keto reductase-1 (AKR1) protect cellular enzymes from salt stress by detoxifying reactive cytotoxic compounds

Cytotoxic compounds like reactive carbonyl compounds such as methylglyoxal (MG), melandialdehyde (MDA), besides the ROS accumulate significantly at higher levels under salinity stress conditions and affect lipids and proteins that inhibit plant growth and productivity. The detoxification of these cytotoxic compounds by overexpression of NADPH-dependent Aldo-ketoreductase (AKR1) enzyme enhances the salinity stress tolerance in tobacco. The PsAKR1 overexpression plants showed higher survival and chlorophyll content and reduced MDA, H2O2, and MG levels under NaCl stress. The transgenic plants showed reduced levels of Na+ levels in both root and shoot due to reduced reactive carbonyl compounds (RCCs) and showed enhanced membrane stability resulted in higher root growth and biomass. The increased levels of antioxidant glutathione and enhanced activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) suggest AKR1 could protect these enzymes from the RCC induced protein carbonylation by detoxification process. The transgenics also showed higher activity of delta 1-pyrroline-5- carboxylate synthase (P5CS) enzyme resulted in increasedproline levels to maintain osmotic homeostasis. The results demonstrates that the AKR1 protects proteins or enzymes that are involved in scavenging of cytotoxic compounds by detoxifying RCCs generated under salinity stress.

Dark septate endophyte decreases stress on rice plants

Abiotic stress is one of the major limiting factors for plant development and productivity, which makes it important to identify microorganisms capable of increasing plant tolerance to stress. Dark septate endophytes can be symbionts of plants. In the present study, we evaluated the ability of dark septate endophytes isolates to reduce the effects of water stress in the rice varieties Nipponbare and Piauí. The experiments were performed under gnotobiotic conditions, and the water stress was induced with PEG. Four dark septate endophytes were isolated from the roots of wild rice (Oryza glumaepatula) collected from the Brazilian Amazon. Plant height as well as shoot and root fresh and dry matter were measured. Leaf protein concentrations and antioxidant enzyme activity were also estimated. The dark septate endophytes were grown in vitro in Petri dishes containing culture medium; they exhibited different levels of tolerance to salinity and water stress. The two rice varieties tested responded differently to inoculation with dark septate endophytes. Endophytes promoted rice plant growth both in the presence and in the absence of a water deficit. Decreased oxidative stress in plants in response to inoculation was observed in nearly all inoculated treatments, as indicated by the decrease in antioxidant enzyme activity. Dark septate endophytes fungi were shown to increase the tolerance of rice plants to stress caused by water deficiency.

Melatonin and resveratrol reverse the toxic effect of high boron (B) and modulate biochemical parameters in pepper plants (Capsicum annuum L.)

The objectives of this research were to test a possible involvement of melatonin (MEL) and resveratrol (RES) in restoring growth and to control boron (B) toxicity in peppers. The plants were subjected to four different nutrient solution treatments as following: 1) half-strength Hoagland's nutrient solution (Control), 2) half-strength Hoagland's nutrient solution+100 μM B (100 μMB), 3) half-strength Hoagland's nutrient solution+100 μM boron+100 μMresveratrol (100 μMRES), and 4) half-strength Hoagland's nutrient solution+100 μM B+1 μMmelatonin (1 μM MEL). Pepper plants subjected to B excess (100 μM) for 68 days (d) exhibited visible B toxicity symptoms, reduced rate of photosynthesis (Pn) and reduced dry weight (DW), while their leaf and fruit had the greatest increase of B concentration. The reduction of photosynthesis was restored, the reduction of DW was prevented, while the B leaf and fruit accumulation was moderated with the application of both 100 μMresveratrol (RES) and 1 μMmelatonin (MEL). Moreover, plants exposed to MEL and/or RES displayed no visible B toxicity symptoms. The present study revealed a novel role of MEL and/or RES in the adaptation of pepper plants to B excess based on plant growth, physiological and biochemical criteria.

Terpenoid trans-caryophyllene inhibits weed germination and induces plant water status alteration and oxidative damage in adult Arabidopsis

trans-Caryophyllene (TC) is a sesquiterpene commonly found as volatile component in many different aromatic plants. Although the phytotoxic effects of trans-caryophyllene on seedling growth are relatively explored, not many information is available regarding the phytotoxicity of this sesquiterpenes on weed germination and on adult plants. The phytotoxic potential of TC was assayed in vitro on weed germination and seedling growth to validate its phytotoxic potential on weed species. Moreover, it was assayed on the metabolism of Arabidopsis thaliana adult plants, through two different application ways, spraying and watering, in order to establish the primary affected organ and to deal with the unknown mobility of the compound. The results clearly indicated that TC inhibited both seed germination and root growth, as demonstrated by comparison of the ED50 values. Moreover, although trans-caryophyllene-sprayed adult Arabidopsis plants did not show any effect, trans-caryophyllene-watered plants became strongly affected. The results suggested that root uptake was a key step for the effectiveness of this natural compound and its phytotoxicity on adult plants was mainly due to the alteration of plant water status accompanied by oxidative damage.

OsSAPK2 Confers Abscisic Acid Sensitivity and Tolerance to Drought Stress in Rice

SNF 1-RELATED PROTEIN KINASE 2 (SnRK2) is a family of plant-specific protein kinases which is the key regulator of hyper-osmotic stress signaling and abscisic acid (ABA)-dependent development in various plants. Among the rice subclass-I and -II SnRK2s, osmotic stress/ABA-activated protein kinase 2 (SAPK2) may be the primary mediator of ABA signaling. However, SAPK2 has not been comprehensively characterized. In this study, we elucidated the functional properties of SAPK2 using loss-of-function mutants produced with the CRISPR/Cas9 system. The SAPK2 expression level was strongly upregulated by drought, high-salinity, and polyethylene glycol (PEG) treatments. The sapk2 mutants exhibited an ABA-insensitive phenotype during the germination and post-germination stages, suggesting that SAPK2 had a pivotal role related to ABA-mediated seed dormancy. The sapk2 mutants were more sensitive to drought stress and reactive oxygen species (ROS) than the wild-type plants, indicating that SAPK2 was important for responses to drought conditions in rice. An additional investigation revealed that SAPK2 increased drought tolerance in the following two ways: (i) by reducing water loss via the accumulation of compatible solutes, promoting stomatal closure, and upregulating the expression levels of stress-response genes such as OsRab16b, OsRab21, OsbZIP23, OsLEA3, OsOREB1 and slow anion channel (SLAC)-associated genes such as OsSLAC1 and OsSLAC7; (ii) by inducing the expression of antioxidant enzyme genes to promote ROS-scavenging abilities that will ultimately decrease ROS damages. Moreover, we also observed that SAPK2 significantly increased the tolerance of rice plants to salt and PEG stresses. These findings imply that SAPK2 is a potential candidate gene for future crop improvement studies.

A CBL-Interacting Protein Kinase TaCIPK2 Confers Drought Tolerance in Transgenic Tobacco Plants through Regulating the Stomatal Movement

In plants, the CBL-CIPK signaling pathways play key roles in the response to abiotic stresses. However, functional studies of CIPKs in the important staple crop wheat are very rare. In this study, we identified a CIPK gene from wheat, designated TaCIPK2. Expression analysis results showed that TaCIPK2 could be up-regulated in wheat leaves by polyethylene glycol, abscisic acid and H2O2 treatments. Subcellular localization analyses revealed that TaCIPK2 was present in whole wheat epidermal cells. A yeast two-hybrid assay indicated that TaCIPK2 interacted with TaCBL1, 2, 3 and 4 in vitro. Transgenic tobacco plants over-expressing TaCIPK2 exhibited increased drought tolerance, indicated by a larger proportion of green cotyledons and higher survival rates under the osmotic and drought stress conditions compared with control plants. Additionally, physiological index analyses revealed that the transgenic tobacco plants had lower water loss rates and ion leakage, accumulated less malondialdehyde and H2O2, and had higher catalase and superoxide dismutase activities than the control plants. The transgenic plants also exhibited faster stomatal closure following exposure to osmotic stress conditions. The seed germination rates and stomatal aperture of TaCIPK2-overexpressing tobacco plants decreased after exogenous abscisic acid treatment was applied, implying that the transgenic tobacco plants were more sensitive to exogenous abscisic acid than the control plants. Our results indicate that TaCIPK2 plays a positive regulatory role in drought stress responses in transgenic tobacco plants.