Abscisic acid regulation of gene expression during water-deficit stress in the era of the Arabidopsis genome

Identification and characterization of the Remorin gene family in Saccharum and the involvement of ScREM1.5e-1/-2 in SCMV infection on sugarcane

Introduction

Remorins (REMs) are plant-specific membrane-associated proteins that play important roles in plant-pathogen interactions and environmental adaptations. Group I REMs are extensively involved in virus infection. However, little is known about the REM gene family in sugarcane (Saccharum spp. hyrid), the most important sugar and energy crop around world.

Methods

Comparative genomics were employed to analyze the REM gene family in Saccharum spontaneum. Transcriptomics or RT-qPCR were used to analyze their expression files in different development stages or tissues under different treatments. Yeast two hybrid, bimolecular fluorescence complementation and co-immunoprecipitation assays were applied to investigate the protein interaction.

Results

In this study, 65 REMs were identified from Saccharum spontaneum genome and classified into six groups based on phylogenetic tree analysis. These REMs contain multiple cis-elements associated with growth, development, hormone and stress response. Expression profiling revealed that among different SsREMs with variable expression levels in different developmental stages or different tissues. A pair of alleles, ScREM1.5e-1/-2, were isolated from the sugarcane cultivar ROC22. ScREM1.5e-1/-2 were highly expressed in leaves, with the former expressed at significantly higher levels than the latter. Their expression was induced by treatment with H2O2, ABA, ethylene, brassinosteroid, SA or MeJA, and varied upon Sugarcane mosaic virus (SCMV) infection. ScREM1.5e-1 was localized to the plasma membrane (PM), while ScREM1.5e-2 was localized to the cytoplasm or nucleus. ScREM1.5e-1/-2 can self-interact and interact with each other, and interact with VPgs from SCMV, Sorghum mosaic virus, or Sugarcane streak mosaic virus. The interactions with VPgs relocated ScREM1.5e-1 from the PM to the cytoplasm.

Discussion

These results reveal the origin, distribution and evolution of the REM gene family in sugarcane and may shed light on engineering sugarcane resistance against sugarcane mosaic pathogens.

Hormonal Balance, Photosynthesis, and Redox Reactions in the Leaves of Caragana korshinskii Kom. under Water Deficit

To evaluate the physiological responses of Korshinsk peashrub (Caragana korshinskii Kom.) to water deficit, photosynthetic gas exchange, chlorophyll fluorescence, and the levels of superoxide anion (O₂^•-), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), antioxidant enzymes, and endogenous hormones in its leaves were investigated under different irrigation strategies during the entire growth period. The results showed that leaf growth-promoting hormones were maintained at a higher level during the stages of leaf expansion and vigorous growth, and zeatin riboside (ZR) and gibberellic acid (GA) gradually decreased with an increase in water deficit. At the leaf-shedding stage, the concentration of abscisic acid (ABA) dramatically increased, and the ratio of ABA to growth-promoting hormones increased to a high level, which indicated that the rate of leaf senescence and shedding was accelerated. At the stages of leaf expansion and vigorous growth, the actual efficiency of photosystem II (PSII) (Φ_PSii) was downregulated with an increment in non-photochemical quenching (NPQ) under moderate water deficit. Excess excitation energy was dissipated, and the maximal efficiency of PSII (F_v/F_m) was maintained. However, with progressive water stress, the photo-protective mechanism was inadequate to avoid photo-damage; F_v/F_m was decreased and photosynthesis was subject to non-stomatal inhibition under severe water deficit. At the leaf-shedding stage, non-stomatal factors became the major factors in limiting photosynthesis under moderate and severe water deficits. In addition, the generation of O₂^•- and H₂O₂ in the leaves of Caragana was accelerated under moderate and severe water deficits, which caused an enhancement of antioxidant enzyme activities to maintain the oxidation-reduction balance. However, when the protective enzymes were insufficient in eliminating excessive reactive oxygen species (ROS), the activity of catalase (CAT) was reduced at the leaf-shedding stage. Taken all together, Caragana has strong drought resistance at the leaf expansion and vigorous growth stages, but weak drought resistance at the leaf-shedding stage.

Molecular characterization and expression analysis of the remorin genes in tomato (Solanum lycopersicum L.)

Remorin (REMs) are plant-specific and plasma membrane-associated proteins that play an essential role in the growth and development of plants and adaptations to adverse environments. To our knowledge, a genome-scale investigation of the REM genes in tomato has never been systematically studied. In this study, a total of 17 SlREM genes were identified in the tomato genome using bioinformatics methods. Our results demonstrated that the 17 members of SlREM were classified into 6 groups based on phylogenetic analysis and unevenly distributed on the eight chromosomes of tomato. There were 15 REM homologous gene pairs between tomato and Arabidopsis. The SlREM gene structures and motif compositions were similar. Promoter sequence analysis showed that the SlREM gene promoters contained some tissue-specific, hormones and stress-related cis-regulatory elements. Expression analysis based on qRT-PCR (Real-time quantitative PCR) analysis showed that SlREM family genes were were differentially expressed in different tissues, and they responded to ABA, MeJA, SA, low-temperature, drought and NaCl treatments. These results potentially provide relevant information for further research on the biological functions of SlREM family genes.

Transcriptome reveals the crucial role of exogenous hydrogen sulfide in alleviation of thiocyanate (SCN-) toxicity in rice seedlings

Application of exogenous hydrogen sulfide (H₂S) is a novel strategy for alleviation of the adverse effects caused by abiotic stresses. However, little is known about H₂S-mediated global molecular response of rice seedlings to thiocyanate (SCN^-) exposure. Herein, a hydroponic experiment was carried out to investigate the crucial role of exogenous H₂S in alleviation of SCN^- toxicity generated at different effective concentrations (EC₂₀: 24.0 mg SCN/L, EC₅₀: 96.0 mg SCN/L, and EC₇₅: 300.0 mg SCN/L) in rice seedlings through transcriptome analysis. The results showed that the total numbers of differentially expressed genes (DEGs, upregulated genes/downregulated genes) in rice roots were 755/313, 1114/3303, and 2184/7427, while they were 427/292, 2134/526, and 2378/890 in rice shoots at EC₂₀, EC₅₀, and EC₇₅ of SCN^-, respectively. When exogenous H₂S was supplied to rice seedlings exposed to SCN^-, the total number of DEGs (upregulated genes/downregulated genes) in rice roots was 1158/316, 1943/2959, and 1737/5392, while it was 2067/937, 2689/683, and 3492/1062 in rice shoots at EC₂₀, EC₅₀, and EC₇₅ of SCN^-, respectively. Upregulated DEGs in shoots were positively correlated with SCN^- concentration in the presence of exogenous H₂S, suggesting its crucial role in regulating the phytotoxicity of SCN^-. Gene function and pathway enrichment analyses showed that exogenous H₂S triggered "secondary metabolite synthesis," "metabolic pathways," and "signal transduction mechanisms" in rice seedlings corresponding to different effective concentrations of SCN^- exposure.

Arbuscular Mycorrhizal Fungi Mediated Alleviation of Drought Stress via Non-Enzymatic Antioxidants: A Meta-Analysis

Drought stress constrains plant cell metabolism and induces the production of reactive oxygen species (ROS). In response to drought stress, plants induce a series of physiological and biochemical changes, scavenging ROS. Among soil microbes, arbuscular mycorrhizal fungi (AMF) are found to be effective ameliorators of ROS under drought-stress conditions. However, the comprehensive roles of the oxidative stress ameliorators mediated by AMF in alleviating drought stress are not studied in detail. The present study aims to determine the oxidative stress ameliorators using meta-analysis highlighting AMF inoculation efficacy on drought stress alleviation. The results confirmed that AMF inoculation had a significant reduction in hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL). Nevertheless, proline accumulation was found to have a non-significant correlation with AMF inoculation. Further, carotenoids and soluble sugars increased positively in AMF-inoculated plants under drought stress and there was a subsequent reduction of abscisic acid (ABA). The results of the meta-analysis reveal the benefits of AMF inoculation with reduced H₂O₂ levels leading to reduced lipid peroxidation (MDA) and increased membrane stability (EL). Thus, the present assessment reveals the sequence of events involved in eliciting drought stress alleviation due to AMF inoculation.

Tangerine tomato roots show increased accumulation of acyclic carotenoids, less abscisic acid, drought sensitivity, and impaired endomycorrhizal colonization

The Heirloom Golden tangerine tomato fruit variety is highly nutritious due to accumulation of tetra-cis-lycopene, that has a higher bioavailability and recognised health benefits in treating anti-inflammatory diseases compared to all-trans-lycopene isomers found in red tomatoes. We investigated if photoisomerization of tetra-cis-lycopene occurs in roots of the MicroTom tangerine (tang^mic) tomato and how this affects root to shoot biomass, mycorrhizal colonization, abscisic acid accumulation, and responses to drought. tang^mic plants grown in soil under glasshouse conditions displayed a reduction in height, number of flowers, fruit yield, and root length compared to wild-type (WT). Soil inoculation with Rhizophagus irregularis revealed fewer arbuscules and other fungal structures in the endodermal cells of roots in tang^mic relative to WT. The roots of tang^mic hyperaccumulated acyclic cis-carotenes, while only trace levels of xanthophylls and abscisic acid were detected. In response to a water deficit, leaves from the tang^mic plants displayed a rapid decline in maximum quantum yield of photosystem II compared to WT, indicating a defective root to shoot signalling response to drought. The lack of xanthophylls biosynthesis in tang^mic roots reduced abscisic acid levels, thereby likely impairing endomycorrhizal colonisation and drought-induced root to shoot signalling.

In-Silico Study of Brassinosteroid Signaling Genes in Rice Provides Insight Into Mechanisms Which Regulate Their Expression

Brassinosteroids (BRs) regulate a diverse spectrum of processes during plant growth and development and modulate plant physiology in response to environmental fluctuations and stress factors. Thus, the BR signaling regulators have the potential to be targeted for gene editing to optimize the architecture of plants and make them more resilient to environmental stress. Our understanding of the BR signaling mechanism in monocot crop species is limited compared to our knowledge of this process accumulated in the model dicot species - Arabidopsis thaliana. A deeper understanding of the BR signaling and response during plant growth and adaptation to continually changing environmental conditions will provide insight into mechanisms that govern the coordinated expression of the BR signaling genes in rice (Oryza sativa) which is a model for cereal crops. Therefore, in this study a comprehensive and detailed in silico analysis of promoter sequences of rice BR signaling genes was performed. Moreover, expression profiles of these genes during various developmental stages and reactions to several stress conditions were analyzed. Additionally, a model of interactions between the encoded proteins was also established. The obtained results revealed that promoters of the 39 BR signaling genes are involved in various regulatory mechanisms and interdependent processes that influence growth, development, and stress response in rice. Different transcription factor-binding sites and cis-regulatory elements in the gene promoters were identified which are involved in regulation of the genes’ expression during plant development and reactions to stress conditions. The in-silico analysis of BR signaling genes in O. sativa provides information about mechanisms which regulate the coordinated expression of these genes during rice development and in response to other phytohormones and environmental factors. Since rice is both an important crop and the model species for other cereals, this information may be important for understanding the regulatory mechanisms that modulate the BR signaling in monocot species. It can also provide new ways for the plant genetic engineering technology by providing novel potential targets, either cis-elements or transcriptional factors, to create elite genotypes with desirable traits.

Mathematical quantification of interactive complexity of transcription factors involved in proline-mediated regulative strategies in Oryza sativa under chromium stress

Involvement of transcription factor (TFs) in governing genes at transcription or post transcription level is known to have affirmative impact on plant physiological and morphological development, especially during environmental abuse. Application of exogenous proline (Pro) is one among the effective approaches to strengthen plant resistance against stresses. However, Pro-mediated regulative strategies of TFs in responses to the chromium (Cr) in rice plants through the gene interaction network are still not clear. In the current study, Pro-mediated interactive complexity of various TFs (i.e., MYB, NAC, WRKY, bHLH, and bZIP) under hexavalent chromium [Cr(VI)] was investigated using Agilent 4 × 44 K rice gene chip and gene interactive probability model (GIPM). Results showed that exogenous Pro had a negligible effect on Cr uptake in rice plants, while a small positive response in biomass accretion of rice seedlings was observed under Cr(VI)+Pro treatments which was to certain extend greater than single Cr(VI) treatments. Rice microarray analysis showed that Cr(VI) significantly (p < 0.05) repressed the expression of TFs in the rice roots and shoots, while the application of exogenous Pro significantly (p < 0.05) up-regulated the expression levels of some TFs in rice tissues. Mathematical modularization indicated that Pro-mediated interaction between MYB and NAC carried more weightage than other TFs in rice roots and shoots under Cr(VI) stress. Overall, our study provides convincing evidence to confirm a positive role of exogenous Pro on reducing the negative impact exerted by Cr(VI) on rice plants through regulating expression and interaction of different TFs.

The soybean Phytoglobin1 (GmPgb1) is involved in water deficit responses through changes in ABA metabolism

Soybean (Glycine max), a major grain crop worldwide, is susceptible to severe yield loss due to drought. Soybean plants over-expressing and downregulating the soybean Phytoblobin1 (GmPgb1) were evaluated for their ability to cope with polyethylene glycol (PEG)-induced water deficit. Sense transformation of GmPgb1, which was more expressed in shoot tissue relative to roots, increased overall plant performance and tolerance to water stress by attenuating the PEG depression of photosynthetic gas exchange parameters and chlorophyll content, as well as reducing leaf injury and promoting root growth. The higher plant relative water content, as a result of GmPgb1 over-expression, was associated with higher transcript levels of three aquaporins: GmTIP1;5 and GmTIP2;5 GmPIP2;9, known to confer water stress tolerance. Opposite results were observed in plants suppressing GmPgb1, which were highly susceptible to PEG-induced stress. Transcriptional and metabolic analyses revealed higher ABA synthesis in dehydrating leaves of plants over-expressing GmPgb1 relative to those suppressing the same gene. The latter plants exhibited a transcriptional induction of ABA catabolic enzymes and higher accumulation of the ABA catabolite dehydrophaseic acid (DPA). Administration of 8'-acetylene ABA, an ABA agonist resistant to the ABA catabolic activity, was sufficient to restore tolerance in the GmPgb1 down-regulating plants suggesting that regulation of ABA catabolism is as important as ABA synthesis in conferring PEG-induced water stress tolerance. Screening of natural soybean germplasm also revealed a rapid and transient increase in foliar GmPgb1 in tolerant plants relative to their susceptible counterparts, thus confirming the key role exercised by this gene during water stress.

Characterization of a transcription factor SlNAC7 gene from Suaeda liaotungensis and its role in stress tolerance

NAC (NAM, ATAF1/2, CUC2) transcription factors play important roles in plant growth, development, and responses to abiotic stress. In this study, we cloned an NAC2 subfamily transcription factor gene (SlNAC7) from the halophyte Suaeda liaotungensis K., and conducted a series of studies to determine the characteristics and functions of this gene. The SlNAC7 coding region contains 1719 base pairs that encode a 573 amino acid long protein. SlNAC7 is expressed in the roots, stems, and leaves of S. liaotungensis, with the highest expression in the leaves. We found that SlNAC7 expression can be induced by drought, salt, cold, and abscisic acid. Transient expression in onion epidermal cells revealed that SlNAC7 is located in both the nucleus and cytoplasm. A transcriptional activation experiment in yeast showed that the transcriptional activation domain of SlNAC7 is located at the C terminus. When SlNAC7 was transformed into Arabidopsis under the control of a CaMV 35S promoter its overexpression was found to enhance the ability of transgenic plants to resist drought, salt, and cold stress. Moreover, these plants showed multiple changes in growth characteristics and physiological and biochemical indices in response to different stresses, as well as the upregulation of numerous stress-related genes. We have thus characterized a new halophyte-derived NAC transcription factor, SlNAC7, which can regulate plant growth and physiological and biochemical changes under adverse conditions by regulating the expression of stress-related genes, thereby enhancing plant stress resistance. SlNAC7 is a promising candidate for breeding new varieties of stress-tolerant crops.

Effect of RIP Overexpression on Abiotic Stress Tolerance and Development of Rice

Ribosome-inactivating proteins (RIPs) are a class of cytotoxic enzymes that can inhibit protein translation by depurinating rRNA. Most plant RIPs are synthesized with a leader sequence that sequesters the proteins to a cell compartment away from the host ribosomes. However, several rice RIPs lack these signal peptides suggesting they reside in the cytosol in close proximity to the plant ribosomes. This paper aims to elucidate the physiological function of two nucleocytoplasmic RIPs from rice, in particular, the type 1 RIP referred to as OsRIP1 and a presumed type 3 RIP called nuRIP. Transgenic rice lines overexpressing these RIPs were constructed and studied for developmental effects resulting from this overexpression under greenhouse conditions. In addition, the performance of transgenic seedlings in response to drought, salt, abscisic acid and methyl jasmonate treatment was investigated. Results suggest that both RIPs can affect methyl jasmonate mediated stress responses.

Common bean SNP alleles and candidate genes affecting photosynthesis under contrasting water regimes

Water deficit is a major worldwide constraint to common bean (Phaseolus vulgaris L.) production, being photosynthesis one of the most affected physiological processes. To gain insights into the genetic basis of the photosynthetic response of common bean under water-limited conditions, a collection of 158 Portuguese accessions was grown under both well-watered and water-deficit regimes. Leaf gas-exchange parameters were measured and photosynthetic pigments quantified. The same collection was genotyped using SNP arrays, and SNP-trait associations tested considering a linear mixed model accounting for the genetic relatedness among accessions. A total of 133 SNP-trait associations were identified for net CO2 assimilation rate, transpiration rate, stomatal conductance, and chlorophylls a and b, carotenes, and xanthophyll contents. Ninety of these associations were detected under water-deficit and 43 under well-watered conditions, with only two associations common to both treatments. Identified candidate genes revealed that stomatal regulation, protein translocation across membranes, redox mechanisms, hormone, and osmotic stress signaling were the most relevant processes involved in common bean response to water-limited conditions. These candidates are now preferential targets for common bean water-deficit-tolerance breeding. Additionally, new sources of water-deficit tolerance of Andean, Mesoamerican, and admixed origin were detected as accessions valuable for breeding, and not yet explored.

Practical Implications of Different Phenotypic and Molecular Responses of Evergreen Conifer and Broadleaf Deciduous Forest Tree Species to Regulated Water Deficit in a Container Nursery

Recent climatic changes have resulted in an increased frequency and prolonged periods of drought and strained water resources affecting plant production. We explored the possibility of reducing irrigation in a container nursery and studied the growth responses of seedlings of four economically important forest trees: broadleaf deciduous angiosperms Fagus sylvatica L., Quercus petraea (Matt.) Liebl., and evergreen conifers Abies alba Mill. and Pinus sylvestris L. We also studied markers of water stress including modifications of biomass allocation, leaf anatomy, proline accumulation, and expression of selected genes. Growth of the broadleaved deciduous species was more sensitive to the reduced water supply than that of conifers. Remarkably, growth of the shade tolerant Abies was not affected. Adjustment of biomass allocations was strongest in P. sylvestris, with a remarkable increase in allocation to roots. In response to water deficit both deciduous species accumulated proline in leaves and produced leaves with shorter palisade cells, reduced vascular tissues, and smaller conduit diameters. These responses did not occur in conifers. Relative transcript abundance of a gene encoding the Zn-finger protein in Q. petraea and a gene encoding the pore calcium channel protein 1 in A. alba increased as water deficit increased. Our study shows major differences between functional groups in response to irrigation, with seedlings of evergreen conifers having higher tolerance than the deciduous species. This suggests that major water savings could be achieved by adjusting irrigation regime to functional group or species requirements.

Enhanced N-metabolites, ABA and IAA-conjugate in anthers instigate heat sensitivity in spring wheat

Unraveling the metabolic and phytohormonal changes in anthers exposed to heat stress would help identify mechanisms regulating heat stress tolerance during the sensitive reproductive stage. Two spring wheat genotypes contrasting for heat tolerance were exposed to heat stress during heading in controlled environment chambers. Anthers were collected from main and primary spikes for metabolic and phytohormonal profiling. A significant reduction in seed set (38%), grain number (54%) and grain weight (52%) per plant was recorded in the sensitive (KSG1177) but not in the tolerant (KSG1214) genotype under heat stress compared to control. Anther metabolite accumulation did not vary quantitatively between main and primary spikes. Hierarchical clustering of the genotypes and treatments using metabolites and phytohormones revealed a distinct cluster for KSG1177 under heat stress from that of control and KSG1214. A significant increase in N-based amino acids, ABA, IAA-conjugate and a decrease in polyamines and organic acids were observed in wheat anthers exposed to heat stress. Unlike KSG1214, a significantly higher accumulation of amino acids, ABA and IAA-conjugate in anthers of the sensitive KSG1177 was recorded under heat stress. These findings provide the rationale and direction towards developing molecular markers for enhancing heat stress tolerance in wheat.

The SUPPRESSOR of MAX2 1 (SMAX1)-Like SMXL6, SMXL7 and SMXL8 Act as Negative Regulators in Response to Drought Stress in Arabidopsis

Drought represents a major threat to crop growth and yields. Strigolactones (SLs) contribute to regulating shoot branching by targeting the SUPPRESSOR OF MORE AXILLARY GROWTH2 (MAX2)-LIKE6 (SMXL6), SMXL7 and SMXL8 for degradation in a MAX2-dependent manner in Arabidopsis. Although SLs are implicated in plant drought response, the functions of the SMXL6, 7 and 8 in the SL-regulated plant response to drought stress have remained unclear. Here, we performed transcriptomic, physiological and biochemical analyses of smxl6, 7, 8 and max2 plants to understand the basis for SMXL6/7/8-regulated drought response. We found that three D53 (DWARF53)-Like SMXL members, SMXL6, 7 and 8, are involved in drought response as the smxl6smxl7smxl8 triple mutants showed markedly enhanced drought tolerance compared to wild type (WT). The smxl6smxl7smxl8 plants exhibited decreased leaf stomatal index, cuticular permeability and water loss, and increased anthocyanin biosynthesis during dehydration. Moreover, smxl6smxl7smxl8 were hypersensitive to ABA-induced stomatal closure and ABA responsiveness during and after germination. In addition, RNA-sequencing analysis of the leaves of the D53-like smxl mutants, SL-response max2 mutant and WT plants under normal and dehydration conditions revealed an SMXL6/7/8-mediated network controlling plant adaptation to drought stress via many stress- and/or ABA-responsive and SL-related genes. These data further provide evidence for crosstalk between ABA- and SL-dependent signaling pathways in regulating plant responses to drought. Our results demonstrate that SMXL6, 7 and 8 are vital components of SL signaling and are negatively involved in drought responses, suggesting that genetic manipulation of SMXL6/7/8-dependent SL signaling may provide novel ways to improve drought resistance.

Overexpression of Medicago sativa LEA4-4 can improve the salt, drought, and oxidation resistance of transgenic Arabidopsis

Late embryogenesis abundant (LEA) proteins are widely involved in many adverse conditions among plants. In this study, we isolated a LEA4 gene from alfalfa (Medicago sativa L.) termed MsLEA4-4 via a homology cloning strategy. MsLEA4-4 encodes 166 amino acids, and the structural analysis showed that the gene contained five repeating TAQAAKEKTQQ amino acid motifs. There were a large number of α-helix in MsLEA4-4, and belongs to hydrophilic amino acid. Subcellular localization analysis showed that MsLEA4-4 was localized in the nucleus. The MsLEA4-4 promoter consisted of G-box and A-box elements, abscisic acid-responsive elements (ABREs), photo regulation and photoperiodic-controlling cis-acting elements, and endosperm expression motifs. The MsLEA4-4 overexpressing in Arabidopsis conferred late-germination phenotypes. Resistance of the overexpressed plants to abiotic stress significantly outperformed the wild-type (WT) plants. Under salt stress and abscisic acid treatment, with more lateral roots and higher chlorophyll content, the overexpressed plants has a higher survival rate measured against WT. Compared to those in the WT plants, the levels of soluble sugar and the activity of various antioxidant enzymes were elevated in the overexpressed plants, whereas the levels of proline and malondialdehyde were significantly reduced. The expression levels of several genes such as ABF3, ABI5, NCED5, and NCED9 increased markedly in the overexpressed plants compared to the WT under osmotic stress.

Contrasting patterns of hormonal and photoprotective isoprenoids in response to stress in Cistus albidus during a Mediterranean winter

Seasonal accumulation of hormonal and photoprotective isoprenoids, particularly α-tocopherol, carotenoids and abscisic acid, indicate their important role in protecting Cistus albidus plants from environmental stress during a Mediterranean winter. The high diurnal amounts of α-tocopherol and xanthophylls 3 h before maximum light intensity suggest a photoprotective response against the prevailing diurnal changes. The timing to modulate acclimatory/defense responses under changing environmental conditions is one of the most critical points for plant fitness and stress tolerance. Here, we report seasonal and diurnal changes in the contents of isoprenoids originated from the methylerythritol phosphate pathway, including chlorophylls, carotenoids, tocochromanols, and phytohormones (abscisic acid, cytokinins, and gibberellins) in C. albidus during a Mediterranean winter. Plants were subjected not only to typically low winter temperatures but also to drought, as shown by a mean plant water status of 54% during the experimental period. The maximum PSII efficiency, however, remained consistently high (F_v/F_m > 0.8), proving that C. albidus had efficient mechanisms to tolerate combined stress conditions during winter. While seasonal α-tocopherol contents remained high (200-300 µg/g DW) during the experimental period, carotenoid contents increased during winter attaining maximum levels in February (minimum air temperature ≤ 5 °C for 13 days). Following the initial transient increases of bioactive trans-zeatin (about fivefold) during winter, the increased abscisic acid contents proved its important role during abiotic stress tolerance. Diurnal amounts of α-tocopherol and xanthophylls, particularly lutein, zeaxanthin and neoxanthin including the de-epoxidation state, reached maximum levels as early as 2 h after dawn, when solar intensity was 68% lower than the maximum solar radiation at noon. It is concluded that (1) given their proven antioxidant properties, both α-tocopherol and carotenoids seem to play a crucial role protecting the photosynthetic apparatus under severe stress conditions; (2) high seasonal amounts of abscisic acid indicate its important role in abiotic stress tolerance within plant hormones, although under specific environmental conditions, accumulation of bioactive cytokinins appears to be involved to enhance stress tolerance; (3) the concerted diurnal adjustment of α-tocopherol and xanthophylls as early as 3 h before maximum light intensity suggests that plants anticipated the predictable diurnal changes in the environment to protect the photosynthetic apparatus.

Elevated carbon dioxide decreases the adverse effects of higher temperature and drought stress by mitigating oxidative stress and improving water status in Arabidopsis thaliana

This study revealed that elevated carbon dioxide increases Arabidopsis tolerance to higher temperature and drought stress by mitigating oxidative stress and improving water status of plants. Few studies have considered multiple aspects of plant responses to key components of global climate change, including higher temperature, elevated carbon dioxide (ECO₂), and drought. Hence, their individual and combinatorial effects on plants need to be investigated in the context of understanding climate change impact on plant growth and development. We investigated the interactive effects of temperature, CO₂, watering regime, and genotype on Arabidopsis thaliana (WT and ABA-insensitive mutant, abi1-1). Plants were grown in controlled-environment growth chambers under two temperature regimes (22/18 °C and 28/24 °C, 16 h light/8 h dark), two CO₂ concentrations (400 and 700 μmol mol^-1), and two watering regimes (well-watered and water-stressed) for 18 days. Plant growth, anatomical, physiological, molecular, and hormonal responses were determined. Our study provided valuable information about plant responses to the interactive effects of multiple environmental factors. We showed that drought and ECO₂ had larger effects on plants than higher temperatures. ECO₂ alleviated the detrimental effects of temperature and drought by mitigating oxidative stress and plant water status, and this positive effect was consistent across multiple response levels. The WT plants performed better than the abi1-1 plants; the former had higher rosette diameter, total dry mass, leaf and soil water potential, leaf moisture, proline, ethylene, trans-zeatin, isopentyladenine, and cis-zeatin riboside than the latter. The water-stressed plants of both genotypes accumulated more abscisic acid (ABA) than the well-watered plants; however, higher temperatures decreased the ability of WT plants to produce ABA in response to drought. We conclude that drought strongly, while higher temperature to a lesser extent, affects Arabidopsis seedlings, and ECO₂ reduces the adverse effects of these stressors more efficiently in the WT plants than in the abi1-1 plants. Findings from this study can be extrapolated to other plant species that share similar characteristics and/or family with Arabidopsis.

Global transcriptome analysis provides new insights in Thellungiella salsuginea stress response

Thellungiella salsuginea is highly tolerant to abiotic stress, while its a close relative Arabidopsis thaliana is sensitive to stress. This characteristic makes T. salsuginea an excellent model for uncovering the mechanisms of abiotic stress tolerance. Abscisic acid (ABA) plays essential roles in plant abiotic and biotic stress tolerance. To test the changes in gene expression of T. salsuginea under ABA treatment, in this study, the transcriptomes of T. salsuginea roots and leaves were compared in response to exogenously application of ABA. The results showed that ABA treatment caused different expression of 2,200 and 3,305 genes in leaves and roots, respectively, compared with the untreated control. In particular, genes encoding transcription factors such as WRKY, MYB, NAC, GATA, ethylene-responsive factors (ERFs), heat stress transcription factors, basic helix-loop-helix, PLATZ and B3 domain-containing family members were enriched. In addition, 49 and 114 differentially expressed genes were identified as ABA-regulated genes, separately in leaves and roots, respectively, which were related to biotic and abiotic stresses. The expression levels of some genes were validated by qRT-PCR. Different responses of genes to ABA treatment were discovered in T. salsuginea and A. thaliana. This transcriptome analysis expands our understanding of the role of ABA in stress tolerance in T. salsuginea. Our study provides a wealth of information for improving stress tolerance in crop plants.

Comprehensive transcriptome analysis reveals genes in response to water deficit in the leaves of Saccharum narenga (Nees ex Steud.) hack

BACKGROUND

Sugarcane is an important sugar and energy crop that is widely planted in the world. Among the environmental stresses, the water-deficit stress is the most limiting to plant productivity. Some groups have used PCR-based and microarray technologies to investigate the gene expression changes of multiple sugarcane cultivars under water stress. Our knowledge about sugarcane genes in response to water deficit is still poor.

RESULTS

A wild sugarcane type, Saccharum narenga, was selected and treated with drought stress for 22 days. Leaves from drought treated (DTS) and control (CK) plants were obtained for deep sequencing. Paired-end sequencing enabled us to assemble 104,644 genes (N50 = 1605 bp), of which 38,721 were aligned to other databases, such as UniProt, NR, GO, KEGG and Pfam. Single-end and paired-end sequencing identified 30,297 genes (> 5 TPM) in all samples. Compared to CK, 3389 differentially expressed genes (DEGs) were identified in DTS samples, comprising 1772 up-regulated and 1617 down-regulated genes. Functional analysis showed that the DEGs were involved in biological pathways like response to blue light, metabolic pathways and plant hormone signal transduction. We further observed the expression patterns of several important gene families, including aquaporins, late embryogenesis abundant proteins, auxin related proteins, transcription factors (TFs), heat shock proteins, light harvesting chlorophyll a-b binding proteins, disease resistance proteins, and ribosomal proteins. Interestingly, the regulation of genes varied among different subfamilies of aquaporin and ribosomal proteins. In addition, DIVARICATA and heat stress TFs were first reported in sugarcane leaves in response to water deficit. Further, we showed potential miRNAs that might be involved in the regulation of gene changes in sugarcane leaves under the water-deficit stress.

CONCLUSIONS

This is the first transcriptome study of Saccharum narenga and the assembled genes are a valuable resource for future research. Our findings will improve the understanding of the mechanism of gene regulation in sugarcane leaves under the water-deficit stress. The output of this study will also contribute to the sugarcane breeding program.

Three stress-responsive NAC transcription factors from Populus euphratica differentially regulate salt and drought tolerance in transgenic plants

Stress-responsive NAM, Arabidopsis transcription activation factor 1/2 (ATAF1/2) and CUC2 (SNAC) genes are being used to alter stress tolerance in Arabidopsis or grasses through genetic engineering. However, limited reports are available about the functional characteristics of SNAC in trees. In this study, three putative NAC proteins were identified from Populus euphratica. PeNAC034 and PeNAC045 were classified into the ATAF subgroup and PeNAC036 into the ANAC072 subgroup. These three SNAC transcription factors were localized in the nucleus and contained the transcription activation domain in their C-terminal. Under drought and salt stresses, PeNAC036 was strongly induced in the whole plant, but PeNAC034 was significantly suppressed in the roots and stems, and PeNAC045 was inhibited in the roots. PeNAC036 overexpression in Arabidopsis wild-type (WT) (OEPeNAC036) and PeNAC036 complementation in mutant anac072 (anac072/PeNAC036) lines increased tolerance to salt and drought, whereas PeNAC034 overexpression in WT (OEPeNAC034) and PeNAC034 complementation in mutant ataf1 (ataf1/PeNAC034) lines enhanced salt and drought sensitivity. After drought and salt treatments, the expression levels of COR47, RD29B, ERD11, RD22 and DREB2A were upregulated in OEPeNAC036 and anac072/PeNAC036 lines, but were downregulated in OEPeNAC034 and ataf1/PeNAC034 plants. Compared with WT and Vector lines, PeNAC045 overexpression in poplar WT (OEPeNAC045) led to a significant decrease in the net photosynthesis rate, stomatal conductance and transpiration rate under salinity and drought conditions. These results suggest that P. euphratica can adapt to the environment of high salinity and drought, which may be related to the differential expression patterns of SNAC genes.

Kunitz Proteinase Inhibitors Limit Water Stress Responses in White Clover (Trifolium repens L.) Plants

The response of plants to water deficiency or drought is a complex process, the perception of which is triggered at the molecular level before any visible morphological responses are detected. It was found that different groups of plant proteinase inhibitors (PIs) are induced and play an active role during abiotic stress conditions such as drought. Our previous work with the white clover (Trifolium repens L.) Kunitz Proteinase Inhibitor (Tr-KPI) gene family showed that Tr-KPIs are differentially regulated to ontogenetic and biotic stress associated cues and that, at least some members of this gene family may be required to maintain cellular homeostasis. Altered cellular homeostasis may also affect abiotic stress responses and therefore, we aimed to understand if distinct Tr-PKI members function during drought stress. First, the expression level of three Tr-KPI genes, Tr-KPI1, Tr-KPI2, and Tr-KPI5, was measured in two cultivars and one white clover ecotype with differing capacity to tolerate drought. The expression of Tr-KPI1 and Tr-KPI5 increased in response to water deficiency and this was exaggerated when the plants were treated with a previous period of water deficiency. In contrast, proline accumulation and increased expression of Tr-NCED1, a gene encoding a protein involved in ABA biosynthesis, was delayed in plants that experienced a previous drought period. RNAi knock-down of Tr-KPI1 and Tr-KPI5 resulted in increased proline accumulation in leaf tissue of plants grown under both well-watered and water-deficit conditions. In addition, increased expression of genes involved in ethylene biosynthesis was found. The data suggests that Tr-KPIs, particularly Tr-KPI5, have an explicit function during water limitation. The results also imply that the Tr-KPI family has different in planta proteinase targets and that the functions of this protein family are not solely restricted to one of storage proteins or in response to biotic stress.

Comparative Study on Reagents Involved in Grape Bud Break and Their Effects on Different Metabolites and Related Gene Expression during Winter

To elucidate promoting and inhibiting effects of hydrogen cynamide (HC) and abscisic acid (ABA) on quiescence release of grape buds, physiological and molecular approaches were used to explore the mechanisms of quiescence based on metabolic and gene expression analysis. Physiological and molecular mechanisms involved in bud quiescence of grape were studied before and after application of HC, ABA, and ABA-HC. The data showed that ABA inhibited proclamation of quiescence in grape buds and attenuated the influence of HC. Bud quiescence was promoted and regulated by HC and ABA pre-treatment on buds of grape cultivar "Shine Muscat" with 5% HC, 100 μM ABA and combination of ABA-HC (5% HC+100 μM ABA) during quiescence under forcing condition. Exogenous application of ABA elevated superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) related specific activities, while catalase (CAT) activity was increased during initial period of forcing and then decreased. The concentration of plant growth hormones including gibberellins (GA) and indole acetic acid increased by HC application but decreased the ABA contents under forcing condition. ABA increased the fructose content during quiescence under forcing condition while sucrose and total soluble sugars peaked in HC treated buds as compared to control. Genes related to ABA pathway, protein phosphatase 2C (PP2C family) were down regulated in the buds treated with HC, ABA and ABA-HC as compared to control while two genes related to GA pathway (GID1 family), out of which one gene showed down regulation during initial period of forcing while other gene was up regulated in response to HC and ABA-HC treatments as compared to control. Exogenous ABA application up regulated genes related to antioxidant enzymes as compared to control. The gene probable fructose-bisphosphate aldolase 1, chloroplastic-like, was up regulated in response to ABA treatment as compared to control. Analysis of metabolites and related gene expression pattern would provide a comprehensive view of quiescence after HC, ABA, and ABA-HC treatments in grape buds which may helpful for ultimate improvement in table grape production.

Abscisic Acid Signaling and Abiotic Stress Tolerance in Plants: A Review on Current Knowledge and Future Prospects

Abiotic stress is one of the severe stresses of environment that lowers the growth and yield of any crop even on irrigated land throughout the world. A major phytohormone abscisic acid (ABA) plays an essential part in acting toward varied range of stresses like heavy metal stress, drought, thermal or heat stress, high level of salinity, low temperature, and radiation stress. Its role is also elaborated in various developmental processes including seed germination, seed dormancy, and closure of stomata. ABA acts by modifying the expression level of gene and subsequent analysis of cis- and trans-acting regulatory elements of responsive promoters. It also interacts with the signaling molecules of processes involved in stress response and development of seeds. On the whole, the stress to a plant can be susceptible or tolerant by taking into account the coordinated activities of various stress-responsive genes. Numbers of transcription factor are involved in regulating the expression of ABA responsive genes by acting together with their respective cis-acting elements. Hence, for improvement in stress-tolerance capacity of plants, it is necessary to understand the mechanism behind it. On this ground, this article enlightens the importance and role of ABA signaling with regard to various stresses as well as regulation of ABA biosynthetic pathway along with the transcription factors for stress tolerance.

Overexpression of MpCYS4, A Phytocystatin Gene from Malus prunifolia (Willd.) Borkh., Enhances Stomatal Closure to Confer Drought Tolerance in Transgenic Arabidopsis and Apple

Phytocystatins (PhyCys) comprise a group of inhibitors for cysteine proteinases in plants. They play a wide range of important roles in regulating endogenous processes and protecting plants against various environmental stresses, but the underlying mechanisms remain largely unknown. Here, we detailed the biological functions of MpCYS4, a member of cystatin genes isolated from Malus prunifolia. This gene was activated under water deficit, heat (40°C), exogenous abscisic acid (ABA), or methyl viologen (MV) (Tan et al., 2014a). At cellular level, MpCYS4 protein was found to be localized in the nucleus, cytoplasm, and plasma membrane of onion epidermal cells. Recombinant MpCYS4 cystatin expressed in Escherichia coli was purified and it exhibited cysteine protease inhibitor activity. Transgenic overexpression of MpCYS4 in Arabidopsis (Arabidopsis thaliana) and apple (Malus domestica) led to ABA hypersensitivity and series of ABA-associated phenotypes, such as enhanced ABA-induced stomatal closing, altered expression of many ABA/stress-responsive genes, and enhanced drought tolerance. Taken together, our results demonstrate that MpCYS4 is involved in ABA-mediated stress signal transduction and confers drought tolerance at least in part by enhancing stomatal closure and up-regulating the transcriptional levels of ABA- and drought-related genes. These findings provide new insights into the molecular mechanisms by which phytocystatins influence plant growth, development, and tolerance to stress.

Molecular cloning and characterization of drought stress responsive abscisic acid-stress-ripening (Asr 1) gene from wild jujube, Ziziphus nummularia (Burm.f.) Wight & Arn

Drought is a calamitous abiotic stress hampering agricultural productivity all over the world and its severity is likely to increase further. Abscisic acid-stress-ripening proteins (ASR), are a group of small hydrophilic proteins which are induced by abscisic acid, stress and ripening in many plants. In the present study, ZnAsr 1 gene was fully characterized for the first time from Ziziphus nummularia, which is one of the most low water forbearing plant. Full length ZnAsr 1 gene was characterised and in silico analysis of ZnASR1 protein was done for predicting its phylogeny and physiochemical properties. To validate transcriptional pattern of ZnAsr 1 in response to drought stress, expression profiling in polyethylene glycol (PEG) induced Z. nummularia seedlings was studied by RT-qPCR analysis and heterologous expression of the recombinant ZnAsr1 in Escherichia coli. The nucleotide sequence analysis revealed that the complete open reading frame of ZnAsr 1 is 819 bp long encoding a protein of 273 amino acid residues, consisting of a histidine rich N terminus with an abscisic acid/water deficit stress domain and a nuclear targeting signal at the C terminus. In expression studies, ZnAsr 1 gene was found to be highly upregulated under drought stress and recombinant clones of E. coli cells expressing ZnASR1 protein showed better survival in PEG containing media. ZnAsr1 was proven to enhance drought stress tolerance in the recombinant E.coli cells expressing ZnASR1. The cloned ZnAsr1 after proper validation in a plant system, can be used to develop drought tolerant transgenic crops.

CarNAC4, a NAC-type chickpea transcription factor conferring enhanced drought and salt stress tolerances in Arabidopsis

CarNAC4 is a typical stress-responsive NAC transcription factor and enhances drought and salt stress tolerances in transgenic Arabidopsis. Chickpea (Cicer arietinum L.) is relatively vulnerable to abiotic stress conditions, but the tolerance mechanisms for such stresses in chickpea are largely unknown. To identify stress-related factors in chickpea, we previously constructed a cDNA library of chickpea leaves exposed to drought stress conditions. A cDNA encoding a putative NAC transcription factor (CarNAC4) was identified as a putative stress-responsive gene. Our study indicated that the transcript levels of CarNAC4 were enhanced in response to several abiotic stresses and phytohormones. Promoter analysis demonstrated that multiple stress-related cis-acting elements exist in promoter region of CarNAC4. CarNAC4 is localized in the nucleus and binds to the DNA sequence containing CGT[G/A], while the C-terminal region of CarNAC4 contains a transcriptional activation domain. Over-expression of CarNAC4 in Arabidopsis plants improved tolerance to drought and salt stresses. Transgenic plants exhibited greater reduced rates of water loss and more proline accumulation than Col-0 plants under drought stress and less MDA contents than Col-0 plants under salt stress. In addition, over-expression of CarNAC4 enhanced the expression of stress-responsive genes such as RD29A, ERD10, COR15A, COR47, KIN1 and DREB2A. These results indicated that CarNAC4 functions as a transcription factor involved in the regulation of drought and salt stress response.

Gene expression regulation in roots under drought

Stress signalling and regulatory networks controlling expression of target genes are the basis of plant response to drought. Roots are the first organs exposed to water deficiency in the soil and are the place of drought sensing. Signalling cascades transfer chemical signals toward the shoot and initiate molecular responses that lead to the biochemical and morphological changes that allow plants to be protected against water loss and to tolerate stress conditions. Here, we present an overview of signalling network and gene expression regulation pathways that are actively induced in roots under drought stress. In particular, the role of several transcription factor (TF) families, including DREB, AP2/ERF, NAC, bZIP, MYC, CAMTA, Alfin-like and Q-type ZFP, in the regulation of root response to drought are highlighted. The information provided includes available data on mutual interactions between these TFs together with their regulation by plant hormones and other signalling molecules. The most significant downstream target genes and molecular processes that are controlled by the regulatory factors are given. These data are also coupled with information about the influence of the described regulatory networks on root traits and root development which may translate to enhanced drought tolerance. This is the first literature survey demonstrating the gene expression regulatory machinery that is induced by drought stress, presented from the perspective of roots.

Potential role of phytohormones and plant growth-promoting rhizobacteria in abiotic stresses: consequences for changing environment

Plants are sessile beings, so the need of mechanisms to flee from unfavorable circumstances has provided the development of unique and sophisticated responses to environmental stresses. Depending on the degree of plasticity, many morphological, cellular, anatomical, and physiological changes occur in plants in response to abiotic stress. Phytohormones are small molecules that play critical roles in regulating plant growth and development, as well as stress tolerance to promote survival and acclimatize to varying environments. To congregate the challenges of salinity, temperature extremes, and osmotic stress, plants use their genetic mechanism and different adaptive and biological approaches for survival and high production. In the present attempt, we review the potential role of different phytohormones and plant growth-promoting rhizobacteria in abiotic stresses and summarize the research progress in plant responses to abiotic stresses at physiological and molecular levels. We emphasized the regulatory circuits of abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene, and triazole on exposure to abiotic stresses. Current progress is exemplified by the identification and validation of several significant genes that enhanced crop tolerance to stress in the field. These findings will make the modification of hormone biosynthetic pathways for the transgenic plant generation with augmented abiotic stress tolerance and boosting crop productivity in the coming decades possible.

Azospirillum brasilense ameliorates the response of Arabidopsis thaliana to drought mainly via enhancement of ABA levels

Production of phytohormones is one of the main mechanisms to explain the beneficial effects of plant growth-promoting rhizobacteria (PGPR) such as Azospirillum sp. The PGPRs induce plant growth and development, and reduce stress susceptibility. However, little is known regarding the stress-related phytohormone abscisic acid (ABA) produced by bacteria. We investigated the effects of Azospirillum brasilense Sp 245 strain on Arabidopsis thaliana Col-0 and aba2-1 mutant plants, evaluating the morphophysiological and biochemical responses when watered and in drought. We used an in vitro-grown system to study changes in the root volume and architecture after inoculation with Azospirillum in Arabidopsis wild-type Col-0 and on the mutant aba2-1, during early growth. To examine Arabidopsis development and reproductive success as affected by the bacteria, ABA and drought, a pot experiment using Arabidopsis Col-0 plants was also carried out. Azospirillum brasilense augmented plant biomass, altered root architecture by increasing lateral roots number, stimulated photosynthetic and photoprotective pigments and retarded water loss in correlation with incremented ABA levels. As well, inoculation improved plants seed yield, plants survival, proline levels and relative leaf water content; it also decreased stomatal conductance, malondialdehyde and relative soil water content in plants submitted to drought. Arabidopsis inoculation with A. brasilense improved plants performance, especially in drought.

Differential physiological and molecular response of barley genotypes to water deficit

Changes in physiological parameters (relative water content (RWC), biomass, water use efficiency (WUE), net photosynthetic yield (PN) and quantum yield of PSII (Fv/Fm)), in proline and sugar content, and expression profile of genes reported to be associated with the barley response to water deficit, including LEA genes, NHX1, Hsdr4, BLT101 and genes encoding transcription factors (HvDREB1, HvABF1, HvABI5 and HvZIP1), were analyzed in seedlings of nine barley genotypes subjected to a progressive increase in water deficit. Seedlings of all genotypes wilted when the soil water content (SWC) declined from 65% (control conditions) to 10% (severe drought conditions), but recovered turgor within a few hours of re-watering. However, when severe drought conditions were prolonged for a week, large differences in survival characteristics were observed between genotypes after re-watering. Multivariate analysis of the changes in physiological and molecular characteristics allowed several different homogenous groups within the genotypes to be distinguished, depending on stress intensity. Furthermore, integration between the stress-response traits was found and was shown to vary depending on the genotype and the stress level. Based on analysis of physiological traits and survival characteristics, two barley genotypes with high adaptability to the stress conditions (cv. Saida and breeding line Cam/B1), and two with low adaptability (cv. Express and breeding line Harmal), were identified. In addition, only changes in expression of the genes HvZIP1, encoding a b-ZIP-type transcription factor, and Hsdr4, encoding a protein of unknown function, were shown to be linked with adaptability of barley to water deficit. In summary, physiological and molecular data revealed large, stress-level-dependent differences between the barley cultivars and breeding lines tested in their response to water deficit.

Discovery of genes related to witches broom disease in Paulownia tomentosa × Paulownia fortunei by a De Novo assembled transcriptome

In spite of its economic importance, very little molecular genetics and genomic research has been targeted at the family Paulownia spp. The little genetic information on this plant is a big obstacle to studying the mechanisms of its ability to resist Paulownia Witches' Broom (PaWB) disease. Analysis of the Paulownia transcriptome and its expression profile data are essential to extending the genetic resources on this species, thus will greatly improves our studies on Paulownia. In the current study, we performed the de novo assembly of a transcriptome on P. tomentosa × P. fortunei using the short-read sequencing technology (Illumina). 203,664 unigenes with a mean length of 1,328 bp was obtained. Of these unigenes, 32,976 (30% of all unigenes) containing complete structures were chosen. Eukaryotic clusters of orthologous groups, gene orthology, and the Kyoto Encyclopedia of Genes and Genomes annotations were performed of these unigenes. Genes related to PaWB disease resistance were analyzed in detail. To our knowledge, this is the first study to elucidate the genetic makeup of Paulownia. This transcriptome provides a quick way to understanding Paulownia, increases the number of gene sequences available for further functional genomics studies and provides clues to the identification of potential PaWB disease resistance genes. This study has provided a comprehensive insight into gene expression profiles at different states, which facilitates the study of each gene's roles in the developmental process and in PaWB disease resistance.

Effects of exogenous abscisic acid on carbohydrate metabolism and the expression levels of correlative key enzymes in winter wheat under low temperature

Two wheat (Triticum aestivum) cultivars, freeze-tolerant Dongnongdongmai 1 and freeze-sensitive Jimai 22, were used in this study. They were grown under field conditions, the leaves were sprayed with 1 × 10(-5) mol/L ABA and distilled water as control respectively at the three-true-leaf stage. Application of exogenous ABA increased the accumulation of carbohydrates in both cultivars, mainly in sucrose and fructose, except that the fructose content decreased in the leaves of Jimai 22. Exogenous ABA also enhanced the expression of key enzyme genes, especially in Dongnongdongmai 1 above 0 °C and in Jimai 22 below 0 °C. The carbohydrate contents and expression levels of the genes encoding key enzymes showed co-regulation in some, but not all of the pathways examined. Taken together, the higher sugar accumulation and the upregulation in expression of key enzymes in freeze-tolerant Dongnongdongmai 1 due to exogenous ABA suggest that active carbohydrate metabolism is mainly associated with the freeze tolerance of Dongnongdongmai 1.

Morphophysiological plasticity in a wheat variety in response to NaCl stress and its alleviation by exogenous abscisic acid

Nowadays, soil salinity is the most unfavourable abiotic factors for plant growth, causing important yield loss of many crops. A partial solution to this situation is to establish crop varieties in these areas affected which are tolerant to stress. The aim of this study was to evaluate in a wheat variety, the morphophysiological plasticity to sodium chloride (NaCl) stress and the effect of exogenous Abscisic Acid (ABA) on physiological variables. This was carried out by using the BI3000 wheat variety, for regional adaptability experiments. The germination percentage, coleoptile and radicle growth and root anatomic were evaluated, both seedling irrigated with water or saline solution. On the other hand, ABA sprays were applied to wheat plants and their biomass, pigment, stomatal behaviour and cellular membrane injuries were determined after salt treatments. In this study, it was possible to determine that the BI3000 wheat variety can grow in high electrical conductivity, with good germination and seedling growth. This variety showed less radical anatomic variations under salinity, what allows a faster plasticity to adapt. ABA applications suggest a protective role in plants under salinity, due to an increase in chlorophyll and carotene content, stability of cell membranes and stomatal behavior. This study is a contribution to a better understanding of the morphophysiological responses of glycophytic plants to salt stress. This have been pointed out as a useful approach to show more tolerance to salt stress crops in the future and it suggests that ABA could help improve agriculture production in areas affected by this stress.

Molecular cloning, characteristics and low temperature response of raffinose synthase gene in Cucumis sativus L

Raffinose synthase (RS, EC2.4.1.82) is one of the key enzymes that channels sucrose into the raffinose family oligosaccharides (RFOs) biosynthetic pathway. However, the gene encoding RS is poorly characterized in cucumber (Cucumis sativus L.), which is a typical RFOs-translocating plant species. Here we isolated the gene encoding RS (CsRS) from the leaves of cucumber plants. The complete cDNA of CsRS consisted of 2552 nucleotides with an open reading frame encoding a polypeptide of 784 amino acid residues. Reverse transcription-polymerase chain reaction and RNA hybridization analysis revealed that expression of CsRS was the highest in leaves followed by roots, fruits, and stems. The RS activity was up-regulated and the raffinose content was high in the leaves of transgenic tobacco with over-expression of CsRS, while both the RS activity and the raffinose content decreased in the transgenic cucumber plants with anti-sense expression of CsRS. The expression of CsRS could be induced by low temperature and exogenous phytohormone abscisic acid (ABA). In cucumber growing under low temperature stress, CsRS expression, RS activity and raffinose content increased gradually in the leaves, the fruits, the stems and the roots. The most notable increase was observed in the leaves. Similarly, the expression of CsRS was induced in cucumber leaves and fruits with 200 μM and 150 μM ABA treatments, respectively.

Non-coding RNAs in the plant response to abiotic stress

As sessile organisms, plants have to cope with the ever-changing environment as well as with numerous forms of stress. To react to these external cues, plants have evolved a suite of response mechanisms operating at many different levels, ranging from physiological to molecular processes that provide the organism with a wide phenotypic plasticity, allowing for fine tuning of the reactions to these adverse circumstances. During the past decade, non-coding RNAs (ncRNAs) have emerged as key regulatory molecules, which contribute to a significant portion of the transcriptome in eukaryotes and are involved in the control of transcriptional and post-transcriptional gene regulatory pathways. Although accumulated evidence supports an important role for ncRNAs in plant response and adaptation to abiotic stress, their mechanism(s) of action still remains obscure and a functional characterization of the ncRNA repertoire in plants is still needed. Moreover, common features in the biogenesis of different small ncRNAs, and in some cases, cross talk between different gene regulatory pathways may add to the complexity of these pathways and could play important roles in modulating stress responses. Here we review the various ncRNAs that have been reported to participate in the response to abiotic stress in plants, focusing on their importance in plant adaptation and evolution. Understanding how ncRNAs work may reveal novel mechanisms involved in the plant responses to the environment.

Phenotyping for drought tolerance of crops in the genomics era

Improving crops yield under water-limited conditions is the most daunting challenge faced by breeders. To this end, accurate, relevant phenotyping plays an increasingly pivotal role for the selection of drought-resilient genotypes and, more in general, for a meaningful dissection of the quantitative genetic landscape that underscores the adaptive response of crops to drought. A major and universally recognized obstacle to a more effective translation of the results produced by drought-related studies into improved cultivars is the difficulty in properly phenotyping in a high-throughput fashion in order to identify the quantitative trait loci that govern yield and related traits across different water regimes. This review provides basic principles and a broad set of references useful for the management of phenotyping practices for the study and genetic dissection of drought tolerance and, ultimately, for the release of drought-tolerant cultivars.

Complex genetics controls natural variation among seed quality phenotypes in a recombinant inbred population of an interspecific cross between Solanum lycopersicum × Solanum pimpinellifolium

Seed quality in tomato is associated with many complex physiological and genetic traits. While plant processes are frequently controlled by the action of small- to large-effect genes that follow classic Mendelian inheritance, our study suggests that seed quality is primarily quantitative and genetically complex. Using a recombinant inbred line population of Solanum lycopersicum × Solanum pimpinellifolium, we identified quantitative trait loci (QTLs) influencing seed quality phenotypes under non-stress, as well as salt, osmotic, cold, high-temperature and oxidative stress conditions. In total, 42 seed quality traits were analysed and 120 QTLs were identified for germination traits under different conditions. Significant phenotypic correlations were observed between germination traits under optimal conditions, as well as under different stress conditions. In conclusion, one or more QTLs were identified for each trait with some of these QTLs co-locating. Co-location of QTLs for different traits can be an indication that a locus has pleiotropic effects on multiple traits due to a common mechanistic basis. However, several QTLs also dissected seed quality in its separate components, suggesting different physiological mechanisms and signalling pathways for different seed quality attributes.

Jasmonic acid accumulation and systemic photosynthetic and electrical changes in locally burned wild type tomato, ABA-deficient sitiens mutants and sitiens pre-treated by ABA

Burning the terminal leaflet of younger tomato (Lycopersicon esculentum Mill.) leaf caused local and systemic changes in the surface electrical potential (SEP) and gas exchange (GE) parameters. The local and systemic accumulation of endogenous abscisic acid (ABA) and jasmonic acid (JA) was measured 85 min after burning. The experiments were conducted with wild type (WT) plants, ABA-deficient mutant sitiens (SIT) and ABA pre-treated SIT plants (SITA). First changes in SEP were detected within 1.5 min after burning and were followed by a decrease in GE parameters within 3-6 min in WT, SIT and SITA plants. GE and SEP time courses of SIT were different and wave amplitudes of SEP of SIT were lower compared to WT and SITA. ABA content in WT and SITA control plants was similar and substantially higher compared to SIT, JA content was similar among WT, SIT and SITA. While changes in the ABA content in systemic leaves have not been recorded after burning, the systemic JA content was substantially increased in WT and more in SIT and SITA. The results suggest that ABA content governs the systemic reaction of GE and the SEP shape upon local burning. ABA, JA and SEP participate in triggering the GE reaction. The ABA shortage in the SIT in the reaction to burning is partly compensated by an enhanced JA accumulation. This JA compensation is maintained even in SIT endogenously supplied with ABA. A correlation between the systemic JA content and changes in GE parameters or SEP was not found.

ABA signal in rice under stress conditions

Ever since its discovery, abscisic acid (ABA) has been intensively studied due to its versatile functions in plant developmental and physiological processes. Many signaling details of ABA have been well elucidated and reviewed. The identification of ABA receptors is a great breakthrough in the field of ABA study, whereas the discovery of ABA transporter has changed our concept that ABA is delivered solely by passive transport. The intensity of ABA signaling pathway is well known to be controlled by multi-regulators. Nonetheless, the interaction and coordination among ABA biosynthesis, catabolism, conjugation and transportation are seldom discussed. Here, we summarize the biological functions of ABA in response to different stresses, especially the roles of ABA in plant defense to pathogen attack, and discuss the possible relationships of these determinants in controlling the specificity and intensity of ABA signaling pathway in the rice.

Common and unique elements of the ABA-regulated transcriptome of Arabidopsis guard cells

Background

In the presence of drought and other desiccating stresses, plants synthesize and redistribute the phytohormone abscisic acid (ABA). ABA promotes plant water conservation by acting on specialized cells in the leaf epidermis, guard cells, which border and regulate the apertures of stomatal pores through which transpirational water loss occurs. Following ABA exposure, solute uptake into guard cells is rapidly inhibited and solute loss is promoted, resulting in inhibition of stomatal opening and promotion of stomatal closure, with consequent plant water conservation. There is a wealth of information on the guard cell signaling mechanisms underlying these rapid ABA responses. To investigate ABA regulation of gene expression in guard cells in a systematic genome-wide manner, we analyzed data from global transcriptomes of guard cells generated with Affymetrix ATH1 microarrays, and compared these results to ABA regulation of gene expression in leaves and other tissues.

Results

The 1173 ABA-regulated genes of guard cells identified by our study share significant overlap with ABA-regulated genes of other tissues, and are associated with well-defined ABA-related promoter motifs such as ABREs and DREs. However, we also computationally identified a unique cis-acting motif, GTCGG, associated with ABA-induction of gene expression specifically in guard cells. In addition, approximately 300 genes showing ABA-regulation unique to this cell type were newly uncovered by our study. Within the ABA-regulated gene set of guard cells, we found that many of the genes known to encode ion transporters associated with stomatal opening are down-regulated by ABA, providing one mechanism for long-term maintenance of stomatal closure during drought. We also found examples of both negative and positive feedback in the transcriptional regulation by ABA of known ABA-signaling genes, particularly with regard to the PYR/PYL/RCAR class of soluble ABA receptors and their downstream targets, the type 2C protein phosphatases. Our data also provide evidence for cross-talk at the transcriptional level between ABA and another hormonal inhibitor of stomatal opening, methyl jasmonate.

Conclusions

Our results engender new insights into the basic cell biology of guard cells, reveal common and unique elements of ABA-regulation of gene expression in guard cells, and set the stage for targeted biotechnological manipulations to improve plant water use efficiency.

Enhancing drought tolerance in C(4) crops

Adaptation to abiotic stresses is a quantitative trait controlled by many different genes. Enhancing the tolerance of crop plants to abiotic stresses such as drought has therefore proved to be somewhat elusive in terms of plant breeding. While many C(4) species have significant agronomic importance, most of the research effort on improving drought tolerance has focused on maize. Ideally, drought tolerance has to be achieved without penalties in yield potential. Possibilities for success in this regard are highlighted by studies on maize hybrids performed over the last 70 years that have demonstrated that yield potential and enhanced stress tolerance are associated traits. However, while our understanding of the molecular mechanisms that enable plants to tolerate drought has increased considerably in recent years, there have been relatively few applications of DNA marker technologies in practical C(4) breeding programmes for improved stress tolerance. Moreover, until recently, targeted approaches to drought tolerance have concentrated largely on shoot parameters, particularly those associated with photosynthesis and stay green phenotypes, rather than on root traits such as soil moisture capture for transpiration, root architecture, and improvement of effective use of water. These root traits are now increasingly considered as important targets for yield improvement in C(4) plants under drought stress. Similarly, the molecular mechanisms underpinning heterosis have considerable potential for exploitation in enhancing drought stress tolerance. While current evidence points to the crucial importance of root traits in drought tolerance in C(4) plants, shoot traits may also be important in maintaining high yields during drought.

Environmental stress enhances biosynthesis of flavor precursors, S-3-(hexan-1-ol)-glutathione and S-3-(hexan-1-ol)-L-cysteine, in grapevine through glutathione S-transferase activation

The biosynthesis of S-(3-hexan-1-ol)-glutathione (3MH-S-glut) and S-(3-hexan-l-ol)-L-cysteine (3MH-S-cys), which act as flavour precursors in wines, in Vitis vinifera grapes exposed to various environmental stress conditions is reported here. Ultraviolet (UV-C) irradiation, water deficit, and biological stimulation up-regulated 3MH-S-glut and 3MH-S-cys biosynthesis in grape leaves. 3MH-S-glut and 3MH-S-cys contents in grape berries were increased by cold shock, heat shock, UV-C irradiation, and biological stimulation. The results suggest that environmental stress enhances the biosynthesis of both flavour precursors in grapevine. The transcription of VvGST1, VvGST3, VvGST4, and GGT in grapevine exposed to the stress conditions was increased markedly compared with that in control grapevine. Also, UV irradiation increased GST (glutathione S-transferase) and GGT (γ-glutamyl transferase) enzyme activities in grape berries. Recombinant VvGST3 and VvGST4, but not VvGST1, mediated the synthesis of 3MH-S-glut from reduced glutathione and trans-2-hexenal in vitro. The enzymatic mediation of flavour precursor production is a novel function of plant GSTs and may result in the detoxification of damaged grape cells under stress conditions.