Coordinate transcriptional induction of myo-inositol metabolism during environmental stress

Metabolomics reveals the phytotoxicity mechanisms of foliar spinach exposed to bulk and nano sizes of PbCO3

PbCO3 is an ancient raw material for Pb minerals and continues to pose potential risks to the environment and human health through mining and industrial processes. However, the specific effects of unintentional PbCO3 discharge on edible plants remain poorly understood. This study unravels how foliar application of PbCO3 induces phytotoxicity by potentially influencing leaf morphology, photosynthetic pigments, oxidative stress, and metabolic pathways related to energy regulation, cell damage, and antioxidant defense in Spinacia oleracea L. Additionally, it quantifies the resultant human health risks. Plants were foliarly exposed to PbCO3 nanoparticles (NPs) and bulk products (BPs), as well as Pb2+ at 0, 5, 10, 25, 50, and 100 mg·L-1 concentrations once a day for three weeks. The presence and localization of PbCO3 NPs inside the plant cells were confirmed by TEM-EDS analysis. The maximum accumulation of total Pb was recorded in the root (2947.77 mg·kg-1 DW for ion exposure), followed by the shoot (942.50 mg·kg-1 DW for NPs exposure). The results revealed that PbCO3 and Pb2+ exposure had size- and dose-dependent inhibitory effects on spinach length, biomass, and photosynthesis attributes, inducing impacts on the antioxidase activity of CAT, membrane permeability, and nutrient elements absorption and translocation. Pb2+ exhibited pronounced toxicity in morphology and chlorophyll; PbCO3 BP exposure accumulated the most lipid peroxidation products of MDA and H2O2; and PbCO3 NPs triggered the largest cell membrane damage. Furthermore, PbCO3 NPs at 10 and 100 mg·L-1 induced dose-dependent metabolic reprogramming in spinach leaves, disturbing the metabolic mechanisms related to amino acids, antioxidant defense, oxidative phosphorylation, fatty acid cycle, and the respiratory chain. The spinach showed a non-carcinogenic health risk hierarchy: Pb2+ > PbCO3 NPs > PbCO3 BPs, with children more vulnerable than adults. These findings enhance our understanding of PbCO3 particle effects on food security, emphasizing the need for further research to minimize their impact on human dietary health.

Changes in the Carbohydrate Profile in Common Buckwheat (Fagopyrum esculentum Moench) Seedlings Induced by Cold Stress and Dehydration

Plant species are sensitive to stresses, especially at the seedling stage, and they respond to these conditions by making metabolic changes to counteract the negative effects of this. The objectives of this study were to determine carbohydrate profile in particular organs (roots, hypocotyl, and cotyledons) of common buckwheat seedlings and to verify whether carbohydrate accumulation is similar or not in the organs in response to cold stress and dehydration. Roots, hypocotyl, and cotyledons of common buckwheat seedlings have various saccharide compositions. The highest concentrations of cyclitols, raffinose, and stachyose were found in the hypocotyl, indicating that they may be transported from cotyledons, although this needs further studies. Accumulation of raffinose and stachyose is a strong indicator of the response of all buckwheat organs to introduced cold stress. Besides, cold conditions reduced d-chiro-inositol content, but did not affect d-pinitol level. Enhanced accumulation of raffinose and stachyose were also a distinct response of all organs against dehydration at ambient temperature. The process causes also a large decrease in the content of d-pinitol in buckwheat hypocotyl, which may indicate its transformation to d-chiro-inositol whose content increased at that time. In general, the sucrose and its galactosides in hypocotyl tissues were subject to the highest changes to the applied cold and dehydration conditions compared to the cotyledons and roots. This may indicate tissue differences in the functioning of the protective system(s) against such threats.

Exogenous myo-inositol increases salt tolerance and accelerates CAM induction in the early juvenile stage of the facultative halophyte Mesembryanthemum crystallinum but not in the late juvenile stage

Mesembryanthemum crystallinum L. (ice plant) develops salt tolerance during the transition from the juvenile to the adult stage through progressive morphological, physiological, biochemical, and molecular changes. Myo -inositol is the precursor for the synthesis of compatible solute D-pinitol and promotes Na+ transport in ice plants. We previously showed that supplying myo -inositol to 9-day-old seedlings alleviates salt damage by coordinating the expression of genes involved in inositol synthesis and transport, affecting osmotic adjustment and the Na/K balance. In this study, we examined the effects of myo -inositol on physiological parameters and inositol-related gene expression in early- and late-stage juvenile plants. The addition of myo -inositol to salt-treated, hydroponically grown late juvenile plants had no significant effects on growth or photosynthesis. In contrast, supplying exogenous myo -inositol to salt-treated early juvenile plants increased leaf biomass, relative water content, and chlorophyll content and improved PSII activity and CO2 assimilation. The treatment combining high salt and myo -inositol synergistically induced the expression of myo -inositol phosphate synthase (INPS ), myo -inositol O -methyltransferase (IMT ), and inositol transporters (INTs ), which modulated root-to-shoot Na/K ratio and increased leaf D-pinitol content. The results indicate that sufficient myo -inositol is a prerequisite for high salt tolerance in ice plant.

Salt Stress-Regulation of Root Water Uptake in a Whole-Plant and Diurnal Context

This review focuses on the regulation of root water uptake in plants which are exposed to salt stress. Root water uptake is not considered in isolation but is viewed in the context of other potential tolerance mechanisms of plants-tolerance mechanisms which relate to water relations and gas exchange. Plants spend between one third and half of their lives in the dark, and salt stress does not stop with sunset, nor does it start with sunrise. Surprisingly, how plants deal with salt stress during the dark has received hardly any attention, yet any growth response to salt stress over days, weeks, months and years is the integrative result of how plants perform during numerous, consecutive day/night cycles. As we will show, dealing with salt stress during the night is a prerequisite to coping with salt stress during the day. We hope to highlight with this review not so much what we know, but what we do not know; and this relates often to some rather basic questions.

Mitochondrial Complex I Disruption Causes Broad Reorchestration of Plant Lipidome Including Chloroplast Lipids

Mitochondrial complex I (CI) plays a crucial role in oxidising NADH generated by the metabolism (including photorespiration) and thereby participates in the mitochondrial electron transfer chain feeding oxidative phosphorylation that generates ATP. However, CI mutations are not lethal in plants and cause moderate phenotypes, and therefore CI mutants are instrumental to examine consequences of mitochondrial homeostasis disturbance on plant cell metabolisms and signalling. To date, the consequences of CI disruption on the lipidome have not been examined. Yet, in principle, mitochondrial dysfunction should impact on lipid synthesis through chloroplasts (via changes in photorespiration, redox homeostasis, and N metabolism) and the endoplasmic reticulum (ER) (via perturbed mitochondrion-ER crosstalk). Here, we took advantage of lipidomics technology (by LC-MS), phospholipid quantitation by ³¹P-NMR, and total lipid quantitation to assess the impact of CI disruption on leaf, pollen, and seed lipids using three well-characterised CI mutants: CMSII in N. sylvestris and both ndufs4 and ndufs8 in Arabidopsis. Our results show multiple changes in cellular lipids, including galactolipids (chloroplastic), sphingolipids, and ceramides (synthesised by ER), suggesting that mitochondrial homeostasis is essential for the regulation of whole cellular lipidome via specific signalling pathways. In particular, the observed modifications in phospholipid and sphingolipid/ceramide molecular species suggest that CI activity controls phosphatidic acid-mediated signalling.

Myo-inositol transport and metabolism participate in salt tolerance of halophyte ice plant seedlings

Myo-inositol and its metabolic derivatives such as pinitol, galactinol, and raffinose affect growth and development and are also involved in stress adaptation. Previous studies have identified myo-inositol transporters (INTs) as transporters of Na⁺ from root to shoot in the halophyte ice plant (Mesembryanthemum crystallinum). We found that the supply of myo-inositol could alleviate the dehydration effects of salt-stressed ice plant seedlings by decreasing the Na/K ratio in roots and increasing the Na/K ratio in shoots. Analyses of the uptake of exogenous myo-inositol revealed that ice plant seedlings contained intrinsic high-affinity transporters and inducible low-affinity uptake systems. The presence of Na⁺ facilitated both high- and low-affinity myo-inositol uptake. Six INT genes were identified from the ice plant transcriptome and named McINT1a, 1b, 2, 4a, 4b, and 4c, according to the classification of the Arabidopsis INT family. In seedlings treated with myo-inositol, salt, or myo-inositol plus salt, the expression patterns of all McINT members differed in shoot and root, which indicates organ-specific regulation of McINTs by salt and myo-inositol. The expression of McINT2, 4a, 4b, and 4c was induced by salt stress in shoot and root, but that of McINT1a and 1b was salt-induced only in shoot. The expression of pinitol biosynthesis gene IMT1 was induced by salt and myo-inositol, and their combination had a synergistic effect on the accumulation of pinitol. Supply of myo-inositol to salt-treated seedlings alleviated the detrimental effects by maintaining a low root Na/K ratio and providing precursors for the synthesis of compatible solute to maintain the osmotic balance.

Comparative physiological and full-length transcriptome analyses reveal the molecular mechanism of melatonin-mediated salt tolerance in okra (Abelmoschus esculentus L.)

BACKGROUND

Melatonin, a multifunctional signal molecule, has been reported to play crucial roles in growth and development and stress responses in various plant species. Okra (Abelmoschus esculentus L.) is a food crop with extremely high values of nutrition and healthcare. Recent reports have revealed the protective role of melatonin in alleviating salt stress. However, little is known about its regulatory mechanisms in response to salt stress in okra.

RESULTS

In this study, we explored whether exogenous melatonin pretreatment could alleviate salt stress (300 mM NaCl) of okra plants. Results showed that exogenous application of melatonin (50 μM) significantly enhanced plant tolerance to salt stress, as demonstrated by the plant resistant phenotype, as well as by the higher levels of the net photosynthetic rate, chlorophyll fluorescence and chlorophyll content in comparison with nontreated salt-stressed plants. Additionally, melatonin pretreatment remarkably decreased the levels of lipid peroxidation and H₂O₂ content and scavenged O₂^•- in melatonin-pretreated plants, which may be attributed to the higher levels of enzyme activities including POD and GR. Moreover, a combination of third- (PacBio) and second-generation (Illumina) sequencing technologies was applied to sequence full-length transcriptomes of okra. A total of 121,360 unigenes was obtained, and the size of transcript lengths ranged from 500 to 6000 bp. Illumina RNA-seq analysis showed that: Comparing with control, 1776, 1063 and 1074 differential expression genes (DEGs) were identified from the three treatments (NaCl, MT50 and MT + NaCl, respectively). These genes were enriched in more than 10 GO terms and 34 KEGG pathways. Nitrogen metabolism, sulfur metabolism, and alanine, aspartate and glutamate metabolism were significantly enriched in all three treatments. Many transcription factors including MYB, WRKY, NAC etc., were also identified as DEGs.

CONCLUSIONS

Our preliminary results suggested that melatonin pretreatment enhanced salt tolerance of okra plants for the first time. These data provide the first set of full-length isoforms in okra and more comprehensive insights into the molecular mechanism of melatonin responses to salt stress.

Systems biology reveals key tissue-specific metabolic and transcriptional signatures involved in the response of Medicago truncatula plant genotypes to salt stress

•

Τhe response of different Medicago truncatula genotypes to salt stress was examined.

•

Systems biology revealed tissue-specific metabolic and transcriptional signatures.

•

RFO metabolites linked with tolerance were identified.

•

Several genes belonging to the TIR-NBS-LRR class were linked with hyper-sensitivity.

Salt stress is an important factor limiting plant productivity by affecting plant physiology and metabolism. To explore salt tolerance adaptive mechanisms in the model legume Medicago truncatula, we used three genotypes with differential salt-sensitivity: TN6.18 (highly sensitive), Jemalong A17 (moderately sensitive), and TN1.11 (tolerant). Cellular damage was monitored in roots and leaves 48 h after 200 mM NaCl treatment by measuring lipid peroxidation, nitric oxide, and hydrogen peroxide contents, further supported by leaf stomatal conductance and chlorophyll readings. The salt-tolerant genotype TN1.11 displayed the lowest level of oxidative damage, in contrast to the salt sensitive TN6.18, which showed the highest responses. Metabolite profiling was employed to explore the differential genotype-related responses to stress at the molecular level. The metabolic data in the salt tolerant TN1.11 roots revealed an accumulation of metabolites related to the raffinose pathway. To further investigate the sensitivity to salinity, global transcriptomic profiling using microarray analysis was carried out on the salt-stressed sensitive genotypes. In TN6.18, the transcriptomic analysis identified a lower expression of many genes related to stress signalling, not previously linked to salinity, and corresponding to the TIR-NBS-LRR gene class. Overall, this global approach contributes to gaining significant new insights into the complexity of stress adaptive mechanisms and to the identification of potential targets for crop improvement.

Metabolic engineering: Towards water deficiency adapted crop plants

Water deficiency caused by drought is one of the severe environmental conditions limiting plant growth, development, and yield. In this review article, we will summarize the changes in transcription, metabolism, and phytohormones under drought stress conditions and show the key transcription factors in these processes. We will also highlight the recent attempts to enhance stress tolerance without growth retardation and discuss the perspective on the development of stress adapted crops by engineering transcription factors.

Metabolite/phytohormone-gene regulatory networks in soybean organs under dehydration conditions revealed by integration analysis

Metabolites, phytohormones, and genes involved in dehydration responses/tolerance have been predicted in several plants. However, metabolite/phytohormone-gene regulatory networks in soybean organs under dehydration conditions remain unclear. Here, we analyzed the organ specificity of metabolites, phytohormones, and gene transcripts and revealed the characteristics of their regulatory networks in dehydration-treated soybeans. Our metabolite/phytohormone analysis revealed the accumulation of raffinose, trehalose, and cis-zeatin (cZ) specifically in dehydration-treated roots. In dehydration-treated soybeans, raffinose, and trehalose might have additional roles not directly involved in protecting the photosynthetic apparatus; cZ might contribute to root elongation for water uptake from the moisture region in soil. Our integration analysis of metabolites-genes indicated that galactinol, raffinose, and trehalose levels were correlated with transcript levels for key enzymes (galactinol synthase, raffinose synthase, trehalose 6-phosphate synthase, trehalose 6-phosphate phosphatase) at the level of individual plants but not at the organ level under dehydration. Genes encoding these key enzymes were expressed in mainly the aerial parts of dehydration-treated soybeans. These results suggested that raffinose and trehalose are transported from aerial plant parts to the roots in dehydration-treated soybeans. Our integration analysis of phytohormones-genes indicated that cZ and abscisic acid (ABA) levels were correlated with transcript levels for key enzymes (cytokinin nucleoside 5'-monophosphate phosphoribohydrolase, cytokinin oxidases/dehydrogenases, 9-cis-epoxycarotenoid dioxygenase) at the level of individual plants but not at the organ level under dehydration conditions. Therefore, processes such as ABA and cZ transport, among others, are important for the organ specificity of ABA and cZ production under dehydration conditions.

Inositol Pyrophosphate Pathways and Mechanisms: What Can We Learn from Plants?

The ability of an organism to maintain homeostasis in changing conditions is crucial for growth and survival. Eukaryotes have developed complex signaling pathways to adapt to a readily changing environment, including the inositol phosphate (InsP) signaling pathway. In plants and humans the pyrophosphorylated inositol molecules, inositol pyrophosphates (PP-InsPs), have been implicated in phosphate and energy sensing. PP-InsPs are synthesized from the phosphorylation of InsP6, the most abundant InsP. The plant PP-InsP synthesis pathway is similar but distinct from that of the human, which may reflect differences in how molecules such as Ins(1,4,5)P3 and InsP6 function in plants vs. animals. In addition, PP-InsPs can potentially interact with several major signaling proteins in plants, suggesting PP-InsPs play unique signaling roles via binding to protein partners. In this review, we will compare the biosynthesis and role of PP-InsPs in animals and plants, focusing on three central themes: InsP6 synthesis pathways, synthesis and regulation of the PP-InsPs, and function of a specific protein domain called the Syg1, Pho1, Xpr1 (SPX ) domain in binding PP-InsPs and regulating inorganic phosphate (Pi) sensing. This review will provide novel insights into the biosynthetic pathway and bioactivity of these key signaling molecules in plant and human systems.

Insight into the Characteristics and New Mechanism of Nicosulfuron Biodegradation by a Pseudomonas sp. LAM1902

A total of five strains of nicosulfuron-degrading bacteria were isolated from a continuously cultivated microbial consortium using culturomics. Among them, a novel Pseudomonas strain, LAM1902, with the highest degradation efficiency was investigated in detail. The characteristics of nicosulfuron-degradation by LAM1902 were investigated and optimized by response surface analysis. Furthermore, non-targeted metabolomic analysis of extracellular and intracellular biodegradation of nicosulfuron by LAM1902 was carried out by liquid chromatography/mass spectroscopy (LC-MS) and gas chromatography-time-of-flight/mass spectroscopy (GC-TOF/MS). It was found that nicosulfuron was degraded by LAM1902 mainly via breaking the sulfonylurea bridge, and this degradation might be attributed to oxalate accumulation. The results of GC-TOF/MS also showed that the intracellular degradation of nicosulfuron did not occur. However, nicosulfuron exerted a significant influence on the metabolism of inositol phosphate, pyrimidine, arginine/proline, glyoxylate, and dicarboxylate metabolism and streptomycin biosynthesis. The changes of myo-inositol, trehalose, and 3-aminoisobutanoic acid were proposed as a mechanism of self-protection against nicosulfuron stress.

Halophyte Common Ice Plants: A Future Solution to Arable Land Salinization

The problems associated with the salinization of soils and water bodies and the increasing competition for scarce freshwater resources are increasing. Current attempts to adapt to these conditions through sustainable agriculture involves searching for new highly salt-tolerant crops, and wild species that have potential as saline crops are particularly suitable. The common ice plant (Mesembryanthemum crystallinum L.) is an edible halophyte member of the Aizoaceae family, which switches from C3 photosynthesis to crassulacean acid metabolism (CAM) when exposed to salinity or water stress. The aim of this review was to examine the potential of using the ice plant in both the wild and as a crop, and to describe its ecology and morphology, environmental and agronomic requirements, and physiology. The antioxidant properties and mineral composition of the ice plant are also beneficial to human health and have been extensively examined.

Two-step d-ononitol epimerization pathway in Medicago truncatula

Methylated inositol, d-pinitol (3-O-methyl-d-chiro-inositol), is a common constituent in legumes. It is synthesized from myo-inositol in two reactions: the first reaction, catalyzed by myo-inositol-O-methyltransferase (IMT), consists of a transfer of a methyl group from S-adenosylmethionine to myo-inositol with the formation of d-ononitol, while the second reaction, catalyzed by d-ononitol epimerase (OEP), involves epimerization of d-ononitol to d-pinitol. To identify the genes involved in d-pinitol biosynthesis in a model legume Medicago truncatula, we conducted a BLAST search on its genome using soybean IMT cDNA as a query and found putative IMT (MtIMT) gene. Subsequent co-expression analysis performed on publicly available microarray data revealed two potential OEP genes: MtOEPA, encoding an aldo-keto reductase and MtOEPB, encoding a short-chain dehydrogenase. cDNAs of all three genes were cloned and expressed as recombinant proteins in E. coli. In vitro assays confirmed that putative MtIMT enzyme catalyzes methylation of myo-inositol to d-ononitol and showed that MtOEPA enzyme has NAD+ -dependent d-ononitol dehydrogenase activity, while MtOEPB enzyme has NADP+ -dependent d-pinitol dehydrogenase activity. Both enzymes are required for epimerization of d-ononitol to d-pinitol, which occurs in the presence of NAD+ and NADPH. Introduction of MtIMT, MtOEPA, and MtOEPB genes into tobacco plants resulted in production of d-ononitol and d-pinitol in transformants. As this two-step pathway of d-ononitol epimerization is coupled with a transfer of reducing equivalents from NADPH to NAD+ , we speculate that one of the functions of this pathway might be regeneration of NADP+ during drought stress.

Seed targeted RNAi-mediated silencing of GmMIPS1 limits phytate accumulation and improves mineral bioavailability in soybean

Phytic acid (PA), the major phosphorus reserve in soybean seeds (60-80%), is a potent ion chelator, causing deficiencies that leads to malnutrition. Several forward and reverse genetics approaches have ever since been explored to reduce its phytate levels to improve the micronutrient and phosphorous availability. Transgenic technology has met with success by suppressing the expression of the PA biosynthesis-related genes in several crops for manipulating their phytate content. In our study, we targeted the disruption of the expression of myo-inositol-3-phosphate synthase (MIPS1), the first and the rate limiting enzyme in PA biosynthesis in soybean seeds, by both antisense (AS) and RNAi approaches, using a seed specific promoter, vicilin. PCR and Southern analysis revealed stable integration of transgene in the advanced progenies. The transgenic seeds (T4) of AS (MS14-28-12-29-3-5) and RNAi (MI51-32-22-1-13-6) soybean lines showed 38.75% and 41.34% reduction in phytate levels respectively, compared to non-transgenic (NT) controls without compromised growth and seed development. The electron microscopic examination also revealed reduced globoid crystals in the Protein storage vacoules (PSVs) of mature T4 seeds compared to NT seed controls. A significant increase in the contents of Fe2+ (15.4%, 21.7%), Zn2+ (7.45%, 11.15%) and Ca2+ (10.4%, 15.35%) were observed in MS14-28-12-29-3-5 and MI51-32-22-1-13-6 transgenic lines, respectively, compared to NT implicating improved mineral bioavailability. This study signifies proof-of-concept demonstration of seed-specific PA reduction and paves the path towards low phytate soybean through pathway engineering using the new and precise editing tools.

Efficient Bioconversion of Sucrose to High-Value-Added Glucaric Acid by In Vitro Metabolic Engineering

Glucaric acid (GA) is a major value-added chemicals feedstock and additive, especially in the food, cosmetics, and pharmaceutical industries. The increasing demand for GA is driving the search for a more efficient and less costly production pathway. In this study, a new in vitro multi-enzyme cascade system was developed, which converts sucrose efficiently to GA in a single vessel. The in vitro system, which does not require adenosine triphosphate (ATP) or nicotinamide adenine dinucleotide (NAD⁺ ) supplementation, contains seven enzymes. All enzymes were chosen from the BRENDA and NCBI databases and were expressed efficiently in Escherichia coli BL21(DE3). All seven enzymes were combined in an in vitro cascade system, and the reaction conditions were optimized. Under the optimized conditions, the in vitro seven-enzyme cascade system converted 50 mm sucrose to 34.8 mm GA with high efficiency (75 % of the theoretical yield). This system represents an alternative pathway for more efficient and less costly production of GA, which could be adapted for the synthesis of other value-added chemicals.

Water Deficit Elicits a Transcriptional Response of Genes Governing d-pinitol Biosynthesis in Soybean (Glycine max)

d-pinitol is the most commonly accumulated sugar alcohol in the Leguminosae family and has been observed to increase significantly in response to abiotic stress. While previous studies have identified genes involved in d-pinitol synthesis, no study has investigated transcript expression in planta. The present study quantified the expression of several genes involved in d-pinitol synthesis in different plant tissues and investigated the accumulation of d-pinitol, myo-inositol and other metabolites in response to a progressive soil drought in soybean (Glycine max). Expression of myo-inositol 1-phosphate synthase (INPS), the gene responsible for the conversion of glucose-6-phosphate to myo-inositol-1-phosphate, was significantly up regulated in response to a water deficit for the first two sampling weeks. Expression of myo-inositol O-methyl transferase (IMT1), the gene responsible for the conversion of myo-inositol into d-ononitol was only up regulated in stems at sampling week 3. Assessment of metabolites showed significant changes in their concentration in leaves and stems. d-Pinitol concentration was significantly higher in all organs sampled from water deficit plants for all three sampling weeks. In contrast, myo-inositol, had significantly lower concentrations in leaf samples despite up regulation of INPS suggesting the transcriptionally regulated flux of carbon through the myo-inositol pool is important during water deficit.

The Healing-Promoting Properties of Selected Cyclitols-A Review

INTRODUCTION

Myo-inositol and its derivatives cyclitols play an important role in the processes of cell regulation, signal transduction, osmoregulation, and ion channel physiology, and are a component of the cell membrane. Free cyclitols present in food or released during the degradation of galactosyl cyclitols by bacteria (in digestive tract) show some physiological benefits.

AIM

The aim of this paper is to present and analyze the documented data about curative and healing properties of cyclitols.

RESULTS AND DISCUSSION

Cyclitols are well known compounds in the treatment of an accompanied diabetes insulin resistance, and also obesity and polycystic ovarian syndrome. d-chiro-Inositol deficiency exacerbates insulin resistance in the liver, muscles, and fat, while depletion of myo-inositol results in the development of diabetic complications. Cyclitols are successfully applied in treatment of polycystic ovarian syndrome, simultaneous are observed effective reducing of BMI, improving the hormonal profile, and increasing fertility. Moreover, cyclitols have anti-atherogenic, anti-oxidative, anti-inflammatory, and anti-cancer properties.

CONCLUSION

The properties of cyclitols may be a good therapeutic option in the reduction of metabolically induced inflammation. Due to well drugs tolerance and low toxicity of these compounds, cyclitols are recommend for pregnant women and also for children. Another advantage is their widespread presence and easy availability, which encourages their use in medicine.

The Tonoplastic Inositol Transporter INT1 From Arabidopsis thaliana Impacts Cell Elongation in a Sucrose-Dependent Way

The tonoplastic inositol transporter INT1 is the only known transport protein in Arabidopsis that facilitates myo-inositol import from the vacuole into the cytoplasm. Impairment of the release of vacuolar inositol by knockout of INT1 results in a severe inhibition of cell elongation in roots as well as in etiolated hypocotyls. Importantly, a more strongly reduced cell elongation was observed when sucrose was supplied in the growth medium, and this sucrose-dependent effect can be complemented by the addition of exogenous myo-inositol. Comparing int1 mutants (defective in transport) with mutants defective in myo-inositol biosynthesis (mips1 mutants) revealed that the sucrose-induced inhibition in cell elongation does not just depend on inositol depletion. Secondary effects as observed for altered availability of inositol in biosynthesis mutants, as disturbed membrane turnover, alterations in PIN protein localization or alterations in inositol-derived signaling molecules could be ruled out to be responsible for impairing the cell elongation in int1 mutants. Although the molecular mechanism remains to be elucidated, our data implicate a crucial role of INT1-transported myo-inositol in regulating cell elongation in a sucrose-dependent manner and underline recent reports of regulatory roles for sucrose and other carbohydrate intermediates as metabolic semaphores.

Increased salt and drought tolerance by D-pinitol production in transgenic Arabidopsis thaliana

D-ononitol epimerase (OEP) catalyzes the conversion of D-ononitol to D-pinitol, which is the last step in the biosynthetic pathway, where myo-inositol is converted to pinitol in higher plants. In this study, OEP cDNA was isolated from Glycine max (GmOEP) and was functionally characterized, which confirmed that GmOEP expression was induced by high salinity and drought stress treatments. To understand the biological function of GmOEP, transgenic Arabidopsis plants overexpressing this protein were constructed. The transgenic Arabidopsis plants displayed enhanced tolerance to high salinity and drought stress treatments.

Sugar metabolism in the desiccation tolerant grass Oropetium thomaeum in response to environmental stresses

Oropetium thomaeum is a desiccation tolerant grass and acquisition of desiccation tolerance is correlated with changes in carbohydrate metabolism. Here we address the question whether the changes in carbohydrate metabolism are specific to the dehydration process or whether other environmental factors such as high temperature, low temperature, hypoxia, salinity or exogenous ABA application trigger the same or different changes in the sugar metabolism. Fifteen different sugar metabolites were identified by GC/MS, including erythritol, arabinose, fructose, galactose, glucose, myo-inositol, sedoheptulose, sucrose, trehalose, galactinol, maltose, raffinose, manninotriose and stachyose. Together with starch, these sugars were placed into the pathways of sucrose metabolism and raffinose family oligosaccharides (RFOs) metabolism, as well as into the group of rare sugars. By comparing the changes of sugars under various stresses, we concluded that the changes in the sugar metabolism are both convergent and divergent in response to different stresses. Except for the general response to stress, such as starch degradation, the changes of specific sugar metabolites reflect a stress-specific response of O. thomaeum. Erythritol seems to be specific for dehydration, myo-inositol for salt stress and trehalose for hypoxia stress. Similar as dehydration, low temperature, salt stress and ABA application resulted in the accumulation of sucrose and RFOs in O. thomaeum, which indicates that these stresses share high similarity with dehydration. Thus it is proposed that sucrose and RFOs have a general protective role under these stresses. In contrast sucrose and RFOs did not accumulate in response to high temperature or hypoxia whose effects tend to be consumptive and destructive. The accumulation of galactose, melibiose and manninotriose demonstrate that RFOs are degraded under stress. The accumulation of these sugar metabolites might result from the reaction of RFOs and stress-produced hydroxyl radicals, which supports a possible role of RFOs in stress defense. In addition, ABA application led to substantial synthesis of stachyose which occurs only in response to dehydration, indicating that stachyose synthesis is possibly closely related to ABA in O. thomaeum.

Rice intermediate filament, OsIF, stabilizes photosynthetic machinery and yield under salinity and heat stress

Cytoskeleton plays a vital role in stress tolerance; however, involvement of intermediate filaments (IFs) in such a response remains elusive in crop plants. This study provides clear evidence about the unique involvement of IFs in cellular protection against abiotic stress in rice. Transcript abundance of Oryza sativa intermediate filament (OsIF) encoding gene showed 2-10 fold up-regulation under different abiotic stress. Overexpression of OsIF in transgenic rice enhanced tolerance to salinity and heat stress, while its knock-down (KD) rendered plants more sensitive thereby indicating the role of IFs in promoting survival under stress. Seeds of OsIF overexpression rice germinated normally in the presence of high salt, showed better growth, maintained chloroplast ultrastructure and favourable K+/Na+ ratio than the wild type (WT) and KD plants. Analysis of photosynthesis and chlorophyll a fluorescence data suggested better performance of both photosystem I and II in the OsIF overexpression rice under salinity stress as compared to the WT and KD. Under salinity and high temperature stress, OsIF overexpressing plants could maintain significantly high yield, while the WT and KD plants could not. Further, metabolite profiling revealed a 2-4 fold higher accumulation of proline and trehalose in OsIF overexpressing rice than WT, under salinity stress.

Proteomic analysis of early salt stress responsive proteins in alfalfa roots and shoots

Background

Alfalfa (Medicago sativa) is the most extensively cultivated forage legume in the world, and salinity stress is the most problematic environmental factors limiting alfalfa production. To evaluate alfalfa tissue variations in response to salt stress, comparative physiological and proteomic analyses were made of salt responses in the roots and shoots of the alfalfa.

Method

A two-dimensional gel electrophoresis (2-DE)-based proteomic technique was employed to identify the differentially abundant proteins (DAPs) from salt-treated alfalfa roots and shoots of the salt tolerance cultivars Zhongmu No 1 cultivar, which was subjected to a range of salt stress concentrations for 9 days. In parallel, REL, MAD and H₂O₂ contents, and the activities of antioxidant enzymes of shoots and roots were determinand.

Result

Twenty-seven spots in the shoots and 36 spots in the roots that exhibited showed significant abundance variations were identified by MALDI-TOF-TOF MS. These DAPs are mainly involved in the biological processes of photosynthesis, stress and defense, carbohydrate and energy metabolism, second metabolism, protein metabolism, transcriptional regulation, cell wall and cytoskeleton metabolism, ion transpor, signal transduction. In parallel, physiological data were correlated well with our proteomic results. It is worth emphasizing that some novel salt-responsive proteins were identified, such as CP12, pathogenesis-related protein 2, harvest-induced protein, isoliquiritigenin 2′-O-methyltransferase. qRT-PCR was used to study the gene expression levels of the four above-mentioned proteins; four patterns are consistent with those of induced protein.

Conclusion

The primary mechanisms underlying the ability of alfalfa seedlings to tolerate salt stress were photosynthesis, detoxifying and antioxidant, secondary metabolism, and ion transport. And it also suggests that the different tissues responded to salt-stress in different ways.

Salt tolerance response revealed by RNA-Seq in a diploid halophytic wild relative of sweet potato

Crop wild relatives harbor exotic and novel genetic resources, which hold great potential for crop improvement. Ipomoea imperati is a wild diploid relative of sweet potato with the capability of high salinity tolerance. We compared the transcriptomes of I. imperati under salt stress vs. control to identify candidate genes and pathways involved in salt response. De novo assembly produced 67,911 transcripts with a high depth of coverage. A total of 39,902 putative genes were assigned annotations, and 936 and 220 genes involved in salt response in roots and leaves, respectively. Functional analysis indicated a whole system response during salt stress in I. imperati, which included four metabolic processes: sensory initiation, transcriptional reprogramming, cellular protein component change, and cellular homeostasis regulation. We identified a number of candidate genes involved in the ABA signaling pathway, as well as transcription factors, transporters, antioxidant enzymes, and enzymes associated with metabolism of synthesis and catalysis. Furthermore, two membrane transporter genes, including vacuole cation/proton exchanger and inositol transporter, were considered to play important roles in salt tolerance. This study provided valuable information not only for understanding the genetic basis of ecological adaptation but also for future application in sweet potato and other crop improvements.

Overexpression of the OsIMP Gene Increases the Accumulation of Inositol and Confers Enhanced Cold Tolerance in Tobacco through Modulation of the Antioxidant Enzymes' Activities

Inositol is a cyclic polyol that is involved in various physiological processes, including signal transduction and stress adaptation in plants. l-myo-inositol monophosphatase (IMPase) is one of the metal-dependent phosphatase family members and catalyzes the last reaction step of biosynthesis of inositol. Although increased IMPase activity induced by abiotic stress has been reported in chickpea plants, the role and regulation of the IMP gene in rice (Oryza sativa L.) remains poorly understood. In the present work, we obtained a full-length cDNA sequence coding IMPase in the cold tolerant rice landraces in Gaogonggui, which is named as OsIMP. Multiple alignment results have displayed that this sequence has characteristic signature motifs and conserved enzyme active sites of the phosphatase super family. Phylogenetic analysis showed that IMPase is most closely related to that of the wild rice Oryza brachyantha, while transcript analysis revealed that the expression of the OsIMP is significantly induced by cold stress and exogenous abscisic acid (ABA) treatment. Meanwhile, we cloned the 5' flanking promoter sequence of the OsIMP gene and identified several important cis-acting elements, such as LTR (low-temperature responsiveness), TCA-element (salicylic acid responsiveness), ABRE-element (abscisic acid responsiveness), GARE-motif (gibberellin responsive), MBS (MYB Binding Site) and other cis-acting elements related to defense and stress responsiveness. To further investigate the potential function of the OsIMP gene, we generated transgenic tobacco plants overexpressing the OsIMP gene and the cold tolerance test indicated that these transgenic tobacco plants exhibit improved cold tolerance. Furthermore, transgenic tobacco plants have a lower level of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and a higher content of total chlorophyll as well as increased antioxidant enzyme activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), when compared to wild type (WT) tobacco plants under normal and cold stress conditions.

Identification of Biochemical Pathways Associated with Lead Tolerance and Detoxification in Chrysopogon zizanioides L. Nash (Vetiver) by Metabolic Profiling

Lead (Pb) is a major urban pollutant, due to deteriorating lead-based paint in houses built before 1978. Phytoremediation is an inexpensive and effective technique for remediation of Pb-contaminated homes. Vetiver (Chrysopogon zizanioides), a noninvasive, fast-growing grass with high biomass, can tolerate and accumulate large quantities of Pb in its tissues. Lead is known to induce phytochelatins and antioxidative enzymes in vetiver; however, the overall impact of Pb stress on metabolic pathways of vetiver is unknown. In the current study, vetiver plants were treated with different concentrations of Pb in a hydroponic setup. Metabolites were extracted and analyzed using LC/MS/MS. Multivariate analysis of metabolites in both root and shoot tissue showed tremendous induction in key metabolic pathways including sugar metabolism, amino acid metabolism, and an increase in production of osmoprotectants, such as betaine and polyols, and metal-chelating organic acids. The data obtained provide a comprehensive insight into the overall stress response mechanisms in vetiver.

Water deficit stress-induced changes in carbon and nitrogen partitioning in Chenopodium quinoa Willd

Water deficit stress followed by re-watering during grain filling resulted in the induction of the ornithine pathway and in changes in Quinoa grain quality. The genetic diversity of Chenopodium quinoa Willd. (Quinoa) is accompanied by an outstanding environmental adaptability and high nutritional properties of the grains. However, little is known about the biochemical and physiological mechanisms associated with the abiotic stress tolerance of Quinoa. Here, we characterized carbon and nitrogen metabolic changes in Quinoa leaves and grains in response to water deficit stress analyzing their impact on the grain quality of two lowland ecotypes (Faro and BO78). Differences in the stress recovery response were found between genotypes including changes in the activity of nitrogen assimilation-associated enzymes that resulted in differences in grain quality. Both genotypes showed a common strategy to overcome water stress including the stress-induced synthesis of reactive oxygen species scavengers and osmolytes. Particularly, water deficit stress induced the stimulation of the ornithine and raffinose pathways. Our results would suggest that the regulation of C- and N partitioning in Quinoa during grain filling could be used for the improvement of the grain quality without altering grain yields.

Cell type-specific responses to salinity - the epidermal bladder cell transcriptome of Mesembryanthemum crystallinum

Mesembryanthemum crystallinum (ice plant) exhibits extreme tolerance to salt. Epidermal bladder cells (EBCs), developing on the surface of aerial tissues and specialized in sodium sequestration and other protective functions, are critical for the plant's stress adaptation. We present the first transcriptome analysis of EBCs isolated from intact plants, to investigate cell type-specific responses during plant salt adaptation. We developed a de novo assembled, nonredundant EBC reference transcriptome. Using RNAseq, we compared the expression patterns of the EBC-specific transcriptome between control and salt-treated plants. The EBC reference transcriptome consists of 37 341 transcript-contigs, of which 7% showed significantly different expression between salt-treated and control samples. We identified significant changes in ion transport, metabolism related to energy generation and osmolyte accumulation, stress signalling, and organelle functions, as well as a number of lineage-specific genes of unknown function, in response to salt treatment. The salinity-induced EBC transcriptome includes active transcript clusters, refuting the view of EBCs as passive storage compartments in the whole-plant stress response. EBC transcriptomes, differing from those of whole plants or leaf tissue, exemplify the importance of cell type-specific resolution in understanding stress adaptive mechanisms.

Genome-wide screening of salt tolerant genes by activation-tagging using dedifferentiated calli of Arabidopsis and its application to finding gene for Myo-inositol-1-p-synthase

Salinity represents a major abiotic stress factor that can adversely limit the production, quality and geographical distribution of crops. In this study we focused on dedifferentiated calli with fundamental cell functions, the salt tolerance of which had not been previously examined. The experimental approach was based on activation tagging without regeneration of plants for the identification of salt-tolerant mutants of Arabidopsis. Among 62,000 transformed calli that were screened, 18 potential mutants resistant to 150 mM NaCl were obtained. Thermal asymmetric interlaced (TAIL)-PCR was performed to determine the location of T-DNA integration in the genome. In one line, referred to as salt tolerant callus 1 (stc1), expression of a gene [At4g39800: myo-inositol-1-P-synthase 1 (MIPS1)] was considerably enhanced in calli. Plants regenerated from calli showed tolerance to salt in germination and subsequent growth. Retransformation of wild-type Arabidopsis with MIPS1 conferred salt tolerance, indicating that MIPS1 is the causal gene. The over-expression of MIPS1 increased the content of total inositol. The involvement of MIPS1 in salt tolerance through the fundamental cell growth has been proved in Arabidopsis.

Ectopic expression of myo-inositol 3-phosphate synthase induces a wide range of metabolic changes and confers salt tolerance in rice

Salt stress is an important factor that limits crop production worldwide. The salt tolerance of plants is a complex biological process mediated by changes in gene expression and metabolite composition. The enzyme myo-inositol 3-phosphate synthase (MIPS; EC 5.5.1.4) catalyzes the first step of myo-inositol biosynthesis, and overexpression of the MIPS gene enhances salt stress tolerance in several plant species. In this study, we performed metabolite profiling of both MIPS-overexpressing and wild-type rice. The enhanced salt stress tolerance of MIPS-overexpressing plants was clear based on growth and the metabolites under salt stress. We found that constitutive overexpression of the rice MIPS gene resulted in a wide range of metabolic changes. This study demonstrates for the first time that overexpression of the MIPS gene increases various metabolites responsible for protecting plants from abiotic stress. Activation of both basal metabolism, such as glycolysis, the pentose phosphate pathway, and the tricarboxylic acid cycle, and inositol metabolism is induced in MIPS-overexpressing plants. We discuss the relationship between the metabolic changes and the improved salt tolerance observed in transgenic rice.

Characterization of the salt stress vulnerability of three invasive freshwater plant species using a metabolic profiling approach

The effects of salt stress on freshwater plants has been little studied up to now, despite the fact that they are expected to present different levels of salt sensitivity or salt resistance depending on the species. The aim of this work was to assess the effect of NaCl at two concentrations on three invasive freshwater species, Elodea canadensis, Myriophyllum aquaticum and Ludwigia grandiflora, by examining morphological and physiological parameters and using metabolic profiling. The growth rate (biomass and stem length) was reduced for all species, whatever the salt treatment, but the response to salt differed between the three species, depending on the NaCl concentration. For E. canadensis, the physiological traits and metabolic profiles were only slightly modified in response to salt, whereas M. aquaticum and L. grandiflora showed great changes. In both of these species, root number, photosynthetic pigment content, amino acids and carbohydrate metabolism were affected by the salt treatments. Moreover, we are the first to report the salt-induced accumulation of compatible solutes in both species. Indeed, in response to NaCl, L. grandiflora mainly accumulated sucrose. The response of M. aquaticum was more complex, because it accumulated not only sucrose and myo-inositol whatever the level of salt stress, but also amino acids such as proline and GABA, but only at high NaCl concentrations. These responses are the metabolic responses typically found in terrestrial plants.

Diversity, distribution and roles of osmoprotective compounds accumulated in halophytes under abiotic stress

BACKGROUND AND AIMS

Osmolytes are low-molecular-weight organic solutes, a broad group that encompasses a variety of compounds such as amino acids, tertiary sulphonium and quaternary ammonium compounds, sugars and polyhydric alcohols. Osmolytes are accumulated in the cytoplasm of halophytic species in order to balance the osmotic potential of the Na(+) and Cl(-) accumulated in the vacuole. The advantages of the accumulation of osmolytes are that they keep the main physiological functions of the cell active, the induction of their biosynthesis is controlled by environmental cues, and they can be synthesized at all developmental stages. In addition to their role in osmoregulation, osmolytes have crucial functions in protecting subcellular structures and in scavenging reactive oxygen species.

SCOPE

This review discusses the diversity of osmolytes among halophytes and their distribution within taxonomic groups, the intrinsic and extrinsic factors that influence their accumulation, and their role in osmoregulation and osmoprotection. Increasing the osmolyte content in plants is an interesting strategy to improve the growth and yield of crops upon exposure to salinity. Examples of transgenic plants as well as exogenous applications of some osmolytes are also discussed. Finally, the potential use of osmolytes in protein stabilization and solvation in biotechnology, including the pharmaceutical industry and medicine, are considered.

Polyols in grape berry: transport and metabolic adjustments as a physiological strategy for water-deficit stress tolerance in grapevine

Polyols are important metabolites that often function as carbon and energy sources and/or osmoprotective solutes in some plants. In grapevine, and in the grape berry in particular, the molecular aspects of polyol transport and metabolism and their physiological relevance are virtually unknown to date. Here, the biochemical function of a grapevine fruit mesocarp polyol transporter (VvPLT1) was characterized after its heterologous expression in yeast. This H(+)-dependent plasma membrane carrier transports mannitol (K m=5.4mM) and sorbitol (K m=9.5mM) over a broad range of polyols and monosaccharides. Water-deficit stress triggered an increase in the expression of VvPLT1 at the fully mature stage, allowing increased polyol uptake into pulp cells. Plant polyol dehydrogenases are oxireductases that reversibly oxidize polyols into monosaccharides. Mannitol catabolism in grape cells (K m=30.1mM mannitol) and mature berry mesocarps (K m=79mM) was, like sorbitol dehydrogenase activity, strongly inhibited (50-75%) by water-deficit stress. Simultaneously, fructose reduction into polyols via mannitol and sorbitol dehydrogenases was stimulated, contributing to their higher intracellular concentrations in water-deficit stress. Accordingly, the concentrations of mannitol, sorbitol, galactinol, myo-inositol, and dulcitol were significantly higher in berry mesocarps from water-deficit-stressed Tempranillo grapevines. Metabolomic profiling of the berry pulp by GC-TOF-MS also revealed many other changes in its composition induced by water deficit. The impact of polyols on grape berry composition and plant response to water deficit stress, via modifications in polyol transport and metabolism, was analysed by integrating metabolomics with transcriptional analysis and biochemical approaches.

Melatonin combined with ascorbic acid provides salt adaptation in Citrus aurantium L. seedlings

Ascorbic acid (AsA) and melatonin (Mel) are known molecules participating in stress resistance, however, their combined role in counteracting the impact of salinity in plants is still unknown. In this work the effect of exogenous application of 0.50 mΜ AsA, 1 μΜ Mel and their combination (AsA + Mel) on various stress responses in leaves and roots of Citrus aurantium L. seedlings grown under 100 mΜ NaCl for 30 days was investigated. Application of AsA, Mel or AsA + Mel to saline solution decreased NaCl-induced electrolyte leakage and lipid peroxidation and prevented NaCl-associated toxicity symptoms and pigments degradation. Also, leaves exposed to combined AsA + Mel treatment displayed lower Cl(-) accumulation. Treatments with AsA and/or Mel modulated differently carbohydrates, proline, phenols, glutathione and the total antioxidant power of tissues as well as the activities of SOD, APX, POD, GR and PPO compared to NaCl alone treatment. Exposure of leaves and roots to chemical treatments and especially to combined AsA and Mel application was able to regulate CaMIPS, CaSLAH1 and CaMYB73 expression, indicating that sugar metabolism, ion homeostasis and transcription regulation were triggered by AsA and Mel. These results provide evidence that the activation of the metabolic pathways associated with combined AsA and Mel application are linked with salt adaptation in citrus plants.

ROS homeostasis in halophytes in the context of salinity stress tolerance

Halophytes are defined as plants that are adapted to live in soils containing high concentrations of salt and benefiting from it, and thus represent an ideal model to understand complex physiological and genetic mechanisms of salinity stress tolerance. It is also known that oxidative stress signalling and reactive oxygen species (ROS) detoxification are both essential components of salinity stress tolerance mechanisms. This paper comprehensively reviews the differences in ROS homeostasis between halophytes and glycophytes in an attempt to answer the questions of whether stress-induced ROS production is similar between halophytes and glycophytes; is the superior salinity tolerance in halophytes attributed to higher antioxidant activity; and is there something special about the specific 'pool' of enzymatic and non-enzymatic antioxidants in halophytes. We argue that truly salt-tolerant species possessing efficient mechanisms for Na(+) exclusion from the cytosol may not require a high level of antioxidant activity, as they simply do not allow excessive ROS production in the first instance. We also suggest that H2O2 'signatures' may operate in plant signalling networks, in addition to well-known cytosolic calcium 'signatures'. According to the suggested concept, the intrinsically higher superoxide dismutase (SOD) levels in halophytes are required for rapid induction of the H2O2 'signature', and to trigger a cascade of adaptive responses (both genetic and physiological), while the role of other enzymatic antioxidants may be in decreasing the basal levels of H2O2, once the signalling has been processed. Finally, we emphasize the importance of non-enzymatic antioxidants as the only effective means to prevent detrimental effects of hydroxyl radicals on cellular structures.

Molecular and functional characterization of cold-responsive C-repeat binding factors from Brachypodium distachyon

BACKGROUND

Adverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields. The C-repeat binding factors (CBFs) are critical transcription factors constituting the gene regulatory network that mediates the acclimation process to low temperatures. They regulate a large number of cold-responsive genes, including COLD-REGULATED (COR) genes, via the CBF-COR regulon. Recent studies have shown that the CBF transcription factors also play a role in plant responses to drought and salt stresses. Putative CBF gene homologues and their downstream genes are also present in the genome of Brachypodium distachyon, which is perceived as a monocot model in recent years. However, they have not been functionally characterized at the molecular level.

RESULTS

Three CBF genes that are responsive to cold were identified from Brachypodium, designated BdCBF1, BdCBF2, and BdCBF3, and they were functionally characterized by molecular biological and transgenic approaches in Brachypodium and Arabidopsis thaliana. Our results demonstrate that the BdCBF genes contribute to the tolerance response of Brachypodium to cold, drought, and salt stresses by regulating downstream targets, such as DEHYDRIN5.1 (Dhn5.1) and COR genes. The BdCBF genes are induced under the environmental stress conditions. The BdCBF proteins possess transcriptional activation activity and bind directly to the promoters of the target genes. Transgenic Brachypodium plants overexpressing the BdCBF genes exhibited enhanced resistance to drought and salt stresses as well as low temperatures, and accordingly endogenous contents of proline and soluble sugars were significantly elevated in the transgenic plants. The BdCBF transcription factors are also functional in the heterologous system Arabidopsis. Transgenic Arabidopsis plants overexpressing the BdCBF genes were also tolerant to freezing, drought, and salt stresses, and a set of stress-responsive genes was upregulated in the transgenic Arabidopsis plants.

CONCLUSIONS

Taken together, our results strongly support that the BdCBF transcription factors are key regulators of cold stress responses in Brachypodium and the CBF-mediated cold stress signaling pathway is conserved in this plant species. We believe that this study would confer great impact on stress biology in monocot species and could be applied to engineer abiotic stress tolerance of bioenergy grass species.

Cytoplasmic genome substitution in wheat affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations

Background

Alloplasmic lines provide a unique tool to study nuclear-cytoplasmic interactions. Three alloplasmic lines, with nuclear genomes from Triticum aestivum and harboring cytoplasm from Aegilops uniaristata, Aegilops tauschii and Hordeum chilense, were investigated by transcript and metabolite profiling to identify the effects of cytoplasmic substitution on nuclear-cytoplasmic signaling mechanisms.

Results

In combining the wheat nuclear genome with a cytoplasm of H. chilense, 540 genes were significantly altered, whereas 11 and 28 genes were significantly changed in the alloplasmic lines carrying the cytoplasm of Ae. uniaristata or Ae. tauschii, respectively. We identified the RNA maturation-related process as one of the most sensitive to a perturbation of the nuclear-cytoplasmic interaction. Several key components of the ROS chloroplast retrograde signaling, together with the up-regulation of the ROS scavenging system, showed that changes in the chloroplast genome have a direct impact on nuclear-cytoplasmic cross-talk. Remarkably, the H. chilense alloplasmic line down-regulated some genes involved in the determination of cytoplasmic male sterility without expressing the male sterility phenotype. Metabolic profiling showed a comparable response of the central metabolism of the alloplasmic and euplasmic lines to light, while exposing larger metabolite alterations in the H. chilense alloplasmic line as compared with the Aegilops lines, in agreement with the transcriptomic data. Several stress-related metabolites, remarkably raffinose, were altered in content in the H. chilense alloplasmic line when exposed to high light, while amino acids, as well as organic acids were significantly decreased. Alterations in the levels of transcript, related to raffinose, and the photorespiration-related metabolisms were associated with changes in the level of related metabolites.

Conclusion

The replacement of a wheat cytoplasm with the cytoplasm of a related species affects the nuclear-cytoplasmic cross-talk leading to transcript and metabolite alterations. The extent of these modifications was limited in the alloplasmic lines with Aegilops cytoplasm, and more evident in the alloplasmic line with H. chilense cytoplasm. We consider that, this finding might be linked to the phylogenetic distance of the genomes.

Differentially expressed myo-inositol monophosphatase gene (CaIMP) in chickpea (Cicer arietinum L.) encodes a lithium-sensitive phosphatase enzyme with broad substrate specificity and improves seed germination and seedling growth under abiotic stresses

myo-Inositol monophosphatase (IMP) is an essential enzyme in the myo-inositol metabolic pathway where it primarily dephosphorylates myo-inositol 1-phosphate to maintain the cellular inositol pool which is important for many metabolic and signalling pathways in plants. The stress-induced increased accumulation of inositol has been reported in a few plants including chickpea; however, the role and regulation of IMP is not well defined in response to stress. In this work, it has been shown that IMP activity is distributed in all organs in chickpea and was noticeably enhanced during environmental stresses. Subsequently, using degenerate oligonucleotides and RACE strategy, a full-length IMP cDNA (CaIMP) was cloned and sequenced. Biochemical study revealed that CaIMP encodes a lithium-sensitive phosphatase enzyme with broad substrate specificity, although maximum activity was observed with the myo-inositol 1-phosphate and l-galactose 1-phosphate substrates. Transcript analysis revealed that CaIMP is differentially expressed and regulated in different organs, stresses and phytohormones. Complementation analysis in Arabidopsis further confirmed the role of CaIMP in l-galactose 1-phosphate and myo-inositol 1-phosphate hydrolysis and its participation in myo-inositol and ascorbate biosynthesis. Moreover, Arabidopsis transgenic plants over-expressing CaIMP exhibited improved tolerance to stress during seed germination and seedling growth, while the VTC4/IMP loss-of-function mutants exhibited sensitivity to stress. Collectively, CaIMP links various metabolic pathways and plays an important role in improving seed germination and seedling growth, particularly under stressful environments.

Isolation and developmental expression analysis of L-myo-inositol-1-phosphate synthase in four Actinidia species

Myo-inositol (MI) is an important polyol involved in cellular signal transduction, auxin storage, osmotic regulation, and membrane formation. It also serves as a precursor for the production of pinitol, ascorbic acid, and members of the raffinose family. The first committed step for MI formation is catalyzed by L-myo-inositol-1-phosphate synthase (MIPS). We isolated MIPS cDNA sequences from Actinidia eriantha, Actinidia rufa, and Actinidia arguta and compared them with that of Actinidia deliciosa. Each comprised 1533 bp, encoding 510 amino acids with a predicted molecular weight of 56.5 KDa. The MIPS protein was highly conserved in Actinidia, sharing 98.94% identity among species. The MIPS gene was expressed in the flowers, leaves, petioles, and carpopodia. Similarly high levels of expression were detected in the young fruit of all four species. Overall activity of the enzyme was also maximal in young fruit, indicating that this developmental stage is the key point for MI synthesis in Actinidia. Among the four species, A. arguta had the greatest concentration of MI as well as the highest ratios of MI:sucrose and MI:glucose+fructose. This suggests that conversion to MI from carbohydrates was most efficient in A. arguta during early fruit development.

RNAi mediated down regulation of myo-inositol-3-phosphate synthase to generate low phytate rice

BACKGROUND

Phytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates in cereal grains. Reduction of phytic acid level in cereal grains is desirable in view of its antinutrient properties to maximize mineral bioavailability and minimize the load of phosphorus waste management. We report here RNAi mediated seed-specific silencing of myo-inositol-3-phosphate synthase (MIPS) gene catalyzing the first step of phytic acid biosynthesis in rice. Moreover, we also studied the possible implications of MIPS silencing on myo-inositol and related metabolism, since, first step of phytic acid biosynthesis is also the rate limiting step of myo-inositol synthesis, catalyzed by MIPS.

RESULTS

The resulting transgenic rice plants (T3) showed a 4.59 fold down regulation in MIPS gene expression, which corresponds to a significant decrease in phytate levels and a simultaneous increment in the amount of inorganic phosphate in the seeds. A diminution in the myo-inositol content of transgenic plants was also observed due to disruption of the first step of phytic acid biosynthetic pathway, which further reduced the level of ascorbate and altered abscisic acid (ABA) sensitivity of the transgenic plants. In addition, our results shows that in the transgenic plants, the lower phytate levels has led to an increment of divalent cations, of which a 1.6 fold increase in the iron concentration in milled rice seeds was noteworthy. This increase could be attributed to reduced chelation of divalent metal (iron) cations, which may correlate to higher iron bioavailability in the endosperm of rice grains.

CONCLUSION

The present study evidently suggests that seed-specific silencing of MIPS in transgenic rice plants can yield substantial reduction in levels of phytic acid along with an increase in inorganic phosphate content. However, it was also demonstrated that the low phytate seeds had an undesirable diminution in levels of myo-inositol and ascorbate, which probably led to sensitiveness of seeds to abscisic acid during germination. Therefore, it is suggested that though MIPS is the prime target for generation of low phytate transgenic plants, down-regulation of MIPS can have detrimental effect on myo-inositol synthesis and related pathways which are involved in key plant metabolism.

Arabidopsis plants constitutively overexpressing a myo-inositol 1-phosphate synthase gene (SaINO1) from the halophyte smooth cordgrass exhibits enhanced level of tolerance to salt stress

Salinity is one of the most important environmental constraints limiting agricultural productivity. Considering the importance of the accumulation of osmolytes, myo-inositol in particular, in halophytic plant's adaptive response to salinity, an effort was made to overexpress the SaINO1 gene from the grass halophyte Spartina alterniflora encoding myo-inositol 1-phosphate synthase (MIPS) in Arabidopsis thaliana. We demonstrated that SaINO1 is a stress-responsive gene and its constitutive over expression in Arabidopsis provides significantly improved tolerance to salt stress during germination and seedling growth and development. The transgenics retained more chlorophyll and carotenoid by protecting the photosystem II. The low level of stress-induced cellular damage in the transgenics was clearly evident by lower accumulation of proline in comparison to WT. Our results indicated that possible overaccumulation of MIPS enzyme in the cytosol protected the transgenic Arabidopsis plants overexpressing SaINO1 from the toxic effect of Na(+) under salt stress by reducing cellular damage and chlorophyll loss.

Hydrogen peroxide and nitric oxide mediated cold- and dehydration-induced myo-inositol phosphate synthase that confers multiple resistances to abiotic stresses

myo-Inositol phosphate synthase (MIPS) is the key enzyme of myo-inositol synthesis, which is a central molecule required for cell metabolism and plant growth as a precursor to a large variety of compounds. A full-length fragment of MfMIPS1 cDNA was cloned from Medicago falcata that is more cold-tolerant than Medicago sativa. While MfMIPS1 transcript was induced in response to cold, dehydration and salt stress, MIPS transcript and myo-inositol were maintained longer and at a higher level in M. falcata than in M. sativa during cold acclimation at 5 °C. MfMIPS1 transcript was induced by hydrogen peroxide (H(2) O(2)) and nitric oxide (NO), but was not responsive to abscisic acid (ABA). Pharmacological experiments revealed that H(2) O(2) and NO are involved in the regulation of MfMIPS1 expression by cold and dehydration, but not by salt. Overexpression of MfMIPS1 in tobacco increased the MIPS activity and levels of myo-inositol, galactinol and raffinose, resulting in enhanced resistance to chilling, drought and salt stresses in transgenic tobacco plants. It is suggested that MfMIPS1 is induced by diverse environmental factors and confers resistance to various abiotic stresses.

Ectopic expression of the ABA-inducible dehydration-responsive chickpea L-myo-inositol 1-phosphate synthase 2 (CaMIPS2) in Arabidopsis enhances tolerance to salinity and dehydration stress

Myo-inositol participates in many different aspects of plant physiology and myo-inositol 1-phosphate synthase (MIPS; EC 5.5.1.4) catalyzes the rate limiting step of inositol biosynthetic pathway. Chickpea (Cicer arietinum), a drought-tolerant leguminous crop plant, is known to accumulate increased inositol during dehydration stress. Previously, we reported two differentially expressed divergent genes (CaMIPS1 and CaMIPS2) encoding two MIPS isoforms in chickpea. In this communication, we demonstrated that CaMIPS2 is an early dehydration-responsive gene and is also rapidly induced by exogenous ABA application, while CaMIPS1 expression is not much influenced by dehydration or ABA. The regulation of expression of these two genes has been studied by examining their promoter activity through GUS reporter gene and differential promoter activity has been observed. Moreover, unlike CaMIPS1 promoter, CaMIPS2 promoter contains CRT/DRE cis-regulatory element which seems to play a key role in dehydration-induced expression of CaMIPS2. Furthermore, CaMIPS1 and CaMIPS2 have been successfully complemented and shown to repair the defect of seedling growth and altered seed phenotype of Atmips1 mutant. Moreover, Arabidopsis transgenic plants overexpressing CaMIPS1 or CaMIPS2 exhibit improved tolerance to salinity and dehydration stresses and such tolerance of transgenic plants is correlated with their elevated level of inositol. Remarkably, CaMIPS2 transgenic lines perform better in all attributes than CaMIPS1 transformants under such stress conditions, due to comparatively unabated production of inositol by CaMIPS2 enzyme, as this enzyme retains significant activity under stress conditions.

An omics approach to understand the plant abiotic stress

Abiotic stress can lead to changes in development, productivity, and severe stress and may even threaten survival of plants. Several environmental stresses cause drastic changes in the growth, physiology, and metabolism of plants leading to the increased accumulation of secondary metabolites. As medicinal plants are important sources of drugs, steps are taken to understand the effect of stress on the physiology, biochemistry, genomic, proteomic, and metabolic levels. The molecular responses of plants to abiotic stress are often considered as a complex process. They are mainly based on the modulation of transcriptional activity of stress-related genes. Many genes have been induced under stress conditions. The products of stress-inducible genes protecting against these stresses includes the enzymes responsible for the synthesis of various osmoprotectants. Genetic engineering of tolerance to abiotic stresses help in molecular understanding of pathways induced in response to one or more of the abiotic stresses. Systems biology and virtual experiments allow visualizing and understanding how plants work to overcome abiotic stress. This review discusses the omic approach to understand the plant response to abiotic stress with special emphasis on medicinal plant.

Isolation and identification of myo-inositol crystals from dragon fruit (Hylocereus polyrhizus)

Crystals isolated from Hylocereus polyrhizus were analyzed using four different approaches—X-ray Crystallography, High Performance Liquid Chromatography (HPLC), Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) and Nuclear Magnetic Resonance (NMR) and identified as myo-inositol. The X-ray crystallography analysis showed that the unit-cell parameters were: a = 6.6226 (3) Å, b = 12.0462 (5) Å, c = 18.8942 (8) Å, α = 90.00, β = 93.98, δ = 90.00. The purity of the crystals were checked using HPLC, whereupon a clean single peak was obtained at 4.8 min with a peak area of 41232 μV*s. The LC-MS/MS technique, which is highly sensitive and selective, was used to provide a comparison of the isolated crystals with a myo-inositol standard where the results gave an identical match for both precursor and product ions. NMR was employed to confirm the molecular structure and conformation of the crystals, and the results were in agreement with the earlier results in this study. The discovery of myo-inositol crystals in substantial amount in H. polyrhizus has thus far not been reported and this is an important finding which will increase the marketability and importance of H. polyrhizus as a crop with a wide array of health properties.

Day/night regulation of aquaporins during the CAM cycle in Mesembryanthemum crystallinum

Mesembryanthemum crystallinum exhibits induction of Crassulacean acid metabolism (CAM) after a threshold stage of development, by exposure to long days with high light intensities or by water and salt stress. During the CAM cycle, fluctuations in carbon partitioning within the cell lead to transient drops in osmotic potential, which are likely stabilized/balanced by passive movement of water via aquaporins (AQPs). Protoplast swelling assays were used to detect changes in water permeability during the day/night cycle of CAM. To assess the role of AQPs during the same period, we followed transcript accumulation and protein abundance of four plasma membrane intrinsic proteins (PIPs) and one tonoplast intrinsic protein (TIP). CAM plants showed a persistent rhythm of specific AQP protein abundance changes throughout the day/night cycle, including changes in amount of McPIP2;1, McTIP1;2, McPIP1;4 and McPIP1;5, while the abundance of McPIP1;2 was unchanged. These protein changes did not appear to be coordinated with transcript levels for any of the AQPs analysed; however, they did occur in parrallel to alterations in water permeability, as well as variations in cell osmolarity, pinitol, glucose, fructose and phosphoenolpyruvate carboxylase (PEPc) levels measured throughout the day/night CAM cycle. Results suggest a role for AQPs in maintaining water balance during CAM and highlight the complexity of protein expression during the CAM cycle.