海藻糖介导的信号转导与植物抗逆性

海藻糖是一种非还原性二糖,它广泛存在于细菌、真菌、酵母、昆虫、无脊椎动物和植物等生物体内。海藻糖不仅作为碳水化合物的储备,而且还是一个多功能分子。海藻糖作为一种信号分子,启动信号转导级联反应,改变基因表达和酶的活性,与激素也有一定的关系。采用基因工程和通过外源施加的方法增加海藻糖在植物体内的积累可以提高植物的抗逆性,这为提高农作物的抗逆性提供了新的策略。     

Thermodynamics and mechanism of cutinase stabilization by trehalose

Trehalose has been widely used to stabilize cellular structures such as membranes and proteins. The effect of trehalose on the stability of the enzyme cutinase was studied. Thermal unfolding of cutinase reveals that trehalose delays thermal unfolding, thus increasing the temperature at the midpoint of unfolding by 7.2 degrees . Despite this stabilizing effect, trehalose also favors pathways that lead to irreversible denaturation. Stopped-flow kinetics of cutinase folding and unfolding was measured and temperature was introduced as experimental variable to assess the mechanism and thermodynamics of protein stabilization by trehalose. The main stabilizing effect of trehalose was to delay the rate constant of the unfolding of an intermediate. A full thermodynamic analysis of this step has revealed that trehalose induces the phenomenon of entropy-enthalpy compensation, but the enthalpic contribution increases more significantly leading to a net stabilizing effect that slows down unfolding of the intermediate. Regarding the molecular mechanism of stabilization, trehalose increases the compactness of the unfolded state. The conformational space accessible to the unfolded state decreases in the presence of trehalose when the unfolded state acquires residual native interactions that channel the folding of the protein. This residual structure results into less hydrophobic groups being newly exposed upon unfolding, as less water molecules are immobilized upon unfolding.     

Experimental and computational studies investigating trehalose protection of HepG2 cells from palmitate-induced toxicity

Understanding the mechanism of saturated fatty acid-induced hepatocyte toxicity may provide insight into cures for diseases such as obesity-associated cirrhosis. Trehalose, a nonreducing disaccharide shown to protect proteins and cellular membranes from inactivation or denaturation caused by different stress conditions, also protects hepatocytes from palmitate-induced toxicity. Our results suggest that trehalose serves as a free radical scavenger and alleviates damage from hydrogen peroxide secreted by the compromised cells. We also observe that trehalose protects HepG2 cells by interacting with the plasma membrane to counteract the changes in membrane fluidity induced by palmitate. The experimental results are supported by molecular dynamics simulations of model cell membranes that closely reflect the experimental conditions. Simulations were performed to understand the specific interactions between lipid bilayers, palmitate, and trehalose. The simulations results reveal the early stages of how palmitate induces biophysical changes to the cellular membrane and the role of trehalose in protecting the membrane structure.     

New insights on trehalose: a multifunctional molecule

Trehalose is a nonreducing disaccharide in which the two glucose units are linked in an alpha,alpha-1,1-glycosidic linkage. This sugar is present in a wide variety of organisms, including bacteria, yeast, fungi, insects, invertebrates, and lower and higher plants, where it may serve as a source of energy and carbon. In yeast and plants, it may also serve as a signaling molecule to direct or control certain metabolic pathways or even to affect growth. In addition, it has been shown that trehalose can protect proteins and cellular membranes from inactivation or denaturation caused by a variety of stress conditions, including desiccation, dehydration, heat, cold, and oxidation. Finally, in mycobacteria and corynebacteria, trehalose is an integral component of various glycolipids that are important cell wall structures. There are now at least three different pathways described for the biosynthesis of trehalose. The best known and most widely distributed pathway involves the transfer of glucose from UDP-glucose (or GDP-glucose in some cases) to glucose 6-phosphate to form trehalose-6-phosphate and UDP. This reaction is catalyzed by the trehalose-P synthase (TPS here, or OtsA in Escherichia coli ). Organisms that use this pathway usually also have a trehalose-P phosphatase (TPP here, or OtsB in E. coli) that converts the trehalose-P to free trehalose. A second pathway that has been reported in a few unusual bacteria involves the intramolecular rearrangement of maltose (glucosyl-alpha1,4-glucopyranoside) to convert the 1,4-linkage to the 1,1-bond of trehalose. This reaction is catalyzed by the enzyme called trehalose synthase and gives rise to free trehalose as the initial product. A third pathway involves several different enzymes, the first of which rearranges the glucose at the reducing end of a glycogen chain to convert the alpha1,4-linkage to an alpha,alpha1,1-bond. A second enzyme then releases the trehalose disaccharide from the reducing end of the glycogen molecule. Finally, in mushrooms there is a trehalose phosphorylase that catalyzes the phosphorolysis of trehalose to produce glucose-1-phosphate and glucose. This reaction is reversible in vitro and could theoretically give rise to trehalose from glucose-1-P and glucose. Another important enzyme in trehalose metabolism is trehalase (T), which may be involved in energy metabolism and also have a regulatory role in controlling the levels of trehalose in cells. This enzyme may be important in lowering trehalose concentrations once the stress is alleviated. Recent studies in yeast indicate that the enzymes involved in trehalose synthesis (TPS, TPP) exist together in a complex that is highly regulated at the activity level as well as at the genetic level.     

Trehalose Biosynthesis in Response to Abiotic Stresses

Trehalose is a non‐reducing disaccharide that is present in diverse organisms ranging from bacteria and fungi to invertebrates, in which it serves as an energy source, osmolyte or protein/membrane protectant. The occurrence of trehalose and trehalose biosynthesis pathway in plants has been discovered recently. Multiple studies have revealed regulatory roles of trehalose‐6‐phosphate, a precursor of trehalose, in sugar metabolism, growth and development in plants. Trehalose levels are generally quite low in plants but may alter in response to environmental stresses. Transgenic plants overexpressing microbial trehalose biosynthesis genes have been shown to contain increased levels of trehalose and display drought, salt and cold tolerance. In‐silico expression profiling of all Arabidopsis trehalose‐6‐phosphate synthases (TPSs) and trehalose‐6‐phosphate phosphatases (TPPs) revealed that certain classes of TPS and TPP genes are differentially regulated in response to a variety of abiotic stresses. These studies point to the importance of trehalose biosynthesis in stress responses.     

Trehalose-enzyme interactions result in structure stabilization and activity inhibition. The role of viscosity

Stress resistance is essential for survival. The mechanisms of molecule stabilization during stress are of interest for biotechnology, where many enzymes and other biomolecules are increasingly used at high temperatures and/or salt concentrations. Diverse organisms, exhibit rapid synthesis and accumulation of the disaccharide trehalose in response to stress. Trehalose is also rapidly hydrolyzed as soon as stress ends. In isolated enzymes, trehalose stabilizes both, structure and activity. In contrast, at optimal assay conditions, trehalose inhibits enzyme activity. A general mechanism underlying the trehalose effects observed at all temperatures probably is the trehalose-mediated increase in solution viscosity that leads to protein domain motion inhibition. This may be analyzed using Kramer's theory. The role of viscosity in the effects of trehalose is analyzed in examples from the literature and in studies on the plasma membrane H(+)-ATPase from Kluyveromyces lactis. In the cell, it may be proposed that the large concentration of trehalose reached during stress stabilizes structures through viscosity. However, once stress ends trehalose has to be rapidly hydrolyzed in order to avoid the viscosity-mediated inhibition of enzymes.     

Contribution of trehalose biosynthetic pathway to drought stress tolerance of Capparis ovata Desf

Trehalose and the trehalose biosynthetic pathway are important contributors and regulators of stress responses in plants. Among recent findings for trehalose and its metabolism, the role of signalling in the regulation of growth and development and its potential for use as a storage energy source can be listed. The xerophytic plant Capparis ovata (caper) is well adapted to drought and high temperature stress in arid and semi‐arid regions of the Mediterranean. The contribution of trehalose and the trehalose biosynthetic pathway to drought stress responses and tolerance in C. ovata are not known. We investigated the effects of PEG‐mediated drought stress in caper plants and analysed physiological parameters and trehalose biosynthetic pathway components, trehalose‐6‐phosphate synthase (TPS), trehalose‐6‐phosphate phosphatase (TPP), trehalase activity, trehalose and proline content in drought stress‐treated and untreated plants. Our results indicated that trehalose and the trehalose biosynthetic pathway contributed to drought stress tolerance of C. ovata. Overall growth and leaf water status were not dramatically affected by drought, as both high relative growth rate and relative water content were recorded even after 14 days of drought stress. Trehalose accumulation increased in parallel to induced TPS and TPP activities and decreased trehalase activity in caper plants on day 14. Constitutive trehalose levels were 28.75 to 74.75 μg·g·FW^?1, and drought stress significantly induced trehalose accumulation (385.25 μg·g·FW^?1 on day 14) in leaves of caper. On day 14 of drought, proline levels were lower than on day 7. Under drought stress the discrepancy between trehalose and proline accumulation trends might result from the mode of action of these osmoprotectant molecules in C. ovata.     

Trehalose: A Key Organic Osmolyte Effectively Involved in Plant Abiotic Stress Tolerance

Trehalose is a natural non-reducing sugar that is found in the vast majority of organisms such as bacteria, yeasts, invertebrates and even in plants. Regarding its features, it is considered as a unique compound. It plays a key role as a carbon source in lower organisms and as an osmoprotectant or a stabilizing molecule in higher animals and plants. Although in plants it is present in a minor quantity, its levels rise upon exposure to abiotic stresses. Trehalose is believed to play a protective role against different abiotic stressful cues such as temperature extremes, salinity, desiccation. Moreover, it regulates water use efficiency and stomatal movement in most plants. Detectable endogenous trehalose levels are vital for sustaining growth under stressful cues. Exogenously applied trehalose in low amounts mitigates physiological and biochemical disorders induced by various abiotic stresses, delays leaf abscission and stimulates flowering in crops. External application of trehalose also up-regulates the stress responsive genes in plants exposed to environmental cues. The genetically modified plants with trehalose biosynthesis genes exhibit improved tolerance against stressful conditions. An increased level of trehalose has been observed in transgenic plants over-expressing genes of microbial trehalose biosynthesis. However, these transgenic plants display enhanced tolerance to heat, cold, salinity, and drought tolerance. Due to multiple bio-functions of this sugar, it has gained considerable ground in various fields. However, exogenous use of this bio-safe sugar would only be possible under field conditions upon adopting strategies of low-cost production of trehalose. In short, trehalose is a unique chemical that preserves vitality of plant life under harsh ecological conditions. Certainly, the new findings of this disaccharide will revolutionize a wide array of new avenues.

     

Trehalose extends longevity in the nematode Caenorhabditis elegans

Trehalose is a disaccharide of glucose found in diverse organisms and is suggested to act as a stress protectant against heat, cold, desiccation, anoxia, and oxidation. Here, we demonstrate that treatment of Caenorhabditis elegans with trehalose starting from the young‐adult stage extended the mean life span by over 30% without any side effects. Surprisingly, trehalose treatment starting even from the old‐adult stage shortly thereafter retarded the age‐associated decline in survivorship and extended the remaining life span by 60%. Demographic analyses of age‐specific mortality rates revealed that trehalose extended the life span by lowering age‐independent vulnerability. Moreover, trehalose increased the reproductive span and retarded the age‐associated decrease in pharyngeal‐pumping rate and the accumulation of lipofuscin autofluorescence. Trehalose also enhanced thermotolerance and reduced polyglutamine aggregation. These results suggest that trehalose suppressed aging by counteracting internal or external stresses that disrupt protein homeostasis. On the other hand, the life span‐extending effect of trehalose was abolished in long‐lived insulin/IGF‐1‐like receptor (daf‐2) mutants. RNA interference‐mediated inactivation of the trehalose‐biosynthesis genes trehalose‐6‐phosphate synthase‐1 (tps‐1) and tps‐2, which are known to be up‐regulated in daf‐2 mutants, decreased the daf‐2 life span. These findings indicate that a reduction in insulin/IGF‐1‐like signaling extends life span, at least in part, through the aging‐suppressor function of trehalose. Trehalose may be a lead compound for potential nutraceutical intervention of the aging process.     

Trends in bacterial trehalose metabolism and significant nodes of metabolic pathway in the direction of trehalose accumulation

The current knowledge of trehalose biosynthesis under stress conditions is incomplete and needs further research. Since trehalose finds industrial and pharmaceutical applications, enhanced accumulation of trehalose in bacteria seems advantageous for commercial production. Moreover, physiological role of trehalose is a key to generate stress resistant bacteria by metabolic engineering. Although trehalose biosynthesis requires few metabolites and enzyme reactions, it appears to have a more complex metabolic regulation. Trehalose biosynthesis in bacteria is known through three pathways – OtsAB, TreYZ and TreS. The interconnections of in vivo synthesis of trehalose, glycogen or maltose were most interesting to investigate in recent years. Further, enzymes at different nodes (glucose‐6‐P, glucose‐1‐P and NDP‐glucose) of metabolic pathways influence enhancement of trehalose accumulation. Most of the study of trehalose biosynthesis was explored in medically significant Mycobacterium, research model Escherichia coli, industrially applicable Corynebacterium and food and probiotic interest Propionibacterium freudenreichii. Therefore, the present review dealt with the trehalose metabolism in these bacteria. In addition, an effort was made to recognize how enzymes at different nodes of metabolic pathway can influence trehalose accumulation.     

Trehalose protects wine yeast against oxidation under thermal stress

Accumulation of trehalose in yeasts has been suggested to be an important mechanism of tolerance against adverse stress conditions, particularly in thermal stress. However, under thermal stress, it is not clear if the mechanism of protection is related to its antioxidant role. In this study, a newly isolated wine yeast Saccharomyces cerevisia was used to examine the protective effect of trehalose against oxidation during thermal stress treatment. Cells were treated either with a mild heat treatment at 37°C (which leads to trehalose accumulation) or with a 50 mM trehalose solution and then exposed to a high temperature of 53°C. According to our results, mild heat treatment at 37°C and trehalose addition which promote accumulation of trehalose significantly increased cell survival upon exposure to thermal stress at 53°C which seems to be correlated with decrease in reactive oxygen species levels and lipid peroxidation. Trehalose could protect yeast from oxidative injuries under thermal stress.     

Its Preferential Interactions with Biopolymers Account for Diverse Observed Effects of Trehalose

Biopolymer homeostasis underlies the health of organisms, and protective osmolytes have emerged as one strategy used by Nature to preserve biopolymer homeostasis. However, a great deal remains unknown about the mechanism of action of osmolytes. Trehalose, as a prominent example, stabilizes proteins against denaturation by extreme temperature and denaturants, preserves membrane integrity upon freezing or in dry conditions, inhibits polyQ-mediated protein aggregation, and suppresses the aggregation of denatured proteins. The underlying thermodynamic mechanisms of such diverse effects of trehalose remain unclear or controversial. In this study, we applied the surface-additive method developed in the Record laboratory to attack this issue. We characterized the key features of trehalose-biopolymer preferential interactions and found that trehalose has strong unfavorable interactions with aliphatic carbon and significant favorable interactions with amide/anionic oxygen. This dissection has allowed us to elucidate the diverse effects of trehalose and to identify the crucial functional group(s) responsible for its effects. With (semi)quantitative thermodynamic analysis, we discovered that 1) the unfavorable interaction of trehalose with hydrophobic surfaces is the dominant factor in its effect on protein stability, 2) the favorable interaction of trehalose with polar amides enables it to inhibit polyQ-mediated protein aggregation and the aggregation of denatured protein in general, and 3) the favorable interaction of trehalose with phosphate oxygens, together with its unfavorable interaction with aliphatic carbons, enables trehalose to preserve membrane integrity in aqueous solution. These results provide a basis for a full understanding of the role of trehalose in biopolymer homeostasis and the reason behind its evolutionary selection as an osmolyte, as well as for a better application of trehalose as a chemical chaperone.     

The induction of trehalose and glycerol in Saccharomyces cerevisiae in response to various stresses

Trehalose and glycerol have been implicated as potential stress protectants that accumulate in yeasts during various stress conditions. We investigated the levels of glycerol and trehalose and the expression profiles of genes involved in their metabolism to determine their involvement in the response of Saccharomyces cerevisiae XQ1 to thermal, sorbitol and ethanol stresses. The results showed that the genes involved in the synthesis and degradation of trehalose and glycerol were stress induced, and that trehalose and glycerol were synthesized simultaneously during the initial stages (a sensitive response period) of diverse stress treatments. Trehalose accumulated markedly under heat treatment, but not under sorbitol or ethanol stress, whereas glycerol accumulated strikingly under sorbitol stress conditions. Interestingly, extracellular trehalose seemed to be involved in protecting cells from damage under unfavorable conditions. Moreover, our results suggest that the stress-activated futile ATP cycles of trehalose and glycerol turnover are of general importance during cellular stress adaptation.     

Trehalose determination in linseed subjected to osmotic stress. HPAEC‐PAD analysis: an inappropriate method

Trehalose is a non‐reducing disaccharide involved in stress tolerance in plants. To understand better the role of trehalose in the osmotic stress response in linseed (Linum usitatissimum), trehalose content in leaves was studied. First, the method commonly used for sugar determination, high performance anion exchange chromatography with pulsed amperometric detection (HPAEC‐PAD), gave unsatisfactory results and the separation efficiency could not be improved by varying the elution conditions. The same problem was also found in the model plant: Arabidopsis thaliana. After clearly highlighting a co‐elution of trehalose in these two species by a trehalase assay and liquid chromatography‐high resolution mass spectrometry analysis, gas chromatography–mass spectrometry (GC‐MS) was used as the analytical method instead. These results confirmed that trehalose content is currently overestimated by HPAEC‐PAD analysis, approximately 7 and 13 times for A. thaliana and linseed respectively. Thus GC‐MS gave more satisfactory results for trehalose quantification in plants. With this method, trehalose accumulation was observed in linseed during an osmotic stress (?0.30 MPa), the quantity (31.49 nmol g^–1 dry weight after 48 h) appears too low to assign an osmoprotector or osmoregulator role to trehalose in stressed linseed.     

Aphid-induced accumulation of trehalose in Arabidopsis thaliana is systemic and dependent upon aphid density

Trehalose is a disaccharide sugar that is now considered to be widely distributed among higher plants. Trehalose has been attributed a number of roles, including control of basic plant processes, such as photosynthesis, and conferring tolerance to abiotic stresses, such as desiccation and high salinity. Trehalose is also a common storage sugar used by insects. In this study, we used laboratory investigations to examine various aspects of trehalose dynamics in an aphid–host plant system (Arabidopsis and the peach potato aphid, Myzus persicae). Trehalose concentrations were measured by [1-H]-NMR. Myzus persicae reared on Arabidopsis, but not on black mustard or spring cabbage, contained considerable quantities of trehalose (5 % w/w dry matter). In Arabidopsis foliage, feeding by aphids induced a density-dependent accumulation of trehalose up to 5 mg g^?1 dry weight. Leaves that were not challenged directly by aphids also exhibited increased trehalose concentrations, indicating that this accumulation was systemic. Trehalose was measured at high concentrations in the phloem sap of plants challenged by aphids, suggesting that aphid feeding induced the plant to produce significant quantities of trehalose, which moved through the plant and into the aphids via the phloem sap. Trehalose was also excreted in the aphid honeydew. Further work is required to clarify whether this trehalose accumulation in Arabidopsis has a direct role or a signalling function in plant tolerance of, or resistance to, aphid feeding, and if a similar accumulation of this sugar occurs when other species or genotypes of aphids are reared on this host plant.     

Trehalose production: exploiting novel approaches

Trehalose (alpha-D-glucopyranosyl alpha-D-glucopyranoside) is a unique sugar capable of protecting biomolecules against environmental stress. It is a stable, colorless, odor-free and non-reducing disaccharide, and is widespread in nature. Trehalose has a key role in the survival of some plants and insects, termed anhydrobionts, in harsh environments, even when most of their water body is removed. The properties of these types of organisms drove attention towards the study of trehalose. Since then, it proved to be an active stabilizer of enzymes, proteins, biomasses, pharmaceutical preparations and even organs for transplantation. Recently, trehalose has been accepted as a safe food ingredient by the European regulation system following approval by the US Food and Drug Administration. The wide range of applications of this sugar has increased the interest of many research groups into the development of novel and economically feasible production systems. This article provides a comprehensive review of the current achievements in the biotechnological production of trehalose.