Characterization of tpp1(+) as encoding a main trehalose-6P phosphatase in the fission yeast Schizosaccharomyces pombe

A Snapshot of the Trehalose Pathway During Seed Imbibition in Medicago truncatula Reveals Temporal- and Stress-Dependent Shifts in Gene Expression Patterns Associated With Metabolite Changes

Trehalose, a non-reducing disaccharide with multiple functions, among which source of energy and carbon, stress protectant, and signaling molecule, has been mainly studied in relation to plant development and response to stress. The trehalose pathway is conserved among different organisms and is composed of three enzymes: trehalose-6-phosphate synthase (TPS), which converts uridine diphosphate (UDP)-glucose and glucose-6-phosphate to trehalose-6-phosphate (T6P), trehalose-6-phosphatase (TPP), which dephosphorylates T6P to produce trehalose, and trehalase (TRE), responsible for trehalose catabolism. In plants, the trehalose pathway has been mostly studied in resurrection plants and the model plant Arabidopsis thaliana, where 11 AtTPS, 10 AtTPP, and 1 AtTRE genes are present. Here, we aim to investigate the involvement of the trehalose pathway in the early stages of seed germination (specifically, seed imbibition) using the model legume Medicago truncatula as a working system. Since not all the genes belonging to the trehalose pathway had been identified in M. truncatula, we first conducted an in silico analysis using the orthologous gene sequences from A. thaliana. Nine MtTPSs, eight MtTPPs, and a single MtTRE gene were hereby identified. Subsequently, the expression profiles of all the genes (together with the sucrose master-regulator SnRK1) were investigated during seed imbibition with water or stress agents (polyethylene glycol and sodium chloride). The reported data show a temporal distribution and preferential expression of specific TPS and TPP isoforms during seed imbibition with water. Moreover, it was possible to distinguish a small set of genes (e.g., MtTPS1, MtTPS7, MtTPS10, MtTPPA, MtTPPI, MtTRE) having a potential impact as precocious hallmarks of the seed response to stress. When the trehalose levels were measured by high-performance liquid chromatography, a significant decrease was observed during seed imbibition, suggesting that trehalose may act as an energy source rather than osmoprotectant. This is the first report investigating the expression profiles of genes belonging to the trehalose pathway during seed imbibition, thus ascertaining their involvement in the pre-germinative metabolism and their potential as tools to improve seed germination efficiency.

Central Role of the Trehalose Biosynthesis Pathway in the Pathogenesis of Human Fungal Infections: Opportunities and Challenges for Therapeutic Development

Invasive fungal infections cause significant morbidity and mortality in part due to a limited antifungal drug arsenal. One therapeutic challenge faced by clinicians is the significant host toxicity associated with antifungal drugs. Another challenge is the fungistatic mechanism of action of some drugs. Consequently, the identification of fungus-specific drug targets essential for fitness in vivo remains a significant goal of medical mycology research. The trehalose biosynthetic pathway is found in a wide variety of organisms, including human-pathogenic fungi, but not in humans. Genes encoding proteins involved in trehalose biosynthesis are mechanistically linked to the metabolism, cell wall homeostasis, stress responses, and virulence of Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. While there are a number of pathways for trehalose production across the tree of life, the TPS/TPP (trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase) pathway is the canonical pathway found in human-pathogenic fungi. Importantly, data suggest that proteins involved in trehalose biosynthesis play other critical roles in fungal metabolism and in vivo fitness that remain to be fully elucidated. By further defining the biology and functions of trehalose and its biosynthetic pathway components in pathogenic fungi, an opportunity exists to leverage this pathway as a potent antifungal drug target. The goal of this review is to cover the known roles of this important molecule and its associated biosynthesis-encoding genes in the human-pathogenic fungi studied to date and to employ these data to critically assess the opportunities and challenges facing development of this pathway as a therapeutic target.

Role of Oxidative Stress Response and Trehalose Accumulation in the Longevity of Fission Yeast

Background:

Glucose is the preferred carbon and energy source in most organisms and plays an active role in the regulation of many biological processes. However, an excess of glucose leads to such undesirable conditions as diabetes and age-related diseases. Since Schizosaccharomyces pombe homologous of many human genes, it offers several advantages for the investigation of the molecular mechanisms underlying human disease and aging studies. We have identified two glucose-repression-resistant mutants (ird5 and ird11) of S. pombe.

Objectives:

We aimed to investigate the possible relationship between lifespan extension and oxidative stress response induced by exposure to hydrogen peroxide alongside the trehalose accumulation level by using the two S. pombe mutants (i.e. ird5 and ird11), which are repressed by glucose and are resistant to oxidative stress.

Materials and Methods:

We employed trehalose accumulation measurement and colony-forming unit (CFU) counting using the ird mutants in exponential and stationary phases and compared them to the wild type grown in repressed, de-repressed, and stressed conditions to clarify the possible relationship between glucose signaling, oxidative stress response, and lifespan in S. pombe.

Results:

The lifespan of the ird5 mutant was significantly longer that of either the ird11 mutant or the wild type cells. Under repressed condition, the trehalose content was increased remarkably on the 3rd day of the study in the ird11 mutant and the wild type. Under de-repressed condition, the level of intracellular trehalose was notably increased on the 3rd day in ird11. Under stressed condition, the trehalose level in ird11 was increased on the 3rd day as a pattern similar to that observed in the wild type.

Conclusions:

Our results demonstrated no significant correlation between the ird5 lifespan and the trehalose concentration. Likewise, the correlation between lifespan extension, trehalose accumulation, and cellular resistance to hydrogen peroxide was not significant.

Increased thermal and osmotic stress resistance in Listeria monocytogenes 568 grown in the presence of trehalose due to inactivation of the phosphotrehalase-encoding gene treA

The food-borne pathogen Listeria monocytogenes is a problem for food processors and consumers alike, as the organism is resistant to harsh environmental conditions and inimical barriers implemented to prevent the survival and/or growth of harmful bacteria. One mechanism by which listeriae mediate survival is through the accumulation of compatible solutes, such as proline, betaine and carnitine. In other bacteria, including Escherichia coli, the synthesis and accumulation of another compatible solute, trehalose, are known to aid in the survival of stressed cells. The objective of this research was to investigate trehalose metabolism in L. monocytogenes, where the sugar is thought to be transferred across the cytoplasmic membrane via a specific phosphoenolpyruvate phosphotransferase system and phosphorylation to trehalose-6-phosphate (T6P). The latter is subsequently broken down into glucose and glucose-6-phosphate by α,α-(1,1) phosphotrehalase, the putative product of the treA gene. Here we report on an isogenic treA mutant of L. monocytogenes 568 (568:ΔTreA) which, relative to the wild-type strain, displays increased tolerances to multiple stressors, including heat, high osmolarity, and desiccation. This is the first study to examine the putative trehalose operon in L. monocytogenes, and we demonstrate that lmo1254 (treA) in L. monocytogenes 568 indeed encodes a phosphotrehalase required for the hydrolysis of T6P. Disruption of the treA gene results in the accumulation of T6P which is subsequently dephosphorylated to trehalose in the cytosol, thereby contributing to the stress hardiness observed in the treA mutant. This study highlights the importance of compatible solutes for microbial survival in adverse environments.

Trehalose turnover during abiotic stress in arbuscular mycorrhizal fungi

Trehalose is a common reserve carbohydrate in fungi, whose role has been recently extended to other cellular functions, such as stress tolerance, glycolysis control, sporulation and infectivity of some pathogenic strains. To gain some insight into the role of trehalose during abiotic stress in arbuscular mycorrhizal (AM) fungi, we assessed trehalose content as well as transcriptional regulation and enzyme activity of neutral trehalase and trehalose-6-phosphate phosphatase in Glomus intraradices in response to heat shock, chemical or osmotic stress. Prolonged or intensive exposure to heat or chemical stress, but not osmotic stress, caused an increase of trehalose in the cell. We found this associated with transient up-regulation of the trehalose-6-P phosphatase (GiTPS2) transcript that coincided with moderate increases in enzyme activity. By contrast, there were no changes in neutral trehalase (GiNTH1) RNA accumulation in response to stress treatments, while they promoted, in most cases, an increase in activity. After stress had ceased, trehalose returned to basal concentrations, pointing to a role of neutral trehalase activity in heat shock recovery. A yeast complementation assay confirmed the role of neutral trehalase in thermotolerance. Taken together, these results indicate that trehalose could play a role in AM fungi during the recovery from certain stresses such as heat shock and chemical treatment.

Characterization and regulation of the trehalose synthesis pathway and its importance in the pathogenicity of Cryptococcus neoformans

The disaccharide trehalose has been found to play diverse roles, from energy source to stress protectant, and this sugar is found in organisms as diverse as bacteria, fungi, plants, and invertebrates but not in mammals. Recent studies in the pathobiology of Cryptococcus neoformans identified the presence of a functioning trehalose pathway during infection and suggested its importance for C. neoformans survival in the host. Therefore, in C. neoformans we created null mutants of the trehalose-6-phosphate (T6P) synthase (TPS1), trehalose-6-phophate phosphatase (TPS2), and neutral trehalase (NTH1) genes. We found that both TPS1 and TPS2 are required for high-temperature (37 degrees C) growth and glycolysis but that the block at TPS2 results in the apparent toxic accumulation of T6P, which makes this enzyme a fungicidal target. Sorbitol suppresses the growth defect in the tps1 and tps2 mutants at 37 degrees C, which supports the hypothesis that these sugars (trehalose and sorbitol) act primarily as stress protectants for proteins and membranes during exposure to high temperatures in C. neoformans. The essential nature of this pathway for disease was confirmed when a tps1 mutant strain was found to be avirulent in both rabbits and mice. Furthermore, in the system of the invertebrate C. elegans, in which high in vivo temperature is no longer an environmental factor, attenuation in virulence was still noted with the tps1 mutant, and this supports the hypothesis that the trehalose pathway in C. neoformans is involved in more host survival mechanisms than simply high-temperature stresses and glycolysis. These studies in C. neoformans and previous studies in other pathogenic fungi support the view of the trehalose pathway as a selective fungicidal target for use in antifungal development.

A cooperative role for Atf1 and Pap1 in the detoxification of the oxidative stress induced by glucose deprivation in Schizosaccharomyces pombe

In Schizosaccharomyces pombe, glucose concentrations below a certain threshold trigger the stress-activated protein kinase (SAPK) signal transduction pathway and promote increased transcription of Atf1-dependent genes coding for the general stress response. Removal of glucose specifically induces the nuclear accumulation of green fluorescent protein-labeled Pap1 (GFP-Pap1) and the expression of genes dependent on this transcription factor. In contrast, depletion of the nitrogen source triggers the SAPK pathway but does not activate Pap1-dependent gene transcription, indicating that carbon stress rather than growth arrest leads to an endogenous oxidative condition that favors nuclear accumulation of Pap1. The reductant agents glutathione or N-acetylcysteine suppress the nuclear accumulation of GFP-Pap1 induced by glucose deprivation without inhibiting the activation of the MAPK Sty1. In addition, cells expressing a mutant GFP-Pap1 unable to accumulate into the nucleus upon hydrogen peroxide-mediated oxidative stress failed to show this protein into the nucleus in the absence of glucose. These results support the concept of a concerted action between the SAPK pathway and the Pap1 transcription factor during glucose exhaustion by which glucose limitation induces activation of the SAPK pathway prior to the oxidative stress caused by glucose deprivation. The ensuing induction of Atf1-dependent genes (catalase) decreases the level of hydroperoxides allowing Pap1 nuclear accumulation and function. Congruent with this interpretation, glucose-depleted cells show higher adaptive response to exogenous oxidative stress than those maintained in the presence of glucose.

The importance of a functional trehalose biosynthetic pathway for the life of yeasts and fungi

The view of the role of trehalose in yeast has changed in the last few years. For a long time considered a reserve carbohydrate, it gained new importance when its function in the acquisition of thermotolerance was demonstrated. More recently the cellular processes in which the trehalose biosynthetic pathway has been implicated range from the control of glycolysis to sporulation and infectivity by certain fungal pathogens. There is now enough experimental evidence to conclude that trehalose 6-phosphate, an intermediate of trehalose biosynthesis, is an important metabolic regulator in such different organisms as yeasts or plants. Its inhibition of hexokinase plays a key role in the control of the glycolytic flux in Saccharomyces cerevisiae but other, likely important, sites of action are still unknown. We present examples of the phenotypes produced by mutations in the two steps of the trehalose biosynthetic pathway in different yeasts and fungi, and whenever possible examine the molecular explanations advanced to interpret them.

Different roles for the stress-activated protein kinase pathway in the regulation of trehalose metabolism in Schizosaccharomyces pombe

The Wis1p-Sty1p mitogen-activated protein kinase cascade is a major signalling system in the fission yeast Schizosaccharomyces pombe for a wide range of stress responses. It is known that trehalose functions as a protective metabolite to counteract deleterious effects of environmental stresses. Herein it is reported that the expression of genes related to trehalose metabolism in S. pombe, ntp1(+) (neutral trehalase) and tps1(+) [trehalose-6-phosphate (T6P) synthase], is partially regulated by the Sty1p kinase under salt-induced osmotic stress and conditions of slight oxidative stress and is fully dependent on this kinase under severe oxidative stress. This control is carried out through transcription factors Atf1p/Pcr1p during osmotic stress and through Pap1p during exposure to low levels of oxidative stress. However, all three transcription factors are needed for gene expression under conditions of extreme oxidative stress. In addition, a role for Sty1p in the modulation of post-transcriptional activation of trehalase mediated by Pka1p/Sck1p kinases, as well as in the activity of T6P synthase under such stressful conditions has been demonstrated. These results reveal a novel dual action of the Wis1p-Sty1p pathway in the regulation of trehalose metabolism in fission yeast.

Cold induces stress-activated protein kinase-mediated response in the fission yeast Schizosaccharomyces pombe

In the fission yeast Schizosaccharomyces pombe the Wak1p/Win1p-Wis1p-Sty1p stress-activated protein kinase (SAPK) pathway relays environmental signals to the transcriptional machinery and modulates gene expression via a cascade of protein phosphorylation. Cells of S. pombe subjected to cold shock (transfer from 28 degrees C to 15 degrees C) transiently activated the Sty1p mitogen-activated protein kinase (MAPK) by phosphorylation. Induction of this response was completely abolished in cells disrupted in the upstream response regulator Mcs4p. The cold-triggered Sty1p activation was partially dependent on Wak1p MAPKKK and fully dependent on Wis1p MAPKK suggesting that the signal transmission follows a branched pathway, with the redundant MAPKKK Win1p as alternative transducer to Wis1p, which subsequently activates the effector Sty1p MAPK. Also, the bZIP transcription factor Atf1p became phosphorylated in a Sty1p-dependent way during the cold shock and this phosphorylation was found responsible for the increased expression of gpd1+, ctt1+, tps1+ and ntp1+ genes. Strains deleted in transcription factors Atf1p or Pcr1p were unable to grow upon incubation at low temperature whereas those disrupted in any member of the SAPK pathway were able to do so. These data reveal that S. pombe responds to cold by inducing the SAPK pathway. However, such activation is dispensable for yeast growth in cold conditions, supporting that the presence of Atf1/Pcr1 heterodimers, rather than an operative SAPK pathway, is critical to ensure yeast growth at low temperature by an as yet undefined mechanism.

Molecular interaction of neutral trehalase with other enzymes of trehalose metabolism in the fission yeast Schizosaccharomyces pombe

Trehalose metabolism is an essential component of the stress response in yeast cells. In this work we show that the products of the principal genes involved in trehalose metabolism in Schizosaccharomyces pombe, tps1+ (coding for trehalose-6-P synthase, Tps1p), ntp1+ (encoding neutral trehalase, Ntp1p) and tpp1+ (that codes for trehalose-6-P phosphatase, Tpp1p), interact in vitro with each other and with themselves to form protein complexes. Disruption of the gene tps1+ blocks the activation of the neutral trehalase induced by heat shock but not by osmotic stress. We propose that this association may reflect the Tps1p-dependent requirement for thermal activation of trehalase. Data reported here indicate that following a heat shock the enzyme activity of trehalase is associated with Ntp1p dimers or trimers but not with either Ntp1p monomers or with complexes involving Tps1p. These results raise the possibility that heat shock and osmotic stress activate trehalase differentially by acting in the first case through an specific mechanism involving Tps1p-Ntp1p complexes. This study provides the first evidence for the participation of the catabolic enzyme trehalase in the structural framework of a regulatory macromolecular complex containing trehalose-6-P synthase in the fission yeast.

Disruption in Candida albicans of the TPS2 gene encoding trehalose-6-phosphate phosphatase affects cell integrity and decreases infectivity

The gene CaTPS2 encoding trehalose-6-phosphate (T6P) phosphatase from Candida albicans has been cloned and disrupted in this organism. The Catps2/Catps2 mutant did not accumulate trehalose but accumulated high levels of T6P. Disruption of the two copies of the CaTPS2 gene did not abolish growth even at 42 degrees C, but decreased the growth rate. In the stationary phase, the Catps2/Catps2 mutant aggregated, more than 50% of its cells became permeable to propidium iodide and a large amount of protein was found in the culture medium. Aggregation occurred only at pH values higher than 7 and was avoided by osmoprotectants; it was never observed during the exponential phase of growth. The mutant formed colonies with a smooth border on Spider medium. Mice inoculated with 1.5 x 10(6) c.f.u. of wild-type cells died after 8 days, while 80% of those inoculated with the same number of c.f.u. of the Catps2/Catps2 mutant survived for at least 1 month. Reintroduction of the wild-type CaTPS2 gene in the Catps2/Catps2 mutant abolished the phenotypes described. It is hypothesized that the accumulation of T6P interferes with the assembly of a normal cell wall.

Disruption of the Candida albicans TPS2 gene encoding trehalose-6-phosphate phosphatase decreases infectivity without affecting hypha formation

Deletion of trehalose-6-phosphate phosphatase, encoded by TPS2, in Saccharomyces cerevisiae results in accumulation of trehalose-6-phosphate (Tre6P) instead of trehalose under stress conditions. Since trehalose is an important stress protectant and Tre6P accumulation is toxic, we have investigated whether Tre6P phosphatase could be a useful target for antifungals in Candida albicans. We have cloned the C. albicans TPS2 (CaTPS2) gene and constructed heterozygous and homozygous deletion strains. As in S. cerevisiae, complete inactivation of Tre6P phosphatase in C. albicans results in 50-fold hyperaccumulation of Tre6P, thermosensitivity, and rapid death of the cells after a few hours at 44 degrees C. As opposed to inactivation of Tre6P synthase by deletion of CaTPS1, deletion of CaTPS2 does not affect hypha formation on a solid glucose-containing medium. In spite of this, virulence of the homozygous deletion mutant is strongly reduced in a mouse model of systemic infection. The pathogenicity of the heterozygous deletion mutant is similar to that of the wild-type strain. CaTPS2 is a new example of a gene not required for growth under standard conditions but required for pathogenicity in a host. Our results suggest that Tre6P phosphatase may serve as a potential target for antifungal drugs. Neither Tre6P phosphatase nor its substrate is present in mammals, and assay of the enzymes is simple and easily automated for high-throughput screening.

Neurospora clock-controlled gene 9 (ccg-9) encodes trehalose synthase: circadian regulation of stress responses and development

The circadian clock of Neurospora crassa regulates the rhythmic expression of a number of genes encoding diverse functions which, as an ensemble, are adaptive to life in a rhythmic environment of alternating levels of light and dark, warmth and coolness, and dryness and humidity. Previous differential screens have identified a number of such genes based solely on their cycling expression, including clock-controlled gene 9 (ccg-9). Sequence analysis now shows the predicted CCG-9 polypeptide to be homologous to a novel form of trehalose synthase; as such it would catalyze the synthesis of the disaccharide trehalose, which plays an important role in protecting many cells from environmental stresses. Consistent with this, heat, glucose starvation, and osmotic stress induce ccg-9 transcript accumulation. Surprisingly, however, a parallel role in development is suggested by the finding that inactivation of ccg-9 results in altered conidiophore morphology and abolishes the normal circadian rhythm of asexual macroconidial development. Examination of a clock component, FRQ, in the ccg-9-null strain revealed normal cycling, phosphorylation, and light induction, indicating that loss of the conidiation rhythm is not due to changes in either the circadian oscillator or light input into the clock but pointing instead to a defect in circadian output. These data imply an interplay between a role of trehalose in stress protection and an apparent requirement for trehalose in clock regulation of conidiation under constant environmental conditions. This requirement can be bypassed by a daily light signal which drives a light-entrained rhythm in conidiation in the ccg-9-null strain; this bypass suggests that the trehalose requirement is related to clock control of development and not to the developmental process itself. Circadian control of trehalose synthase suggests a link between clock control of stress responses and that of development.