The role of the trehalose transporter during germination

Impact of temperature stress and validamycin A on compatible solutes and fumonisin production in F. verticillioides: role of trehalose-6-phosphate synthase

Fusarium verticillioides is a pathogen of maize that causes root, stalk and ear rot and produces fumonisins, toxic secondary metabolites associated with disease in livestock and humans. Environmental stresses such as heat and drought influence disease severity and toxin production, but the effects of abiotic stress on compatible solute production by F. verticillioides have not been fully characterized. We found that decreasing the growth temperature leads to a long-term reduction in polyol levels, whereas increasing the temperature leads to a transient increase in polyols. The effects of temperature shifts on trehalose levels are opposite the effects on polyols and more dramatic. Treatment with validamycin A, a trehalose analog with antifungal activity, leads to a rapid reduction in trehalose levels, despite its known role as a trehalase inhibitor. Mutant strains lacking TPS1, which encodes a putative trehalose-6-phosphate synthase, have altered growth characteristics, do not produce detectable amounts of trehalose under any condition tested, and accumulate glycogen at levels significantly higher than wild-type F. verticillioides. TPS1 mutants also produce significantly less fumonisin than wild type and are also less pathogenic than wild type on maize. These data link trehalose biosynthesis, secondary metabolism, and disease, and suggest that trehalose metabolic pathways may be a viable target for the control of Fusarium diseases and fumonisin contamination of maize.

Proteomic analysis of insecticide triazophos-induced mating-responsive proteins of Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a classic example of a resurgent pest induced by insecticides. It has been demonstrated that triazophos treatment causes an increase in the content of male accessory gland proteins (Acps) that can be transferred to females via mating, influencing female reproduction. However, the mechanism of this type of insecticide-induced Acps in males and the subsequent stimulation of reproduction in females are not well understood. To identify changes in the types of Acps and reproductive proteins in mated females, we conducted a comparative proteomic analysis. Six samples were categorized into four different groups: (1) untreated unmated males compared to treated unmated males (UUM vs TUM); (2) treated unmated males compared to treated mated males (TUM vs TMM); (3) untreated unmated females compared to treated unmated females (UUF vs TUF); (4) treated unmated females compared to treated mated females (TUF vs TMF). Protein expression changes among the four different groups were examined by two-dimensional gel electrophoresis (2-DE) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Of the 500-600 reproducibly detected protein spots on each gel, 107 protein spots were differentially expressed between the four different groups. Of the 63 proteins identified by LC-MS/MS analysis, 38 were up-regulated and 25 were down-regulated in the four different groups. Some novel proteins related to fecundity were observed including spermatogenesis-associated protein 5, testis development protein NYD-SP6, arginine kinase, actin-5C, vitellogenin, and ovarian serine protease nudel. The elevated expression of novel fecundity proteins in six samples of N. lugens females and males due to exposure to triazophos was confirmed by quantitative real-time PCR (qRT-PCR). The results suggest that these proteins may participate in the reproductive process of N. lugens adult females and males. Our findings fill a gap in understanding the relationship between insecticide-treated males and the stimulated reproduction of N. lugens females.

Effects of physical and nutritional stress conditions during mycelial growth on conidial germination speed, adhesion to host cuticle, and virulence of Metarhizium anisopliae, an entomopathogenic fungus

Growth under stress may influence pathogen virulence and other phenotypic traits. Conidia of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (isolate ARSEF 2575) were produced under different stress conditions and then examined for influences on in vitro conidial germination speed, adhesion to the insect cuticle, and virulence to an insect host, Tenebrio molitor. Conidia were produced under non-stress conditions [on potato-dextrose agar plus 1gl(-1) yeast extract (PDAY; control)], or under the following stress conditions: osmotic (PDAY+sodium chloride or potassium chloride, 0.6 or 0.8m); oxidative [(PDAY+hydrogen peroxide, 5mm) or UV-A (irradiation of mycelium on PDAY)]; heat shock (heat treatment of mycelium on PDAY at 45 degrees C, 40min); and nutritive [minimal medium (MM) with no carbon source, or on MM plus 3gl(-1) lactose (MML)]. Conidia were most virulent (based on mortality at 3d) and had the fastest germination rates when produced on MML, followed by MM. In addition, conidial adhesion to host cuticle was greatest when the conidia were produced on MML. Media with high osmolarity (0.8m) produced conidia with slightly elevated virulence and faster germination rates than conidia produced on the control medium (PDAY), but this trend did not hold for media with the lower osmolarity, (0.6m). Conidia produced from mycelium irradiated with UV-A while growing on PDAY had somewhat elevated virulence levels similar to that of conidia produced on MM, but their germination rate was not increased. Hydrogen peroxide and heat shock treatments did not alter virulence. These results demonstrate that the germination, adhesion and virulence of M. anisopliae conidia can be strongly influenced by culture conditions (including stresses) during production of the conidia.

New insights into trehalose metabolism by Saccharomyces cerevisiae: NTH2 encodes a functional cytosolic trehalase, and deletion of TPS1 reveals Ath1p-dependent trehalose mobilization

In the yeast Saccharomyces cerevisiae, the synthesis of endogenous trehalose is catalyzed by a trehalose synthase complex, TPS, and its hydrolysis relies on a cytosolic/neutral trehalase encoded by NTH1. In this work, we showed that NTH2, a paralog of NTH1, encodes a functional trehalase that is implicated in trehalose mobilization. Yeast is also endowed with an acid trehalase encoded by ATH1 and an H+/trehalose transporter encoded by AGT1, which can together sustain assimilation of exogenous trehalose. We showed that a tps1 mutant defective in the TPS catalytic subunit cultivated on trehalose, or on a dual source of carbon made of galactose and trehalose, accumulated high levels of intracellular trehalose by its Agt1p-mediated transport. The accumulated disaccharide was mobilized as soon as cells entered the stationary phase by a process requiring a coupling between its export and immediate extracellular hydrolysis by Ath1p. Compared to what is seen for classical growth conditions on glucose, this mobilization was rather unique, since it took place prior to that of glycogen, which was postponed until the late stationary phase. However, when the Ath1p-dependent mobilization of trehalose identified in this study was impaired, glycogen was mobilized earlier and faster, indicating a fine-tuning control in carbon storage management during periods of carbon and energy restriction.

Isoforms of trehalase and invertase of Fusarium oxysporum

Enzymatic assays and native PAGE were used to study trehalase and invertase activities, depending on culture age and different sugar conditions, in cell-free extracts, culture filtrates and ribosomal wash of Fusarium oxysporum. The activity of invertase preceded that of trehalase; in the exponential phase of growth, mainly invertase activity was produced, whereas trehalase activity was high in the stationary phase. In this last phase of growth, the activity of intracellular trehalase was repressed by monosaccharides, whereas disaccharides, especially lactose and starch, enhanced the activity of intracellular and extracellular trehalase. However, invertase activity was not repressed under these conditions and had the maximal activity in the presence of saccharose. Intracellular trehalase appeared in a single, high-molecular weight (120 kDa) form, whereas the extracellular enzyme appeared in a single, low-molecular weight (60 kDa) form. The activity pattern of invertase isoforms indicated the occurrence of three forms of intracellular enzyme with the main activity band at 120 kDa and two isoforms of extracellular enzyme. In the ribosomal wash, high-molecular weight isoforms of both trehalase and invertase were identified. A possible role of trehalase and invertase in carbohydrate metabolism of fungal pathogens is also discussed.

Impact of heterologous expression of Escherichia coli UDP-glucose pyrophosphorylase on trehalose and glycogen synthesis in Corynebacterium glutamicum

Trehalose is a disaccharide with a wide range of applications in the food industry. We recently proposed a strategy for trehalose production based on improved strains of the gram-positive bacterium Corynebacterium glutamicum. This microorganism synthesizes trehalose through two major pathways, OtsBA and TreYZ, by using UDP-glucose and ADP-glucose, respectively, as the glucosyl donors. In this paper we describe improvement of the UDP-glucose supply through heterologous expression in C. glutamicum of the UDP-glucose pyrophosphorylase gene from Escherichia coli, either expressed alone or coexpressed with the E. coli ots genes (galU otsBA synthetic operon). The impact of such expression on trehalose accumulation and excretion, glycogen accumulation, and the growth pattern of new recombinant strains is described. Expression of the galU otsBA synthetic operon resulted in a sixfold increase in the accumulated and excreted trehalose relative to that in a wild-type strain. Surprisingly, single expression of galU also resulted in an increase in the accumulated trehalose. This increase in trehalose synthesis was abolished upon deletion of the TreYZ pathway. These results proved that UDP-glucose has an important role not only in the OtsBA pathway but also in the TreYZ pathway.

Osmotic stress response: quantification of cell maintenance and metabolic fluxes in a lysine-overproducing strain of Corynebacterium glutamicum

Osmotic stress diminishes cell productivity and may cause cell inactivation in industrial fermentations. The quantification of metabolic changes under such conditions is fundamental for understanding and describing microbial behavior during bioprocesses. We quantified the gradual changes that take place when a lysine-overproducing strain of Corynebacterium glutamicum is grown in continuous culture with saline gradients at different dilution rates. The use of compatible solutes depended on environmental conditions; certain osmolites predominated at different dilution rates and extracellular osmolalities. A metabolic flux analysis showed that at high dilution rates C. glutamicum redistributed its metabolic fluxes, favoring energy formation over growth. At low dilution rates, cell metabolism accelerated as the osmolality was steadily increased. Flexibility in the oxaloacetate node proved to be key for the energetic redistribution that occurred when cells were grown at high dilution rates. Substrate and ATP maintenance coefficients increased 30- and 5-fold, respectively, when the osmolality increased, which demonstrates that energy pool management is fundamental for sustaining viability.

Cryopreservation of Stem Cells Using Trehalose: Evaluation of the Method Using a Human Hematopoietic Cell Line

While stem cell cryopreservation methods have been optimized using dimethylsulfoxide (DMSO), the established techniques are not optimal when applied to unfertilized human embryonic cells. In addition, important questions remain regarding the toxicity and characteristics of DMSO for treatment of stem cells for clinical use. The objective of this study was to establish an optimal method for cryopreservation of stem cells using low concentrations (0.2 M) of trehalose, a nontoxic disaccharide of glucose, which possesses excellent protective characteristics, in place of current methods utilizing high concentrations (1-2 M) of DMSO. A human hematopoietic cell line was used in this investigation as a surrogate for human stem cells. Trehalose was loaded into cells using a genetically engineered mutant of the pore-forming protein alpha-hemolysin from Staphylococcus aureus. This method results in a nonselective pore equipped with a metal-actuated switch that is sensitive to extracellular zinc concentrations, thus permitting controlled loading of trehalose. Preliminary experiments characterized the effects of poration on TF-1 cells and established optimal conditions for trehalose loading and cell survival. TF-1 cells were frozen at 1 degrees C/min to -80 degrees C with and without intra- and extracellular trehalose. Following storage at -80 degrees C for 1 week, cells were thawed and evaluated for viability, differentiation capacity, and clonogenic activity in comparison to cells frozen with DMSO. Predictably, cells frozen without any protective agent did not survive freezing. Colony-forming units (CFU) generated from cells frozen with intra- and extracellular trehalose, however, were comparable in size, morphology, and number to those generated by cells frozen in DMSO. There was no observable alteration in phenotypic markers of differentiation in either trehalose- or DMSO-treated cells. These data demonstrate that low concentrations of trehalose can protect hematopoietic progenitors from freezing injury and support the concept that trehalose may be useful for freezing embryonic stem cells and other primitive stem cells for therapeutic and investigational use.

Induction of trehalase in Arabidopsis plants infected with the trehalose-producing pathogen Plasmodiophora brassicae

Various microorganisms produce the disaccharide trehalose during their symbiotic and pathogenic interactions with plants. Trehalose has strong effects on plant metabolism and growth; therefore, we became interested to study its possible role in the interaction of Arabidopsis thaliana with Plasmodiophora brassicae, the causal agent of clubroot disease. We found that trehalose accumulated strongly in the infected organs (i.e., the roots and hypocotyls) and, to a lesser extent, in the leaves and stems of infected plants. This accumulation pattern of trehalose correlated with the expression of a putative trehalose-6-phosphate synthase (EC 2.4.1.15) gene from P. brassicae, PbTPS1. Clubroot formation also resulted in an induction of the Arabidopsis trehalase gene, ATTRE1, and in a concomitant increase in trehalase (EC 3.2.1.28) activity in the roots and hypocotyls, but not in the leaves and stems of infected plants. Thus, induction of ATTRE1 expression was probably responsible for the increased trehalase activity. Trehalase activity increased before trehalose accumulated; therefore, it is unlikely that trehalase was induced by its substrate. The induction of trehalase may be part of the plant's defense response and may prevent excess accumulation of trehalose in the plant cells, where it could interfere with the regulation of carbon metabolism.

The trehalose myth revisited: introduction to a symposium on stabilization of cells in the dry state

This essay is an introduction to a series of papers arising from a symposium on stabilization of cells in the dry state. Nearly all of these investigations have utilized the sugar trehalose as a stabilizing molecule. Over the past two decades a myth has grown up about special properties of trehalose for stabilization of biomaterials. We review many of such uses here and show that under ideal conditions for drying and storage trehalose has few, if any, special properties. However, under suboptimal conditions trehalose has some distinct advantages and thus may remain the preferred excipient. We review the available mechanisms for introducing trehalose into the cytoplasm of living cells as an introduction to the papers that follow.