Nitrogen depletion causes up-regulation of glutathione content and gamma-glutamyltranspeptidase in Schizosaccharomyces pombe

Ethephon increases photosynthetic-nitrogen use efficiency, proline and antioxidant metabolism to alleviate decrease in photosynthesis under salinity stress in mustard

Salinity is a serious threat to plant growth and development worldwide reducing agricultural productivity each year. Ethylene is an important phytohormone that affects plants performance under normal and abiotic stress conditions. In this study, role of ethylene was investigated in mitigating salinity stress (100 mM NaCl) effects on photosynthesis in mustard plants subjected to different nitrogen (N; 5 and 10 mM) levels. Plants under salinity stress exhibited marked increase in proline and reduced glutathione (GSH) content and activity of antioxidant enzymes. Nitrogen supplementation at 10 mM was better than 200 µl l^-1 ethephon treatment under no stress. However, under salinity stress, both N and ethephon were equally effective. The combined application of 10 mM N and ethephon to salinity stressed plants produced greatest increase in photosynthesis by increasing proline and antioxidant metabolism. Ethylene evolution was high under salinity stress, but treatment of 10 mM N and 200 µl l^-1 ethephon greatly decreased ethylene evolution that was equivalent to the 10 mM N treatment alone. This concentration of ethylene decreased the oxidative stress and increased the photosynthetic nitrogen use efficiency (NUE) maximally to increase photosynthesis. The use of ethylene action inhibitor, norbornadiene (NBD) showed reduction in ethylene mediated effects in alleviating salinity. Norbornadiene decreased the photosynthetic-NUE, proline and GSH content that resulted in decrease in photosynthesis under salinity stress. This study indicated that ethylene regulated the proline and antioxidant metabolism under salinity stress to increase photosynthetic functions of mustard grown with low and optimum N. The modulation of ethylene could be adopted in agricultural practices to increase photosynthesis under salinity stress.

Functional human induced hepatocytes (hiHeps) with bile acid synthesis and transport capacities: A novel in vitro cholestatic model

Drug-induced cholestasis is a leading cause of drug withdrawal. However, the use of primary human hepatocytes (PHHs), the gold standard for predicting cholestasis in vitro, is limited by their high cost and batch-to-batch variability. Mature hepatocyte characteristics have been observed in human induced hepatocytes (hiHeps) derived from human fibroblast transdifferentiation. Here, we evaluated whether hiHeps could biosynthesize and excrete bile acids (BAs) and their potential as PHH alternatives for cholestasis investigations. Quantitative real-time PCR (qRT-PCR) and western blotting indicated that hiHeps highly expressed BA synthases and functional transporters. Liquid chromatography tandem mass spectrometry (LC-MS/MS) showed that hiHeps produced normal intercellular unconjugated BAs but fewer conjugated BAs than human hepatocytes. When incubated with representative cholestatic agents, hiHeps exhibited sensitive drug-induced bile salt export pump (BSEP) dysfunction, and their response to cholestatic agent-mediated cytotoxicity correlated well with that of PHHs (r² = 0.8032). Deoxycholic acid (DCA)-induced hepatotoxicity in hiHeps was verified by elevated aspartate aminotransferase (AST) and γ-glutamyl-transferase (γ-GT) levels. Mitochondrial damage and cell death suggested DCA-induced toxicity in hiHeps, which were attenuated by hepatoprotective drugs, as in PHHs. For the first time, hiHeps were reported to biosynthesize and excrete BAs, which could facilitate predicting cholestatic hepatotoxicity and screening potential therapeutic drugs against cholestasis.

Metabolomic Analysis of Schizosaccharomyces pombe: Sample Preparation, Detection, and Data Interpretation

Metabolomics is a modern field of chemical biology that strives to simultaneously quantify hundreds of cellular metabolites. Techniques for metabolomic analysis in Schizosaccharomyces pombe have only recently been developed. Here we introduce methods that provide a complete workflow for metabolomic analysis in S. pombe Based on available literature, we estimate the yeast metabolome to comprise on the order of several thousand different metabolites. We discuss the feasibility of extraction and detection of such a large number of metabolites, and the influences of various parameters on the results. Among the parameters addressed are cell cultivation conditions, metabolite extraction techniques, and detection and quantification methods. Further, we provide recommendations on data management and data processing for metabolomic experiments, and describe possible pitfalls regarding the interpretation of metabolomic data. Finally, we briefly discuss potential future developments of this technique.

γ-Glutamyltransferases (GGT) in Colletotrichum graminicola: mRNA and enzyme activity, and evidence that CgGGT1 allows glutathione utilization during nitrogen deficiency

Gamma-glutamyltransferase (GGT, EC 2.3.2.2) cleaves the γ-glutamyl linkage in glutathione (GSH). Three GGTs in the hemibiotrophic plant pathogen Colletotrichum graminicola were identified in silico. GGT mRNA expression was monitored by quantitative reverse-transcriptase PCR. Expression of all three genes was detected in planta during the biotrophic and necrotrophic stages of infection. Of the three GGTs, CgGGT1 mRNA (from gene GLRG_09590) was the most highly expressed. All three GGT mRNAs were up-regulated in wild type nitrogen-starved germlings in comparison to non-starved germlings. CgGGT1 was insertionally mutagenized in C. graminicola, complemented with the wild type form of the gene, and over-expressed. Enzyme assays of two independent CgGGT1 knockouts and the wild type indicated that CgGGT1 is the major GGT and accounts for 86% and 68% of total GGT activity in conidia and mycelia, respectively. The over-expressing strain had 8-fold and 3-fold more enzyme activity in conidia and mycelia, respectively, than the wild type. In an analysis of the GGT knockout, complemented and over-expressing strains, GGT1 transcript levels are highly correlated (r=0.95) with levels of total GGT enzyme activity. CgGGT1 and CgGGT2 genes in strains that had ectopic copies of CgGGT1 were not up-regulated by nitrogen-starvation, in contrast to the wild type. Deletion or over-expression of CgGGT1 had no effect on mRNA expression of CgGGT2 and CgGGT3. In broth in which 3 and 6mM glutathione (GSH) was the nitrogen source, the CgGGT1 over-expressing strain produced significantly (P<0.0001) more biomass than the wild type and complemented strains, whereas the CgGGT1Δ strains produced significantly (P<0.0001) less biomass than the wild type strain. This suggests that CgGGT1 is involved in utilizing GSH as a nitrogen source. However, deletion and over-expression of CgGGT1 had no effect on either virulence in wounded corn leaf sheaths or GSH levels in conidia and mycelia. Thus, the regulation of GSH concentration is apparently independent of CgGGT1 activity.

Glutathione degradation is a key determinant of glutathione homeostasis

Glutathione (GSH) has several important functions in eukaryotic cells, and its intracellular concentration is tightly controlled. Combining mathematical models and (35)S labeling, we analyzed Saccharomyces cerevisiae sulfur metabolism. This led us to the observation that GSH recycling is markedly faster than previously estimated. We set up additional in vivo assays and concluded that under standard conditions, GSH half-life is around 90 min. Sulfur starvation and growth with GSH as the sole sulfur source strongly increase GSH degradation, whereas cadmium (Cd(2+)) treatment inhibits GSH degradation. Whatever the condition tested, GSH is degraded by the cytosolic Dug complex (composed of the three subunits Dug1, Dug2, and Dug3) but not by the γ-glutamyl-transpeptidase, raising the question of the role of this enzyme. In vivo, both DUG2/3 mRNA levels and Dug activity are quickly induced by sulfur deprivation in a Met4-dependent manner. This suggests that Dug activity is mainly regulated at the transcriptional level. Finally, analysis of dug2Δ and dug3Δ mutant cells shows that GSH degradation activity strongly impacts on GSH intracellular concentration and that GSH intracellular concentration does not affect GSH synthesis rate. Altogether, our data led us to reconsider important aspects of GSH metabolism, challenging notions on GSH synthesis and GSH degradation that were considered as established.

Expression of the atf1+ gene is upregulated in fission yeast under nitrosative and nutritional stresses

This work was designed to assess regulation of the atf1+ gene in the fission yeast Schizosaccharomyces pombe under nitrosative and nutritional stresses, using the atf1+-lacZ fusion gene and RT-PCR. Nitric oxide (NO)-generating sodium nitroprusside (SNP; 10 micromol/L) and nitrogen depletion significantly enhanced synthesis of beta-galactosidase from the atf1+-lacZ fusion gene in S. pombe Pap1-positive KP1 cells, but not in S. pombe Pap1-negative TP108-3C cells. SNP (10 micromol/L) and nitrogen depletion also caused a significant increase in atf1+ mRNA levels in Pap1-positive cells, but not in Pap1-negative cells. Depletion of glucose marginally increased synthesis of beta-galactosidase from the fusion gene in S. pombe Pap1-positive cells. Taken together, the S. pombe atf1+ gene is upregulated by nitrosative and nutritional stresses on a transcriptional level, possibly via the mediation of Pap1.