The molecular chaperone Hsp90 is required for high osmotic stress response in Saccharomyces cerevisiae

Exposure of Saccharomyces cerevisiae to high osmotic stress evokes a number of adaptive changes that are necessary for its survival. These adaptive responses are mediated via multiple mitogen-activated protein kinase pathways, of which the high-osmolarity glycerol (HOG) pathway has been studied most extensively. Yeast strains that bear the hsp82T22I or hsp82G81S mutant alleles are osmosensitive. Interestingly, the osmosensitive phenotype is not due to inappropriate functioning of the HOG pathway, as Hog1p phosphorylation and downstream responses including glycerol accumulation are not affected. Rather, the hsp82 mutants display features that are characteristic for cell-wall mutants, i.e. resistance to Zymolyase and sensitivity to Calcofluor White. The osmosensitivity of the hsp82T22I or hsp82G81S strains is suppressed by over-expression of the Hsp90 co-chaperone Cdc37p but not by other co-chaperones. Hsp90 is shown to be required for proper adaptation to high osmolarity via a novel signal transduction pathway that operates parallel to the HOG pathway and requires Cdc37p.     

Transcriptomic insights into the molecular response of Saccharomyces cerevisiae to linoleic acid hydroperoxide

Abstract

Eukaryotic microorganisms are constantly challenged by reactive oxygen species derived endogenously or encountered in their environment. Such adversity is particularly applied to Saccharomyces cerevisiae under harsh industrial conditions. One of the major oxidants to challenge S. cerevisiae is linoleic acid hydroperoxide (LoaOOH). This study, which used genome-wide microarray analysis in conjunction with deletion mutant screening, uncovered the molecular pathways of S. cerevisiae that were altered by an arresting concentration of LoaOOH (75 μM). The oxidative stress response, iron homeostasis, detoxification through PDR transport and direct lipid β-oxidation were evident through the induction of the genes encoding for peroxiredoxins (GPX2, TSA2), the NADPH:oxidoreductase (OYE3), iron uptake (FIT2, ARN2, FET3), PDR transporters (PDR5, PDR15, SNQ2) and β-oxidation machinery (FAA2, POX1). Further, we discovered that Gpx3p, the dual redox sensor and peroxidase, is required for protection against LoaOOH, indicated by the sensitivity of gpx3Δ to a mild dose of LoaOOH (37.5 μM). Deletion of GPX3 conferred a greater sensitivity to LoaOOH than the loss of its signalling partner YAP1. Deletion of either of the iron homeostasis regulators AFT1 or AFT2 also resulted in sensitivity to LoaOOH. These novel findings for Gpx3p, Aft1p and Aft2p point to their distinct roles in response to the lipid peroxide. Finally, the expression of 89 previously uncharacterised genes was significantly altered against LoaOOH, which will contribute to their eventual annotation.     

The chronological life span of Saccharomyces cerevisiae

Simple model systems have played an important role in the discovery of fundamental mechanisms of aging. Studies in yeast, worms and fruit flies have resulted in the identification of proteins and signalling pathways that regulate stress resistance and longevity. New findings indicate that these pathways may have evolved to prevent damage and postpone aging during periods of starvation and may be conserved from yeast to mammals. We will review the yeast S. cerevisiae model system with emphasis on the chronological life span as a model system to study aging and the regulation of stress resistance in eukaryotes.     

Comprehensive phenotypic analysis for identification of genes affecting growth under ethanol stress in Saccharomyces cerevisiae

We quantified the growth behavior of all available single gene deletion strains of budding yeast under ethanol stress. Genome-wide analyses enabled the extraction of the genes and determination of the functional categories required for growth under this condition. Statistical analyses revealed that the growth of 446 deletion strains under stress induced by 8% ethanol was defective. We classified these deleted genes into known functional categories, and found that many were important for growth under ethanol stress including several categories that have not been characterized, such as peroxisome. We also performed genome-wide screening under osmotic stress and identified 329 osmotic-sensitive strains. We excluded these strains from the 446 ethanol-sensitive strains to extract the genes whose deletion caused sensitivity to ethanol-specific (359 genes), osmotic-specific (242 genes), and both stresses (87 genes). We also extracted the functional categories that are specifically important for growth under ethanol stress. The genes and functional categories identified in the analysis might provide clues to improving ethanol stress tolerance among yeast cells.     

Everything old is new again: An update on current research on the Cpx envelope stress response

The Cpx envelope stress response (ESR) has been linked to proteins that are integrated into and secreted across the inner membrane for several decades. Initial studies of the cpx locus linked it to alterations in the protein content of both the inner and outer membrane, together with changes in proton motive driven transport and conjugation. Since the mid 1990s, the predominant view of the Cpx envelope stress response has been that it serves to detect and respond to secreted, misfolded proteins in the periplasm. Recent studies in Escherichia coli and other Gram negative organisms highlight a role for the Cpx ESR in specifically responding to perturbations that occur at the inner membrane (IM). It is clear that Cpx adaptation involves a broad suite of changes that encompass many functions in addition to protein folding. Interestingly, recent studies have refocused attention on Cpx-regulated phenotypes that were initially published over 30 years ago, including antibiotic resistance and transport across the IM. In this review I will focus on the insights and models that have arisen from recent studies and that may help explain some of the originally published Cpx phenotypes. Although the molecular nature of the inducing signal for the Cpx ESR remains enigmatic, recently solved structures of signaling proteins are yielding testable models concerning the molecular mechanisms behind signaling. The identification of connections between the Cpx ESR and other stress responses in the cell reveals a complex web of interactions that involves Cpx-regulated expression of other regulators as well as small proteins and sRNAs. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.     

Mitochondrial fission facilitates mitophagy in Saccharomyces cerevisiae

As a highly dynamic organelle, mitochondria undergo constitutive fusion and fission as well as biogenesis and degradation. Mitophagy, selective mitochondrial degradation through autophagy, is a conserved cellular process used for the elimination of excessive and damaged mitochondria in eukaryotes. Despite the significance of mitophagy in cellular physiology and pathophysiologies, the underlying mechanism of this process is far from clear. In this report, we studied the role of mitochondrial fission during mitophagy, and uncover a direct link between the fission complex and mitophagy machinery in Saccharomyces cerevisiae.     

酿酒酵母菌葡萄糖信号传导途径研究进展

简要概述了酿酒酵母细胞的葡萄糖信号传导途径的研究进展,总结了葡萄糖的抑制途径和诱导途径.     

酿酒酵母细胞中钙离子信号传导途径的研究进展

酿酒酵母（SaccharomycescP增v括fdP）细胞可以通过ca2＋／钙调磷酸酶信号途径来应对许多外界环境胁迫。在交配信息素、盐或者其他环境压力存在的条件下,钙离子会通过细胞质膜上的未鉴定的钙转运蛋白x和M或者由Cchl和Midl组成的钙通道进入细胞质。胞质内钙离子浓度的增加会激活细胞质里的钙调磷酸酶（calcineurin）。钙调磷酸酶的一个非常重要的作用是去磷酸化细胞质内的转录因子Crzl,造成它快速地从细胞质转移到细胞核,从而诱导包括液泡膜上钙泵蛋白基因PMCl以及内质网膜和高尔基体膜上钙泵蛋白基因尸脚,在内的目标基因的表达。这两个钙泵蛋白和液泡膜上的Ca2＋／H＋交换蛋白Vcxl一起作用,将细胞质内的钙离子浓度控制在50～200nmol／L的正常生理浓度内．使细胞能够正常生长。该综述主要论述了酿酒酵母细胞内Ca2＋／钙调磷酸酶信号途径的最新研究进展。     

Phospholipase C: Diverse functions in plant biotic stress resistance and fungal pathogenicity

Phospholipase C (PLC) generates various second messenger molecules and mediates phospholipid hydrolysis. In recent years, the important roles of plant and fungal PLC in disease resistance and pathogenicity, respectively, have been determined. However, the roles of PLC in plants and fungi are unintegrated and relevant literature is disorganized. This makes it difficult for researchers to implement PLC-based strategies to improve disease resistance in plants. In this comprehensive review, we summarize the structure, classification, and phylogeny of the PLCs involved in plant biotic stress resistance and fungal pathogenicity. PLCs can be divided into two groups, nonspecific PLC (NPC) and phosphatidylinositol-specific PLC (PI-PLC), which present marked differences in phylogenetic evolution. The products of PLC genes in fungi play significant roles in physiological activity and pathogenesis, whereas those encoded by plant PLC genes mediate the immune response to fungi. This review provides a perspective for the future control of plant fungal diseases.     

Stress co-tolerance and trehalose content in baking strains of Saccharomyces cerevisiae

Fourteen wild-type baking strains of Saccharomyces cerevisiae were grown in batch culture to true stationary phase (exogenous carbon source exhausted) and tested for their trehalose content and their tolerance to heat (52°C for 4.5 min), ethanol (20% v/v for 30 min), H₂O₂ (0.3 M for 60 min), rapid freezing (−196°C for 20 min, cooling rate 200°C min⁻¹), slow freezing (−20°C for 24 h, cooling rate 3°C min⁻¹), salt (growth in 1.5 M NaCl agar) or acetic acid (growth in 0.4% w/v acetic acid agar) stresses. Stress tolerance among the strains was highly variable and up to 1000-fold differences existed between strains for some types of stress. Compared with previously published reports, all strains were tolerant to H₂O₂ stress. Correlation analysis of stress tolerance results demonstrated relationships between tolerance to H₂O₂ and tolerance to all stresses except ethanol. This may imply that oxidative processes are associated with a wide variety of cellular stresses and also indicate that the general robustness associated with industrial yeast may be a result of their oxidative stress tolerance. In addition, H₂O₂ tolerance might be a suitable marker for the general assessment of stress tolerance in yeast strains. Trehalose content failed to correlate with tolerance to any stress except acetic acid. This may indicate that the contribution of trehalose to tolerance to other stresses is either small or inconsistent and that trehalose may not be used as a general predictor of stress tolerance in true stationary phase yeast. Received 10 October 1995/ Accepted in revised form 10 September 1996     

Evidence for autotetraploidy associated with reproductive isolation in Saccharomyces cerevisiae: towards a new domesticated species

Partial or whole‐genome duplications have played a major role in the evolution of new species. We have investigated the variation of ploidy level in a panel of domesticated strains of Saccharomyces cerevisiae coming from different geographical origins. Segregation studies and crosses with tester strains of different ploidy levels showed that part of the strains were well‐balanced autotetraploids displaying tetrasomic inheritance. The presence of up to four different alleles for various loci is consistent with a polyploidization mechanism relying on the fusion of two nonreduced meiospores coming from two S. cerevisiae strains. Autotetraploidy was also in accordance with karyotype and flow cytometry analyses. Interestingly, most bakery strains were tetraploids, suggesting a link between ploidy level and human use. The null or drastically reduced fertility of the hybrids between tetraploid and diploid strains indicated that domesticated S. cerevisiae strains are composed of two groups isolated by post‐zygotic reproductive barriers.