Every cell has developed mechanisms to respond to changes in its environment and to adapt its growth and metabolism to unfavorable conditions. The unicellular eukaryote yeast has long proven as a particularly useful model system for the analysis of cellular stress responses, and the completion of the yeast genome sequence has only added to its power This volume comprehensively reviews both the basic features of the yeast genral stress response and the specific adapations to different stress types (nutrient depletion, osmotic and heat shock as well as salt and oxidative stress). It includes the latest findings in the field and discusses the implications for the analysis of stress response mechanisms in higher eukaryotes as well.
Every cell has developed mechanisms to respond to changes in its environment and to adapt its growth and metabolism to unfavorable conditions. The unicellular eukaryote yeast has long proven as a particularly useful model system for the analysis of cellular stress responses, and the completion of the yeast genome sequence has only added to its powerThis volume comprehensively reviews both the basic features of the yeast genral stress response and the specific adapations to different stress types (nutrient depletion, osmotic and heat shock as well as salt and oxidative stress). It includes the latest findings in the field and discusses the implications for the analysis of stress response mechanisms in higher eukaryotes as well.
Proper stress responses are pivotal for cells to survive and adapt to new environments. Stressed cells coordinate a multi-faceted response spanning many levels of physiology involving growth and cell cycle arrest, metabolites changes, translation arrest and a large fraction of transcriptomic change, which includes the common environmental stress response (ESR). Yet knowledge of the complete stress-activated regulatory network, principles for signal integration as well as the rationale of ESR activation upon stress remains elusive. To decipher complicated signaling networks, we developed an experimental and computational approach to integrate available protein interaction data with gene fitness contributions, mutant transcriptome profiles, and phospho-proteome changes in cells responding to salt stress, to infer the salt-responsive signaling network in yeast. The inferred subnetwork presented many novel predictions by implicating new regulators, uncovering unrecognized crosstalk between known pathways, and pointing to previously unknown 'hubs' of signal integration. We exploited these predictions to show that Cdc14 phosphatase is a central hub in the network and that modification of RNA polymerase II coordinates ESR activation: induction of stress-defense genes with reduction of growth-related transcripts. Additionally, we show that the yeast ESR cannot be simply explained as a byproduct of altered cell-cycle distribution or arrested growth upon stress, given that arrest of growth and cell cycle progression did not trigger strong ESR activation. Furthermore, ESR transcripts did not fluctuate with cell cycle phase in dividing cells and did not respond to arrest points as proposed previously. We also show that activation of the ESR is an active response to stress as arrested cells show robust, dose-dependent ESR activation in response to stress. We propose that ESR activation helps reallocate transcription and translation capacity to stress defense genes upon stresses.
This book covers both the molecular basics of fungal stress response strategies as well as biotechnological applications thereof. The complex regulatory mechanisms of stress response pathways are presented in a concise and well-readable manner. Also, light will be shed on the interconnection of pathways responding to different types of stress. Profound knowledge of stress responses in yeast and filamentous fungi is crucial for further optimization of industrial processes. Applications are manifold, for example in fungicide development, for improving the resistance of crop plants to fungal pathogens, but also in medicine to help curing fungal infections. The book targets researchers from academia and industry, as well as graduate students interested in microbiology, mycology and biomedicine.
Boron is a versatile element distributed in every part of the environment but most of its deposit reserves are localized in a few countries, Turkey being one of the most prominent. Boron is known to be an essential micronutrient for plants and some animals. Like any other essential element it has toxicity in high concentrations. Herein the mechanism of toxicity and the elements of the boron stress response were investigated in Saccharomyces cerevisiae with a proteomics approach. Boron is believed to have played a role in the evolution of life on earth. It has strongly electrophile organic compounds, the most important physiological form being boric acid. Boric acid has a capacity to bind cis-located hydroxl groups and some amino groups. Some of these groups are located at the active sites of some enzymes and at the carbohydrates with five-membered furanose rings. The riboses of some metabolically important molecules like S-adenosyl methionine, diadenosine phosphate family members and 3'end of RNAs are prone to be affected. The yeast cells subjected to boron in this study expressed higher amounts of carbohydrate metabolic enzymes, proteins involved in protein synthesis, protein folding and catabolism, redox homeostasis and nucleotide synthesis. All of these proteins are common to metal stress responses in yeasts. Some of them involve in other stress responses like peroxide, salt or herbicide stresses showing complex interplay between responses.
Applications for Industrial Brewing and Fermentation
Author: Hiroshi Takagi
This book describes cutting-edge science and technology of the characterization, breeding, and development of yeasts and fungi used worldwide in fermentation industries such as alcohol beverage brewing, bread making, and bioethanol production. The book also covers numerous topics and important areas the previous literature has missed, ranging widely from molecular mechanisms to biotechnological applications related to stress response/tolerance of yeasts and fungi. During fermentation processes, cells of yeast and fungus, mostly Saccharomyces and Aspergillus oryzae spp., respectively, are exposed to a variety of fermentation “stresses”. Such stresses lead to growth inhibition or cell death. Under severe stress conditions, their fermentation ability and enzyme productivity are rather limited. Therefore, in terms of industrial application, stress tolerance is the key characteristic for yeast and fungal cells. The first part of this book provides stress response/tolerance mechanisms of yeast used for the production of sake, beer, wine, bread, and bioethanol. The second part covers stress response/tolerance mechanisms of fungi during environmental changes and biological processes of industrial fermentation. Readers benefit nicely from the novel understandings and methodologies of these industrial microbes. The book is suitable for both academic scientists and graduate-level students specialized in applied microbiology and biochemistry and biotechnology and for industrial researchers and engineers who are involved in fermentation-based technologies. The fundamental studies described in this book can be applied to the breeding of useful microbes (yeasts, fungi), the production of valuable compounds (ethanol, CO2, amino acids, organic acids, and enzymes) and the development of promising processes to solve environmental issues (bioethanol, biorefinery).
Natural environments are dynamic, and organisms must sense and respond to changing conditions. One common way organisms deal with stressful environments is through gene expression changes, allowing for stress acclimation and resistance. Variation in stress sensing and signaling can potentially play a large role in how individuals with different genetic backgrounds are more or less resilient to stress. However, the mechanisms underlying how gene expression variation affects organismal fitness is often obscure. To understand connections between gene expression variation and stress defense phenotypes, we have been exploiting natural variation in Saccharomyces cerevisiae stress responses using a unique phenotype called acquired stress resistance, where cells that are pretreated with a sub-lethal dose of stress survive lethal high doses of stress. This response is observed in organisms ranging from bacteria to humans, though the specific mechanisms governing acquisition of higher stress resistance are poorly understood. This dissertation explores the mechanistic underpinnings of natural variation in yeast stress responses and resistance, thus identifying strategies that I argue are likely conserved across diverse organisms. We first show that a commonly-used lab strain fails to acquire oxidative stress resistance when pretreated with ethanol, while a wild oak strain can. Using genetic mapping, we provided new evidence that Hap1p, heme-dependent transcription factor, was responsible for variation in this trait through the regulation of CTT1-encoding cytosolic catalase T- hydrogen peroxide scavenging enzyme. Interestingly, the lab strain can still acquire higher hydrogen peroxide resistance when pretreated with salt, and this cross protection requires CTT1. To determine whether CTT1 was universally required for acquired hydrogen peroxide resistance, we tested over a dozen diverse yeast strains and found a wide range of catalase dependency suggesting that acquired hydrogen peroxide resistance arises through multiple anti-oxidant defense strategies. We used transcriptional profiling to identify potential signaling pathways and transcription factors that regulate differentially-expressed modules of genes during salt or ethanol stress and potential compensatory oxidative stress proteins. These experiments highlight the power of using yeast natural variation to uncover novel aspects of conserved signaling networks and stress defenses, providing a framework for understanding the mechanistic underpinnings of natural variation in other organisms.