The natural environment of unicellular organisms like yeast does not provide constant growth conditions. Yeast cells are challenged by changes in e.g., temperature, osmolarity, pH, the presence of reactive oxygen intermediates, the availability of nutrients or a combination of these agents. In order to continue growth, cells have to sense and properly respond to these changes to adapt their growth potential. Adverse growth conditions induce the general stress response and specific responses. The former evoke common molecular responses such as expression of heat shock proteins (Hsp12, Hsp26, Hsp104), degradation of damaged proteins as a result of increased expression of polyubiquitin gene (UBI4), increase in trehalose synthesis (higher expression of TPS2 encoding trehalose phosphate phosphatase) etc. The general stress response is sometimes called methabolic stress and is regulated by Ras-cAMP signalling pathway. Apart from inducing general stress response differential extracellular conditions trigger also specific pathways regulating expression of genes necessary under certain circumstances. Sacharomyces cerevisiae posses at least five MAP kinase pathways (Mitogen Activating Protein) responding to different extra-or intracellular stimuli. Among them are: cell integrity (protein kinase C) pathway induced by elevated temperature, morphogenetic events, hypo-osmotic shock or cell wall perturbation, HOG (High Osmolarity Glycerol) pathway activated upon hyper-osmotic conditions, Filamentous/Invasive Growth - FG pathway and Sporulation pathway, activated upon starvation and Mating pathway, activated by mating pheromone. Our focus is on the interplay between signalling pathways activated by the osmotic stress and elevated temperature. We show that the osmosensitive phenotype of the hog1 strain is suppressed at elevated temperature and the same holds true for the other commonly used HOG pathway mutant strains pbs2 and sho1ssk2ssk22, but not for the ste11ssk2ssk22. Instead, the ste11ssk2ssk2 strain displayed a hyperosmosensitive phenotype at 37⁰C, suggesting the additional role of Ste11p in the maintenance of cellular integrity. This phenotype can be suppressed by genes involved in cell wall maintenance and genes increasing internal glycerol level. Also we show that sensing and response to osmotic stress is temperature-dependent. For example activation Hog1p MAP kinase, which occurs under hyperosmotic condtions, is very transient at 37⁰C in comparson to optimal growth temperature (28⁰C), and activation of Mpk1p/Slt2p – the MAP kinase activated at elevated temperature is inhibited under hyperosmotic conditions and this phenomenon is independent of HOG-pathway activity. Additionally, accumulation of intracellular glycerol, the osmolyte in yeast, is different under the same osmotic stress at different temperatures. Finally we discuss the role of intracellular glycerol in the maintenance of cellular integrity in Saccharomyces cerevisiae.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/10760 must be provided.

1. Thermolysin – an inductor of Galleria mellonella immune response
2. Antimicrobial peptides of Galleria mellonella degraded in vitro and in vivo by Pseudomonas aeruginosa protease B
3. Humoral immune response of Galleria mellonella larvae after infection with entomopathogenic strain Bacillus thuringiensis subsp. kurstaki
4. Protein kinase A activity in haemocytes of Galleria mellonella larvae upon immune challenge conditions