A downshift in temperature activates the high osmolarity glycerol (HOG) pathway, which determines freeze tolerance in Saccharomyces cerevisiae.
The molecular mechanisms that enable yeast cells to detect and transmit cold signals and their physiological significance in the adaptive response to low temperatures are unknown. Here, we have demonstrated that the MAPK Hog1p is specifically activated in response to cold. Phosphorylation of Hog1p was dependent on Pbs2p, the MAPK kinase (MAPKK) of the high osmolarity glycerol (HOG) pathway, and Ssk1p, the response regulator of the two-component system Sln1p-Ypd1p. However, Sho1p was not required. Interestingly, phosphorylation of Hog1p was stimulated at 30 degrees C in cells exposed to the membrane rigidifier agent dimethyl sulfoxide. Moreover, Hog1p activation occurred specifically through the Sln1 branch. This suggests that Sln1p monitors changes in membrane fluidity caused by cold. Quite remarkably, activation of Hog1p at low temperatures affected the transcriptional response to cold shock. Indeed, the absence of Hog1p impaired the cold-instigated expression of genes for trehalose- and glycerol-synthesizing enzymes and small chaperones. Moreover, a downward transfer to 12 or 4 degrees C stimulated the overproduction of glycerol in a Hog1p-dependent manner. However, hog1Delta mutant cells showed no growth defects at 12 degrees C as compared with the wild type. On the contrary, deletion of HOG1 or GPD1 decreased tolerance to freezing of wild-type cells preincubated at a low temperature, whereas no differences could be detected in cells shifted directly from 30 to -20 degrees C. Thus, exposure to low temperatures triggered a Hog1p-dependent accumulation of glycerol, which is essential for freeze protection.
Panadero
Joaquín
J
Department of Biotechnology, Instituto de Agroquímica y Tecnología de los Alimentos, Consejo Superior de Investigaciones Científicas, P. O. Box 73, E-46100-Burjassot Valencia, Spain.
Pallotti
Claudia
C
Rodríguez-Vargas
Sonia
S
Randez-Gil
Francisca
F
Prieto
Jose A
JA
D021581:Active Transport, Cell Nucleus; D015152:Blotting, Northern; D015153:Blotting, Western; D004268:DNA-Binding Proteins / Q000378:metabolism; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D005615:Freezing; D005656:Fungal Proteins / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009994:Osmolar Concentration; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011494:Protein Kinases; D012313:RNA / Q000378:metabolism; D012331:RNA, Fungal / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism* / Q000502:physiology; D013045:Species Specificity; D013696:Temperature; D013697:Thermosensing
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012331:RNA, Fungal; C459787:SHO1 protein, S cerevisiae; C087199:SSK1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D012313:RNA; D011494:Protein Kinases; C102035:YPD1 protein, S cerevisiae; C088589:HOG1 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; C089356:PBS2 protein, S cerevisiae; C083749:SLN1 protein, S cerevisiae; D005990:Glycerol; D004121:Dimethyl Sulfoxide