BACKGROUND: Glucose is a signaling molecule which regulates multiple events in 
eukaryotic organisms and the most preferred carbon source in the fission yeast 
Schizosaccharomyces pombe. The ability of this yeast to grow in the absence of 
glucose becomes strongly limited due to lack of enzymes of the glyoxylate cycle 
that support diauxic growth. The stress-activated protein kinase (SAPK) pathway 
and its effectors, Sty1 MAPK and transcription factor Atf1, play a critical role 
in the adaptation of fission yeast to grow on alternative non-fermentable carbon 
sources by inducing the expression of fbp1+ gene, coding for the gluconeogenic 
enzyme fructose-1,6-bisphosphatase. The cell integrity Pmk1 pathway is another 
MAPK cascade that regulates various processes in fission yeast, including cell 
wall construction, cytokinesis, and ionic homeostasis. Pmk1 pathway also becomes 
strongly activated in response to glucose deprivation but its role during 
glucose exhaustion and ensuing adaptation to respiratory metabolism is currently 
unknown.
RESULTS: We found that Pmk1 activation in the absence of glucose takes place 
only after complete depletion of this carbon source and that such activation is 
not related to an endogenous oxidative stress. Notably, Pmk1 MAPK activation 
relies on de novo protein synthesis, is independent on known upstream activators 
of the pathway like Rho2 GTPase, and involves PKC ortholog Pck2. Also, the 
Glucose/cAMP pathway is required operative for full activation of the Pmk1 
signaling cascade. Mutants lacking Pmk1 displayed a partial growth defect in 
respiratory media which was not observed in the presence of glucose. This 
phenotype was accompanied by a decreased and delayed expression of transcription 
factor Atf1 and target genes fbp1+ and pyp2+. Intriguingly, the kinetics of Sty1 
activation in Pmk1-less cells was clearly altered during growth adaptation to 
non-fermentable carbon sources.
CONCLUSIONS: Unknown upstream elements mediate Pck2-dependent signal 
transduction of glucose withdrawal to the cell integrity MAPK pathway. This 
signaling cascade reinforces the adaptive response of fission yeast to such 
nutritional stress by enhancing the activity of the SAPK pathway.