Regulation der Sporenzahl durch Bicarbonat und den cAMP/PKA-Signaltransduktionsweg in Saccharomyces cerevisiae

Sporulation in Saccharomyces cerevisiae is induced under specific conditions of nutrient deficiency and consists of meiosis and the subsequent formation of ascospores. In the course of sporulation a diploid mother cell transforms into an ascus, which contains up to four ascospores. The number of spores formed depends on the nutritional situation, the maximum number of four spores per cell is only formed when adequate nutrients, for example potassium acetate, are available. This adjustment of spore numbers to the nutrient conditions is called spore number control. It is not known how the nutrient signal is perceived and converted into an adaptation of spore numbers. In this study it was shown that the cAMP/PKA signaling pathway, which is essential for vegetative growth and the initiation of sporulation, is also involved in the regulation of spore numbers. To inactivate key components of the signal transduction pathway during meiosis, a method was modified to allow meiosis-specific destabilization of proteins. Using this method it was shown that the cAMP/PKA signaling pathway has a negative influence on spore formation. The data collected indicate that the activity of the adenylyl cyclase Cyr1 is influenced by bicarbonate positively during vegetative growth and negatively during sporulation. Furthermore, it has been shown that in addition to the modulation, the temporal coordination of PKA activity is important for spore number control. Additionaly to the influence on spore number control, a correlation between low PKA activity and an increase in cell and ascus size was identified. A possible, meiosis specific target of PKA is the protein Ady1. A genetic interaction between Ady1 and components of the spindle pole bodies was identified. In summary, this work has shown that the activity of the cAMP/PKA signaling pathway is regulated by the Ras proteins and bicarbonate during sporulation. By this, varying acetate concentrations lead to differences in PKA activity, which consequently lead to the adjustment of spore numbers to the nutrient conditions.