TRANSCRIPTOMIC ANALYSIS OF GLYCOGEN METABOLISM AFTER CAFFEINE TREATMENT IN Saccharomyces cerevisiae

Saccharomyces cerevisiae is used as a model organism for investigating the metabolic andgenetic regulations in higher organisms. Glycogen is a storage carbohydrate in yeast cells and is used asan energy source. Glycogen is accumulated at the onset of the stationary phase and the logarithmic phaseduring different environmental and intracellular stress conditions. Glycogen level in the cell is regulatedby different sensory and signaling pathways. TOR signaling pathway is activated when the environmentalconditions are suitable, but it is repressed after rapamycin/caffeine treatment or nutrient starvation. In thisstudy, the effect of the TOR signaling pathway on glycogen metabolism was determined with the NextGeneration Sequencing method in S. cerevisiae. The total RNA isolated from yeast cells grown in amedium containing caffeine was used for the Next Generation Sequencing analysis. The differentiallyexpressed genes after caffeine treatment were determined by comparing the caffeine-treated cells tountreated cells. It was determined that the transcription of 44% of the genes was expressed differentiallyafter caffeine treatment, and 20% of differentially expressed genes were found to be up-regulated. Thetranscription of genes involved in glycogen metabolism, except PGM1, was up-regulated after caffeinetreatment. The inactivation of Tor1p caused to increase in PGM2, UGP1, GLG1, GSY1, GSY2, GLC3,GPH1, and GDB1 transcription at least 2 fold. In silico analysis revealed that these genes include at leastone STRE sequence in their promoter regions for binding of Msn2/4 transcription factors. It was observedthat after caffeine treatment MSN2 transcription was down-regulated while MSN4 transcription wasupregulated. This indicates that the Msn4 transcription factor was more effective than Msn2p in upregulating genes in glycogen metabolism. In conclusion, repression of the TOR signaling pathway bycaffeine causes Msn4p-dependent transcriptional activation of genes involved in glycogen metabolism.