酵母菌 Saccharomyces cerevisiae 在滲透壓力下的訊息調控演化

Abstract

Nucleotide differences in coding regions or in regulatory elements could cause variation among individuals in a species. However, evolutionary changes in transcription regulation are still poorly understood on species divergence. In this thesis, I studied the relative evolutionary roles of cis and/or trans regulatory variation for yeast cells to cope with environmental changes, specifically focusing on the osmotic stress response. I used yeast Saccharomyces cerevisiae BY and RM strains to study the expression evolution when cells are under osmotic stress condition. It has been shown that the expression of about 378 genes were induced and about 365 genes whose expression was repressed at least two folds in response to osmotic stress in S. cerevisiae from microarray studies. I randomly selected 75 genes from 378 genes which induced overexpression under osmotic stress for further pyrosequencing analysis to determine the relative contributions of cis and trans regulatory variations to the expression divergences between BY and RM. My results indicated the expression divergence of BY and RM were mainly due to trans regulatory variations under both standard growth condition and osmotic stress condition, 76.0% and 62.2% of the genes were affected by the trans major regulatory variations, respectively. My results showed that 41.3% (31/75) of genes showed the same trend of cis or trans variation effect even after osmotic stress, 33.3% (25/75) of genes showed decrease of trans variation effect and 25.3% (19/75) of genes showed increase of trans variation effect after osmotic stress. Further analysis showed a positive correlation between the upstream TF numbers and the changes in trans variation effect, the more TF the easier to show the changes in trans variation effect. My results also indicated that the Sko1 and Msn4 may exhitbit greater expression divergence between BY and RM strains under osmotic stress condition compared to the normal unstress condition. More detail analysis is presented in the main text. According to my analysis results, most of genes showed decrease of trans variation effect in osmotic stress condition. Thus my conclusion for this thesis is cis regulatory variations played an important role when yeast adapt to environment of osmotic stress.