RUI: Evolution of Signal Transduction Pathways in Yeast

Villanova University, Villanova PA

Investigators

Abstract

The goal of this project is to understand how differences in metabolism have arisen in the response of related organisms to changes in their environment. Each of the fungal species to be studied experiences a slightly different environment and each species is expected to have tailored its metabolism, over evolutionary time, to be best suited for that environment. The thiamine signal transduction pathway will be studied in the yeast species Candida glabrata and Schizosaccharomyces pombe and compared to the well-studied pathway in Saccharomyces cerevisiae. This project will answer questions about how thiamine (vitamin B1) synthesis is regulated in these organisms and how this system has evolved to impact growth in different environments. All organisms require thiamine and its uptake or synthesis is critical for growth. Understanding how the thiamine signal transduction pathways have evolved in yeast species will give a better understanding of the extent to which the gain and loss of genes affects how an organism is able to respond to its environment. This project will be carried out at Villanova University (a primarily undergraduate institution) and will provide research training and experiences for Masters level students and undergraduate students from Villanova and Immaculata University. Undergraduates working on this project will, on average, spend over two years working on their research, and will be encouraged to take responsibility for their projects and to present their data at professional meetings Thiamine is synthesized de novo in most microorganisms and is a dietary requirement in all animals. This project examines in detail the thiamine signal transduction pathways in C. glabrata (a mammalian commensal that is closely related to the model yeast S. cerevisiae) and S. pombe. The goal of this work is to understand the evolutionary changes that have permitted these organisms to occupy different environments. In S. cerevisiae, transcription of the thiamine biosynthetic genes requires the transcription factor Thi2 which is surprisingly lacking in C. glabrata. Although C. glabrata can synthesize thiamine with reduced efficiency it appears to scavenge thiamine efficiently from the environment. This work will test the hypothesis that the gain of Thi2 in some yeast species has allowed for more efficient thiamine synthesis and that C. glabrata lost Thi2 because it grows in mammalian tissues which are likely a rich source of thiamine. The project will: 1) examine the evolution of thiamine-regulated promoters through rt-qPCR, reporter fusions, and cross complementation experiments, 2) examine the changes in environmental niche that have allowed for loss of some thiamine regulatory genes in C. glabrata, 3) examine the neofunctionalization of the C. glabrata PMU gene array to generate a highly specific thiamine pyrophosphatase, and 4) examine the consequences on fitness using competitions between species or strains with given thiamine gene network architectectures. This project will elucidate 1) the evolution of thiamine signal transduction/synthesis pathways in fungi 2) the role of the Thi2 transcription factor in this pathway and 3) determine the impact of signal transduction pathway re-wiring on environmental specialization.