Cold Adaptation in Yeast: The Role of ER-Associated Degradation and Sterol Metabolism

Intellectual Merit: The story of life on Earth is likely to be a story of cold. The first organic molecules and cells may have arisen on Earth in icy conditions, providing an evolutionary 'cold start' to life. As recently as 500 million years ago, life has had to survive through global glaciations. Even today, Earth's biosphere is largely cold, with as much as 80% having an average temperature of less than 5oC. Clearly, understanding how organisms adapt to cold temperature is important for a variety of disciplines, from the evolution of life to the ecology of arctic environments to cellular biology and physiology. However, surprisingly large gaps exist in our exploration of the biology of cold adaptation. Most notably, investigations of cold adaptation are nearly non-existent in fungi, one of the 5 classical kingdoms of life. In addition, investigations of the roles of sterol metabolism in cold adaptation in any organism are similarly uncommon. The experiments that will be performed in this project will lay the foundations for deep exploration of the genetics, molecular and cellular biology, and physiology of cold adaptation in yeast, a unicellular fungus. It is likely that results of these studies will have relevance to other fungi, and perhaps to other kingdoms of life.

In a search for genes required for ER biogenesis in the yeast Saccharomyces cerevisiae, the Wright lab discovered that mutations in a subset of genes involved in ER-associated degradation (ERAD) result in cold sensitivity. In collaboration with co-PI Dr. Martin Bard (Indiana University - Purdue University Indianapolis), they also discovered that these genes are required for proper regulation of sterol metabolism. These observations lead to the foundational hypothesis for the experiments to be performed in this project: ERAD regulates key aspects of sterol metabolism in yeast and this regulation is required for cold adaptation. To test this hypothesis, the PIs will use genetic, biochemical, and cell biological approaches to determine both the molecular mechanisms by which ERAD regulates sterol metabolism and also whether this regulation underlies the role of ERAD itself in cold adaptation. To examine the ecological and evolutionary relevance of sterol metabolism in cold adaptation, experiments in S. cerevisiae will be coordinated with analyses of sterols in psychrophilic yeast species isolated in Antarctic environments. In addition, the genes in S. cerevisiae that are necessary for cold adaptation will be determined. Thus, results of these experiments will provide specific insights into the role of sterol metabolism and ERAD in cold adaptation, as well as create a framework for long-term investigations of cold adaptation in yeast.

Broader Impacts: The experimental plan has the orthodox value of basic research for training graduate and undergraduate students. At least one graduate student and six undergraduates will be involved in these experiments in traditional laboratory research contexts. However, this project will also serve as an incubator and crucible for novel educational strategies, specifically the incorporation of authentic research experiences into introductory biology laboratories. For example, in one project, student teams in introductory biology will clone the gene for HMG-CoA reductase (a highly conserved sterol biosynthetic enzyme) from a variety of Antarctic yeast species, sequence these genes, and use this information to study the phylogeny of the yeasts. Such experimental results would be potentially publishable, the hallmark of 'authentic' research. Because no standards currently exist to define the types of projects most suited to the teaching-lab environment, these teaching laboratory-based projects will be comprehensively assessed to develop benchmarks for successful teaching-laboratory based research projects. This information will be used to evaluate potential projects from other investigators. By developing opportunities for faculty to bring research projects into teaching laboratories, this effort will promote more extensive and productive integration of the research and education missions of faculty, a better learning experience for students, and more rapid advance of science.