Molecular Mechanisms of Adaptive Evolution

Molecular Sciences Institute, Berkeley CA

Investigators

Abstract

Organisms evolve by changing their genomes, including small changes (point mutations) and gross changes (genomic rearrangements). Genomic rearrangements are more likely than point mutations to quickly produce novel traits by rearranging functional domains and expression control sequences. Although genomic rearrangements have profoundly impacted genome evolution, they have yet to be shown to be directly advantageous in an experimentally evolving population of a eukaryotic organism. The investigators have recently shown that the exposure of budding yeast Saccharomyces cerevisiae to suboptimal conditions such as starvation or heavy water induces recombination genes in a small subset of cells. It is important to understand whether this induction of recombination genes plays a role in adaptation by producing adaptive genomic rearrangements and, if so, what are the mechanisms that control such processes. Three ideas will be tested in this work: 1) The rate of recombination is increased in populations adapting to adverse environments, 2) Cells recombine at different rates in adapting populations and 3) Adaptation-associated genomic rearrangements are under genetic control. The investigators will analyze genomic rearrangements arising in populations during adaptation to growth in heavy water, a mild and broad selective agent that models previously unencountered habitats, and compare it to starvation, a common selective condition that parallels selection in nature. The rates of genomic rearrangements in adapting yeast populations will be assayed using novel chromosome recombination reporter constructs, genomic arrays and genomic polymorphism analysis. Distributions of recombinants in adapting populations will be assayed by fluorescent protein reporters coupled with flow cytometry. Finally, the investigators will analyze genetic pathways that control the adaptation-associated rearrangements, using available expression array data to find candidate genes, and analyze the candidate pool using recombination reporter assays. Learning about molecular mechanisms that control genomic rearrangements in suboptimal conditions will help us understand the process and control of adaptive evolution in eukaryotes. With the aid of genomic information available, we will better understand how genomes are shaped by evolutionary forces. Finally, the project may help to predict the evolutionary response of organisms exposed to novel environments.