EEB Student Dissertation Defense - Divergence in Gene Expression Plasticity

Defense Preview:
Organisms respond to shifts in their environment by changing the abundance of different mRNA transcripts in their cells, a process called "gene expression plasticity". We understand that gene expression plasticity itself can evolve---the same environmental shift can cause different patterns of gene expression plasticity in different genetic backgrounds. We don't, however, know much about how gene expression plasticity tends to evolve. Is divergence in gene expression plasticity common between closely related species? Are certain genes more or less likely to experience evolutionary changes to their patterns of expression plasticity? In this dissertation defense, I characterize gene expression plasticity divergence in two yeast species: the baker's yeast Saccharomyces cerevisiae and one of its closest related species, Saccharomyces paradoxus. To describe the extent of gene expression plasticity divergence, I cluster gene expression responses to six different environments. I find that each of the six environments identifies a unique set of at least 100 genes that have diverged in gene expression plasticity. Interestingly, the genes most likely to experience this expression plasticity divergence are the genes with the fewest connections in the regulatory network. My work demonstrates that different environments can reveal hidden dimensions of molecular evolution, and that network connectivity is associated with more robust expression plasticity over evolutionary time.