CAREER: Determining the impact of asexual ploidy transitions on evolutionary trajectories

Emory University, Atlanta GA

Investigators

Abstract

The research will determine how the ability to change the number of copies of genes within a cell affects evolution. Genetic variation is important for species to be able to survive and adapt to changing environments. For most plants and animals, mating creates new combinations of genes, generating variation. However for many fungi, mating is rare or absent. Instead, during growth fungi often change the number of chromosomes and chromosome sets (ploidy) they contain. This research uses Candida albicans, a fungal pathogen of humans, to identify how frequently changes in ploidy occur, and what environments promote these changes, including antifungal drugs. One result will be a better understanding of the evolution of virulence and drug resistance. The project will develop an upper-division writing-intensive class using C. albicans ploidy variation as a compelling biological context; the course will be designed to teach students how to transform experimental results from data to knowledge while challenging students to distill scientific knowledge into a framework accessible to the general public. The data will be generated in an introductory biology lab module that measures mutation rates in C. albicans strains with different ploidy states. While asexual ploidy transitions are well-documented to occur in many fungal species and across diverse growth environments, whether they drive evolutionary processes or are simply a consequence of elevated genome instability remains to be explicitly tested. The environmental signals and pathways to ploidy changes have not been well characterized, nor have the consequences of asexual ploidy transitions been tested within an evolutionary framework. By screening for Candida genome size changes across many in vitro and host environments at short- and mid-length time scales, environments that promote ploidy transitions will be identified. By constructing C. albicans strains that are genetically-locked into the diploid or polyploid state, the researchers will test how ploidy transitions contribute to evolutionary processes by comparing the rates and outcomes of selection for virulence and antifungal drug resistance. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.