PgmNr Y465: Ploidy tug-of-war: evolutionary and genetic environments influence the rate of ploidy drive in a human fungal pathogen.

Authors:
M. A. Hickman 1 ; A. C. Gerstein 2 ; H. Kim 2 ; J. Berman 2,3


Institutes
1) Emory Univ, Atlanta, GA; 2) Univ of Minnesota, Minneapolis, MN; 3) Tel Aviv Univ, Tel Aviv, Isreal.


Keyword: 02. Chromosome structure, variation, evolution and dynamics

Abstract:

Ploidy contributes to the evolutionary dynamics and to the cellular physiology of organisms. Significant variation for ploidy is seen throughout the tree of life yet the factors that determine why one ploidy level is selected over another remain poorly understood. Asexual fungal microbes are a unique system to study ploidy dynamics as they are incredibly tolerant to karyotypic variation in both the number of chromosome sets as well as single (or few) chromosomes deviations from euploidy. Such variation can be rapidly selected for or against depending on the environment, yet evolution experiments have revealed a propensity to return to the historical baseline ploidy level under a variety of environmental conditions, a phenomenon that we term here as ‘ploidy drive’. To assess the interplay between environmental pressure and strain genotype on ploidy drive, we evolved ten strains of the human fungal pathogen Candida albicans of varying initial ploidy under four environmental conditions. We found selection for increased genome sizes under nitrogen limitation and in a complete medium yet selection for smaller genome sizes was observed under phosphorus limitation and in minimal medium. Furthermore, genetic background had a significant role in ploidy drive dynamics, as some genotypes were markedly less stable than others. Combined, this work demonstrates a role for selection at both the environmental and genotypic level in the rate of ploidy drive.