Experimental Evolution Reveals Interplay between Sch9 and Polyploid Stability in Yeast.

Yi-Jin Lu,Jun-Yi Leu,Krishna B S Swamy,Andrew W Murray

doi:10.1371/journal.pgen.1006409

Abstract

Polyploidization has crucial impacts on the evolution of different eukaryotic lineages including fungi, plants and animals. Recent genome data suggest that, for many polyploidization events, all duplicated chromosomes are maintained and genome reorganizations occur much later during evolution. However, newly-formed polyploid genomes are intrinsically unstable and often quickly degenerate into aneuploidy or diploidy. The transition between these two states remains enigmatic. In this study, laboratory evolution experiments were conducted to investigate this phenomenon. We show that robust tetraploidy is achieved in evolved yeast cells by increasing the abundance of Sch9—a protein kinase activated by the TORC1 (Target of Rapamycin Complex 1) and other signaling pathways. Overexpressing SCH9, but not TOR1, allows newly-formed tetraploids to exhibit evolved phenotypes and knocking out SCH9 diminishes the evolved phenotypes. Furthermore, when cells were challenged with conditions causing ancestral cells to evolve aneuploidy, tetraploidy was maintained in the evolved lines. Our results reveal a determinant role for Sch9 during the early stage of polyploid evolution.

Highlights

Polyploid organisms that contain more than two sets of genomes are commonly found in natural eukaryotic populations
Artificially-constructedpolyploids often display chromosome instability and quickly convert to aneuploids. This phenomenon conflicts with observations that many species derived from ancient genome duplications have maintained the extra number of chromosomes following polyploidization
What happened during the early stages of these polyploidy events that stabilized the duplicated genomes? We used laboratory evolution experiments to investigate this process

Summary

Introduction

Polyploid organisms that contain more than two sets of genomes are commonly found in natural eukaryotic populations (reviewed in [1]). Polyploidization (or events of whole genome duplication) immediately poses a reproductive isolation barrier between the newly-formed and parental populations. Such events have been speculated to accelerate the speciation process, especially in plants [9]. Newly-formed polyploid genomes can perturb cellular homeostasis and are intrinsically unstable [10, 11]. Chromosome instability and rapid genome repatterning are often observed in newly-formed polyploid cells [12,13,14,15]. Little is known about the early stage of polyploidy evolution and the mechanisms underlying stabilized polyploid cells are poorly understood [23]

Methods

Results

Discussion

Conclusion