PgmNr Y3152: Investigation of the genetic basis of hybrid vigor in yeast.

Authors:
N. Sampaio; J. L. Argueso


Institutes
Colorado State University, Fort Collins, CO.


Keyword: Genomics

Abstract:

Highly heterozygous organisms often display enhanced phenotypic manifestations, a phenomenon known as hybrid vigor. Despite the economic importance of hybrid vigor, the genetic mechanisms that promote these superior phenotypes are still unknown. The genomic complexity typically observed in crop plants and livestock often hinders the investigation of the specific role of heterozygosity in the superior phenotype of the hybrid progeny. Thus, this type of analysis would be greatly facilitated by the use of a tractable model organism, such as the yeast Saccharomyces cerevisiae. The natural hybrid diploid yeast strain JAY270 is widely adopted in sugarcane-based bioethanol production. Our group has determined that heterozygous alleles are present in about 60% of JAY270’s genome, suggesting that its robust growth and high fermentative performance may be associated with hybrid vigor. In this study, we are establishing JAY270 as a model for investigating the mechanisms through which heterozygosity may promote fitness. We are developing an approach to identify individual heteroalleles in the JAY270 genome that contribute to hybrid vigor in this strain. The genomes of 56 haploid derivatives of JAY270 (14 full tetrads) were sequenced. The haploids were then intercrossed to create a systematic collection of inbred diploids, containing varying known fractions of the original heterozygosity present in JAY270. The whole-genome information from all the parental haploids provided precise genome-wide maps of where each inbred diploid is still heterozygous and where they are homozygous for either parental allele. The relative fitness of 78 of such inbred diploids was assessed using a high throughput flow cytometry-based growth competition assay against the fully heterozygous JAY270 parent strain. In addition, the inbred diploid collection was challenged with various growth stress conditions (high temperature, salt, DNA damage, etc.). Alignment of the genomic of heterozygosity maps and correlation to high or low fitness in the inbred diploids will allow us to identify genomic regions where allele-dependent contributors to hybrid vigor reside. We will present the results of the phenotypic characterization of the inbred diploid collection, and will discuss progress in the mapping of specific loci in the genome associated with hybrid vigor. The characterization of these heteroalleles will shed new light on the genetic basis of this complex process, contributing discoveries that could have important practical implications for human health, agriculture, biotechnology, as well as for genome sciences.