Phenotypic effects of mitochondrial inheritance in hybrid yeast

Background:

Polyploidization generates diversity by increasing the number of copies of each chromosome. Polyploids are common among plants, as well as among certain groups of fish and amphibians. It usually makes a distinction between polyploids that arise within a species and those that arise due to the hybridization of two distinct species. The former is known as autopolyploids, while the latter is referred to as allopolyploids. Allopolyploidy instantly adds chromosomal variation from multiple species through hybridization, while autopolyploidy leads to variation as gene copies from a single species diverge during evolution [3].

Saccharomyces is a genus of fungi that includes eight species of yeasts. The hybrids of Saccharomyces species are used as a model of polyploidy for studying how this phenomenon is facilitating adaptation to new environments within the Domain Eukarya. Moreover, the choice of mitochondrial DNA (mtDNA)retention after yeast hybridization is a determinant of population fitness hence the study of mitochondrial inheritance is a very relevant parameter for characterizing new polyploids.

Mitochondria are often referred to as the powerhouses of the cell because of their major role in generating cellular energy in the form of adenosine triphosphate (ATP) through the TCA cycle and oxidative phosphorylation. However, mitochondria are also involved in other metabolic processes, such as amino acid, lipid, and intermediary metabolism, synthesis of iron¨Csulfur clusters, and maintenance of cellular redox state [1].

Saccharomyces yeasts can both respire, which requires functioning mitochondria, or ferment, which does not. In fact, these yeasts can survive adequately without functional mitochondria, and form smaller ¡°petite¡± colonies. Moreover, the mitochondrial genome makes a significant contribution to one of the most distinct phenotypic differences among the Saccharomyces species: their thermal growth profile [2].

Hybrids between Saccharomycetes tend to carry mtDNA from just one parent i.e., they are homoplasmic. All the strains of S. pastorianus, a natural lager brewing yeast hybrid between S. cerevisiae and S. eubayanus, contain only mtDNA from the cryotolerant parent, S. eubayanus [4,5,6]. 

Here, we plan to review yeast mitochondrial metabolism and function with a focus on hybrids of Saccharomyces species. We will test the effects of mitochondrial inheritance in polyploid yeast in different environmental conditions, i.e., a fermentable carbon source or a carbon source that can only be respired, and a range of temperatures to better understand how the mitochondrial DNA impacts fitness and evolution of the hybrid genome.

Keywords

hybrid, yeast, mitochondria, respiratory chain, growth assay.

Aims of this project

The aims of this MSc project are:

1. Characterization of allotetraploids (a recently generated collection of all Saccharomyces species carrying mtDNA from one parent) by:

• Drop test:  Serial dilutions of hybrid cell cultures will be plated in different grown conditions to infer the phenotypic effects of mitochondrial inheritance.
• ATP Assay: Adenosine triphosphate (ATP) is a nucleoside triphosphate formed exclusively in the mitochondria. We will measure the ATP concentration in each new hybrid for evaluating mitochondrial respiration which indirectly serves to assess the cellular energy capacity. 

2. Develop a new method, using CRISPR/Cas technology, to generate autopolyploids. For this purpose, you will make use of all Saccharomyces diploid yeasts, and generate higher polyploidy levels for each species.

Both master project aims are part of the PloidYeast RCN project.

Methodology

Media preparation, microbiological culture, genetic engineering, yeast mating, molecular biology testing: PCR, RFLP.

Work Place and Environment

https://www.mn.uio.no/ibv/english/research/sections/evogene/groups/mycology/index.html

The UiO FunGIALab belongs to the Oslo Mycology Group. We perform interdisciplinary projects related with fungal evolution and biotechnology. We are part of the EVOGENE section at IBV. The international group members have diverse scientific backgrounds and career stages. The working language in the group is English.

Requirements

This project is best suited for students of the study programs Ecology/Evolution, Genetics/Developmental Biology or Molecular Biology/Biochemistry - but students from all study programs and form other departments are welcome to contact us. A strong background in Microbiology, Evolution or Genetic Engineering is an advantage.

Literature

• Malina C., Larsson C., Nielsen J. Yeast mitochondria: an overview of mitochondrial biology and the potential of mitochondrial systems biology. FEMS Yeast Res. 2018 Aug 1;18(5). doi: 10.1093/femsyr/foy040.
• Hewitt S., Duangrattanalert K., Burgis T., Zeef L., Naseeb S., Delneri D. Plasticity of Mitochondrial DNA Inheritance and Its Impact on Nuclear Gene Transcription in Yeast Hybrids. Microorganisms. Res. 2020 Mar 31;8(4):494. doi: 10.3390/microorganisms8040494.
• Peris, D., Alexander, W. G., Fisher, K. J., Moriarty, R. V., Basuino, M. G., Ubbelohde, E. J., et al. (2020). Synthetic hybrids of six yeast species. Nat. Commun. 11, 1¨C11. doi: 10.1038/s41467-020-15559-4
• Peris D., Sylvester K., Libkind D., Goncalves P., Sampaio J.P., Alexander W.G., Hittinger C.T. Population structure and reticulate evolution of Saccharomyces eubayanus and its lager-brewing hybrids. Mol. Ecol. 2014;23:2031¨C2045. doi: 10.1111/mec.12702. 
• Dunn B., Sherlock G. Reconstruction of the genome origins and evolution of the hybrid lager yeast Saccharomyces pastorianus. Genome Res. 2008;18:1610¨C1623. doi: 10.1101/gr.076075.108. 
• Rainieri S., Kodama Y., Nakao Y., Pulvirenti A., Giudici P. The inheritance of mtDNA in lager brewing strains. FEMS Yeast Res. 2008;8:586¨C596. doi: 10.1111/j.1567-1364.2008.00363.x.