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Wolters JF, LaBella AL, Opulente DA, Rokas A, Hittinger CT. Mitochondrial genome diversity across the subphylum Saccharomycotina. Front Microbiol 2023; 14:1268944. [PMID: 38075892 PMCID: PMC10701893 DOI: 10.3389/fmicb.2023.1268944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 10/31/2023] [Indexed: 12/20/2023] Open
Abstract
Introduction Eukaryotic life depends on the functional elements encoded by both the nuclear genome and organellar genomes, such as those contained within the mitochondria. The content, size, and structure of the mitochondrial genome varies across organisms with potentially large implications for phenotypic variance and resulting evolutionary trajectories. Among yeasts in the subphylum Saccharomycotina, extensive differences have been observed in various species relative to the model yeast Saccharomyces cerevisiae, but mitochondrial genome sampling across many groups has been scarce, even as hundreds of nuclear genomes have become available. Methods By extracting mitochondrial assemblies from existing short-read genome sequence datasets, we have greatly expanded both the number of available genomes and the coverage across sparsely sampled clades. Results Comparison of 353 yeast mitochondrial genomes revealed that, while size and GC content were fairly consistent across species, those in the genera Metschnikowia and Saccharomyces trended larger, while several species in the order Saccharomycetales, which includes S. cerevisiae, exhibited lower GC content. Extreme examples for both size and GC content were scattered throughout the subphylum. All mitochondrial genomes shared a core set of protein-coding genes for Complexes III, IV, and V, but they varied in the presence or absence of mitochondrially-encoded canonical Complex I genes. We traced the loss of Complex I genes to a major event in the ancestor of the orders Saccharomycetales and Saccharomycodales, but we also observed several independent losses in the orders Phaffomycetales, Pichiales, and Dipodascales. In contrast to prior hypotheses based on smaller-scale datasets, comparison of evolutionary rates in protein-coding genes showed no bias towards elevated rates among aerobically fermenting (Crabtree/Warburg-positive) yeasts. Mitochondrial introns were widely distributed, but they were highly enriched in some groups. The majority of mitochondrial introns were poorly conserved within groups, but several were shared within groups, between groups, and even across taxonomic orders, which is consistent with horizontal gene transfer, likely involving homing endonucleases acting as selfish elements. Discussion As the number of available fungal nuclear genomes continues to expand, the methods described here to retrieve mitochondrial genome sequences from these datasets will prove invaluable to ensuring that studies of fungal mitochondrial genomes keep pace with their nuclear counterparts.
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Affiliation(s)
- John F. Wolters
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, United States
| | - Abigail L. LaBella
- Department of Bioinformatics and Genomics, University of North Carolina at Charlotte, Charlotte, NC, United States
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, United States
| | - Dana A. Opulente
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, United States
- Biology Department, Villanova University, Villanova, PA, United States
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, United States
| | - Chris Todd Hittinger
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, United States
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Wolters JF, LaBella AL, Opulente DA, Rokas A, Hittinger CT. Mitochondrial Genome Diversity across the Subphylum Saccharomycotina. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.28.551029. [PMID: 37577532 PMCID: PMC10418067 DOI: 10.1101/2023.07.28.551029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Eukaryotic life depends on the functional elements encoded by both the nuclear genome and organellar genomes, such as those contained within the mitochondria. The content, size, and structure of the mitochondrial genome varies across organisms with potentially large implications for phenotypic variance and resulting evolutionary trajectories. Among yeasts in the subphylum Saccharomycotina, extensive differences have been observed in various species relative to the model yeast Saccharomyces cerevisiae, but mitochondrial genome sampling across many groups has been scarce, even as hundreds of nuclear genomes have become available. By extracting mitochondrial assemblies from existing short-read genome sequence datasets, we have greatly expanded both the number of available genomes and the coverage across sparsely sampled clades. Comparison of 353 yeast mitochondrial genomes revealed that, while size and GC content were fairly consistent across species, those in the genera Metschnikowia and Saccharomyces trended larger, while several species in the order Saccharomycetales, which includes S. cerevisiae, exhibited lower GC content. Extreme examples for both size and GC content were scattered throughout the subphylum. All mitochondrial genomes shared a core set of protein-coding genes for Complexes III, IV, and V, but they varied in the presence or absence of mitochondrially-encoded canonical Complex I genes. We traced the loss of Complex I genes to a major event in the ancestor of the orders Saccharomycetales and Saccharomycodales, but we also observed several independent losses in the orders Phaffomycetales, Pichiales, and Dipodascales. In contrast to prior hypotheses based on smaller-scale datasets, comparison of evolutionary rates in protein-coding genes showed no bias towards elevated rates among aerobically fermenting (Crabtree/Warburg-positive) yeasts. Mitochondrial introns were widely distributed, but they were highly enriched in some groups. The majority of mitochondrial introns were poorly conserved within groups, but several were shared within groups, between groups, and even across taxonomic orders, which is consistent with horizontal gene transfer, likely involving homing endonucleases acting as selfish elements. As the number of available fungal nuclear genomes continues to expand, the methods described here to retrieve mitochondrial genome sequences from these datasets will prove invaluable to ensuring that studies of fungal mitochondrial genomes keep pace with their nuclear counterparts.
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Affiliation(s)
- John F. Wolters
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, 53726, USA
| | - Abigail L. LaBella
- Department of Bioinformatics and Genomics, University of North Carolina at Charlotte, Charlotte NC, 28223, USA
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA; Evolutionary Studies Initiative, Vanderbilt University, Nashville, TN 37235, USA
| | - Dana A. Opulente
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, 53726, USA
- Biology Department Villanova University, Villanova, PA 19085, USA
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA; Evolutionary Studies Initiative, Vanderbilt University, Nashville, TN 37235, USA
| | - Chris Todd Hittinger
- Laboratory of Genetics, DOE Great Lakes Bioenergy Research Center, Wisconsin Energy Institute, Center for Genomic Science Innovation, J. F. Crow Institute for the Study of Evolution, University of Wisconsin-Madison, Madison, WI, 53726, USA
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Thompson SRL, Lee DK, Lachance MA, Smith DR. Mutational Effects of Mobile Introns on the Mitochondrial Genomes of Metschnikowia Yeasts. Front Genet 2021; 12:785218. [PMID: 34804133 PMCID: PMC8601654 DOI: 10.3389/fgene.2021.785218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 10/19/2021] [Indexed: 11/25/2022] Open
Abstract
It has been argued that DNA repair by homologous recombination in the context of endonuclease-mediated cleavage can cause mutations. To better understand this phenomenon, we examined homologous recombination following endonuclease cleavage in a native genomic context: the movement of self-splicing introns in the mitochondrial genomes of Metschnikowia yeasts. Self-splicing mitochondrial introns are mobile elements, which can copy and paste themselves at specific insertion sites in mitochondrial DNA using a homing endonuclease in conjunction with homologous recombination. Here, we explore the mutational effects of self-splicing introns by comparing sequence variation within the intron-rich cox1 and cob genes from 71 strains (belonging to 40 species) from the yeast genus Metschnikowia. We observed a higher density of single nucleotide polymorphisms around self-splicing-intron insertion sites. Given what is currently known about the movement of organelle introns, it is likely that their mutational effects result from the high binding affinity of endonucleases and their interference with repair machinery during homologous recombination (or, alternatively, via gene conversion occurring during the intron insertion process). These findings suggest that there are fitness costs to harbouring self-splicing, mobile introns and will help us better understand the risks associated with modern biotechnologies that use endonuclease-mediated homologous recombination, such as CRISPR-Cas9 gene editing.
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Affiliation(s)
- Scout R L Thompson
- Department of Biology, University of Western Ontario, London, ON, Canada
| | - Dong Kyung Lee
- Department of Biology, University of Western Ontario, London, ON, Canada
| | | | - David Roy Smith
- Department of Biology, University of Western Ontario, London, ON, Canada
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Song H, Chen Y, Liu F, Chen N. Large Differences in the Haptophyte Phaeocystis globosa Mitochondrial Genomes Driven by Repeat Amplifications. Front Microbiol 2021; 12:676447. [PMID: 34276607 PMCID: PMC8283788 DOI: 10.3389/fmicb.2021.676447] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Accepted: 05/31/2021] [Indexed: 01/04/2023] Open
Abstract
The haptophyte Phaeocystis globosa is a well-known species for its pivotal role in global carbon and sulfur cycles and for its capability of forming harmful algal blooms (HABs) with serious ecological consequences. Its mitochondrial genome (mtDNA) sequence has been reported in 2014 but it remains incomplete due to its long repeat sequences. In this study, we constructed the first full-length mtDNA of P. globosa, which was a circular genome with a size of 43,585 bp by applying the PacBio single molecular sequencing method. The mtDNA of this P. globosa strain (CNS00066), which was isolated from the Beibu Gulf, China, encoded 19 protein-coding genes (PCGs), 25 tRNA genes, and two rRNA genes. It contained two large repeat regions of 6.7 kb and ∼14.0 kb in length, respectively. The combined length of these two repeat regions, which were missing from the previous mtDNA assembly, accounted for almost half of the entire mtDNA and represented the longest repeat region among all sequenced haptophyte mtDNAs. In this study, we tested the hypothesis that repeat unit amplification is a driving force for different mtDNA sizes. Comparative analysis of mtDNAs of five additional P. globosa strains (four strains obtained in this study, and one strain previously published) revealed that all six mtDNAs shared identical numbers of genes but with dramatically different repeat regions. A homologous repeat unit was identified but with hugely different numbers of copies in all P. globosa strains. Thus, repeat amplification may represent an important driving force of mtDNA evolution in P. globosa.
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Affiliation(s)
- Huiyin Song
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
| | - Yang Chen
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.,School of Earth and Planetary, University of Chinese Academy of Sciences, Beijing, China
| | - Feng Liu
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China
| | - Nansheng Chen
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.,Laboratory of Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.,Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.,Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, BC, Canada
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Smith DR. Depositing annotated sequences in GenBank: there needs to be a better way. Brief Funct Genomics 2020; 19:337-338. [PMID: 32886090 DOI: 10.1093/bfgp/elaa016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2020] [Revised: 07/31/2020] [Accepted: 08/03/2020] [Indexed: 11/14/2022] Open
Abstract
Submitting sequences to the National Center for Biotechnology Information (NCBI) is an integral part of research and the publication process for many disciplines within the life sciences, and it will only become more important as sequencing technologies continue to improve. Here, I argue that the available infrastructure and resources for uploading data to NCBI-especially the associated annotations of eukaryotic genomes-are inefficient, hard to use and sometimes just plain bad. This, in turn, is causing some researchers to forgo annotations entirely in their submissions. The time is overdue for the development of sophisticated, user-friendly software for depositing annotated sequences in GenBank.
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Affiliation(s)
- David Roy Smith
- Department of Biology, University of Western Ontario, 1151 Richmond Street, London N6A 5B7, Canada
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