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Ahuja N, Cao X, Schultz DT, Picciani N, Lord A, Shao S, Jia K, Burdick DR, Haddock SHD, Li Y, Dunn CW. Giants among Cnidaria: Large Nuclear Genomes and Rearranged Mitochondrial Genomes in Siphonophores. Genome Biol Evol 2024; 16:evae048. [PMID: 38502059 PMCID: PMC10980510 DOI: 10.1093/gbe/evae048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 02/20/2024] [Accepted: 03/07/2024] [Indexed: 03/20/2024] Open
Abstract
Siphonophores (Cnidaria: Hydrozoa) are abundant predators found throughout the ocean and are important constituents of the global zooplankton community. They range in length from a few centimeters to tens of meters. They are gelatinous, fragile, and difficult to collect, so many aspects of the biology of these roughly 200 species remain poorly understood. To survey siphonophore genome diversity, we performed Illumina sequencing of 32 species sampled broadly across the phylogeny. Sequencing depth was sufficient to estimate nuclear genome size from k-mer spectra in six specimens, ranging from 0.7 to 2.3 Gb, with heterozygosity estimates between 0.69% and 2.32%. Incremental k-mer counting indicates k-mer peaks can be absent with nearly 20× read coverage, suggesting minimum genome sizes range from 1.4 to 5.6 Gb in the 25 samples without peaks in the k-mer spectra. This work confirms most siphonophore nuclear genomes are large relative to the genomes of other cnidarians, but also identifies several with reduced size that are tractable targets for future siphonophore nuclear genome assembly projects. We also assembled complete mitochondrial genomes for 33 specimens from these new data, indicating a conserved gene order shared among nonsiphonophore hydrozoans, Cystonectae, and some Physonectae, revealing the ancestral mitochondrial gene order of siphonophores. Our results also suggest extensive rearrangement of mitochondrial genomes within other Physonectae and in Calycophorae. Though siphonophores comprise a small fraction of cnidarian species, this survey greatly expands our understanding of cnidarian genome diversity. This study further illustrates both the importance of deep phylogenetic sampling and the utility of k-mer-based genome skimming in understanding the genomic diversity of a clade.
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Affiliation(s)
- Namrata Ahuja
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
| | - Xuwen Cao
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China
| | - Darrin T Schultz
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna 1010, Austria
| | - Natasha Picciani
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
| | - Arianna Lord
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA
| | - Shengyuan Shao
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China
| | - Kejue Jia
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT, USA
| | | | | | - Yuanning Li
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China
| | - Casey W Dunn
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, USA
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2
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Sloan DB, Warren JM, Williams AM, Kuster SA, Forsythe ES. Incompatibility and Interchangeability in Molecular Evolution. Genome Biol Evol 2023; 15:evac184. [PMID: 36583227 PMCID: PMC9839398 DOI: 10.1093/gbe/evac184] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 12/20/2022] [Accepted: 12/22/2022] [Indexed: 12/31/2022] Open
Abstract
There is remarkable variation in the rate at which genetic incompatibilities in molecular interactions accumulate. In some cases, minor changes-even single-nucleotide substitutions-create major incompatibilities when hybridization forces new variants to function in a novel genetic background from an isolated population. In other cases, genes or even entire functional pathways can be horizontally transferred between anciently divergent evolutionary lineages that span the tree of life with little evidence of incompatibilities. In this review, we explore whether there are general principles that can explain why certain genes are prone to incompatibilities while others maintain interchangeability. We summarize evidence pointing to four genetic features that may contribute to greater resistance to functional replacement: (1) function in multisubunit enzyme complexes and protein-protein interactions, (2) sensitivity to changes in gene dosage, (3) rapid rate of sequence evolution, and (4) overall importance to cell viability, which creates sensitivity to small perturbations in molecular function. We discuss the relative levels of support for these different hypotheses and lay out future directions that may help explain the striking contrasts in patterns of incompatibility and interchangeability throughout the history of molecular evolution.
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Affiliation(s)
- Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, Colorado
| | - Jessica M Warren
- Center for Mechanisms of Evolution, Biodesign Institute and School of Life Sciences, Arizona State University, Tempe, Arizona
| | - Alissa M Williams
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee
| | - Shady A Kuster
- Department of Biology, Colorado State University, Fort Collins, Colorado
| | - Evan S Forsythe
- Department of Biology, Colorado State University, Fort Collins, Colorado
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3
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Kuhle B, Hirschi M, Doerfel LK, Lander GC, Schimmel P. Structural basis for shape-selective recognition and aminoacylation of a D-armless human mitochondrial tRNA. Nat Commun 2022; 13:5100. [PMID: 36042193 PMCID: PMC9427863 DOI: 10.1038/s41467-022-32544-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 08/04/2022] [Indexed: 02/05/2023] Open
Abstract
Human mitochondrial gene expression relies on the specific recognition and aminoacylation of mitochondrial tRNAs (mtRNAs) by nuclear-encoded mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs). Despite their essential role in cellular energy homeostasis, strong mutation pressure and genetic drift have led to an unparalleled sequence erosion of animal mtRNAs. The structural and functional consequences of this erosion are not understood. Here, we present cryo-EM structures of the human mitochondrial seryl-tRNA synthetase (mSerRS) in complex with mtRNASer(GCU). These structures reveal a unique mechanism of substrate recognition and aminoacylation. The mtRNASer(GCU) is highly degenerated, having lost the entire D-arm, tertiary core, and stable L-shaped fold that define canonical tRNAs. Instead, mtRNASer(GCU) evolved unique structural innovations, including a radically altered T-arm topology that serves as critical identity determinant in an unusual shape-selective readout mechanism by mSerRS. Our results provide a molecular framework to understand the principles of mito-nuclear co-evolution and specialized mechanisms of tRNA recognition in mammalian mitochondrial gene expression.
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Affiliation(s)
- Bernhard Kuhle
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, 92037, USA.
| | - Marscha Hirschi
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92121, USA
| | - Lili K Doerfel
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92121, USA
| | - Gabriel C Lander
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92121, USA
| | - Paul Schimmel
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA, 92037, USA
- The Scripps Florida Research Institute at the University of Florida, Jupiter, FL, 33458, USA
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4
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Sabharwal A, Campbell JM, Schwab TL, WareJoncas Z, Wishman MD, Ata H, Liu W, Ichino N, Hunter DE, Bergren JD, Urban MD, Urban RM, Holmberg SR, Kar B, Cook A, Ding Y, Xu X, Clark KJ, Ekker SC. A Primer Genetic Toolkit for Exploring Mitochondrial Biology and Disease Using Zebrafish. Genes (Basel) 2022; 13:1317. [PMID: 35893052 PMCID: PMC9331066 DOI: 10.3390/genes13081317] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2022] [Revised: 07/14/2022] [Accepted: 07/19/2022] [Indexed: 02/04/2023] Open
Abstract
Mitochondria are a dynamic eukaryotic innovation that play diverse roles in biology and disease. The mitochondrial genome is remarkably conserved in all vertebrates, encoding the same 37-gene set and overall genomic structure, ranging from 16,596 base pairs (bp) in the teleost zebrafish (Danio rerio) to 16,569 bp in humans. Mitochondrial disorders are amongst the most prevalent inherited diseases, affecting roughly 1 in every 5000 individuals. Currently, few effective treatments exist for those with mitochondrial ailments, representing a major unmet patient need. Mitochondrial dysfunction is also a common component of a wide variety of other human illnesses, ranging from neurodegenerative disorders such as Huntington's disease and Parkinson's disease to autoimmune illnesses such as multiple sclerosis and rheumatoid arthritis. The electron transport chain (ETC) component of mitochondria is critical for mitochondrial biology and defects can lead to many mitochondrial disease symptoms. Here, we present a publicly available collection of genetic mutants created in highly conserved, nuclear-encoded mitochondrial genes in Danio rerio. The zebrafish system represents a potentially powerful new opportunity for the study of mitochondrial biology and disease due to the large number of orthologous genes shared with humans and the many advanced features of this model system, from genetics to imaging. This collection includes 15 mutant lines in 13 different genes created through locus-specific gene editing to induce frameshift or splice acceptor mutations, leading to predicted protein truncation during translation. Additionally, included are 11 lines created by the random insertion of the gene-breaking transposon (GBT) protein trap cassette. All these targeted mutant alleles truncate conserved domains of genes critical to the proper function of the ETC or genes that have been implicated in human mitochondrial disease. This collection is designed to accelerate the use of zebrafish to study many different aspects of mitochondrial function to widen our understanding of their role in biology and human disease.
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Affiliation(s)
- Ankit Sabharwal
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Jarryd M. Campbell
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Tanya L. Schwab
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Zachary WareJoncas
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Mark D. Wishman
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Hirotaka Ata
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Wiebin Liu
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
- Division of Cardiovascular Diseases, Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
| | - Noriko Ichino
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Danielle E. Hunter
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Jake D. Bergren
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Mark D. Urban
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Rhianna M. Urban
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Shannon R. Holmberg
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Bibekananda Kar
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Alex Cook
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Yonghe Ding
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
- Division of Cardiovascular Diseases, Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
| | - Xiaolei Xu
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
- Division of Cardiovascular Diseases, Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
| | - Karl J. Clark
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
| | - Stephen C. Ekker
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA; (A.S.); (J.M.C.); (T.L.S.); (Z.W.); (M.D.W.); (H.A.); (W.L.); (N.I.); (D.E.H.); (J.D.B.); (M.D.U.); (R.M.U.); (S.R.H.); (B.K.); (A.C.); (Y.D.); (X.X.); (K.J.C.)
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Novosolov M, Yahalomi D, Chang ES, Fiala I, Cartwright P, Huchon D. The Phylogenetic Position of the Enigmatic, Polypodium hydriforme (Cnidaria, Polypodiozoa): Insights from Mitochondrial Genomes. Genome Biol Evol 2022; 14:6648524. [PMID: 35867352 PMCID: PMC9380995 DOI: 10.1093/gbe/evac112] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/13/2022] [Indexed: 11/13/2022] Open
Abstract
Polypodium hydriforme is an enigmatic parasite that belongs to the phylum Cnidaria. Its taxonomic position has been debated: whereas it was previously suggested to be part of Medusozoa, recent phylogenomic analyses based on nuclear genes support the view that P. hydriforme and Myxozoa form a clade called Endocnidozoa. Medusozoans have linear mitochondrial (mt) chromosomes, whereas myxozoans, as most metazoan species, have circular chromosomes. In this work, we determined the structure of the mt genome of P. hydriforme, using Illumina and Oxford Nanopore Technologies reads, and showed that it is circular. This suggests that P. hydriforme is not nested within Medusozoa, as this would entail linearization followed by recirculation. Instead, our results support the view that P. hydriforme is a sister clade to Myxozoa, and mt linearization in the lineage leading to medusozoans occurred after the divergence of Myxozoa + P. hydriforme. Detailed analyses of the assembled P. hydriforme mt genome show that: (1) it is encoded on a single circular chromosome with an estimated size of ∼93,000 base pairs, making it one of the largest metazoan mt genomes; (2) around 78% of the genome encompasses a noncoding region composed of several repeat types; (3) similar to Myxozoa, no mt tRNAs were identified; (4) the codon TGA is a stop codon and does not encode for tryptophan as in other cnidarians; (5) similar to myxozoan mt genomes, it is extremely fast evolving.
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Affiliation(s)
- Maria Novosolov
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Dayana Yahalomi
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 6997801, Israel
| | - E Sally Chang
- Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Haworth Hall, Lawrence, KS, 66045, USA.,Computational and Statistical Genomics Branch, Division of Intramural Research, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ivan Fiala
- Institute of Parasitology, Biology Centre, Academy of Sciences of the Czech Republic, Branišovská 31, 370 05 České Budĕjovice, Czech Republic.,Faculty of Science, University of South Bohemia, Branišovská 31, 370 05 České Budĕjovice, Czech Republic
| | - Paulyn Cartwright
- Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Haworth Hall, Lawrence, KS, 66045, USA
| | - Dorothée Huchon
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 6997801, Israel.,The Steinhardt Museum of Natural History and National Research Center, Tel Aviv University, Tel Aviv 6997801, Israel
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6
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Fan Z, Yang JY, Guo Y, Liu YX, Zhong XY. Altered levels of circulating mitochondrial DNA in elderly people with sarcopenia: Association with mitochondrial impairment. Exp Gerontol 2022; 163:111802. [DOI: 10.1016/j.exger.2022.111802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Revised: 03/25/2022] [Accepted: 04/04/2022] [Indexed: 01/07/2023]
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7
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Abdel-Ghany SE, LaManna LM, Harroun HT, Maliga P, Sloan DB. Rapid sequence evolution is associated with genetic incompatibilities in the plastid Clp complex. PLANT MOLECULAR BIOLOGY 2022; 108:277-287. [PMID: 35039977 DOI: 10.1007/s11103-022-01241-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/23/2021] [Indexed: 06/14/2023]
Abstract
KEY MESSAGE Replacing the native clpP1 gene in the Nicotiana plastid genome with homologs from different donor species showed that the extent of genetic incompatibilities depended on the rate of sequence evolution. The plastid caseinolytic protease (Clp) complex plays essential roles in maintaining protein homeostasis and comprises both plastid-encoded and nuclear-encoded subunits. Despite the Clp complex being retained across green plants with highly conserved protein sequences in most species, examples of extremely accelerated amino acid substitution rates have been identified in numerous angiosperms. The causes of these accelerations have been the subject of extensive speculation but still remain unclear. To distinguish among prevailing hypotheses and begin to understand the functional consequences of rapid sequence divergence in Clp subunits, we used plastome transformation to replace the native clpP1 gene in tobacco (Nicotiana tabacum) with counterparts from another angiosperm genus (Silene) that exhibits a wide range in rates of Clp protein sequence evolution. We found that antibiotic-mediated selection could drive a transgenic clpP1 replacement from a slowly evolving donor species (S. latifolia) to homoplasmy but that clpP1 copies from Silene species with accelerated evolutionary rates remained heteroplasmic, meaning that they could not functionally replace the essential tobacco clpP1 gene. These results suggest that observed cases of rapid Clp sequence evolution are a source of epistatic incompatibilities that must be ameliorated by coevolutionary responses between plastid and nuclear subunits.
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Affiliation(s)
- Salah E Abdel-Ghany
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA.
| | - Lisa M LaManna
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
| | - Haleakala T Harroun
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA
| | - Pal Maliga
- Waksman Institute of Microbiology, Rutgers University, Piscataway, NJ, 08854, USA
- Department of Plant Biology, Rutgers University, New Brunswick, NJ, 08901, USA
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA.
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Muthye V, Mackereth CD, Stewart JB, Lavrov DV. Large dataset of octocoral mitochondrial genomes provides new insights into mt-mutS evolution and function. DNA Repair (Amst) 2022; 110:103273. [DOI: 10.1016/j.dnarep.2022.103273] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2021] [Revised: 01/07/2022] [Accepted: 01/11/2022] [Indexed: 01/09/2023]
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9
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Warren JM, Salinas-Giegé T, Triant DA, Taylor DR, Drouard L, Sloan DB. Rapid shifts in mitochondrial tRNA import in a plant lineage with extensive mitochondrial tRNA gene loss. Mol Biol Evol 2021; 38:5735-5751. [PMID: 34436590 PMCID: PMC8662596 DOI: 10.1093/molbev/msab255] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
In most eukaryotes, transfer RNAs (tRNAs) are one of the very few classes of genes remaining in the mitochondrial genome, but some mitochondria have lost these vestiges of their prokaryotic ancestry. Sequencing of mitogenomes from the flowering plant genus Silene previously revealed a large range in tRNA gene content, suggesting rapid and ongoing gene loss/replacement. Here, we use this system to test longstanding hypotheses about how mitochondrial tRNA genes are replaced by importing nuclear-encoded tRNAs. We traced the evolutionary history of these gene loss events by sequencing mitochondrial genomes from key outgroups (Agrostemma githago and Silene [=Lychnis] chalcedonica). We then performed the first global sequencing of purified plant mitochondrial tRNA populations to characterize the expression of mitochondrial-encoded tRNAs and the identity of imported nuclear-encoded tRNAs. We also confirmed the utility of high-throughput sequencing methods for the detection of tRNA import by sequencing mitochondrial tRNA populations in a species (Solanum tuberosum) with known tRNA trafficking patterns. Mitochondrial tRNA sequencing in Silene revealed substantial shifts in the abundance of some nuclear-encoded tRNAs in conjunction with their recent history of mt-tRNA gene loss and surprising cases where tRNAs with anticodons still encoded in the mitochondrial genome also appeared to be imported. These data suggest that nuclear-encoded counterparts are likely replacing mitochondrial tRNAs even in systems with recent mitochondrial tRNA gene loss, and the redundant import of a nuclear-encoded tRNA may provide a mechanism for functional replacement between translation systems separated by billions of years of evolutionary divergence.
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Affiliation(s)
- Jessica M Warren
- Department of Biology, Colorado State University, Fort Collins, CO, 80523-1878, USA
| | - Thalia Salinas-Giegé
- Institut de biologie moléculaire des plantes-CNRS, Université de Strasbourg, Strasbourg, F-67084, France
| | - Deborah A Triant
- Department of Biochemistry & Molecular Genetics, University of Virginia, Charlottesville, VA, 22908, USA
| | - Douglas R Taylor
- Department of Biology, University of Virginia, Charlottesville, VA, 22904-4328, USA
| | - Laurence Drouard
- Institut de biologie moléculaire des plantes-CNRS, Université de Strasbourg, Strasbourg, F-67084, France
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, 80523-1878, USA
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10
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Macey JR, Pabinger S, Barbieri CG, Buring ES, Gonzalez VL, Mulcahy DG, DeMeo DP, Urban L, Hime PM, Prost S, Elliott AN, Gemmell NJ. Evidence of two deeply divergent co-existing mitochondrial genomes in the Tuatara reveals an extremely complex genomic organization. Commun Biol 2021; 4:116. [PMID: 33514857 PMCID: PMC7846811 DOI: 10.1038/s42003-020-01639-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Accepted: 12/21/2020] [Indexed: 01/30/2023] Open
Abstract
Animal mitochondrial genomic polymorphism occurs as low-level mitochondrial heteroplasmy and deeply divergent co-existing molecules. The latter is rare, known only in bivalvian mollusks. Here we show two deeply divergent co-existing mt-genomes in a vertebrate through genomic sequencing of the Tuatara (Sphenodon punctatus), the sole-representative of an ancient reptilian Order. The two molecules, revealed using a combination of short-read and long-read sequencing technologies, differ by 10.4% nucleotide divergence. A single long-read covers an entire mt-molecule for both strands. Phylogenetic analyses suggest a 7-8 million-year divergence between genomes. Contrary to earlier reports, all 37 genes typical of animal mitochondria, with drastic gene rearrangements, are confirmed for both mt-genomes. Also unique to vertebrates, concerted evolution drives three near-identical putative Control Region non-coding blocks. Evidence of positive selection at sites linked to metabolically important transmembrane regions of encoded proteins suggests these two mt-genomes may confer an adaptive advantage for an unusually cold-tolerant reptile.
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Affiliation(s)
- J Robert Macey
- Peralta Genomics Institute, Chancellor's Office, Peralta Community College District, 333 East 8th Street, Oakland, CA, 94606, USA.
| | - Stephan Pabinger
- AIT Austrian Institute of Technology, Center for Health and Bioresources, Molecular Diagnostics, Giefinggasse 4, 1210, Vienna, Austria
| | - Charles G Barbieri
- Peralta Genomics Institute, Chancellor's Office, Peralta Community College District, 333 East 8th Street, Oakland, CA, 94606, USA
| | - Ella S Buring
- Global Genome Initiative, National Museum of Natural History, Smithsonian Institution, 1000 Constitution Ave., Washington, DC, 20560, USA
| | - Vanessa L Gonzalez
- Global Genome Initiative, National Museum of Natural History, Smithsonian Institution, 1000 Constitution Ave., Washington, DC, 20560, USA
| | - Daniel G Mulcahy
- Global Genome Initiative, National Museum of Natural History, Smithsonian Institution, 1000 Constitution Ave., Washington, DC, 20560, USA
| | - Dustin P DeMeo
- Peralta Genomics Institute, Chancellor's Office, Peralta Community College District, 333 East 8th Street, Oakland, CA, 94606, USA
| | - Lara Urban
- Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand
| | - Paul M Hime
- Biodiversity Institute and Natural History Museum, University of Kansas, 1345 Jayhawk Blvd., Lawrence, KS, 66045, USA
| | - Stefan Prost
- LOEWE-Center for Translational Biodiversity Genomics, Senckenberg Museum, 60325, Frankfurt, Germany
- South African National Biodiversity Institute, National Zoological Garden, Pretoria, 0184, South Africa
| | - Aaron N Elliott
- Peralta Genomics Institute, Chancellor's Office, Peralta Community College District, 333 East 8th Street, Oakland, CA, 94606, USA
| | - Neil J Gemmell
- Department of Anatomy, University of Otago, PO Box 913, Dunedin, 9054, New Zealand
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11
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Hill GE. Genetic hitchhiking, mitonuclear coadaptation, and the origins of mt DNA barcode gaps. Ecol Evol 2020; 10:9048-9059. [PMID: 32953045 PMCID: PMC7487244 DOI: 10.1002/ece3.6640] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Revised: 07/02/2020] [Accepted: 07/06/2020] [Indexed: 01/02/2023] Open
Abstract
DNA barcoding based on mitochondrial (mt) nucleotide sequences is an enigma. Neutral models of mt evolution predict DNA barcoding cannot work for recently diverged taxa, and yet, mt DNA barcoding accurately delimits species for many bilaterian animals. Meanwhile, mt DNA barcoding often fails for plants and fungi. I propose that because mt gene products must cofunction with nuclear gene products, the evolution of mt genomes is best understood with full consideration of the two environments that impose selective pressure on mt genes: the external environment and the internal genomic environment. Moreover, it is critical to fully consider the potential for adaptive evolution of not just protein products of mt genes but also of mt transfer RNAs and mt ribosomal RNAs. The tight linkage of genes on mt genomes that do not engage in recombination could facilitate selective sweeps whenever there is positive selection on any element in the mt genome, leading to the purging of mt genetic diversity within a population and to the rapid fixation of novel mt DNA sequences. Accordingly, the most important factor determining whether or not mt DNA sequences diagnose species boundaries may be the extent to which the mt chromosomes engage in recombination.
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12
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13
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Warren JM, Sloan DB. Interchangeable parts: The evolutionarily dynamic tRNA population in plant mitochondria. Mitochondrion 2020; 52:144-156. [PMID: 32184120 DOI: 10.1016/j.mito.2020.03.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Revised: 03/06/2020] [Accepted: 03/11/2020] [Indexed: 01/31/2023]
Abstract
Transfer RNAs (tRNAs) remain one of the very few classes of genes still encoded in the mitochondrial genome. These key components of the protein translation system must interact with a large enzymatic network of nuclear-encoded gene products to maintain mitochondrial function. Plants have an evolutionarily dynamic mitochondrial tRNA population, including ongoing tRNA gene loss and replacement by both horizontal gene transfer from diverse sources and import of nuclear-expressed tRNAs from the cytosol. Thus, plant mitochondria represent an excellent model for understanding how anciently divergent genes can act as "interchangeable parts" during the evolution of complex molecular systems. In particular, understanding the integration of the mitochondrial translation system with elements of the corresponding machinery used in cytosolic protein synthesis is a key area for eukaryotic cellular evolution. Here, we review the increasingly detailed phylogenetic data about the evolutionary history of mitochondrial tRNA gene loss, transfer, and functional replacement that has created extreme variation in mitochondrial tRNA populations across plant species. We describe emerging tRNA-seq methods with promise for refining our understanding of the expression and subcellular localization of tRNAs. Finally, we summarize current evidence and identify open questions related to coevolutionary changes in nuclear-encoded enzymes that have accompanied turnover in mitochondrial tRNA populations.
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Affiliation(s)
- Jessica M Warren
- Department of Biology, Colorado State University, Fort Collins, CO, USA.
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, USA
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14
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Schultz DT, Eizenga JM, Corbett-Detig RB, Francis WR, Christianson LM, Haddock SH. Conserved novel ORFs in the mitochondrial genome of the ctenophore Beroe forskalii. PeerJ 2020; 8:e8356. [PMID: 32025367 PMCID: PMC6991124 DOI: 10.7717/peerj.8356] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 12/04/2019] [Indexed: 11/20/2022] Open
Abstract
To date, five ctenophore species' mitochondrial genomes have been sequenced, and each contains open reading frames (ORFs) that if translated have no identifiable orthologs. ORFs with no identifiable orthologs are called unidentified reading frames (URFs). If truly protein-coding, ctenophore mitochondrial URFs represent a little understood path in early-diverging metazoan mitochondrial evolution and metabolism. We sequenced and annotated the mitochondrial genomes of three individuals of the beroid ctenophore Beroe forskalii and found that in addition to sharing the same canonical mitochondrial genes as other ctenophores, the B. forskalii mitochondrial genome contains two URFs. These URFs are conserved among the three individuals but not found in other sequenced species. We developed computational tools called pauvre and cuttlery to determine the likelihood that URFs are protein coding. There is evidence that the two URFs are under negative selection, and a novel Bayesian hypothesis test of trinucleotide frequency shows that the URFs are more similar to known coding genes than noncoding intergenic sequence. Protein structure and function prediction of all ctenophore URFs suggests that they all code for transmembrane transport proteins. These findings, along with the presence of URFs in other sequenced ctenophore mitochondrial genomes, suggest that ctenophores may have uncharacterized transmembrane proteins present in their mitochondria.
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Affiliation(s)
- Darrin T. Schultz
- Department of Biomolecular Engineering and Bioinformatics, University of California Santa Cruz, Santa Cruz, CA, USA
- Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA
| | - Jordan M. Eizenga
- Department of Biomolecular Engineering and Bioinformatics, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Russell B. Corbett-Detig
- Department of Biomolecular Engineering and Bioinformatics, University of California Santa Cruz, Santa Cruz, CA, USA
| | - Warren R. Francis
- Department of Biology, University of Southern Denmark, Odense, Denmark
| | | | - Steven H.D. Haddock
- Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA
- Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA, USA
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15
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Igloi GL. Molecular evidence for the evolution of the eukaryotic mitochondrial arginyl-tRNA synthetase from the prokaryotic suborder Cystobacterineae. FEBS Lett 2019; 594:951-957. [PMID: 31705651 DOI: 10.1002/1873-3468.13665] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Revised: 10/25/2019] [Accepted: 10/28/2019] [Indexed: 02/01/2023]
Abstract
The evolutionary origin of the family of eukaryotic aminoacyl-tRNA synthetases that are essential to all living organisms is a matter of debate. In order to shed molecular light on the ancient source of arginyl-tRNA synthetase, a total of 1347 eukaryotic arginyl-tRNA synthetase sequences were mined from databases and analyzed. Their multiple sequence alignment reveals a signature sequence that is characteristic of the nuclear-encoded enzyme, which is imported into mitochondria. Using this molecular beacon, the origins of this gene can be traced to modern prokaryotes. In this way, a previous phylogenetic analysis linking Myxococcus to the emergence of the eukaryotic mitochondrial arginyl-tRNA synthetase is supported by the unique existence of the molecular signature within the suborder Cystobacterineae that includes Myxococcus.
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Affiliation(s)
- Gabor L Igloi
- Institute of Biology, University of Freiburg, Germany
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16
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Forsythe ES, Sharbrough J, Havird JC, Warren JM, Sloan DB. CyMIRA: The Cytonuclear Molecular Interactions Reference for Arabidopsis. Genome Biol Evol 2019; 11:2194-2202. [PMID: 31282937 PMCID: PMC6685490 DOI: 10.1093/gbe/evz144] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/01/2019] [Indexed: 12/11/2022] Open
Abstract
The function and evolution of eukaryotic cells depend upon direct molecular interactions between gene products encoded in nuclear and cytoplasmic genomes. Understanding how these cytonuclear interactions drive molecular evolution and generate genetic incompatibilities between isolated populations and species is of central importance to eukaryotic biology. Plants are an outstanding system to investigate such effects because of their two different genomic compartments present in the cytoplasm (mitochondria and plastids) and the extensive resources detailing subcellular targeting of nuclear-encoded proteins. However, the field lacks a consistent classification scheme for mitochondrial- and plastid-targeted proteins based on their molecular interactions with cytoplasmic genomes and gene products, which hinders efforts to standardize and compare results across studies. Here, we take advantage of detailed knowledge about the model angiosperm Arabidopsis thaliana to provide a curated database of plant cytonuclear interactions at the molecular level. CyMIRA (Cytonuclear Molecular Interactions Reference for Arabidopsis) is available at http://cymira.colostate.edu/ and https://github.com/dbsloan/cymira and will serve as a resource to aid researchers in partitioning evolutionary genomic data into functional gene classes based on organelle targeting and direct molecular interaction with cytoplasmic genomes and gene products. It includes 11 categories (and 27 subcategories) of different cytonuclear complexes and types of molecular interactions, and it reports residue-level information for cytonuclear contact sites. We hope that this framework will make it easier to standardize, interpret, and compare studies testing the functional and evolutionary consequences of cytonuclear interactions.
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Affiliation(s)
| | | | - Justin C Havird
- Department of Integrative Biology, University of Texas, Austin
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17
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Yan Z, Ye G, Werren JH. Evolutionary Rate Correlation between Mitochondrial-Encoded and Mitochondria-Associated Nuclear-Encoded Proteins in Insects. Mol Biol Evol 2019; 36:1022-1036. [PMID: 30785203 DOI: 10.1093/molbev/msz036] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mitochondrion is a pivotal organelle for energy production, and includes components encoded by both the mitochondrial and nuclear genomes. Functional and evolutionary interactions are expected between the nuclear- and mitochondrial-encoded components. The topic is of broad interest in biology, with implications to genetics, evolution, and medicine. Here, we compare the evolutionary rates of mitochondrial proteins and ribosomal RNAs to rates of mitochondria-associated nuclear-encoded proteins, across the major orders of holometabolous insects. There are significant evolutionary rate correlations (ERCs) between mitochondrial-encoded and mitochondria-associated nuclear-encoded proteins, which are likely driven by different rates of mitochondrial sequence evolution and correlated changes in the interacting nuclear-encoded proteins. The pattern holds after correction for phylogenetic relationships and considering protein conservation levels. Correlations are stronger for both nuclear-encoded OXPHOS proteins that are in contact with mitochondrial OXPHOS proteins and for nuclear-encoded mitochondrial ribosomal amino acids directly contacting the mitochondrial rRNAs. We find that ERC between mitochondrial- and nuclear-encoded proteins is a strong predictor of nuclear-encoded proteins known to interact with mitochondria, and ERC shows promise for identifying new candidate proteins with mitochondrial function. Twenty-three additional candidate nuclear-encoded proteins warrant further study for mitochondrial function based on this approach, including proteins in the minichromosome maintenance helicase complex.
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Affiliation(s)
- Zhichao Yan
- State Key Laboratory of Rice Biology & Ministry of Agricultural and Rural Affairs Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China.,Department of Biology, University of Rochester, Rochester, NY
| | - Gongyin Ye
- State Key Laboratory of Rice Biology & Ministry of Agricultural and Rural Affairs Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Insect Sciences, Zhejiang University, Hangzhou, China
| | - John H Werren
- Department of Biology, University of Rochester, Rochester, NY
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18
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Muthye V, Lavrov DV. Characterization of mitochondrial proteomes of nonbilaterian animals. IUBMB Life 2018; 70:1289-1301. [PMID: 30419142 DOI: 10.1002/iub.1961] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 09/08/2018] [Accepted: 09/29/2018] [Indexed: 12/18/2022]
Abstract
Mitochondria require ~1,500 proteins for their maintenance and proper functionality, which constitute the mitochondrial proteome (mt-proteome). Although a few of these proteins, mostly subunits of the electron transport chain complexes, are encoded in mitochondrial DNA (mtDNA), the vast majority are encoded in the nuclear genome and imported to the organelle. Previous studies have shown a continuous and complex evolution of mt-proteome among eukaryotes. However, there was less attention paid to mt-proteome evolution within Metazoa, presumably because animal mtDNA and, by extension, animal mitochondria are often considered to be uniform. In this analysis, two bioinformatic approaches (Orthologue-detection and Mitochondrial Targeting Sequence prediction) were used to identify mt-proteins in 23 species from four nonbilaterian phyla: Cnidaria, Ctenophora, Placozoa, and Porifera, as well as two choanoflagellates, the closest animal relatives. Our results revealed a large variation in mt-proteome in nonbilaterian animals in size and composition. Myxozoans, highly reduced cnidarian parasites, possessed the smallest inferred mitochondrial proteomes, while calcareous sponges possessed the largest. About 513 mitochondrial orthologous groups were present in all nonbilaterian phyla and human. Interestingly, 42 human mitochondrial proteins were not identified in any nonbilaterian species studied and represent putative innovations along the bilaterian branch. Several of these proteins were involved in apoptosis and innate immunity, two processes known to evolve within Metazoa. Conversely, several proteins identified as mitochondrial in nonbilaterian phyla and animal outgroups were absent in human, representing cases of possible loss. Finally, a few human cytosolic proteins, such as histones and cytosolic ribosomal proteins, were predicted to be targeted to mitochondria in nonbilaterian animals. Overall, our analysis provides the first step in characterization of mt-proteomes in nonbilaterian animals and understanding evolution of animal mt-proteome. © 2018 IUBMB Life, 70(12):1289-1301, 2018.
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Affiliation(s)
- Viraj Muthye
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA, USA
| | - Dennis V Lavrov
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA, USA
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19
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Sloan DB, Warren JM, Williams AM, Wu Z, Abdel-Ghany SE, Chicco AJ, Havird JC. Cytonuclear integration and co-evolution. Nat Rev Genet 2018; 19:635-648. [PMID: 30018367 PMCID: PMC6469396 DOI: 10.1038/s41576-018-0035-9] [Citation(s) in RCA: 101] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The partitioning of genetic material between the nucleus and cytoplasmic (mitochondrial and plastid) genomes within eukaryotic cells necessitates coordinated integration between these genomic compartments, with important evolutionary and biomedical implications. Classic questions persist about the pervasive reduction of cytoplasmic genomes via a combination of gene loss, transfer and functional replacement - and yet why they are almost always retained in some minimal form. One striking consequence of cytonuclear integration is the existence of 'chimeric' enzyme complexes composed of subunits encoded in two different genomes. Advances in structural biology and comparative genomics are yielding important insights into the evolution of such complexes, including correlated sequence changes and recruitment of novel subunits. Thus, chimeric cytonuclear complexes provide a powerful window into the mechanisms of molecular co-evolution.
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Affiliation(s)
- Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, USA.
| | - Jessica M Warren
- Department of Biology, Colorado State University, Fort Collins, CO, USA
| | - Alissa M Williams
- Department of Biology, Colorado State University, Fort Collins, CO, USA
| | - Zhiqiang Wu
- Department of Biology, Colorado State University, Fort Collins, CO, USA
| | | | - Adam J Chicco
- Department of Biomedical Sciences, Colorado State University, Fort Collins, CO, USA
| | - Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, CO, USA
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20
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Havird JC, Trapp P, Miller CM, Bazos I, Sloan DB. Causes and Consequences of Rapidly Evolving mtDNA in a Plant Lineage. Genome Biol Evol 2018; 9:323-336. [PMID: 28164243 PMCID: PMC5381668 DOI: 10.1093/gbe/evx010] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/30/2017] [Indexed: 12/23/2022] Open
Abstract
Understanding mechanisms of coevolution between nuclear and mitochondrial (mt) genomes is a defining challenge in eukaryotic genetics. The angiosperm genus Silene is a natural system to investigate the causes and consequences of mt mutation rate variation because closely related species have highly divergent rates. In Silene species with fast-evolving mtDNA, nuclear genes that encode mitochondrially targeted proteins (N-mt genes) are also fast-evolving. This correlation could indicate positive selection to compensate for mt mutations, but might also result from a recent relaxation of selection. To differentiate between these interpretations, we used phylogenetic and population-genetic methods to test for positive and relaxed selection in three classes of N-mt genes (oxidative phosphorylation genes, ribosomal genes, and “RRR” genes involved in mtDNA recombination, replication, and repair). In all three classes, we found that species with fast-evolving mtDNA had: 1) elevated dN/dS, 2) an excess of nonsynonymous divergence relative to levels of intraspecific polymorphism, which is a signature of positive selection, and 3) no clear signals of relaxed selection. “Control” genes exhibited comparatively few signs of positive selection. These results suggest that high mt mutation rates can create selection on N-mt genes and that relaxed selection is an unlikely cause of recent accelerations in the evolution of N-mt genes. Because mt-RRR genes were found to be under positive selection, it is unlikely that elevated mt mutation rates in Silene were caused by inactivation of these mt-RRR genes. Therefore, the causes of extreme increases in angiosperm mt mutation rates remain uncertain.
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Affiliation(s)
- Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Paul Trapp
- Department of Biology, Colorado State University, Fort Collins, CO
| | | | - Ioannis Bazos
- Department of Ecology and Systematics, National and Kapodistrian University of Athens, Panepistimiopolis, Greece
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO
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21
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Arafat H, Alamaru A, Gissi C, Huchon D. Extensive mitochondrial gene rearrangements in Ctenophora: insights from benthic Platyctenida. BMC Evol Biol 2018; 18:65. [PMID: 29703131 PMCID: PMC5924465 DOI: 10.1186/s12862-018-1186-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 04/19/2018] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Complete mitochondrial (mt) genomes have been sequenced for thousands of animals and represent a molecule of choice for many evolutionary studies. Nevertheless, some animal groups have remained under-sampled. Ctenophora (comb jellies) is one such example, with only two complete mt sequences determined hitherto for this phylum, which encompasses ca. 150-200 described species. This lack of data derives from the extremely fast mt evolutionary rate in this lineage, complicating primer design and DNA amplification. Indeed, in the two ctenophore mt genomes sequenced to date, i.e. those of Mnemiopsis leidyi (order Lobata) and Pleurobrachia bachei (order Cydippida), both rRNA and protein coding genes exhibit an extraordinary size reduction and have highly derived sequences. Additionally, all tRNAs, and the atp6 and atp8 genes are absent. In order to determine whether these characteristics are shared by other ctenophores, we obtained the complete mt genomes of three benthic ctenophores belonging to the so far unsampled order of Platyctenida: Coeloplana loyai, Coeloplana yulianicorum and Vallicula multiformis. RESULTS The mt genomes of benthic ctenophores reveal the same peculiarities found in Mnemiopsis and Pleurobrachia, demonstrating that the fast evolutionary rate is a general trait of the ctenophore mt genomes. Our results also indicate that this high evolutionary rate not only affects the nucleotide substitution but also gene rearrangements. Indeed, gene order was highly rearranged among representatives of the different taxonomic orders in which it was close to random, but also quite variable within Platyctenida, in which the genera Coeloplana and Vallicula share only four conserved synteny blocks. However, the two congeneric Coeloplana species display exactly the same gene order. Because of the extreme evolutionary rate, our phylogenetic analyses were unable to resolve the phylogenetic position of ctenophores within metazoans or the relationships among the different Ctenophora orders. Comparative sequence-analyses allowed us to correct the annotation of the Pleurobrachia mt genome, confirming the absence of tRNAs, the presence of both rRNA genes, and the existence of a reassignment of codon TGA from tryptophan to serine for this species. CONCLUSIONS Since Platyctenida is an early diverging lineage among Ctenophora, our findings suggest that the mt traits described above are ancestral characteristics of this phylum.
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Affiliation(s)
- Hanan Arafat
- School of Zoology, Tel-Aviv University, Tel-Aviv, Israel
| | - Ada Alamaru
- School of Zoology, Tel-Aviv University, Tel-Aviv, Israel
| | - Carmela Gissi
- Department of Biosciences, Biotechnology and Biopharmaceutics, University of Bari "Aldo Moro", Bari, Italy.,IBIOM, Istituto di Biomembrane, Bioenergetica e Biotecnologie Molecolari, CNR (Italy), Bari, Italy
| | - Dorothée Huchon
- School of Zoology, Tel-Aviv University, Tel-Aviv, Israel. .,The Steinhardt Museum of Natural History and National Research Center, Tel-Aviv University, Tel-Aviv, Israel.
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22
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Sharbrough J, Havird JC, Noe GR, Warren JM, Sloan DB. The Mitonuclear Dimension of Neanderthal and Denisovan Ancestry in Modern Human Genomes. Genome Biol Evol 2018; 9:1567-1581. [PMID: 28854627 PMCID: PMC5509035 DOI: 10.1093/gbe/evx114] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/21/2017] [Indexed: 12/15/2022] Open
Abstract
Some human populations interbred with Neanderthals and Denisovans, resulting in substantial contributions to modern-human genomes. Therefore, it is now possible to use genomic data to investigate mechanisms that shaped historical gene flow between humans and our closest hominin relatives. More generally, in eukaryotes, mitonuclear interactions have been argued to play a disproportionate role in generating reproductive isolation. There is no evidence of mtDNA introgression into modern human populations, which means that all introgressed nuclear alleles from archaic hominins must function on a modern-human mitochondrial background. Therefore, mitonuclear interactions are also potentially relevant to hominin evolution. We performed a detailed accounting of mtDNA divergence among hominin lineages and used population-genomic data to test the hypothesis that mitonuclear incompatibilities have preferentially restricted the introgression of nuclear genes with mitochondrial functions. We found a small but significant underrepresentation of introgressed Neanderthal alleles at such nuclear loci. Structural analyses of mitochondrial enzyme complexes revealed that these effects are unlikely to be mediated by physically interacting sites in mitochondrial and nuclear gene products. We did not detect any underrepresentation of introgressed Denisovan alleles at mitochondrial-targeted loci, but this may reflect reduced power because locus-specific estimates of Denisovan introgression are more conservative. Overall, we conclude that genes involved in mitochondrial function may have been subject to distinct selection pressures during the history of introgression from archaic hominins but that mitonuclear incompatibilities have had, at most, a small role in shaping genome-wide introgression patterns, perhaps because of limited functional divergence in mtDNA and interacting nuclear genes.
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Affiliation(s)
- Joel Sharbrough
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Gregory R Noe
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Jessica M Warren
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO
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23
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Yahalomi D, Haddas-Sasson M, Rubinstein ND, Feldstein T, Diamant A, Huchon D. The Multipartite Mitochondrial Genome of Enteromyxum leei (Myxozoa): Eight Fast-Evolving Megacircles. Mol Biol Evol 2017; 34:1551-1556. [PMID: 28333349 DOI: 10.1093/molbev/msx072] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Myxozoans are a large group of poorly characterized cnidarian parasites. To gain further insight into their evolution, we sequenced the mitochondrial (mt) genome of Enteromyxum leei and reevaluate the mt genome structure of Kudoa iwatai. Although the typical animal mt genome is a compact, 13-25 kb, circular chromosome, the mt genome of E. leei was found to be fragmented into eight circular chromosomes of ∼23 kb, making it the largest described animal mt genome. Each chromosome was found to harbor a large noncoding region (∼15 kb), nearly identical between chromosomes. The protein coding genes show an unusually high rate of sequence evolution and possess little similarity to their cnidarian homologs. Only five protein coding genes could be identified and no tRNA genes. Surprisingly, the mt genome of K. iwatai was also found to be composed of two chromosomes. These observations confirm the remarkable plasticity of myxozoan mt genomes.
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Affiliation(s)
- Dayana Yahalomi
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Michal Haddas-Sasson
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Nimrod D Rubinstein
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Tamar Feldstein
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.,The Steinhardt Museum of Natural History and Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, Israel
| | - Arik Diamant
- National Center for Mariculture, Israel Oceanographic and Limnological Research, Eilat, Israel
| | - Dorothée Huchon
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.,The Steinhardt Museum of Natural History and Israel National Center for Biodiversity Studies, Tel Aviv University, Tel Aviv, Israel
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24
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Sloan DB, Havird JC, Sharbrough J. The on-again, off-again relationship between mitochondrial genomes and species boundaries. Mol Ecol 2017; 26:2212-2236. [PMID: 27997046 PMCID: PMC6534505 DOI: 10.1111/mec.13959] [Citation(s) in RCA: 154] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2016] [Revised: 11/16/2016] [Accepted: 11/18/2016] [Indexed: 12/12/2022]
Abstract
The study of reproductive isolation and species barriers frequently focuses on mitochondrial genomes and has produced two alternative and almost diametrically opposed narratives. On one hand, mtDNA may be at the forefront of speciation events, with co-evolved mitonuclear interactions responsible for some of the earliest genetic incompatibilities arising among isolated populations. On the other hand, there are numerous cases of introgression of mtDNA across species boundaries even when nuclear gene flow is restricted. We argue that these seemingly contradictory patterns can result from a single underlying cause. Specifically, the accumulation of deleterious mutations in mtDNA creates a problem with two alternative evolutionary solutions. In some cases, compensatory or epistatic changes in the nuclear genome may ameliorate the effects of mitochondrial mutations, thereby establishing coadapted mitonuclear genotypes within populations and forming the basis of reproductive incompatibilities between populations. Alternatively, populations with high mitochondrial mutation loads may be rescued by replacement with a more fit, foreign mitochondrial haplotype. Coupled with many nonadaptive mechanisms of introgression that can preferentially affect cytoplasmic genomes, this form of adaptive introgression may contribute to the widespread discordance between mitochondrial and nuclear genealogies. Here, we review recent advances related to mitochondrial introgression and mitonuclear incompatibilities, including the potential for cointrogression of mtDNA and interacting nuclear genes. We also address an emerging controversy over the classic assumption that selection on mitochondrial genomes is inefficient and discuss the mechanisms that lead lineages down alternative evolutionary paths in response to mitochondrial mutation accumulation.
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Affiliation(s)
- Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA
| | - Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA
| | - Joel Sharbrough
- Department of Biology, Colorado State University, Fort Collins, CO, 80523, USA
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25
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Lavrov DV, Pett W. Animal Mitochondrial DNA as We Do Not Know It: mt-Genome Organization and Evolution in Nonbilaterian Lineages. Genome Biol Evol 2016; 8:2896-2913. [PMID: 27557826 PMCID: PMC5633667 DOI: 10.1093/gbe/evw195] [Citation(s) in RCA: 126] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/06/2016] [Indexed: 12/11/2022] Open
Abstract
Animal mitochondrial DNA (mtDNA) is commonly described as a small, circular molecule that is conserved in size, gene content, and organization. Data collected in the last decade have challenged this view by revealing considerable diversity in animal mitochondrial genome organization. Much of this diversity has been found in nonbilaterian animals (phyla Cnidaria, Ctenophora, Placozoa, and Porifera), which, from a phylogenetic perspective, form the main branches of the animal tree along with Bilateria. Within these groups, mt-genomes are characterized by varying numbers of both linear and circular chromosomes, extra genes (e.g. atp9, polB, tatC), large variation in the number of encoded mitochondrial transfer RNAs (tRNAs) (0-25), at least seven different genetic codes, presence/absence of introns, tRNA and mRNA editing, fragmented ribosomal RNA genes, translational frameshifting, highly variable substitution rates, and a large range of genome sizes. This newly discovered diversity allows a better understanding of the evolutionary plasticity and conservation of animal mtDNA and provides insights into the molecular and evolutionary mechanisms shaping mitochondrial genomes.
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Affiliation(s)
- Dennis V Lavrov
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University
| | - Walker Pett
- Department of Ecology, Evolution, and Organismal Biology, Iowa State University Laboratoire de Biométrie et Biologie Évolutive, Université Lyon 1, Villeurbanne, France
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26
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Havird JC, Sloan DB. The Roles of Mutation, Selection, and Expression in Determining Relative Rates of Evolution in Mitochondrial versus Nuclear Genomes. Mol Biol Evol 2016; 33:3042-3053. [PMID: 27563053 DOI: 10.1093/molbev/msw185] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Eukaryotes rely on proteins encoded by the nuclear and mitochondrial (mt) genomes, which interact within multisubunit complexes such as oxidative-phosphorylation enzymes. Although selection is thought to be less efficient on the asexual mt genome, in bilaterian animals the ratio of nonsynonymous to synonymous substitutions (ω) is lower in mt- compared with nuclear-encoded OXPHOS subunits, suggesting stronger effects of purifying selection in the mt genome. Because high levels of gene expression constrain protein sequence evolution, one proposed resolution to this paradox is that mt genes are expressed more highly than nuclear genes. To test this hypothesis, we investigated expression and sequence evolution of mt and nuclear genes from 84 diverse eukaryotes that vary in mt gene content and mutation rate. We found that the relationship between mt and nuclear ω values varied dramatically across eukaryotes. In contrast, transcript abundance is consistently higher for mt genes than nuclear genes, regardless of which genes happen to be in the mt genome. Consequently, expression levels cannot be responsible for the differences in ω Rather, 84% of the variance in the ratio of ω values between mt and nuclear genes could be explained by differences in mutation rate between the two genomes. We relate these findings to the hypothesis that high rates of mt mutation select for compensatory changes in the nuclear genome. We also propose an explanation for why mt transcripts consistently outnumber their nuclear counterparts, with implications for mitonuclear protein imbalance and aging.
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Affiliation(s)
- Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, CO
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO
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27
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Kayal E, Bentlage B, Collins AG. Insights into the transcriptional and translational mechanisms of linear organellar chromosomes in the box jellyfish Alatina alata (Cnidaria: Medusozoa: Cubozoa). RNA Biol 2016; 13:799-809. [PMID: 27267414 DOI: 10.1080/15476286.2016.1194161] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND In most animals, the mitochondrial genome is characterized by its small size, organization into a single circular molecule, and a relative conservation of the number of encoded genes. In box jellyfish (Cubozoa, Cnidaria), the mitochondrial genome is organized into 8 linear mito-chromosomes harboring between one and 4 genes each, including 2 extra protein-coding genes: mt-polB and orf314. Such an organization challenges the traditional view of mitochondrial DNA (mtDNA) expression in animals. In this study, we investigate the pattern of mitochondrial gene expression in the box jellyfish Alatina alata, as well as several key nuclear-encoded molecular pathways involved in the processing of mitochondrial gene transcription. RESULTS Read coverage of DNA-seq data is relatively uniform for all 8 mito-chromosomes, suggesting that each mito-chromosome is present in equimolar proportion in the mitochondrion. Comparison of DNA and RNA-seq based assemblies indicates that mito-chromosomes are transcribed into individual transcripts in which the beginning and ending are highly conserved. Expression levels for mt-polB and orf314 are similar to those of other mitochondrial-encoded genes, which provides further evidence for them having functional roles in the mitochondrion. Survey of the transcriptome suggests recognition of the mitochondrial tRNA-Met by the cytoplasmic aminoacyl-tRNA synthetase counterpart and C-to-U editing of the cytoplasmic tRNA-Trp after import into the mitochondrion. Moreover, several mitochondrial ribosomal proteins appear to be lost. CONCLUSIONS This study represents the first survey of mitochondrial gene expression of the linear multi-chromosomal mtDNA in box jellyfish (Cubozoa). Future exploration of small RNAs and the proteome of the mitochondrion will test the hypotheses presented herein.
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Affiliation(s)
- Ehsan Kayal
- a Department of Invertebrate Zoology , National Museum of Natural History, Smithsonian Institution , Washington DC , USA
| | - Bastian Bentlage
- a Department of Invertebrate Zoology , National Museum of Natural History, Smithsonian Institution , Washington DC , USA
| | - Allen G Collins
- a Department of Invertebrate Zoology , National Museum of Natural History, Smithsonian Institution , Washington DC , USA.,b National Systematics Laboratory of NOAA's Fisheries Service, National Museum of Natural History , Washington , DC , USA
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28
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Havird JC, Whitehill NS, Snow CD, Sloan DB. Conservative and compensatory evolution in oxidative phosphorylation complexes of angiosperms with highly divergent rates of mitochondrial genome evolution. Evolution 2015; 69:3069-81. [PMID: 26514987 DOI: 10.1111/evo.12808] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Revised: 10/09/2015] [Accepted: 10/22/2015] [Indexed: 12/11/2022]
Abstract
Interactions between nuclear and mitochondrial gene products are critical for eukaryotic cell function. Nuclear genes encoding mitochondrial-targeted proteins (N-mt genes) experience elevated rates of evolution, which has often been interpreted as evidence of nuclear compensation in response to elevated mitochondrial mutation rates. However, N-mt genes may be under relaxed functional constraints, which could also explain observed increases in their evolutionary rate. To disentangle these hypotheses, we examined patterns of sequence and structural evolution in nuclear- and mitochondrial-encoded oxidative phosphorylation proteins from species in the angiosperm genus Silene with vastly different mitochondrial mutation rates. We found correlated increases in N-mt gene evolution in species with fast-evolving mitochondrial DNA. Structural modeling revealed an overrepresentation of N-mt substitutions at positions that directly contact mutated residues in mitochondrial-encoded proteins, despite overall patterns of conservative structural evolution. These findings support the hypothesis that selection for compensatory changes in response to mitochondrial mutations contributes to the elevated rate of evolution in N-mt genes. We discuss these results in light of theories implicating mitochondrial mutation rates and mitonuclear coevolution as drivers of speciation and suggest comparative and experimental approaches that could take advantage of heterogeneity in rates of mtDNA evolution across eukaryotes to evaluate such theories.
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Affiliation(s)
- Justin C Havird
- Department of Biology, Colorado State University, Fort Collins, Colorado, 80523.
| | - Nicholas S Whitehill
- Department of Computer Science, Colorado State University, Fort Collins, Colorado, 80523
| | - Christopher D Snow
- Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado, 80523
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, Colorado, 80523.
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29
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Adrion JR, White PS, Montooth KL. The Roles of Compensatory Evolution and Constraint in Aminoacyl tRNA Synthetase Evolution. Mol Biol Evol 2015; 33:152-61. [PMID: 26416980 PMCID: PMC4693975 DOI: 10.1093/molbev/msv206] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Mitochondrial protein translation requires interactions between transfer RNAs encoded by the mitochondrial genome (mt-tRNAs) and mitochondrial aminoacyl tRNA synthetase proteins (mt-aaRS) encoded by the nuclear genome. It has been argued that animal mt-tRNAs have higher deleterious substitution rates relative to their nuclear-encoded counterparts, the cytoplasmic tRNAs (cyt-tRNAs). This dynamic predicts elevated rates of compensatory evolution of mt-aaRS that interact with mt-tRNAs, relative to aaRS that interact with cyt-tRNAs (cyt-aaRS). We find that mt-aaRS do evolve at significantly higher rates (exemplified by higher dN and dN/dS) relative to cyt-aaRS, across mammals, birds, and Drosophila. While this pattern supports a model of compensatory evolution, the level at which a gene is expressed is a more general predictor of protein evolutionary rate. We find that gene expression level explains 10–56% of the variance in aaRS dN/dS, and that cyt-aaRS are more highly expressed in addition to having lower dN/dS values relative to mt-aaRS, consistent with more highly expressed genes being more evolutionarily constrained. Furthermore, we find no evidence of positive selection acting on either class of aaRS protein, as would be expected under a model of compensatory evolution. Nevertheless, the signature of faster mt-aaRS evolution persists in mammalian, but not bird or Drosophila, lineages after controlling for gene expression, suggesting some additional effect of compensatory evolution for mammalian mt-aaRS. We conclude that gene expression is the strongest factor governing differential amino acid substitution rates in proteins interacting with mitochondrial versus cytoplasmic factors, with important differences in mt-aaRS molecular evolution among taxonomic groups.
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Affiliation(s)
| | - P Signe White
- Department of Biology, Indiana University, Bloomington
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