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Uthanumallian K, Iha C, Repetti SI, Chan CX, Bhattacharya D, Duchene S, Verbruggen H. Tightly Constrained Genome Reduction and Relaxation of Purifying Selection during Secondary Plastid Endosymbiosis. Mol Biol Evol 2022; 39:msab295. [PMID: 34613411 PMCID: PMC8763093 DOI: 10.1093/molbev/msab295] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Endosymbiosis, the establishment of a former free-living prokaryotic or eukaryotic cell as an organelle inside a host cell, can dramatically alter the genomic architecture of the endosymbiont. Plastids or chloroplasts, the light-harvesting organelle of photosynthetic eukaryotes, are excellent models to study this phenomenon because plastid origin has occurred multiple times in evolution. Here, we investigate the genomic signature of molecular processes acting through secondary plastid endosymbiosis-the origination of a new plastid from a free-living eukaryotic alga. We used phylogenetic comparative methods to study gene loss and changes in selective regimes on plastid genomes, focusing on green algae that have given rise to three independent lineages with secondary plastids (euglenophytes, chlorarachniophytes, and Lepidodinium). Our results show an overall increase in gene loss associated with secondary endosymbiosis, but this loss is tightly constrained by the retention of genes essential for plastid function. The data show that secondary plastids have experienced temporary relaxation of purifying selection during secondary endosymbiosis. However, this process is tightly constrained, with selection relaxed only relative to the background in primary plastids. Purifying selection remains strong in absolute terms even during the endosymbiosis events. Selection intensity rebounds to pre-endosymbiosis levels following endosymbiosis events, demonstrating the changes in selection efficiency during different origin phases of secondary plastids. Independent endosymbiosis events in the euglenophytes, chlorarachniophytes, and Lepidodinium differ in their degree of relaxation of selection, highlighting the different evolutionary contexts of these events. This study reveals the selection-drift interplay during secondary endosymbiosis and evolutionary parallels during organellogenesis.
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Affiliation(s)
| | - Cintia Iha
- School of BioSciences, University of Melbourne, Melbourne, VIC, Australia
| | - Sonja I Repetti
- School of BioSciences, University of Melbourne, Melbourne, VIC, Australia
| | - Cheong Xin Chan
- Australian Centre for Ecogenomics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia
| | | | - Sebastian Duchene
- Deptartment of Microbiology and Immunology, Peter Doherty Institute for Infection and Immunity, University of Melbourne, Melbourne, VIC, Australia
| | - Heroen Verbruggen
- School of BioSciences, University of Melbourne, Melbourne, VIC, Australia
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Kelly S. The economics of organellar gene loss and endosymbiotic gene transfer. Genome Biol 2021; 22:345. [PMID: 34930424 PMCID: PMC8686548 DOI: 10.1186/s13059-021-02567-w] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2021] [Accepted: 12/06/2021] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND The endosymbiosis of the bacterial progenitors of the mitochondrion and the chloroplast are landmark events in the evolution of life on Earth. While both organelles have retained substantial proteomic and biochemical complexity, this complexity is not reflected in the content of their genomes. Instead, the organellar genomes encode fewer than 5% of the genes found in living relatives of their ancestors. While many of the 95% of missing organellar genes have been discarded, others have been transferred to the host nuclear genome through a process known as endosymbiotic gene transfer. RESULTS Here, we demonstrate that the difference in the per-cell copy number of the organellar and nuclear genomes presents an energetic incentive to the cell to either delete organellar genes or transfer them to the nuclear genome. We show that, for the majority of transferred organellar genes, the energy saved by nuclear transfer exceeds the costs incurred from importing the encoded protein into the organelle where it can provide its function. Finally, we show that the net energy saved by endosymbiotic gene transfer can constitute an appreciable proportion of total cellular energy budgets and is therefore sufficient to impart a selectable advantage to the cell. CONCLUSION Thus, reduced cellular cost and improved energy efficiency likely played a role in the reductive evolution of mitochondrial and chloroplast genomes and the transfer of organellar genes to the nuclear genome.
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Affiliation(s)
- Steven Kelly
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
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Strassert JFH, Irisarri I, Williams TA, Burki F. A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids. Nat Commun 2021; 12:1879. [PMID: 33767194 PMCID: PMC7994803 DOI: 10.1038/s41467-021-22044-z] [Citation(s) in RCA: 72] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Accepted: 02/25/2021] [Indexed: 01/31/2023] Open
Abstract
In modern oceans, eukaryotic phytoplankton is dominated by lineages with red algal-derived plastids such as diatoms, dinoflagellates, and coccolithophores. Despite the ecological importance of these groups and many others representing a huge diversity of forms and lifestyles, we still lack a comprehensive understanding of their evolution and how they obtained their plastids. New hypotheses have emerged to explain the acquisition of red algal-derived plastids by serial endosymbiosis, but the chronology of these putative independent plastid acquisitions remains untested. Here, we establish a timeframe for the origin of red algal-derived plastids under scenarios of serial endosymbiosis, using Bayesian molecular clock analyses applied on a phylogenomic dataset with broad sampling of eukaryote diversity. We find that the hypotheses of serial endosymbiosis are chronologically possible, as the stem lineages of all red plastid-containing groups overlap in time. This period in the Meso- and Neoproterozoic Eras set the stage for the later expansion to dominance of red algal-derived primary production in the contemporary oceans, which profoundly altered the global geochemical and ecological conditions of the Earth.
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Affiliation(s)
- Jürgen F H Strassert
- Department of Organismal Biology, Program in Systematic Biology, Uppsala University, Uppsala, Sweden
- Department of Ecosystem Research, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany
| | - Iker Irisarri
- Department of Organismal Biology, Program in Systematic Biology, Uppsala University, Uppsala, Sweden
- Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales (MNCN-CSIC), Madrid, Spain
- Department of Applied Bioinformatics, Institute for Microbiology and Genetics, University of Göttingen, and Campus Institute Data Science (CIDAS), Göttingen, Germany
| | - Tom A Williams
- School of Biological Sciences, University of Bristol, Life Sciences Building, Bristol, UK
| | - Fabien Burki
- Department of Organismal Biology, Program in Systematic Biology, Uppsala University, Uppsala, Sweden.
- Science for Life Laboratory, Uppsala University, Uppsala, Sweden.
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Tanifuji G, Kamikawa R, Moore CE, Mills T, Onodera NT, Kashiyama Y, Archibald JM, Inagaki Y, Hashimoto T. Comparative Plastid Genomics of Cryptomonas Species Reveals Fine-Scale Genomic Responses to Loss of Photosynthesis. Genome Biol Evol 2020; 12:3926-3937. [PMID: 31922581 PMCID: PMC7058160 DOI: 10.1093/gbe/evaa001] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/04/2020] [Indexed: 01/20/2023] Open
Abstract
Loss of photosynthesis is a recurring theme in eukaryotic evolution. In organisms that have lost the ability to photosynthesize, nonphotosynthetic plastids are retained because they play essential roles in processes other than photosynthesis. The unicellular algal genus Cryptomonas contains both photosynthetic and nonphotosynthetic members, the latter having lost the ability to photosynthesize on at least three separate occasions. To elucidate the evolutionary processes underlying the loss of photosynthesis, we sequenced the plastid genomes of two nonphotosynthetic strains, Cryptomonas sp. CCAC1634B and SAG977-2f, as well as the genome of the phototroph Cryptomonas curvata CCAP979/52. These three genome sequences were compared with the previously sequenced plastid genome of the nonphotosynthetic species Cryptomonas paramecium CCAP977/2a as well as photosynthetic members of the Cryptomonadales, including C. curvata FBCC300012D. Intraspecies comparison between the two C. curvata strains showed that although their genome structures are stable, the substitution rates of their genes are relatively high. Although most photosynthesis-related genes, such as the psa and psb gene families, were found to have disappeared from the nonphotosynthetic strains, at least ten pseudogenes are retained in SAG977-2f. Although gene order is roughly shared among the plastid genomes of photosynthetic Cryptomonadales, genome rearrangements are seen more frequently in the smaller genomes of the nonphotosynthetic strains. Intriguingly, the light-independent protochlorophyllide reductase comprising chlB, L, and N is retained in nonphotosynthetic SAG977-2f and CCAC1634B. On the other hand, whereas CCAP977/2a retains ribulose-1,5-bisphosphate carboxylase/oxygenase-related genes, including rbcL, rbcS, and cbbX, the plastid genomes of the other two nonphotosynthetic strains have lost the ribulose-1,5-bisphosphate carboxylase/oxygenase protein-coding genes.
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Affiliation(s)
- Goro Tanifuji
- Department of Zoology, National Museum of Nature and Science, Ibaraki, Japan
| | - Ryoma Kamikawa
- Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
| | - Christa E Moore
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Tyler Mills
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Naoko T Onodera
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Yuichiro Kashiyama
- Department of Applied Chemistry and Food Science, Fukui University of Technology, Fukui, Japan
| | - John M Archibald
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Yuji Inagaki
- Center for Computational Sciences, University of Tsukuba, Ibaraki, Japan.,Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
| | - Tetsuo Hashimoto
- Graduate School of Life and Environmental Sciences, University of Tsukuba, Ibaraki, Japan
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Hu Y, Xing W, Hu Z, Liu G. Phylogenetic Analysis and Substitution Rate Estimation of Colonial Volvocine Algae Based on Mitochondrial Genomes. Genes (Basel) 2020; 11:genes11010115. [PMID: 31968709 PMCID: PMC7016891 DOI: 10.3390/genes11010115] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Revised: 01/13/2020] [Accepted: 01/15/2020] [Indexed: 01/30/2023] Open
Abstract
We sequenced the mitochondrial genome of six colonial volvocine algae, namely: Pandorina morum, Pandorina colemaniae, Volvulina compacta, Colemanosphaera angeleri, Colemanosphaera charkowiensi, and Yamagishiella unicocca. Previous studies have typically reconstructed the phylogenetic relationship between colonial volvocine algae based on chloroplast or nuclear genes. Here, we explore the validity of phylogenetic analysis based on mitochondrial protein-coding genes. We found phylogenetic incongruence of the genera Yamagishiella and Colemanosphaera. In Yamagishiella, the stochastic error and linkage group formed by the mitochondrial protein-coding genes prevent phylogenetic analyses from reflecting the true relationship. In Colemanosphaera, a different reconstruction approach revealed a different phylogenetic relationship. This incongruence may be because of the influence of biological factors, such as incomplete lineage sorting or horizontal gene transfer. We also analyzed the substitution rates in the mitochondrial and chloroplast genomes between colonial volvocine algae. Our results showed that all volvocine species showed significantly higher substitution rates for the mitochondrial genome compared with the chloroplast genome. The nonsynonymous substitution (dN)/synonymous substitution (dS) ratio is similar in the genomes of both organelles in most volvocine species, suggesting that the two counterparts are under a similar selection pressure. We also identified a few chloroplast protein-coding genes that showed high dN/dS ratios in some species, resulting in a significant dN/dS ratio difference between the mitochondrial and chloroplast genomes.
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Affiliation(s)
- Yuxin Hu
- Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
- School of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Weiyue Xing
- Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
- School of Life Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhengyu Hu
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
| | - Guoxiang Liu
- Key Laboratory of Algal Biology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China
- Correspondence: ; Tel.: +86-027-6878-0576
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