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Peñafiel-Ayala A, Peralta-Castro A, Mora-Garduño J, García-Medel P, Zambrano-Pereira AG, Díaz-Quezada C, Abraham-Juárez MJ, Benítez-Cardoza CG, Sloan DB, Brieba LG. Plant Organellar MSH1 Is a Displacement Loop-Specific Endonuclease. PLANT & CELL PHYSIOLOGY 2024; 65:560-575. [PMID: 37756637 DOI: 10.1093/pcp/pcad112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Revised: 09/09/2023] [Accepted: 09/19/2023] [Indexed: 09/29/2023]
Abstract
MutS HOMOLOG 1 (MSH1) is an organellar-targeted protein that obstructs ectopic recombination and the accumulation of mutations in plant organellar genomes. MSH1 also modulates the epigenetic status of nuclear DNA, and its absence induces a variety of phenotypic responses. MSH1 is a member of the MutS family of DNA mismatch repair proteins but harbors an additional GIY-YIG nuclease domain that distinguishes it from the rest of this family. How MSH1 hampers recombination and promotes fidelity in organellar DNA inheritance is unknown. Here, we elucidate its enzymatic activities by recombinantly expressing and purifying full-length MSH1 from Arabidopsis thaliana (AtMSH1). AtMSH1 is a metalloenzyme that shows a strong binding affinity for displacement loops (D-loops). The DNA-binding abilities of AtMSH1 reside in its MutS domain and not in its GIY-YIG domain, which is the ancillary nickase of AtMSH1. In the presence of divalent metal ions, AtMSH1 selectively executes multiple incisions at D-loops, but not other DNA structures including Holliday junctions or dsDNA, regardless of the presence or absence of mismatches. The selectivity of AtMSH1 to dismantle D-loops supports the role of this enzyme in preventing recombination between short repeats. Our results suggest that plant organelles have evolved novel DNA repair routes centered around the anti-recombinogenic activity of MSH1.
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Affiliation(s)
- Alejandro Peñafiel-Ayala
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Antolin Peralta-Castro
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Josue Mora-Garduño
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Paola García-Medel
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Angie G Zambrano-Pereira
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Corina Díaz-Quezada
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - María Jazmín Abraham-Juárez
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
| | - Claudia G Benítez-Cardoza
- Laboratorio de Investigación Bioquímica, Programa Institucional en Biomedicina Molecular ENMyH-IPN, Guillermo Massieu Helguera No. 239, La Escalera Ticoman 07320 DF, México
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
| | - Luis G Brieba
- Langebio-Cinvestav Sede Irapuato, Km. 9.6 Libramiento Norte Carretera. Irapuato-León, Irapuato, Guanajuato 36821, México
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2
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Freeman ADJ, Déclais AC, Wilson TJ, Lilley DJ. Biochemical and mechanistic analysis of the cleavage of branched DNA by human ANKLE1. Nucleic Acids Res 2023; 51:5743-5754. [PMID: 37216589 PMCID: PMC10287932 DOI: 10.1093/nar/gkad416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 03/28/2023] [Accepted: 05/04/2023] [Indexed: 05/24/2023] Open
Abstract
ANKLE1 is a nuclease that provides a final opportunity to process unresolved junctions in DNA that would otherwise create chromosomal linkages blocking cell division. It is a GIY-YIG nuclease. We have expressed an active domain of human ANKLE1 containing the GIY-YIG nuclease domain in bacteria, that is monomeric in solution and when bound to a DNA Y-junction, and unilaterally cleaves a cruciform junction. Using an AlphaFold model of the enzyme we identify the key active residues, and show that mutation of each leads to impairment of activity. There are two components in the catalytic mechanism. Cleavage rate is pH dependent, corresponding to a pKa of 6.9, suggesting an involvement of the conserved histidine in proton transfer. The reaction rate depends on the nature of the divalent cation, likely bound by glutamate and asparagine side chains, and is log-linear with the metal ion pKa. We propose that the reaction is subject to general acid-base catalysis, using a combination of tyrosine and histidine acting as general base and water directly coordinated to the metal ion as general acid. The reaction is temperature dependent; activation energy Ea = 37 kcal mol-1, suggesting that cleavage is coupled to opening of DNA in the transition state.
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Affiliation(s)
- Alasdair D J Freeman
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Anne-Cécile Déclais
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Timothy J Wilson
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - David M J Lilley
- Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dow Street, Dundee DD1 5EH, UK
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Wynn E, Purfeerst E, Christensen A. Mitochondrial DNA Repair in an Arabidopsis thaliana Uracil N-Glycosylase Mutant. PLANTS (BASEL, SWITZERLAND) 2020; 9:E261. [PMID: 32085412 PMCID: PMC7076443 DOI: 10.3390/plants9020261] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 02/14/2020] [Accepted: 02/16/2020] [Indexed: 02/07/2023]
Abstract
Substitution rates in plant mitochondrial genes are extremely low, indicating strong selective pressure as well as efficient repair. Plant mitochondria possess base excision repair pathways; however, many repair pathways such as nucleotide excision repair and mismatch repair appear to be absent. In the absence of these pathways, many DNA lesions must be repaired by a different mechanism. To test the hypothesis that double-strand break repair (DSBR) is that mechanism, we maintained independent self-crossing lineages of plants deficient in uracil-N-glycosylase (UNG) for 11 generations to determine the repair outcomes when that pathway is missing. Surprisingly, no single nucleotide polymorphisms (SNPs) were fixed in any line in generation 11. The pattern of heteroplasmic SNPs was also unaltered through 11 generations. When the rate of cytosine deamination was increased by mitochondrial expression of the cytosine deaminase APOBEC3G, there was an increase in heteroplasmic SNPs but only in mature leaves. Clearly, DNA maintenance in reproductive meristem mitochondria is very effective in the absence of UNG while mitochondrial genomes in differentiated tissue are maintained through a different mechanism or not at all. Several genes involved in DSBR are upregulated in the absence of UNG, indicating that double-strand break repair is a general system of repair in plant mitochondria. It is important to note that the developmental stage of tissues is critically important for these types of experiments.
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Affiliation(s)
- Emily Wynn
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (E.W.); (E.P.)
- United States Department of Agriculture, Agricultural Research Service, U.S. Meat Animal Research Center, Clay Center, NE 68933, USA
| | - Emma Purfeerst
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (E.W.); (E.P.)
- Athletics Department, Bethany Lutheran College, Mankato, MN 56001, USA
| | - Alan Christensen
- School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588, USA; (E.W.); (E.P.)
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Klucnika A, Ma H. Mapping and editing animal mitochondrial genomes: can we overcome the challenges? Philos Trans R Soc Lond B Biol Sci 2019; 375:20190187. [PMID: 31787046 DOI: 10.1098/rstb.2019.0187] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The animal mitochondrial genome, although small, can have a big impact on health and disease. Non-pathogenic sequence variation among mitochondrial DNA (mtDNA) haplotypes influences traits including fertility, healthspan and lifespan, whereas pathogenic mutations are linked to incurable mitochondrial diseases and other complex conditions like ageing, diabetes, cancer and neurodegeneration. However, we know very little about how mtDNA genetic variation contributes to phenotypic differences. Infrequent recombination, the multicopy nature and nucleic acid-impenetrable membranes present significant challenges that hamper our ability to precisely map mtDNA variants responsible for traits, and to genetically modify mtDNA so that we can isolate specific mutants and characterize their biochemical and physiological consequences. Here, we summarize the past struggles and efforts in developing systems to map and edit mtDNA. We also assess the future of performing forward and reverse genetic studies on animal mitochondrial genomes. This article is part of the theme issue 'Linking the mitochondrial genotype to phenotype: a complex endeavour'.
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Affiliation(s)
- Anna Klucnika
- Wellcome Trust/Cancer Research UK Gurdon Institute, Tennis Court Road, Cambridge CB2 1QN, UK.,Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK
| | - Hansong Ma
- Wellcome Trust/Cancer Research UK Gurdon Institute, Tennis Court Road, Cambridge CB2 1QN, UK.,Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK
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Guha TK, Edgell DR. Applications of Alternative Nucleases in the Age of CRISPR/Cas9. Int J Mol Sci 2017; 18:ijms18122565. [PMID: 29186020 PMCID: PMC5751168 DOI: 10.3390/ijms18122565] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 11/22/2017] [Accepted: 11/24/2017] [Indexed: 01/10/2023] Open
Abstract
Breakthroughs in the development of programmable site-specific nucleases, including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), meganucleases (MNs), and most recently, the clustered regularly interspaced short palindromic repeats (CRISPR) associated proteins (including Cas9) have greatly enabled and accelerated genome editing. By targeting double-strand breaks to user-defined locations, the rates of DNA repair events are greatly enhanced relative to un-catalyzed events at the same sites. However, the underlying biology of each genome-editing nuclease influences the targeting potential, the spectrum of off-target cleavages, the ease-of-use, and the types of recombination events at targeted double-strand breaks. No single genome-editing nuclease is optimized for all possible applications. Here, we focus on the diversity of nuclease domains available for genome editing, highlighting biochemical properties and the potential applications that are best suited to each domain.
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Affiliation(s)
- Tuhin K Guha
- Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada.
| | - David R Edgell
- Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON N6A 5C1, Canada.
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Arkhipova IR, Yushenova IA, Rodriguez F. Giant Reverse Transcriptase-Encoding Transposable Elements at Telomeres. Mol Biol Evol 2017; 34:2245-2257. [PMID: 28575409 PMCID: PMC5850863 DOI: 10.1093/molbev/msx159] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Transposable elements are omnipresent in eukaryotic genomes and have a profound impact on chromosome structure, function and evolution. Their structural and functional diversity is thought to be reasonably well-understood, especially in retroelements, which transpose via an RNA intermediate copied into cDNA by the element-encoded reverse transcriptase, and are characterized by a compact structure. Here, we report a novel type of expandable eukaryotic retroelements, which we call Terminons. These elements can attach to G-rich telomeric repeat overhangs at the chromosome ends, in a process apparently facilitated by complementary C-rich repeats at the 3′-end of the RNA template immediately adjacent to a hammerhead ribozyme motif. Terminon units, which can exceed 40 kb in length, display an unusually complex and diverse structure, and can form very long chains, with host genes often captured between units. As the principal polymerizing component, Terminons contain Athena reverse transcriptases previously described in bdelloid rotifers and belonging to the enigmatic group of Penelope-like elements, but can additionally accumulate multiple cooriented ORFs, including DEDDy 3′-exonucleases, GDSL esterases/lipases, GIY-YIG-like endonucleases, rolling-circle replication initiator (Rep) proteins, and putatively structural ORFs with coiled-coil motifs and transmembrane domains. The extraordinary length and complexity of Terminons and the high degree of interfamily variability in their ORF content challenge the current views on the structural organization of eukaryotic retroelements, and highlight their possible connections with the viral world and the implications for the elevated frequency of gene transfer.
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Affiliation(s)
- Irina R Arkhipova
- Marine Biological Laboratory, Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Woods Hole, MA
| | - Irina A Yushenova
- Marine Biological Laboratory, Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Woods Hole, MA
| | - Fernando Rodriguez
- Marine Biological Laboratory, Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Woods Hole, MA
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Roy AC, Wilson GG, Edgell DR. Perpetuating the homing endonuclease life cycle: identification of mutations that modulate and change I-TevI cleavage preference. Nucleic Acids Res 2016; 44:7350-9. [PMID: 27387281 PMCID: PMC5009752 DOI: 10.1093/nar/gkw614] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2016] [Accepted: 06/27/2016] [Indexed: 11/14/2022] Open
Abstract
Homing endonucleases are sequence-tolerant DNA endonucleases that act as mobile genetic elements. The ability of homing endonucleases to cleave substrates with multiple nucleotide substitutions suggests a high degree of adaptability in that changing or modulating cleavage preference would require relatively few amino acid substitutions. Here, using directed evolution experiments with the GIY-YIG homing endonuclease I-TevI that targets the thymidylate synthase gene of phage T4, we readily isolated variants that dramatically broadened I-TevI cleavage preference, as well as variants that fine-tuned cleavage preference. By combining substitutions, we observed an ∼10 000-fold improvement in cleavage on some substrates not cleaved by the wild-type enzyme, correlating with a decrease in readout of information content at the cleavage site. Strikingly, we were able to change the cleavage preference of I-TevI to that of the isoschizomer I-BmoI which targets a different cleavage site in the thymidylate synthase gene, recapitulating the evolution of cleavage preference in this family of homing endonucleases. Our results define a strategy to isolate GIY-YIG nuclease domains with distinct cleavage preferences, and provide insight into how homing endonucleases may escape a dead-end life cycle in a population of saturated target sites by promoting transposition to different target sites.
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Affiliation(s)
- Alexander C Roy
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, N6A 5C1, Canada
| | | | - David R Edgell
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, N6A 5C1, Canada
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8
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Gruber AJ, Olsen TM, Dvorak RH, Cox MM. Function of the N-terminal segment of the RecA-dependent nuclease Ref. Nucleic Acids Res 2015; 43:1795-803. [PMID: 25618854 PMCID: PMC4330346 DOI: 10.1093/nar/gku1330] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The bacteriophage P1 Ref (recombination enhancement function) protein is a RecA-dependent, HNH endonuclease. It can be directed to create targeted double-strand breaks within a displacement loop formed by RecA. The 76 amino acid N-terminal region of Ref is positively charged (25/76 amino acid residues) and inherently unstructured in solution. Our investigation of N-terminal truncation variants shows this region is required for DNA binding, contains a Cys involved in incidental dimerization and is necessary for efficient Ref-mediated DNA cleavage. Specifically, Ref N-terminal truncation variants lacking between 21 and 47 amino acids are more effective RecA-mediated targeting nucleases. We propose a more refined set of options for the Ref-mediated cleavage mechanism, featuring the N-terminal region as an anchor for at least one of the DNA strand cleavage events.
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Affiliation(s)
- Angela J Gruber
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Tayla M Olsen
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Rachel H Dvorak
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Michael M Cox
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
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9
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Abstract
Plant mitochondrial genomes have very low mutation rates. In contrast, they also rearrange and expand frequently. This is easily understood if DNA repair in genes is accomplished by accurate mechanisms, whereas less accurate mechanisms including nonhomologous end joining or break-induced replication are used in nongenes. An important question is how different mechanisms of repair predominate in coding and noncoding DNA, although one possible mechanism is transcription-coupled repair (TCR). This work tests the predictions of TCR and finds no support for it. Examination of the mutation spectra and rates in genes and junk reveals what DNA repair mechanisms are available to plant mitochondria, and what selective forces act on the repair products. A model is proposed that mismatches and other DNA damages are repaired by converting them into double-strand breaks (DSBs). These can then be repaired by any of the DSB repair mechanisms, both accurate and inaccurate. Natural selection will eliminate coding regions repaired by inaccurate mechanisms, accounting for the low mutation rates in genes, whereas mutations, rearrangements, and expansions generated by inaccurate repair in noncoding regions will persist. Support for this model includes the structure of the mitochondrial mutS homolog in plants, which is fused to a double-strand endonuclease. The model proposes that plant mitochondria do not distinguish a damaged or mismatched DNA strand from the undamaged strand, they simply cut both strands and perform homology-based DSB repair. This plant-specific strategy for protecting future generations from mitochondrial DNA damage has the side effect of genome expansions and rearrangements.
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Wolfs JM, Kleinstiver BP, Edgell DR. Rapid screening of endonuclease target site preference using a modified bacterial two-plasmid selection. Methods Mol Biol 2014; 1123:97-104. [PMID: 24510263 DOI: 10.1007/978-1-62703-968-0_8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Homing endonucleases and other site-specific endonucleases have potential applications in genome editing, yet efficient targeting requires a thorough understanding of DNA-sequence specificity. Here, we describe a modified two-plasmid genetic selection in Escherichia coli that allows rapid profiling of nucleotide substitutions within a target site of given endonucleases. The selection utilizes a toxic plasmid (pTox) that encodes a DNA gyrase toxin in addition to the endonuclease target site. Cleavage of the toxic plasmid by an endonuclease expressed from a second plasmid (pEndo) facilitates growth under selective conditions. The modified protocol utilizes competent cells harboring the endonuclease expression plasmid into which target site plasmids are transformed. Replica plating on nonselective and selective media plates identifies cleavable and non-cleavable targets. Thus, a library of randomized target sites, or many individual target sites, can be analyzed using a single transformation. Both cleavable and non-cleavable targets can be analyzed by DNA sequencing to gain information about nucleotide preference in the endonuclease's target site.
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Affiliation(s)
- Jason M Wolfs
- Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada
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11
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Abstract
Plant mitochondrial genomes are notorious for their large and variable size, nonconserved open reading frames of unknown function, and high rates of rearrangement. Paradoxically, the mutation rates are very low. However, mutation rates can only be measured in sequences that can be aligned--a very small part of plant mitochondrial genomes. Comparison of the complete mitochondrial genome sequences of two ecotypes of Arabidopsis thaliana allows the alignment of noncoding as well as coding DNA and estimation of the mutation rates in both. A recent chimeric duplication is also analyzed. A hypothesis is proposed that the mechanisms of plant mitochondrial DNA repair account for these features and includes different mechanisms in transcribed and nontranscribed regions. Within genes, a bias toward gene conversion would keep measured mutation rates low, whereas in noncoding regions, break-induced replication (BIR) explains the expansion and rearrangements. Both processes are types of double-strand break repair, but enhanced second-strand capture in transcribed regions versus BIR in nontranscribed regions can explain the two seemingly contradictory features of plant mitochondrial genome evolution--the low mutation rates in genes and the striking expansions of noncoding sequences.
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Affiliation(s)
- Alan C Christensen
- School of Biological Sciences, E249 Beadle Center, University of Nebraska-Lincoln, USA.
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