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1.
Cell ; 187(5): 1127-1144.e21, 2024 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-38428393

RESUMO

Chloroplasts are green plastids in the cytoplasm of eukaryotic algae and plants responsible for photosynthesis. The plastid-encoded RNA polymerase (PEP) plays an essential role during chloroplast biogenesis from proplastids and functions as the predominant RNA polymerase in mature chloroplasts. The PEP-centered transcription apparatus comprises a bacterial-origin PEP core and more than a dozen eukaryotic-origin PEP-associated proteins (PAPs) encoded in the nucleus. Here, we determined the cryo-EM structures of Nicotiana tabacum (tobacco) PEP-PAP apoenzyme and PEP-PAP transcription elongation complexes at near-atomic resolutions. Our data show the PEP core adopts a typical fold as bacterial RNAP. Fifteen PAPs bind at the periphery of the PEP core, facilitate assembling the PEP-PAP supercomplex, protect the complex from oxidation damage, and likely couple gene transcription with RNA processing. Our results report the high-resolution architecture of the chloroplast transcription apparatus and provide the structural basis for the mechanistic and functional study of transcription regulation in chloroplasts.


Assuntos
RNA Polimerases Dirigidas por DNA , Plastídeos , Cloroplastos/metabolismo , Microscopia Crioeletrônica , RNA Polimerases Dirigidas por DNA/genética , Fotossíntese , Plastídeos/enzimologia
2.
Cell ; 187(5): 1145-1159.e21, 2024 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-38428394

RESUMO

Chloroplast genes encoding photosynthesis-associated proteins are predominantly transcribed by the plastid-encoded RNA polymerase (PEP). PEP is a multi-subunit complex composed of plastid-encoded subunits similar to bacterial RNA polymerases (RNAPs) stably bound to a set of nuclear-encoded PEP-associated proteins (PAPs). PAPs are essential to PEP activity and chloroplast biogenesis, but their roles are poorly defined. Here, we present cryoelectron microscopy (cryo-EM) structures of native 21-subunit PEP and a PEP transcription elongation complex from white mustard (Sinapis alba). We identify that PAPs encase the core polymerase, forming extensive interactions that likely promote complex assembly and stability. During elongation, PAPs interact with DNA downstream of the transcription bubble and with the nascent mRNA. The models reveal details of the superoxide dismutase, lysine methyltransferase, thioredoxin, and amino acid ligase enzymes that are subunits of PEP. Collectively, these data provide a foundation for the mechanistic understanding of chloroplast transcription and its role in plant growth and adaptation.


Assuntos
RNA Polimerases Dirigidas por DNA , Plastídeos , Proteínas de Arabidopsis/metabolismo , Cloroplastos/metabolismo , Microscopia Crioeletrônica , RNA Polimerases Dirigidas por DNA/química , Regulação da Expressão Gênica de Plantas , Proteínas de Plantas/química , Plastídeos/enzimologia , Transcrição Gênica
3.
Cell ; 187(5): 1106-1108, 2024 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-38428392

RESUMO

RNA polymerases (RNAPs) control the first step of gene expression in all forms of life by transferring genetic information from DNA to RNA, a process known as transcription. In this issue of Cell, Webster et al. and Wu et al. report three-dimensional structures of RNAP complexes from chloroplasts.


Assuntos
RNA Polimerases Dirigidas por DNA , RNA Polimerases Dirigidas por DNA/química , RNA Polimerases Dirigidas por DNA/metabolismo , Transcrição Gênica , Plastídeos/enzimologia
4.
Mol Cell ; 84(5): 910-925.e5, 2024 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-38428434

RESUMO

Chloroplasts contain a dedicated genome that encodes subunits of the photosynthesis machinery. Transcription of photosynthesis genes is predominantly carried out by a plastid-encoded RNA polymerase (PEP), a nearly 1 MDa complex composed of core subunits with homology to eubacterial RNA polymerases (RNAPs) and at least 12 additional chloroplast-specific PEP-associated proteins (PAPs). However, the architecture of this complex and the functions of the PAPs remain unknown. Here, we report the cryo-EM structure of a 19-subunit PEP complex from Sinapis alba (white mustard). The structure reveals that the PEP core resembles prokaryotic and nuclear RNAPs but contains chloroplast-specific features that mediate interactions with the PAPs. The PAPs are unrelated to known transcription factors and arrange around the core in a unique fashion. Their structures suggest potential functions during transcription in the chemical environment of chloroplasts. These results reveal structural insights into chloroplast transcription and provide a framework for understanding photosynthesis gene expression.


Assuntos
RNA Polimerases Dirigidas por DNA , RNA de Cloroplastos , RNA de Cloroplastos/metabolismo , RNA Polimerases Dirigidas por DNA/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Cloroplastos/genética , Cloroplastos/metabolismo , Plastídeos/genética , Plastídeos/metabolismo , Regulação da Expressão Gênica de Plantas , Transcrição Gênica
5.
Methods Mol Biol ; 2776: 63-88, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502498

RESUMO

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of morphological, ultrastructural, biochemical, and physiological differences. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization. In addition to basic plastid structural features, the most important plastid types, the newly characterized peculiar plastids, and future perspectives in plastid biology are also provided in this chapter.


Assuntos
Cloroplastos , Embriófitas , Cloroplastos/genética , Cloroplastos/metabolismo , Plastídeos/metabolismo , Embriófitas/genética , Plantas/metabolismo
6.
Methods Mol Biol ; 2776: 21-41, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502496

RESUMO

A considerable part of the diversity of eukaryotic phototrophs consists of algae with plastids that evolved from endosymbioses between two eukaryotes. These complex plastids are characterized by a high number of envelope membranes (more than two) and some of them contain a residual nucleus of the endosymbiotic alga called a nucleomorph. Complex plastid-bearing algae are thus chimeric cell assemblies, eukaryotic symbionts living in a eukaryotic host. In contrast, the primary plastids of the Archaeplastida (plants, green algae, red algae, and glaucophytes) possibly evolved from a single endosymbiosis with a cyanobacterium and are surrounded by two membranes. Complex plastids have been acquired several times by unrelated groups of eukaryotic heterotrophic hosts, suggesting that complex plastids are somewhat easier to obtain than primary plastids. Evidence suggests that complex plastids arose twice independently in the green lineage (euglenophytes and chlorarachniophytes) through secondary endosymbiosis, and four times in the red lineage, first through secondary endosymbiosis in cryptophytes, then by higher-order events in stramenopiles, alveolates, and haptophytes. Engulfment of primary and complex plastid-containing algae by eukaryotic hosts (secondary, tertiary, and higher-order endosymbioses) is also responsible for numerous plastid replacements in dinoflagellates. Plastid endosymbiosis is accompanied by massive gene transfer from the endosymbiont to the host nucleus and cell adaptation of both endosymbiotic partners, which is related to the trophic switch to phototrophy and loss of autonomy of the endosymbiont. Such a process is essential for the metabolic integration and division control of the endosymbiont in the host. Although photosynthesis is the main advantage of acquiring plastids, loss of photosynthesis often occurs in algae with complex plastids. This chapter summarizes the essential knowledge of the acquisition, evolution, and function of complex plastids.


Assuntos
Evolução Biológica , Rodófitas , Simbiose , Plastídeos/genética , Plastídeos/metabolismo , Plantas/genética , Rodófitas/genética , Filogenia
7.
Methods Mol Biol ; 2776: 107-134, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502500

RESUMO

Plastids are organelles delineated by two envelopes playing important roles in different cellular processes such as energy production or lipid biosynthesis. To regulate their biogenesis and their function, plastids have to communicate with other cellular compartments. This communication can be mediated by metabolites, signaling molecules, and by the establishment of direct contacts between the plastid envelope and other organelles such as the endoplasmic reticulum, mitochondria, peroxisomes, plasma membrane, and the nucleus. These interactions are highly dynamic and respond to different biotic and abiotic stresses. However, the mechanisms involved in the formation of plastid-organelle contact sites and their functions are still far from being understood. In this chapter, we summarize our current knowledge about plastid contact sites and their role in the regulation of plastid biogenesis and function.


Assuntos
Retículo Endoplasmático , Plastídeos , Plastídeos/metabolismo , Retículo Endoplasmático/metabolismo , Mitocôndrias/metabolismo , Membrana Celular/metabolismo , Peroxissomos/metabolismo
8.
Methods Mol Biol ; 2776: 177-183, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502504

RESUMO

Phaeodactylum tricornutum, a model pennate diatom, carries a secondary plastid surrounded by four membranes. Its biological function remains mysterious, supposed to combine features of the primary chloroplast and the endomembrane system. Isolation of high-quality plastid from the diatom enables a more conclusive understanding of the special structure and metabolic pathways in the plastid. Due to the direct continuity between the chloroplast endoplasmic reticulum membrane (cERM) and the outer nuclear envelope together with the integration of cERM into the cellular endoplasmic reticulum (ER) system, the plastid isolation is still challenging. In this study, highly purified P. tricornutum plastids with the four-layered membrane are obtained by Percoll density gradient centrifugation. The isolated plastids are unlikely to contain any residue of nuclear and coatomer compartments, and they might contain a relatively small contamination of mitochondrion and ER debris.


Assuntos
Diatomáceas , Diatomáceas/metabolismo , Plastídeos/metabolismo , Retículo Endoplasmático/metabolismo , Cloroplastos
9.
Methods Mol Biol ; 2776: 89-106, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502499

RESUMO

Plastids are semi-autonomous organelles like mitochondria and derive from a cyanobacterial ancestor that was engulfed by a host cell. During evolution, they have recruited proteins originating from the nuclear genome, and only parts of their ancestral metabolic properties were conserved and optimized to limit functional redundancy with other cell compartments. Furthermore, large disparities in metabolic functions exist among various types of plastids, and the characterization of their various metabolic properties is far from being accomplished. In this review, we provide an overview of the main functions, known to be achieved by plastids or shared by plastids and other compartments of the cell. In short, plastids appear at the heart of all main plant functions.


Assuntos
Mitocôndrias , Plastídeos , Plastídeos/metabolismo , Mitocôndrias/genética
10.
Methods Mol Biol ; 2776: 197-204, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502506

RESUMO

Apicomplexan parasites are unicellular eukaryotes responsible for major human diseases such as malaria and toxoplasmosis, which cause massive social and economic burden. Toxoplasmosis, caused by Toxoplasma gondii, is a global chronic infectious disease affecting ~1/3 of the world population and is a major threat for any immunocompromised patient. To date, there is no efficient vaccine against these parasites and existing treatments are threatened by rapid emergence of parasite resistance. Throughout their life cycle, Apicomplexa require large amount of nutrients, especially lipids for propagation and survival. Understanding lipid acquisition is key to decipher host-parasite metabolic interactions. Parasite membrane biogenesis relies on a combination of (a) host lipid scavenging, (b) de novo lipid synthesis in the parasite, and (c) fluxes of lipids between host and parasite and within. We recently uncovered that parasite need to store the host-scavenged lipids to avoid their toxic accumulation and to mobilize them for division. How can parasites orchestrate the many lipids fluxes essential for survival? Here, we developed metabolomics approaches coupled to stable isotope labelling to track, monitor, and quantify fatty acid and lipids fluxes between the parasite, its human host cell, and its extracellular environment to unravel the complex lipid fluxes in any physiological environment the parasite could meet.


Assuntos
Parasitos , Toxoplasma , Toxoplasmose , Animais , Humanos , Parasitos/metabolismo , Plastídeos/metabolismo , Ácidos Graxos/metabolismo , Toxoplasma/metabolismo , Toxoplasmose/metabolismo , Proteínas de Protozoários/metabolismo
11.
Methods Mol Biol ; 2776: 185-196, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502505

RESUMO

Diatoms such as Phaeodactylum tricornutum arose through a process termed secondary endosymbiosis, in which red alga-derived plastids are surrounded by a complicated membrane system. Subcellular marker proteins provide defined localizations on the compartmental and even sub-compartmental levels in the complex plastids of diatoms. Here we introduce how to use subcellular marker proteins and in vivo co-localization in the diatom P. tricornutum by presenting a step-by-step method allowing the determination of subcellular localization of proteins in different membranes of the secondary plastid. This chapter describes the materials required and the procedures of transformation and microscopic observation.


Assuntos
Diatomáceas , Diatomáceas/metabolismo , Proteínas/metabolismo , Membranas , Simbiose , Plastídeos/metabolismo
12.
Methods Mol Biol ; 2776: 161-176, 2024.
Artigo em Inglês | MEDLINE | ID: mdl-38502503

RESUMO

Plastids are organelles playing fundamental roles in different cellular processes such as energy metabolism or lipid biosynthesis. To fulfill their biogenesis and their function in the cell, plastids have to communicate with other cellular compartments. This communication can be mediated by the establishment of direct contact sites between plastids envelop and other organelles. These contacts are dynamic structures regulated in response to stress. For example, during phosphate (Pi) starvation, the number of contact sites between plastids and mitochondria significantly increases. In this situation, these contacts play an important role in the transfer of galactoglycerolipids from plastids to mitochondria. Recently, Pi starvation stress was used to identify key proteins involved in the traffic of galactoglycerolipids from plastids to mitochondria in Arabidopsis thaliana. A mitochondrial lipoprotein complex called MTL (Mitochondrial Transmembrane Lipoprotein) was identified. This complex contains mitochondrial proteins but also proteins located in the plastid envelope, suggesting its presence at the plastid-mitochondria junction. This chapter describes the protocol to isolate the MTL complex by clear-native polyacrylamide gel electrophoresis (CN-PAGE) from the mitochondrial fraction of Arabidopsis cell cultures and the methods to study different features of this complex.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Arabidopsis/metabolismo , Plastídeos/metabolismo , Proteínas de Arabidopsis/metabolismo , Lipoproteínas/metabolismo
14.
BMC Plant Biol ; 24(1): 106, 2024 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-38342898

RESUMO

BACKGROUND: The genus Libanotis Haller ex Zinn, nom. cons., a contentious member of Apiaceae, encompasses numerous economically and medicinally significant plants, comprising approximately 30 species distributed across Eurasia. Despite many previous taxonomic insights into it, phylogenetic studies of the genus are still lacking. And the establishment of a robust phylogenetic framework remains elusive, impeding advancements and revisions in the taxonomic system for this genus. Plastomes with greater variability in their genetic characteristics hold promise for building a more robust Libanotis phylogeny. RESULTS: During our research, we sequenced, assembled, and annotated complete plastomes for twelve Libanotis species belong to three sections and two closely related taxa. We conducted a comprehensive comparative analysis through totally thirteen Libanotis plastomes for the genus, including an additional plastome that had been published. Our results suggested that Libanotis plastome was highly conserved between different subclades, while the coding regions were more conserved than the non-coding regions, and the IR regions were more conserved than the single copy regions. Nevertheless, eight mutation hotspot regions were identified among plastomes, which can be considered as candidate DNA barcodes for accurate species identification in Libanotis. The phylogenetic analyses generated a robustly framework for Libanotis and revealed that Libanotis was not a monophyletic group and their all three sections were polygenetic. Libanotis schrenkiana was sister to L. sibirica, type species of this genus, but the remainders scattered within Selineae. CONCLUSION: The plastomes of Libanotis exhibited a high degree of conservation and was effective in enhancing the support and resolution of phylogenetic analyses within this genus. Based on evidence from both phylogeny and morphology, we propose the recognition of "Libanotis sensu stricto" and provide taxonomic recommendations for other taxa that previously belonged to Libanotis. In conclusion, our study not only revealed the phylogenetic position and plastid evolution of Libanotis, but also provided new insights into the phylogeny of the family Apiaceae and phylogenetic relationships within the tribe Selineae.


Assuntos
Apiaceae , Filogenia , Evolução Molecular , Plastídeos/genética , Plantas
15.
BMC Plant Biol ; 24(1): 111, 2024 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-38360561

RESUMO

BACKGROUND: The ephemeral flora of northern Xinjiang, China, plays an important role in the desert ecosystems. However, the evolutionary history of this flora remains unclear. To gain new insights into its origin and evolutionary dynamics, we comprehensively sampled ephemeral plants of Brassicaceae, one of the essential plant groups of the ephemeral flora. RESULTS: We reconstructed a phylogenetic tree using plastid genomes and estimated their divergence times. Our results indicate that ephemeral species began to colonize the arid areas in north Xinjiang during the Early Miocene and there was a greater dispersal of ephemeral species from the surrounding areas into the ephemeral community of north Xinjiang during the Middle and Late Miocene, in contrast to the Early Miocene or Pliocene periods. CONCLUSIONS: Our findings, together with previous studies, suggest that the ephemeral flora originated in the Early Miocene, and species assembly became rapid from the Middle Miocene onwards, possibly attributable to global climate changes and regional geological events.


Assuntos
Brassicaceae , Ecossistema , Filogenia , Brassicaceae/genética , China , Plastídeos/genética
16.
Int J Mol Sci ; 25(3)2024 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-38338856

RESUMO

Epipogium roseum, commonly known as one of the ghost orchids due to its rarity and almost transparent color, is a non-photosynthetic and fully mycoheterotrophic plant. Given its special nutritional strategies and evolutionary significance, the mitogenome was first characterized, and three plastomes sampled from Asia were assembled. The plastomes were found to be the smallest among Orchidaceae, with lengths ranging from 18,339 to 19,047 bp, and exhibited high sequence variety. For the mitogenome, a total of 414,552 bp in length, comprising 26 circular chromosomes, were identified. A total of 54 genes, including 38 protein-coding genes, 13 tRNA genes, and 3 rRNA genes, were annotated. Multiple repeat sequences spanning a length of 203,423 bp (45.47%) were discovered. Intriguingly, six plastid regions via intracellular gene transfer and four plastid regions via horizontal gene transfer to the mitogenome were observed. The phylogenomics, incorporating 90 plastomes and 56 mitogenomes, consistently revealed the sister relationship of Epipogium and Gastrodia, with a bootstrap percentage of 100%. These findings shed light on the organelle evolution of Orchidaceae and non-photosynthetic plants.


Assuntos
Genomas de Plastídeos , Orchidaceae , Filogenia , Plastídeos , Orchidaceae/genética , Ásia , Evolução Molecular
17.
Int J Mol Sci ; 25(3)2024 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-38338865

RESUMO

Plastid-encoded RNA polymerase (PEP) forms a multisubunit complex in operating chloroplasts, where PEP subunits and a sigma factor are tightly associated with 12 additional nuclear-encoded proteins. Mutants with disrupted genes encoding PEP-associated proteins (PAPs) provide unique tools for deciphering mutual relationships among phytohormones. A block of chloroplast biogenesis in Arabidopsis pap mutants specifying highly altered metabolism in white tissues induced dramatic fluctuations in the content of major phytohormones and their metabolic genes, whereas hormone signaling circuits mostly remained functional. Reprogramming of the expression of biosynthetic and metabolic genes contributed to a greatly increased content of salicylic acid (SA) and a concomitant decrease in 1-aminocyclopropane-1-carboxylic acid (ACC) and oxophytodienoic acid (OPDA), precursors of ethylene and jasmonic acid, respectively, in parallel to reduced levels of abscisic acid (ABA). The lack of differences in the free levels of indole-3-acetic acid (IAA) between the pap mutants and wild-type plants was accompanied by fluctuations in the contents of IAA precursors and conjugated forms as well as multilayered changes in the expression of IAA metabolic genes. Along with cytokinin (CK) overproduction, all of these compensatory changes aim to balance plant growth and defense systems to ensure viability under highly modulated conditions.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Reguladores de Crescimento de Plantas/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cloroplastos/metabolismo , Plastídeos/genética , Regulação da Expressão Gênica de Plantas
18.
Proc Natl Acad Sci U S A ; 121(10): e2318542121, 2024 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-38408230

RESUMO

Pyrenoids are microcompartments that are universally found in the photosynthetic plastids of various eukaryotic algae. They contain ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and play a pivotal role in facilitating CO2 assimilation via CO2-concentrating mechanisms (CCMs). Recent investigations involving model algae have revealed that pyrenoid-associated proteins participate in pyrenoid biogenesis and CCMs. However, these organisms represent only a small part of algal lineages, which limits our comprehensive understanding of the diversity and evolution of pyrenoid-based CCMs. Here we report a pyrenoid proteome of the chlorarachniophyte alga Amorphochlora amoebiformis, which possesses complex plastids acquired through secondary endosymbiosis with green algae. Proteomic analysis using mass spectrometry resulted in the identification of 154 potential pyrenoid components. Subsequent localization experiments demonstrated the specific targeting of eight proteins to pyrenoids. These included a putative Rubisco-binding linker, carbonic anhydrase, membrane transporter, and uncharacterized GTPase proteins. Notably, most of these proteins were unique to this algal lineage. We suggest a plausible scenario in which pyrenoids in chlorarachniophytes have evolved independently, as their components are not inherited from green algal pyrenoids.


Assuntos
Dióxido de Carbono , Clorófitas , Dióxido de Carbono/metabolismo , Ribulose-Bifosfato Carboxilase/genética , Ribulose-Bifosfato Carboxilase/metabolismo , Proteômica , Plastídeos/metabolismo , Fotossíntese/genética , Clorófitas/genética , Clorófitas/metabolismo , Plantas/metabolismo
19.
Nat Commun ; 15(1): 287, 2024 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-38177155

RESUMO

The Plastid Terminal Oxidase (PTOX) is a chloroplast localized plastoquinone oxygen oxidoreductase suggested to have the potential to act as a photoprotective safety valve for photosynthesis. However, PTOX overexpression in plants has been unsuccessful at inducing photoprotection, and the factors that control its activity remain elusive. Here, we show that significant PTOX activity is induced in response to high light in the model species Eutrema salsugineum and Arabidopsis thaliana. This activation correlates with structural reorganization of the thylakoid membrane. Over-expression of PTOX in mutants of Arabidopsis thaliana perturbed in thylakoid stacking also results in such activity, in contrast to wild type plants with normal granal structure. Further, PTOX activation protects against photoinhibition of Photosystem II and reduces reactive oxygen production under stress conditions. We conclude that structural re-arrangements of the thylakoid membranes, bringing Photosystem II and PTOX into proximity, are both required and sufficient for PTOX to act as a Photosystem II sink and play a role in photoprotection.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Oxirredutases , Arabidopsis/genética , Arabidopsis/metabolismo , Transporte de Elétrons/fisiologia , Oxirredutases/genética , Oxirredutases/metabolismo , Oxigênio , Complexo de Proteína do Fotossistema II/genética , Plantas/metabolismo , Plastídeos/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo
20.
Mol Biol Evol ; 41(2)2024 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-38271287

RESUMO

DNA polymerases synthesize DNA from deoxyribonucleotides in a semiconservative manner and serve as the core of DNA replication and repair machinery. In eukaryotic cells, there are 2 genome-containing organelles, mitochondria, and plastids, which were derived from an alphaproteobacterium and a cyanobacterium, respectively. Except for rare cases of genome-lacking mitochondria and plastids, both organelles must be served by nucleus-encoded DNA polymerases that localize and work in them to maintain their genomes. The evolution of organellar DNA polymerases has yet to be fully understood because of 2 unsettled issues. First, the diversity of organellar DNA polymerases has not been elucidated in the full spectrum of eukaryotes. Second, it is unclear when the DNA polymerases that were used originally in the endosymbiotic bacteria giving rise to mitochondria and plastids were discarded, as the organellar DNA polymerases known to date show no phylogenetic affinity to those of the extant alphaproteobacteria or cyanobacteria. In this study, we identified from diverse eukaryotes 134 family A DNA polymerase sequences, which were classified into 10 novel types, and explored their evolutionary origins. The subcellular localizations of selected DNA polymerases were further examined experimentally. The results presented here suggest that the diversity of organellar DNA polymerases has been shaped by multiple transfers of the PolI gene from phylogenetically broad bacteria, and their occurrence in eukaryotes was additionally impacted by secondary plastid endosymbioses. Finally, we propose that the last eukaryotic common ancestor may have possessed 2 mitochondrial DNA polymerases, POP, and a candidate of the direct descendant of the proto-mitochondrial DNA polymerase I, rdxPolA, identified in this study.


Assuntos
Cianobactérias , Organelas , Organelas/genética , Filogenia , DNA Polimerase Dirigida por DNA/genética , Plastídeos/genética , Mitocôndrias , Cianobactérias/genética , Simbiose
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