Has the endosymbiont hypothesis been proven?

Gray, Michael W.; Doolittle, W. Ford

doi:10.1128/mmbr.46.1.1-42.1982

Cited by 327 publications

(88 citation statements)

References 280 publications

(459 reference statements)

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“…prowazekii, whose entire genome has been sequenced [103]. species belonging to a group (K-proteobacteria) that contained the insert [14,15,17,84,116^120].…”

Section: Succinyl-coa Synthetasementioning

confidence: 99%

“…In eukaryotic cells, a single gene is known to encode both mitochondrial and cytosolic valyl-tRNA synthetases [142,143]. Since the origin of mitochondria from an Kproteobacterium is supported by a large body of evidence [14,16,17,116,117,119,120,144,145], it is likely that this in- sert will be eventually found in some species belonging to the K-proteobacterial subdivision.…”

Section: Valyl-trna Synthetasementioning

confidence: 99%

“…The origin of mitochondria from a bacterial endosymbiont related to the K-proteobacterial subdivision is now widely accepted [14,16,17,116,117,119,120]. There is increasing evidence that the eukaryotic nuclear cytosolic homologs of many genes are also of proteobacterial origin and that the ancestral eukaryotic cell itself may have originated by the symbiotic association and ultimate fusion of an archaebacterium and a proteobacterium [30,122,128,172^181].…”

Section: Proteobacteria: Relationships To the Eukaryotic Homologsmentioning

confidence: 99%

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The phylogeny of proteobacteria: relationships to other eubacterial phyla and eukaryotes

Gupta

2000

FEMS Microbiology Reviews

104

161

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The evolutionary relationships of proteobacteria, which comprise the largest and phenotypically most diverse division among prokaryotes, are examined based on the analyses of available molecular sequence data. Sequence alignments of different proteins have led to the identification of numerous conserved inserts and deletions (referred to as signature sequences), which either are unique characteristics of various proteobacterial species or are shared by only members from certain subdivisions of proteobacteria. These signature sequences provide molecular means to define the proteobacterial phyla and their various subdivisions and to understand their evolutionary relationships to the other groups of eubacteria as well as the eukaryotes. Based on signature sequences that are present in different proteins it is now possible to infer that the various eubacterial phyla evolved from a common ancestor in the following order: low-G+C Gram-positive-->high-G+C Gram-positive-->Deinococcus-Thermus (green nonsulfur bacteria)-->cyanobacteria-->Spirochetes-->Chlamydia-Cytophaga-Aquifex -green sulfur bacteria-->Proteobacteria-1 (epsilon and delta)-->Proteobacteria-2 (alpha)-->Proteobacteria-3 (beta)-->Proteobacteria-4 (gamma). An unexpected but important aspect of the relationship deduced here is that the main eubacterial phyla are related to each other linearly rather than in a tree-like manner, suggesting that the major evolutionary changes within Bacteria have taken place in a directional manner. The identified signatures permit placement of prokaryotes into different groups/divisions and could be used for determinative purposes. These signatures generally support the origin of mitochondria from an alpha-proteobacterium and provide evidence that the nuclear cytosolic homologs of many genes are also derived from proteobacteria.

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“…prowazekii, whose entire genome has been sequenced [103]. species belonging to a group (K-proteobacteria) that contained the insert [14,15,17,84,116^120].…”

Section: Succinyl-coa Synthetasementioning

confidence: 99%

Section: Valyl-trna Synthetasementioning

confidence: 99%

Section: Proteobacteria: Relationships To the Eukaryotic Homologsmentioning

confidence: 99%

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The phylogeny of proteobacteria: relationships to other eubacterial phyla and eukaryotes

Gupta

2000

FEMS Microbiology Reviews

104

161

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“…Thus, cyanobacteria appear to be a suitable system for analysing the active mechanisms developed in response to changing environmental conditions. The fact that cyanobacteria are considered to be phylogenetically related to chloroplasts (Gray & Doolittle 1982), and the close similarity of their physiology and metabolism to those of plants, make cyanobacteria good model systems for analysis of plant responses to environmental stresses.…”

Section: Introductionmentioning

confidence: 99%

Calcium transients in response to salinity and osmotic stress in the nitrogen‐fixing cyanobacterium Anabaena sp. PCC7120, expressing cytosolic apoaequorin

Torrecilla

Leganés

Bonilla

et al. 2001

Plant Cell & Environment

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We show here that both salinity and osmotic stress trigger transient increases in intracellular free Ca2+ concentration ([Ca2+]i) in cells of the nitrogen‐fixing filamentous cyanobacterium Anabaena sp. PCC7120, which constitutively expresses apoaequorin. Isoosmolar concentrations of salt (NaCl) and osmoticum (sucrose) induced calcium transients of similar magnitude and shape, suggesting that cells sense, via Ca2+ signalling, mostly osmotic stress. The Ca2+ transients induced by NaCl and sucrose were completely blocked by the calcium chelator ethylene glycol‐bis(b‐aminoethylether)N,N,N¢,N¢‐tetraacetic acid (EGTA) and were partially inhibited by the calcium channel blocker verapamil. Increased external Ca2+ and the Ca2+ ionophore calcimycin (compound A23187) enhanced Ca2+ influx further, suggesting the involvement of extracellular Ca2+ in the observed response to salinity and osmotic stress. However, the plant hormone abscisic acid (ABA) did not provoke any effect on the Ca2+ transients induced by both stresses, indicating that it may not be acting upstream of Ca2+ in the signalling of salinity and/or osmotic stress in Anabaena sp. PCC7120.

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“…-G. C. Williams, Natural Selection In this century, biologists' perspectives on the endosymbiont theory of the origin of the mitochondrion have changed dramatically. Once characterized as "too fantastic for present mention in polite biological society," this theory is now generally accepted, largely because of extensive compilations of supporting evidence (e.g., Margulis 1970Margulis , 1981Schwartz 785 and Dayhoff 1978;Baltscheffsky and Baltscheffsky 1981;Gray and Doolittle 1982;McCarroll et al 1983;Spenser et al 1984;Cavalier-Smith 1987a; Ballantyne and Chamberlin 1988;Gray 1992;Knoll 1992). Corresponding to such broad acceptance, a shift of emphasis is also occurring; presently, the focus is on questions of not merely whether mitochondria arose from endosymbionts, but how, and by what evolutionary mechanisms.…”

mentioning

confidence: 99%

Perspective a Units‐of‐evolution Perspective on the Endosymbiont Theory of the Origin of the Mitochondrion

Blackstone

1995

Evolution

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Discussions of mitochondria and their hosts often conceptualize this relationship in a more or less modern form, focusing on the metabolic benefits of mitochondria to the host cell or on the possibility of intragenomic conflict. A more inclusive units-of-evolution perspective recognizes that both costs and benefits must be viewed from the level of the cells that initiated this interaction, the protomitochondrion and the primitive host cell. From this perspective, ecological and physiological considerations become central to the characterization of initial and subsequent host-mitochondria associations. Foremost among these considerations is the generation of superoxide radicals by modern mitochondria and the deleterious effects of these endogenous oxidants on modern eukaryotic cells. Because of their photosynthetic and aerobic ecologies, protomitochondria likely were relatively tolerant of such oxidants; anaerobic, heterotrophic, primitive host cells, on the other hand, likely were not. In the initial association of host and symbiont, the latter may have manipulated the former's life history by means of both endogenous oxidants and a superabundance of ATP. A resolution of this units-of-evolution conflict was necessary to continue this association, and this resolution, in a ritualized form, may have shaped the evolution of many features of modern eukaryotic cells and mitochondria, for example, the messenger functions of calcium ions, the regulatory role of phosphorylation cascades in cell-division cycles, the absence from the mitochondrial genome of replication factors, transcription factors, and adenine nucleotide carrier genes. The initial host-mitochondria interaction may have further channeled the evolution of multicellular eukaryotes, particularly animals, resulting in the association of mitochondria and the germinal plasm and in the use of extracellular ATP and endogenous oxidants as developmental signals. Evolutionary explanations for "free-radical" theories of development and aging are thus suggested.

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Has the endosymbiont hypothesis been proven?

Abstract: NATURE OF THE ENDOSYMBIONT HYPOTHESIS AND ITS ALTERNATIVE Nearly all eucaryotic cells harbor two physically and functionally distinct genomes-those of the nucleus and the mitochondrion (298, 300, 465). Photosynthetic eucaryotes harbor a thirdthat of the plastid.

Cited by 327 publications

References 280 publications

The phylogeny of proteobacteria: relationships to other eubacterial phyla and eukaryotes

The phylogeny of proteobacteria: relationships to other eubacterial phyla and eukaryotes

Calcium transients in response to salinity and osmotic stress in the nitrogen‐fixing cyanobacterium Anabaena sp. PCC7120, expressing cytosolic apoaequorin

Perspective a Units‐of‐evolution Perspective on the Endosymbiont Theory of the Origin of the Mitochondrion

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