echo and a new taxonomic division was created (the
Prochlorophyta) (Lewin 1975; Lewin and Withers 1975;
Lewin 1976).
But this division proved later to be wrong. Molecular
phylogenies indeed showed that Prochlorophyta are a polyphyletic assemblage in which similarities are due to horizontal gene transfers (HGTs) and that they are not the
direct ancestors of the chloroplasts of Viridiplantae (Turner
et al. 1999; Chen et al. 2005). In the first approximation, all
chloroplasts of eukaryotes therefore have a unique origin,
and the founder event would have occurred in the ancestor
of Archaeplastida. The possibility that several founding
events have occurred however was mentioned for atypical
cases (Stiller et al. 2003; Bodyl 2005; Nakayama and
Ishida 2005; Burki et al. 2012). Apart from these cases,
the uniqueness of the founding event of the chloroplast is
now widely accepted.
The endosymbiotic origin of the mitochondria has been
less debated than that of chloroplasts; the current bacterial
taxon corresponding to the ancestors of mitochondria is
indeed correctly identified: that of Alphaproteobacteria.
The debate has focused more on other energy-converting
organelles such as hydrogenosomes*, peroxisomes, and
mitosomes that, unlike mitochondria, generally do not have
DNA, although DNA was discovered in hydrogenosomes
of the ciliate Nyctotherus ovalis (Boxma et al. 2005).
Hydrogenosomes are present, for example, in ciliates
(Alveolata), in Parabasalia (Excavata), and in
Chytridiomycota (Fungi). Are these organelles having an
autogenous origin, that is to say, not endosymbiotic, by
differentiation from the endo-membranes (endoplasmic
reticulum) of the cytoplasm? Are they corresponding to
endosymbioses distinct from those that have generated
mitochondria, all the DNA being lost or transferred to the
Euglena gracilis
Trypanasoma brucei
Dictyostelium discoideum
Saccharomyces cerevisiae
Oxytricha nova
Prorocentrum micans
Zea mays
Xenopus laevis
Homo sapiens
Thermoproteus tenax
Sulfolobus solfataricus
Methanococcus vannielii
Methanobacterium formicicum
Methanospirillum hungatei
Halobacterium volcanii
Halococcus morhuae
Thermomicrobium roseum
Cyanobacteria and
chloroplasts of Zea mays
Bacillus subtilis
Mitochondria of
Zea mays
Agrobacterium tumefaciens
Escherichia coli
Pseudomonas testosteroni
EUKARYOTES
PROKARYOTES
ARCHAEA
BACTERIA
0.1
Fig. 5.9 Phylogenetic tree based on 16S-like rRNA genes.
Mitochondria and chloroplasts of maize (Zea mays) are clearly positioned within the bacteria. The branch length is proportional to evolutionary distances (except the branch between archaea and eukaryotes).
The scale bar corresponds to 0.1 per nucleotide mutation (10 %). The
topology is based on an analysis of 920 nucleotides from complete
sequences (Modified and redrawn from Woese and Olsen 1986) (The
term 16S rRNA-like is used here to indicate that the 16S RNA
(prokaryotes) and 18S RNA (eukaryotes) of the small subunits of
ribosomes have been grouped to construct the same and common tree)
0,5 μm
Fig. 5.10 The thylakoids of Prochloron seen in electron microscopy
section. Note that they are arranged in clumps. Prochloron is an
oxygenic phototrophic bacterium with chlorophylls a and b
124
C.-F. Boudouresque et al.
Prochlorophyta) (Lewin 1975; Lewin and Withers 1975;
Lewin 1976).
But this division proved later to be wrong. Molecular
phylogenies indeed showed that Prochlorophyta are a polyphyletic assemblage in which similarities are due to horizontal gene transfers (HGTs) and that they are not the
direct ancestors of the chloroplasts of Viridiplantae (Turner
et al. 1999; Chen et al. 2005). In the first approximation, all
chloroplasts of eukaryotes therefore have a unique origin,
and the founder event would have occurred in the ancestor
of Archaeplastida. The possibility that several founding
events have occurred however was mentioned for atypical
cases (Stiller et al. 2003; Bodyl 2005; Nakayama and
Ishida 2005; Burki et al. 2012). Apart from these cases,
the uniqueness of the founding event of the chloroplast is
now widely accepted.
The endosymbiotic origin of the mitochondria has been
less debated than that of chloroplasts; the current bacterial
taxon corresponding to the ancestors of mitochondria is
indeed correctly identified: that of Alphaproteobacteria.
The debate has focused more on other energy-converting
organelles such as hydrogenosomes*, peroxisomes, and
mitosomes that, unlike mitochondria, generally do not have
DNA, although DNA was discovered in hydrogenosomes
of the ciliate Nyctotherus ovalis (Boxma et al. 2005).
Hydrogenosomes are present, for example, in ciliates
(Alveolata), in Parabasalia (Excavata), and in
Chytridiomycota (Fungi). Are these organelles having an
autogenous origin, that is to say, not endosymbiotic, by
differentiation from the endo-membranes (endoplasmic
reticulum) of the cytoplasm? Are they corresponding to
endosymbioses distinct from those that have generated
mitochondria, all the DNA being lost or transferred to the
Euglena gracilis
Trypanasoma brucei
Dictyostelium discoideum
Saccharomyces cerevisiae
Oxytricha nova
Prorocentrum micans
Zea mays
Xenopus laevis
Homo sapiens
Thermoproteus tenax
Sulfolobus solfataricus
Methanococcus vannielii
Methanobacterium formicicum
Methanospirillum hungatei
Halobacterium volcanii
Halococcus morhuae
Thermomicrobium roseum
Cyanobacteria and
chloroplasts of Zea mays
Bacillus subtilis
Mitochondria of
Zea mays
Agrobacterium tumefaciens
Escherichia coli
Pseudomonas testosteroni
EUKARYOTES
PROKARYOTES
ARCHAEA
BACTERIA
0.1
Fig. 5.9 Phylogenetic tree based on 16S-like rRNA genes.
Mitochondria and chloroplasts of maize (Zea mays) are clearly positioned within the bacteria. The branch length is proportional to evolutionary distances (except the branch between archaea and eukaryotes).
The scale bar corresponds to 0.1 per nucleotide mutation (10 %). The
topology is based on an analysis of 920 nucleotides from complete
sequences (Modified and redrawn from Woese and Olsen 1986) (The
term 16S rRNA-like is used here to indicate that the 16S RNA
(prokaryotes) and 18S RNA (eukaryotes) of the small subunits of
ribosomes have been grouped to construct the same and common tree)
0,5 μm
Fig. 5.10 The thylakoids of Prochloron seen in electron microscopy
section. Note that they are arranged in clumps. Prochloron is an
oxygenic phototrophic bacterium with chlorophylls a and b
124
C.-F. Boudouresque et al.