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Plastid establishment did not require a chlamydial partner.

Domman D, Horn M, Embley TM, Williams TA - Nat Commun (2015)

Bottom Line: One hypothesis that has achieved recent prominence suggests that the first role of the cyanobiont was in energy provision for a host cell whose reserves were being depleted by an intracellular chlamydial pathogen.A pivotal claim is that it was chlamydial proteins themselves that converted otherwise unusable cyanobacterial metabolites into host energy stores.We test this hypothesis by investigating the origins of the key enzymes using sophisticated phylogenetics.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Ecosystem Science, University of Vienna, A-1090 Vienna, Austria.

ABSTRACT
Primary plastids descend from the cyanobacterial endosymbiont of an ancient eukaryotic host, but the initial selective drivers that stabilized the association between these two cells are still unclear. One hypothesis that has achieved recent prominence suggests that the first role of the cyanobiont was in energy provision for a host cell whose reserves were being depleted by an intracellular chlamydial pathogen. A pivotal claim is that it was chlamydial proteins themselves that converted otherwise unusable cyanobacterial metabolites into host energy stores. We test this hypothesis by investigating the origins of the key enzymes using sophisticated phylogenetics. Here we show a mosaic origin for the relevant pathway combining genes with host, cyanobacterial or bacterial ancestry, but we detect no strong case for Chlamydiae to host transfer under the best-fitting models. Our conclusion is that there is no compelling evidence from gene trees that Chlamydiae played any role in establishing the primary plastid endosymbiosis.

No MeSH data available.


Related in: MedlinePlus

Single gene trees for key components of archaeplastidal carbohydrate metabolism implicated in the ménage à trois.(a–d) Phylogenies for GlgC, GlgP, GlgX and UhpC. These trees were inferred under the CAT+GTR model in PhyloBayes, which performed better in our analyses of model fit than the single-matrix models originally used to analyse these genes. With the exception of the Chlamydomonas and Ostreococcus GlgC sequences, the Archaeplastida were recovered as a monophyletic group in all of these trees, suggesting that this pathway was already present in its current form in the last common ancestor of the group. However, the closest outgroup to the Archaeplastida varies among the individual gene trees, as discussed in the main text. We rooted the tree in panel (d) between UhpC and its paralogue GlpT. In the other panels, we oriented the trees to most clearly visualize the key relationships between the archaeplastid and chlamydial sequences, and to test the predictions of the ménage à trois hypothesis. Support values are summarized as Bayesian posterior probabilities and branch lengths are proportional to the expected number of substitutions per site, as indicated by the scale bar.
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f3: Single gene trees for key components of archaeplastidal carbohydrate metabolism implicated in the ménage à trois.(a–d) Phylogenies for GlgC, GlgP, GlgX and UhpC. These trees were inferred under the CAT+GTR model in PhyloBayes, which performed better in our analyses of model fit than the single-matrix models originally used to analyse these genes. With the exception of the Chlamydomonas and Ostreococcus GlgC sequences, the Archaeplastida were recovered as a monophyletic group in all of these trees, suggesting that this pathway was already present in its current form in the last common ancestor of the group. However, the closest outgroup to the Archaeplastida varies among the individual gene trees, as discussed in the main text. We rooted the tree in panel (d) between UhpC and its paralogue GlpT. In the other panels, we oriented the trees to most clearly visualize the key relationships between the archaeplastid and chlamydial sequences, and to test the predictions of the ménage à trois hypothesis. Support values are summarized as Bayesian posterior probabilities and branch lengths are proportional to the expected number of substitutions per site, as indicated by the scale bar.

Mentions: The first step in manipulation of the heterotrophic host cell by the ancient chlamydial pathogen is suggested to be the conversion of host energy, in the form of glucose-1-phosphate, to ADP-glucose via the ADP-pyrophosphorylase GlgC. However, our phylogenetic analyses of GlgC homologues from Archaeplastida, Chlamydiaceae, Cyanobacteria and other bacterial groups recovered the archaeplastid sequences clustering with the Cyanobacteria with maximal posterior support (Posterior probability, PP=0.99 in the CAT+GTR analysis; see Fig. 3a and Supplementary Fig. 1). Within this clade, the archaeplastid sequences (with the exception of those from the green algae Chlamydomonas and Ostreococcus) emerged from within the Cyanobacteria, albeit with more modest support (PP=0.84). The simplest interpretation of these results is that glgC of modern Archaeplastida was obtained directly from the cyanobiont by endosymbiotic gene transfer31.


Plastid establishment did not require a chlamydial partner.

Domman D, Horn M, Embley TM, Williams TA - Nat Commun (2015)

Single gene trees for key components of archaeplastidal carbohydrate metabolism implicated in the ménage à trois.(a–d) Phylogenies for GlgC, GlgP, GlgX and UhpC. These trees were inferred under the CAT+GTR model in PhyloBayes, which performed better in our analyses of model fit than the single-matrix models originally used to analyse these genes. With the exception of the Chlamydomonas and Ostreococcus GlgC sequences, the Archaeplastida were recovered as a monophyletic group in all of these trees, suggesting that this pathway was already present in its current form in the last common ancestor of the group. However, the closest outgroup to the Archaeplastida varies among the individual gene trees, as discussed in the main text. We rooted the tree in panel (d) between UhpC and its paralogue GlpT. In the other panels, we oriented the trees to most clearly visualize the key relationships between the archaeplastid and chlamydial sequences, and to test the predictions of the ménage à trois hypothesis. Support values are summarized as Bayesian posterior probabilities and branch lengths are proportional to the expected number of substitutions per site, as indicated by the scale bar.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374161&req=5

f3: Single gene trees for key components of archaeplastidal carbohydrate metabolism implicated in the ménage à trois.(a–d) Phylogenies for GlgC, GlgP, GlgX and UhpC. These trees were inferred under the CAT+GTR model in PhyloBayes, which performed better in our analyses of model fit than the single-matrix models originally used to analyse these genes. With the exception of the Chlamydomonas and Ostreococcus GlgC sequences, the Archaeplastida were recovered as a monophyletic group in all of these trees, suggesting that this pathway was already present in its current form in the last common ancestor of the group. However, the closest outgroup to the Archaeplastida varies among the individual gene trees, as discussed in the main text. We rooted the tree in panel (d) between UhpC and its paralogue GlpT. In the other panels, we oriented the trees to most clearly visualize the key relationships between the archaeplastid and chlamydial sequences, and to test the predictions of the ménage à trois hypothesis. Support values are summarized as Bayesian posterior probabilities and branch lengths are proportional to the expected number of substitutions per site, as indicated by the scale bar.
Mentions: The first step in manipulation of the heterotrophic host cell by the ancient chlamydial pathogen is suggested to be the conversion of host energy, in the form of glucose-1-phosphate, to ADP-glucose via the ADP-pyrophosphorylase GlgC. However, our phylogenetic analyses of GlgC homologues from Archaeplastida, Chlamydiaceae, Cyanobacteria and other bacterial groups recovered the archaeplastid sequences clustering with the Cyanobacteria with maximal posterior support (Posterior probability, PP=0.99 in the CAT+GTR analysis; see Fig. 3a and Supplementary Fig. 1). Within this clade, the archaeplastid sequences (with the exception of those from the green algae Chlamydomonas and Ostreococcus) emerged from within the Cyanobacteria, albeit with more modest support (PP=0.84). The simplest interpretation of these results is that glgC of modern Archaeplastida was obtained directly from the cyanobiont by endosymbiotic gene transfer31.

Bottom Line: One hypothesis that has achieved recent prominence suggests that the first role of the cyanobiont was in energy provision for a host cell whose reserves were being depleted by an intracellular chlamydial pathogen.A pivotal claim is that it was chlamydial proteins themselves that converted otherwise unusable cyanobacterial metabolites into host energy stores.We test this hypothesis by investigating the origins of the key enzymes using sophisticated phylogenetics.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Ecosystem Science, University of Vienna, A-1090 Vienna, Austria.

ABSTRACT
Primary plastids descend from the cyanobacterial endosymbiont of an ancient eukaryotic host, but the initial selective drivers that stabilized the association between these two cells are still unclear. One hypothesis that has achieved recent prominence suggests that the first role of the cyanobiont was in energy provision for a host cell whose reserves were being depleted by an intracellular chlamydial pathogen. A pivotal claim is that it was chlamydial proteins themselves that converted otherwise unusable cyanobacterial metabolites into host energy stores. We test this hypothesis by investigating the origins of the key enzymes using sophisticated phylogenetics. Here we show a mosaic origin for the relevant pathway combining genes with host, cyanobacterial or bacterial ancestry, but we detect no strong case for Chlamydiae to host transfer under the best-fitting models. Our conclusion is that there is no compelling evidence from gene trees that Chlamydiae played any role in establishing the primary plastid endosymbiosis.

No MeSH data available.


Related in: MedlinePlus