The evolution of photosynthesis is complex, but not intractable. Views on the origin of photosynthesis can be summarized like this:
Photosynthesis evolved in a well-defined clade of bacteria and then it was scattered through the bacterial tree of life via horizontal gene transfer.
I have come to the conclusion based on the phylogenies of reaction centers, chlorophyll synthesis, and bacteria, that photosynthesis originated close to the origin of bacteria or even before the last common ancestor to bacteria (Cardona, 2014).
A recent paper has shown that two strains of non-phototrophic bacteria of the genus Rubrobacter (phylum: Actinobacteria) contain proteins closely related to those in the chlorophyll-synthesis pathway (Gupta and Khadka, 2015). In addition, the authors show that the origin of these genes is very ancient and provide some evidence to argue that they were not obtained via horizontal gene transfer. They suggest that the Actinobacteria might have been originally phototrophic.
If we reexamine the tree of life and highlight the phototrophic clades (see Figure 1), we see that Cyanobacteria, Chloroflexi, and Actinobacteria likely shared a common ancestor. This relationship is well supported by phylogenomics from the past decade. I believe this ancestor was phototrophic.
Photosynthesis evolved in a well-defined clade of bacteria and then it was scattered through the bacterial tree of life via horizontal gene transfer.
I have come to the conclusion based on the phylogenies of reaction centers, chlorophyll synthesis, and bacteria, that photosynthesis originated close to the origin of bacteria or even before the last common ancestor to bacteria (Cardona, 2014).
A recent paper has shown that two strains of non-phototrophic bacteria of the genus Rubrobacter (phylum: Actinobacteria) contain proteins closely related to those in the chlorophyll-synthesis pathway (Gupta and Khadka, 2015). In addition, the authors show that the origin of these genes is very ancient and provide some evidence to argue that they were not obtained via horizontal gene transfer. They suggest that the Actinobacteria might have been originally phototrophic.
If we reexamine the tree of life and highlight the phototrophic clades (see Figure 1), we see that Cyanobacteria, Chloroflexi, and Actinobacteria likely shared a common ancestor. This relationship is well supported by phylogenomics from the past decade. I believe this ancestor was phototrophic.
 |
| Figure 1. Tree of life highlighting phototrophic clades. The tree is taken from Segata et al., 2013, it's open access and freely available. |
In these phylogenetic trees the phylum Firmicutes always branches before the divergence of the Cyanobacteria-Chloroflexi-Actinobacteria supergroup, see Cardona (2014) and references within. This implies that the origin of phototrophy must have predated the divergence of the Firmicutes and the Cyno-Chloro-Actino supergroup, immediately placing the origin of phototrophy very close to the root of bacteria.
No comments:
Post a Comment