Another acquisition of a primary photosynthetic organelle is underway in Paulinella chromatophora.
Nakayama T, Ishida K
Current Biology (2009)
Category: chloroplast, endosymbionts, eukaryotes, evolution, HGT ¤ Added: Apr 14, 2009 ¤ Rating: ◊◊
The birth of plastids brought photosynthesis to eukaryotes and had a huge impact on their evolution. Despite its importance, details of the plastid acquisition process through primary endosymbiosis are not well understood. Recently, a cercozoan testate amoeba, Paulinella chromatophora, has received considerable attention because it may be able to provide insights into the transition from a cyanobacterial endosymbiont to a photosynthetic organelle [1–3]. The P. chromatophora cell contains two chromatophores that look like cylindrical cyanobacteria [4,5], and it has been debated whether these chromatophores are endosymbiotic cyanobacteria or photosynthetic organelles [4–7]. The chromatophore genome of P. chromatophora strain M0880/a was recently sequenced, revealing that its size (~1 Mbp) has been reduced and that it lacks several genes important to cyanobacteria, including a few photosynthetic genes [3]. Here, we obtained concrete evidence that psaE, one of the photosynthetic genes, is expressed from the nuclear genome of P. chromatophora. This indicates that the psaE gene has been transferred into the nuclear genome from the chromatophore. Thus, another primary endosymbiotic acquisition of a photosynthetic organelle is under way.