Figure 4

Scenarios to explain the simultaneous presence of cyanobacterial and chlamydial protein homologues in photosynthetic eukaryotes. (A) Multiple HGTs of chlamydial genes from a single donor into different photosynthetic eukaryotes. (B) Single or multiple HGTs of chlamydial genes into the cyanobacterial ancestor of plastids and group-specific gene losses from different photosynthetic eukaryotes. (C) HGT or EGT from intracellular chlamydiae to the cyanobacterial endosymbiont of a photosynthetic eukaryote and group-specific chlamydial gene losses from different photosynthetic eukaryotes. In a variation of this scenario the intracellular chlamydiae donate genes by EGT or HGT to the eukaryotic host little before or at the time of cyanobacterial endosymbiosis and group-specific multiple gene losses of chlamydial genes. (D) Origin of chlamydial proteins in heterokont algae. Two secondary endosymbioses are shown involving sequentially a viridiplant and a rhodoplant symbiont. The endosymbiosis of a cyanobacterium has been omitted from Figure 4D for clarity.