Toward an understanding of the function of Chlamydiales in plastid endosymbiosis

Plastid endosymbiosis defines a process through which a fully evolved cyanobacterial ancestor has transmitted to a eukaryotic phagotroph the hundreds of genes required to perform oxygenic photosynthesis, together with the membrane structures, and cellular compartment associated with this process. In this review, we will summarize the evidence pointing to an active role of Chlamydiales in metabolic integration of free living cyanobacteria, within the cytosol of the last common plant ancestor.