Plastid evolution: origins, diversity, trends

The amazing diversity of extant photosynthetic eukaryotes is largely a resu lt of the presence of formerly free-living photosynthesizing organisms that have been sequestered by eukaryotic hosts and established as plastids in a process known as endosymbiosis. The evolutionary history of these endosymb iotic events was traditionally investigated by studying ultrastructural fea tures and pigment characteristics but in recent years has been approached u sing molecular sequence data and gene trees. Two important developments, mo re detailed studies of members of the Cyanobacteria (from which plastids ul timately derive) and the availability of complete plastid genome sequences from a wide variety of plant and algal lineages, have allowed a more accura te reconstruction of plastid evolution.