The Single Primary Endosymbiotic Event
Eukaryotic phototrophs arose between about 1,600 and 1,200 Mya through the incorporation of a cyanobacterium by a phagotrophic eukaryote. In a very special and complex process, the cyanobacterium and the heterotrophic cell complemented each other that wel
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Abstract Eukaryotic phototrophs arose between about 1,600 and 1,200 Mya through the incorporation of a cyanobacterium by a phagotrophic eukaryote. In a very special and complex process, the cyanobacterium and the heterotrophic cell complemented each other that well to change the predator–prey relationship to a mutualistic one: the cyanobacterium was converted into an obligate endosymbiont allowing phototrophy of the host cell and ultimately into an organelle, the plastid. Pros and cons of a scenario assuming a single primary endosymbiotic event leading to a protoalga ancestral to the kingdom “Plantae” are discussed. Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Endosymbiotic Gene Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insights from Completely Sequenced Plastid Genomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outcome of Phylogenetic Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insights from Comparing the Protein Import Machineries of Plastids . . . . . . . . . . . . . . . . . . . . . . . . . The Cyanobacterial Ancestor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Alternative Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....................................................................................................
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Introduction The striking similarity of cyanobacteria (then called blue-green algae) and plant chloroplasts with respect to morphology, pigmentation, and photosynthetic performance led Konstantin Mereschkowsky more than 100 years ago to propose W. Lo¨ffelhardt (*) Department of Biochemistry and Cell Biology, University of Vienna, Dr. Bohrgasse 9, 1030 Vienna, Austria e-mail: [email protected] W. Lo¨ffelhardt (ed.), Endosymbiosis, DOI 10.1007/978-3-7091-1303-5_3, © Springer-Verlag Wien 2014
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“symbiogenesis” as an evolutionary link between organism and organelle (Mereschkowsky 1905). Later, a similar hypothesis was also formulated for the origin of mitochondria from endosymbiotic aerobic bacteria (Wallin 1925). Both concepts met only limited success and were nearly forgotten (Hagemann 2007) when at the beginning of the 1960s, organelle DNA was found in chloroplasts (Ris and Plaut 1962) and then also in mitochondria. This prompted Lynn Margulis–Sagan to fight for a rev
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