The cellular machineries responsible for the division of endosymbiotic organelles
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Chloroplasts (plastids) and mitochondria evolved from endosymbiotic bacteria. These organelles perform vital functions in photosynthetic eukaryotes, such as harvesting and converting energy for use in biological processes. Consistent with their evolutionary origins, plastids and mitochondria proliferate by the binary fission of pre-existing organelles. Here, I review the structures and functions of the supramolecular machineries driving plastid and mitochondrial division, which were discovered and first studied in the primitive red alga Cyanidioschyzon merolae. In the past decade, intact division machineries have been isolated from plastids and mitochondria and examined to investigate their underlying structure and molecular mechanisms. A series of studies has elucidated how these division machineries assemble and transform during the fission of these organelles, and which of the component proteins generate the motive force for their contraction. Plastid- and mitochondrial-division machineries have important similarities in their structures and mechanisms despite sharing no component proteins, implying that these division machineries evolved in parallel. The establishment of these division machineries might have enabled the host eukaryotic ancestor to permanently retain these endosymbiotic organelles by regulating their binary fission and the equal distribution of resources to daughter cells. These findings provide key insights into the establishment of endosymbiotic organelles and have opened new avenues of research into their evolution and mechanisms of proliferation.
KeywordsChloroplast division Mitochondrial division Endosymbiotic organelle PDR1 MDR1
I gratefully acknowledge the contributions of past members of Kuroiwa laboratory (Rikkyo University) and the Kawano laboratory (The University of Tokyo) to the plastid and mitochondrial division machinery projects, and the efforts of past members of Osteryoung laboratory (Michigan State University) in the reconstituted FtsZ ring project. I am also grateful to the members of the selection committee for Botanical Society of Japan’s Encouragement Prize 2017 for their careful consideration. This work was supported by a Human Frontier Science Program Career Development Award (No. CDA00049/2018-C) and a Japan Society for the Promotion of Science KAKENHI Grant No. JP18K06325.
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