title: Diversification of DnaA dependency for DNA replication in cyanobacterial evolution.
abstract: Regulating DNA replication is essential for all living cells. The DNA replication initiation factor DnaA is highly conserved in prokaryotes and is required for accurate initiation of chromosomal replication at oriC. DnaA-independent free-living bacteria have not been identified. The dnaA gene is absent in plastids and some symbiotic bacteria, although it is not known when or how DnaA-independent mechanisms were acquired. Here, we show that the degree of dependency of DNA replication on DnaA varies among cyanobacterial species. Deletion of the dnaA gene in Synechococcus elongatus PCC 7942 shifted DNA replication from oriC to a different site as a result of the integration of an episomal plasmid. Moreover, viability during the stationary phase was higher in dnaA disruptants than in wild-type cells. Deletion of dnaA did not affect DNA replication or cell growth in Synechocystis sp. PCC 6803 or Anabaena sp. PCC 7120, indicating that functional dependency on DnaA was already lost in some nonsymbiotic cyanobacterial lineages during diversification. Therefore, we proposed that cyanobacteria acquired DnaA-independent replication mechanisms before symbiosis and such an ancestral cyanobacterium was the sole primary endosymbiont to form a plastid precursor.
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.|Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Tokyo, Japan.
authors.forename: Ryudo
authors.initials: R
authors.lastname: Ohbayashi
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Watanabe
authors.affiliation: Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Ehira
authors.affiliation: Genome Research Center, Tokyo University of Agriculture, Tokyo, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Kanesaki
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Chibazakura
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.|Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Tokyo, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshikawa
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D005075:Biological Evolution; D000458:Cyanobacteria / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005618:Fresh Water / Q000382:microbiology*; D046940:Synechococcus / Q000235:genetics / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria