title: Dynamic Interplay between Nucleoid Segregation and Genome Integrity in Chlamydomonas Chloroplasts.
abstract: The chloroplast (cp) genome is organized as nucleoids that are dispersed throughout the cp stroma. Previously, a cp homolog of bacterial recombinase RecA (cpRECA) was shown to be involved in the maintenance of cp genome integrity by repairing damaged chloroplast DNA and by suppressing aberrant recombination between short dispersed repeats in the moss Physcomitrella patens Here, overexpression and knockdown analysis of cpRECA in the green alga Chlamydomonas reinhardtii revealed that cpRECA was involved in cp nucleoid dynamics as well as having a role in maintaining cp genome integrity. Overexpression of cpRECA tagged with yellow fluorescent protein or hemagglutinin resulted in the formation of giant filamentous structures that colocalized exclusively to chloroplast DNA and cpRECA localized to cp nucleoids in a heterogenous manner. Knockdown of cpRECA led to a significant reduction in cp nucleoid number that was accompanied by nucleoid enlargement. This phenotype resembled those of gyrase inhibitor-treated cells and monokaryotic chloroplast mutant cells and suggested that cpRECA was involved in organizing cp nucleoid dynamics. The cp genome also was destabilized by induced recombination between short dispersed repeats in cpRECA-knockdown cells and gyrase inhibitor-treated cells. Taken together, these results suggest that cpRECA and gyrase are both involved in nucleoid dynamics and the maintenance of genome integrity and that the mechanisms underlying these processes may be intimately related in C. reinhardtii cps.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (M.O., Y.K., T.S., Y.N.); and.|Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo 171-8501, Japan (M.O.).
authors.forename: Masaki
authors.initials: M
authors.lastname: Odahara
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (M.O., Y.K., T.S., Y.N.); and.|Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo 171-8501, Japan (M.O.).
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (M.O., Y.K., T.S., Y.N.); and.|Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo 171-8501, Japan (M.O.).
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Shikanai
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan (M.O., Y.K., T.S., Y.N.); and yoshiki@pmg.bot.kyoto-u.ac.jp.|Department of Life Science, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo 171-8501, Japan (M.O.) yoshiki@pmg.bot.kyoto-u.ac.jp.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Nishimura
mesh_terms: D002467:Cell Nucleus / Q000235:genetics*; D002696:Chlamydomonas / Q000187:drug effects / Q000235:genetics*; D002736:Chloroplasts / Q000187:drug effects / Q000235:genetics*; D020090:Chromosome Segregation / Q000187:drug effects / Q000235:genetics*; D027081:DNA Gyrase / Q000378:metabolism; D018742:DNA, Chloroplast / Q000235:genetics; D055785:Gene Knockdown Techniques; D054628:Genome, Chloroplast; D042822:Genomic Instability / Q000187:drug effects; D011938:Rec A Recombinases / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D059005:Topoisomerase II Inhibitors / Q000494:pharmacology
chemical_list: D018742:DNA, Chloroplast; D059005:Topoisomerase II Inhibitors; D011938:Rec A Recombinases; D027081:DNA Gyrase