Proper DNA inheritance is essential for healthy cell growth and division. The same goes for the genetic material found in chloroplasts: the energy centers of all plant cells. Chloroplast genomes -- likely vestiges of ancestral bacteria -- are organized into DNA-protein complexes called nucleoids. While significant work has been done to understand the dynamics of DNA in the nuclei of plant cells, little is known about the dynamics of chloroplast nucleoids. Now Yusuke Kobayashi, PhD, and Yoshiki Nishimura, PhD, of Kyoto University, Osami Misumi, PhD, of Yamaguchi University, and other collaborators have isolated and characterized a protein in chloroplasts that is essential for proper nucleoid segregation. Their findings were published online on May 11, 2017 in Science. The article is titled "Holliday-Junction Resolvases Mediate Chloroplast Nucleoid Segregation.” "To understand the dynamics of chloroplast nucleoids, we focused on their behavior during chloroplast division in the green alga Chlamydomonas reinhardtii," explains Dr. Nishimura. "We screened about 6,000 specimens with random mutations in their DNA and then isolated the ones with defective nucleoid segregation." One of these mutants was found to have a defect in a gene the team calls moc1, for "monokaryotic chloroplast 1". The chloroplasts in this mutant possessed only a single nucleoid, and showed unequal segregation during chloroplast division. A homologous moc1 gene was then found in a land plant commonly used for research, Arabidopsis thaliana.
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