Associate Professor Osamu Misumi of the Graduate School of Sciences and Technology for Innovation (science) and others have unraveled the fundamental mechanism of chloroplast growth - Discovery of an enzyme that controls DNA segregation during chloroplast division and multiplication

A group led by Associate Professor Osamu Misumi of the Graduate School of Sciences and Technology for Innovation (science), Yusuke Kobayashi, Ph.D. of the Graduate School of Science, Kyoto University (who graduated from the Department of Biology and Chemistry, Faculty of Science, Yamaguchi University, and is currently affiliated to the National Institute of Genetics), and Assistant Professor Yoshiki Nishimura, together with groups from Hosei University, Rikkyo University, Tokyo Institute of Technology and Japan Women’s University, has discovered the gene MOC1, which controls the segregation (transmission) of "chloroplast DNA (chloroplast nucleoids)" found in plant chloroplasts, and the chloroplast Holliday junction resolvase encoded by this gene.

A Holliday junction is a structure that is appears in the process of recombination (homologous recombination) between parts with very similar DNA sequences, observed when DNA damage repair, replication and meiosis take place (Fig. 1). However, the mechanism for how this structure is cleaved in chloroplast nucleoids was not known. Furthermore, this research has revealed that this enzyme is an essential factor in the normal DNA segregation when chloroplasts proliferate. It is anticipated that the discovery of this enzyme will lead to elucidation of the mechanism of homologous recombination for chloroplast genomes, and furthermore, to expansion to applied research, such as chloroplast engineering, aimed at the production of new substances.

 The findings were published in the American scientific journal Science that was issued on May 12 (Fri.).



     Fig. 1  Schematic diagram of DNA homologous recombination and the Holliday

     junction formation process. This is the first time a chloroplast Holliday junction

     resolvase enzyme has been discovered.