Decoding mechanism of plastid division: structure and kinetics of the plastid-dividing machinery

Abstract

Chloroplasts (plastids) are able to synthesize energy-containing macromolecules for a great deal of living organisms. Consistent with their endosymbiotic origin, plastids maintain themselves by binary division. Plastid division is carried out by a ring complex called the plastid-dividing (PD) machinery; the PD machinery has inner and outer ring structures across the plastid membranes. Although many studies have been done to reveal the mechanisms of plastid division, much about the components and molecular mechanisms of the PD machinery remain to be discovered. My work demonstrated that: (1) the contractile force of the PD ring is generated via filament-sliding movement by dynamin proteins; (2) the PD ring is composed of polyglucan nanofilaments, synthesized by the glucosyltransferase PDR1; and (3) examination of the FtsZ ring reconstituted in a heterologous system revealed the assembly and contractile dynamics of the FtsZ ring. In addition, we have recently established isolation of the mitochondriondividing (MD) machinery and revealed that the ultrastructure and the dynamics of the isolated MD machinery were similar to those of the isolated PD machinery. Therefore, plastids and mitochondria divide by the action of supramolecular complexes “the PD and MD machineries” including dual contractible rings, the PD/MD ring and the FtsZ ring. These findings will lead to an understanding of how plastids and mitochondria were established during evolution.