Coordination of Chloroplast Envelope Division

Chloroplasts arose from cyanobacteria and, like cyanobacteria, divide by binary fission. These organelles are surrounded by a double membrane, and their division requires the coordinated action of the inner and outer chloroplast membrane constriction machineries (Miyagishima, 2005; Maple and Moller, 2007; Glynn et al., 2007). Division of the inner membrane is mediated by an internal constricting ring at the stromal surface composed of the tubulin-like FtsZ protein, which arose from the prokaryotic endosymbiont. Similarly, division of the outer membrane involves an external constricting ring on the cytoplasmic surface composed of the dynamin-like ARC5 protein, which was contributed by the eukaryotic host. How constriction of the FtsZ and ARC5 rings is coordinated to achieve the concerted division of the two membranes has been unclear until recently.