Three rings for the evolution of plastid shape: a tale of land plant FtsZ.

Nuclear-encoded plant FtsZ genes are derived from endosymbiotic gene transfer of cyanobacteria-like genes. The green lineage (Chloroplastida) and red lineage (Rhodophyta) feature FtsZ1 and FtsZ2 or FtsZB and FtsZA, respectively, which are involved in plastid division. These two proteins show slight differences and seem to heteropolymerize to build the essential inner plastid division ring. A third gene, encoding FtsZ3, is present in glaucophyte and charophyte algae, as well as in land plants except ferns and angiosperms. This gene was probably present in the last common ancestor of the organisms united by having a primary plastid (Archaeplastida) and was lost during vascular plant evolution as well as in the red and green algae. The presence/absence pattern of FtsZ3 mirrors that of a full set of Mur genes and the peptidoglycan wall encoded by them. Based on these findings, we discuss a role for FtsZ3 in the establishment or maintenance of plastid peptidoglycan shells.