Two FtsZ proteins orchestrate archaeal cell division through distinct functions in ring assembly and constriction

AbstractThe tubulin homolog FtsZ assembles a ring in bacteria and plays a key role in the machinery that constricts to divide the cells. Many archaea encode two FtsZs from distinct families, FtsZ1 and FtsZ2, of previously unclear functions. We show that Haloferax volcanii cannot divide properly without either or both but proliferates in alternative ways via remarkable envelope plasticity. The FtsZs co-localize as a dynamic midcell division ring. FtsZ1 independently assembles and stabilizes FtsZ2 in the ring, and influences cell shape, whereas FtsZ2 functions in the constriction mechanism; their GTPase active sites are crucial for these activities. The two FtsZs are widespread in archaea with a single S-layer envelope, but those with a pseudomurein wall only have FtsZ1. FtsZ2 appears to be essential for constriction of the flexible membrane-S-layer, where an internal constriction force might dominate the division mechanism in contrast to bacteria and archaea that divide by wall ingrowth.