FtsZ of Filamentous, Heterocyst-Forming Cyanobacteria Has a Conserved N-Terminal Peptide Required for Normal FtsZ Polymerization and Cell Division

Abstract

Filamentous cyanobacteria grow by intercalary cell division, which should involve distinct steps compared to those producing separate daughter cells. The N-terminal region of FtsZ is highly conserved in the clade of filamentous cyanobacteria capable of cell differentiation. A derivative of the model strain Anabaena sp. PCC 7120 expressing only an FtsZ lacking the amino acids 2¿51 of the N-terminal peptide (1N-FtsZ) could not be segregated. Strain CSL110 expresses both 1N-FtsZ, from the endogenous ftsZ gene promoter, and the native FtsZ from a synthetic regulated promoter. Under conditions of 1N-FtsZ predominance, cells of strain CSL110 progressively enlarge, reflecting reduced cell division, and show instances of asymmetric cell division and aberrant Z-structures notably differing from the Z-ring formed by FtsZ in the wild type. In bacterial 2-hybrid assays FtsZ interacted with 1N-FtsZ. However, 1N-FtsZ-GFP appeared impaired for incorporation into Z-rings when expressed together with FtsZ. FtsZ, but not 1N-FtsZ, interacted with the essential protein SepF. Both FtsZ and 1N-FtsZ polymerize in vitro exhibiting comparable GTPase activities. However, filaments of FtsZ show a distinct curling forming toroids, whereas 1N-FtsZ form thick bundles of straight filaments. Thus, the N-terminal FtsZ sequence appears to contribute to a distinct FtsZ polymerization mode that is essential for cell division and division plane location in Anabaena.