(A, D, G, J) Slice through a tomogram of a dividing (A) spoIIE, (D) spoIIE-ΔregI, (G) spoIIE-ΔregII and (J) malF-spoIIE sporangia. Insets highlight the left side of the invaginating septum for each case. (B, E, H, K) Left panel: zoomed-in view of the inset in (A, D, G, J), respectively, in the xy coordinate plane. Right panel: same as left with peptidoglycan (PG), forespore (FS) and mother cell (MC) compartments indicated in all. Cell membrane (peach), FtsA bundle (pink) and FtsZ bundle (blue) are also highlighted for all. (C, F, I, L) Left panel: view of the septal disc corresponding to (B, E, H, K), respectively, in the xz/yz coordinate plane obtained by rotating the cell around its short axis or long axis by 90o (yz plane for I and xz plane for the rest of the panels). Right panel: same as left with cellular parts and FtsAZ filaments highlighted. (M) Schematic highlighting the different domains of SpoIIE and construction of different spoIIE mutants. (N) Schematic of the arrangement of the cytoskeletal machinery in spoIIE mutant sporangia from (A) to (L). PG (gray), cell membrane (peach), FtsA dots (pink) and FtsZ dots (blue) are indicated. (O) Bar graph depicting the septal thickness in wild-type vegetative, wild-type sporulating cells and spoIIE mutant sporangia. Error bars indicate standard deviation. Each dot indicates a sample point. Scale bars: (A, D, G, J) 200 nm, (B, C, E, F, H, I, K, L) 25 nm. See also Figure 8—figure supplements 1–4, Figure 8—source data 1.