Bgs4 is essential to maintain cell wall thickness and integrity at the poles. (A) Bgs4 absence generates cell lysis and cytoplasm release from the poles (arrow) either during polar growth (top) or after septation (bottom). (B and C) Pole lysis occurs at the OE (arrow) during monopolar and bipolar growth. (A and B) Cells were grown as in Fig. 1 B. (C) Percentage lysis at each pole. Error bars indicate SD. (D) Model of lysis at the OE. Cell growth (red arrow) is mainly at the OE. The new defective cell wall cannot stand the internal pressure (arrowhead), resulting in pole lysis. After septum formation, the increase in internal pressure in a cell generates pole lysis of the sister cell. (E and F) Absence of Bgs4 causes a large pole cell wall thinning and lysis at the pole tip. (E) WT cell morphology and cell wall structure. (F) Bgs4 absence generates a thin cell wall (red arrow) in both new end (close to FS) and OE. A thinner tip wall results in cell lysis and cytoplasm release (right, red arrow). Cells were grown as in A. FS, fission scar; NE, new end. Bars: (A and B) 5 µm; (E and F) 1 µm.