Figure 3. Septin deletion mutants display altered cell morphology and temperature sensitivity.

A. Spot test of tenfold serial dilutions of wild-type and sep1-4 deletion mutants grown at different temperatures. Septin deletion strains were unable to grow at 34°C. B. Double septin deletion mutants. sep4Δsep1Δ and sep4Δsep3Δ strains were lethal while the rest of possible combinations were viable. C. Wild-type and septin deletion mutant cells expressing a nuclear localisation signal tagged with GFP (NLS-GFP) were grown to log phase at 22°C (top panel) or 28°C (bottom panel) and stained with calcofluor (CF) to observe the cell wall. Widefield microscope images were captured. In comparison with wild-type cells, at 22°C a minor bud neck defect was observed in mutant cells (bendy (arrowhead) and wider (arrow) bud necks). However, at 28°C septin deleted cells showed a strong morphology defect characterised by a swollen region in the middle of the cell (asterisk) strongly stained by calcofluor. Cells became rounded at the centre but maintained some polar growth at their tips and divided by placing a septum across the middle of the cell (empty arrowhead).