Figure 3. Lack of correlation between Hog1 activity and pSTL1 expression at the single-cell level.

(a) Microscopy images of a strain with Hog1 tagged with mCitrine and carrying the unstable pSTL1-dPSTR^R that was challenged by 0.2 M NaCl. The nuclear accumulation of Hog1-YFP precedes protein expression. Scale bar, 5 μm. (b–d) Quantification of the cell area (b) Hog1 nuclear accumulation, measured as the ratio between nuclear and cytoplasmic YFP fluorescence (c) and pSTL1-dPSTR^R nuclear enrichment (d) for cells stimulated with 0 (orange, N_C=467), 0.1 (cyan, N_C=558), 0.2 (blue, N_C=655) and 0.4 M NaCl (red, N_C=802). (e) Scatter plot of the signalling output measured as the integral below the Hog1 nuclear accumulation curve versus the expression output measured as the maximum in pSTL1-dPSTR^R nuclear enrichment. The dashed line represents the expression threshold. The mean signalling output versus the mean expression output for the expressing cells (filled circles) and the non-expressing cells (empty circles) is plotted in the inset. The size of the marker is indicative of the percentage of cell in each category. (f) Correlation between the time needed to overcome the expression threshold and the expression output. The mean expression output and the standard deviation were calculated for groups of cells, which exceed the expression threshold at the same time point. The marker size is indicative of the percentage of cells (from the total population) in each group.