Dynamic cotracking of EVs, CW thickness, and deformation during abrupt changes in cell growth or secretion.

(A) Scheme of a hyphal fungal tip, highlighting key assumptions of the mathematical model for tip growth: EVs cluster in the Spitzenkörper and radiate to promote the secretion of CW polysaccharides as well as remodeling enzymes. This allows the CW to thicken as well as deform under stresses created by turgor, at a strain rate, G. The pool of EVs is fed by polarized trafficking and other sources of recycling in proportion to the strain rate of the CW at cell tips (mechanical feedback). (B) Time lapse of EV accumulation (mCherry-RAB11) and CW thickness during a lateral branching event. (C) Dynamics of EVs concentration, CW strain rate, and thickness in branching cells (n = 7) and corresponding model outputs. The origin of time is defined as the first visible emergence of the new branch. (D) Time lapse of a growing cell rinsed at time t = 0 with medium supplemented with 0.2 M sorbitol to reduce turgor pressure. (E) Dynamics of EVs concentration, CW strain rate, and thickness before and after the osmotic shock (n = 10) and corresponding model outputs. The inset in the top curve represents how turgor was modulated in the model to simulate the initial rapid drop and subsequent adaption. (F) Time lapse of a cell treated with benomyl to depolymerize microtubules, displaying CW thickness profiles overlaid with EVs. (G) Dynamics of EVs concentration, CW strain rate, and thickness before and after benomyl addition (n = 5) and corresponding model outputs. (H) Time lapse of a temperature-sensitive sarA6 ts mutant cell switched to restrictive temperature at time 0, showing the CW thickness profiles overlaid with EVs. (I) Dynamics of EVs concentration, CW strain rate, and thickness in sarA6 ts cells at restrictive temperature (n = 8) and corresponding model outputs. Scale bars, 2 μm. In experimental plots presented in 5C, 5E, 5G, and 5I, the black line represents the mean of the data and the blue shade the standard deviation. The data underlying the graphs can be found in S1 Data. CW, cell wall; EV, exocytic vesicle; PM, xxxx.