Fig. 1

Infection by Sclerotinia sclerotiorum releases internal mechanical stress in Arabidopsis thaliana epidermal cells. A At 24 h post-inoculation (hpi), the fungal colony actively grew in plant tissue. The colony center was in necrotic hydrolyzed tissue (brown bright field top left) whereas the colony periphery grew in healthy tissue (fluorescence top right). Z colored-depth micrograph (bottom) showing an under-epidermal growth of S. sclerotiorum (stars). B Confocal micrograph representative of A. thaliana epidermal cells in uninfected tissue (top) and in the vicinity of S. sclerotiorum infection front, with an invasive hyphae visible as a bright thick filament in the upper left corner of the image. Overlays show the experimental analysis of pathogen-derived stretch (blue segments, scale specific to each micrograph) between 24 and 26 hpi, and cell surface variation indicated as a colored background. C Distribution of the magnitude of the absolute value of the relative cell surface variation triggered by pathogen-derived stress release. Individual measures are shown as bars along the X-axis (n=278 cells), the average was 1% in infected tissue and 0.5% healthy tissue. D Mechanical finite element model (FEM) of infection-derived stress. The model was used to simulate stress and strain in a region of interest (ROI) mimicking the leaf sector shown in B and at the left of the panel. Low release of internal stress and Young’s modulus (top). High release of internal stress and Young’s modulus (bottom)