Revisiting fungal polarized growth: from Spitzenkörper to crescent accumulation of secretory vesicles

Polarized elongation in filamentous fungi depends on secretory vesicles being supplied and fusing at the apex. In Ascomycota and Basidiomycota, these vesicles have mostly been reported to accumulate into a spheroidal structure known as the Spitzenkörper. Using time-lapse microscopy, the spatial and temporal dynamics of fluorescently labelled vesicles were investigated in 13 apices of the phytopathogenic fungus Botrytis cinerea. Time-projections of the fluorescent signal highlighted the spheroid Spitzenkörper in half the sample and a crescent-shaped region of the apical dome in the other half. A linear relationship was found between the roundness of the fluorescent region and the hyphal elongation rate. Temporal dynamics clustering and Fourier transform showed periodic pulses of fluorescence intensity in hyphae displaying a Spitzenkörper that were not detected in those exhibiting a crescent-shaped accumulation. These results reveal a dual mode of secretory vesicle accumulation at the apex of growing hyphae from the same culture.