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 . Over time, 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 the spitzenkörper that were absent in the crescent-shape region. These results reveal a dual mode of secretory vesicles accumulation at the apex of growing hyphae.