The Neurospora crassa exocyst complex tethers Spitzenkörper vesicles to the apical plasma membrane during polarized growth

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  • Fungal hyphae are among the most highly polarized cells. Hyphal polarized growth is supported by tip-directed transport of secretory vesicles, which accumulate temporarily in a stratified manner in an apical vesicle cluster, the Spitzenkörper. The exocyst complex is required for tethering of secretory vesicles to the apical plasma membrane. We determined that the presence of an octameric exocyst complex is required for the formation of a functional Spitzenkörper and maintenance of regular hyphal growth in Neurospora crassa. Two distinct localization patterns of exocyst subunits at the hyphal tip suggest the dynamic formation of two assemblies. The EXO-70/EXO-84 subunits are found at the peripheral part of the Spitzenkörper, which partially coincides with the outer macrovesicular layer, whereas exocyst components SEC-5, -6, -8, and -15 form a delimited crescent at the apical plasma membrane. Localization of SEC-6 and EXO-70 to the plasma membrane and the Spitzenkörper, respectively, depends on actin and microtubule cytoskeletons. The apical region of exocyst-mediated vesicle fusion, elucidated by the plasma membrane–associated exocyst subunits, indicates the presence of an exocytotic gradient with a tip-high maximum that dissipates gradually toward the subapex, confirming the earlier predictions of the vesicle supply center model for hyphal morphogenesis.
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  • Riquelme, M., Bredeweg, E. L., Callejas-Negrete, O., Roberson, R. W., Ludwig, S., Beltrán-Aguilar, A., ... & Freitag, M. (2014). The Neurospora crassa exocyst complex tethers Spitzenkörper vesicles to the apical plasma membrane during polarized growth. Molecular Biology of the Cell, 25(8), 1312-1326. doi:10.1091/mbc.E13-06-0299
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  • 25
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  • 8
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  • This workwas supported by the Consejo Nacional de Ciencia y Tecnología,Mexico, Grants U-45818Q, B0C022, and CONACYT-DFG 75306 toM.R., grants from the American Cancer Society (RSG-08-030-01-CCG)and National Institutes of Health (P01GM068087) to M.F., theGerman Research Foundation (SE 1054/3-2 and SE1054/6-1) to S.S.,and the National Science Foundation Collaborative Research:AFTOL: Resolving the Evolutional History of the Fungi (NSFDEB-0732503) to R.W.R. A.B.A. was supported by Consejo Nacionalde Ciencia y Tecnología Grant 206007. We acknowledge a FungalGenetics Stock Center and the Neurospora Functional Genomics ProgramProject grant (National Institutes of Health P01GM068087) formaterials and strains.
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