Intracellular accumulation and secretion of hydrophobin-enriched vesicles aid the rapid sporulation of molds

Abstract

Fungi can rapidly produce large amounts of spores suitable for aerial dispersal. The hydrophobicity of spores is provided by the unique amphiphilic and superior surface-active proteins - hydrophobins (HFBs) - that self-assemble at hydrophobic/hydrophilic interfaces and thus change surface properties. Using the HFB-enriched mold Trichoderma and the HFB-free yeast Pichia pastoris, we revealed a distinctive HFB secretory pathway that includes an intracellular accumulation of HFBs in lipid bodies (LBs) that can internalize in vacuoles. The resulting vacuolar multicisternal structures (VMS) are stabilized by HFB layers that line up on their surfaces. These HFB-enriched VMSs can move to the periplasm for secretion or become fused in large tonoplast-like organelles. The latter contributes to the maintenance of turgor pressure required for the erection of sporogenic structures and rapid HFB secretion by squeezing out periplasmic VMSs through the cell wall. Thus, HFBs are essential accessory proteins for the development of aerial hyphae and colony architecture.