Figure 1.

Secretory pathway in A. oryzae. (A) Secretion mechanisms at the hyphal tip region are depicted. Secretory proteins are transported via vesicles from ER through Golgi to the apical vesicle cluster Spitzenkörper. Apical secretion is thought to be dependent mainly on actin cable and supportively on the microtubule. SV, secretory vesicle. (B) Secretion mechanisms to the septum and plasma membrane around the hyphal middle region are shown. Septum-directed secretion is dependent on the microtubule but independent of the actin cytoskeleton, but further detailed molecular mechanisms are unknown. The cytoplasmic acyl-CoA binding protein AoAcb2 is unconventionally secreted under carbon starvation conditions, in which a compartment for unconventional protein secretion (CUPS) might be involved. Plasma membrane transporters are potentially transported directly from ER, not via Golgi. As an example of secondary metabolite secretion, kojic acid (KA) is synthesized from glucose (Glc) by the biosynthetic enzyme KojA and secreted by the putative plasma membrane transporter KojT. Note that the localization and transport of plasma membrane transporters do not appear to be restricted around the hyphal middle region.