Kinesin-3 and the cargo adaptor Hook1 regulate early endosome and peroxisome motility and are required for mitochondrial and endoplasmic reticulum spatial organization during polarized fungal cell growth in Podospora anserina.

Abstract

Microtubule-based organelle transport is essential for organelle positioning within cells and defines the architecture and function of highly polarized cells, like animal neurons and fungal hyphae. Early endosome transport depends on kinesin-3 motors and on cytoplasmic dynein, which binds to this organelle via Hook adaptor proteins. In filamentous fungi, these proteins can propel the indirect transport of additional organelles that hitchhike on early endosomes, like peroxisomes. However, early endosomes carry different cargoes in different fungi, and the contribution of these systems to the subcellular organization of different polarized cells is unclear. Here, we analyzed the function of the kinesin-3 motor KIN2 and of the HOOK1 adaptor in the model fungus Podospora anserina. We found that hyphal growth and morphogenesis require KIN2 and HOOK1, and that early endosome, peroxisome, vacuole, endoplasmic reticulum and mitochondrial motility depends on microtubules. We show that KIN2 and HOOK1 are required for mitochondrial localization at the sites of polarized cell growth, and for the polarized arrangement of the endoplasmic reticulum and vacuoles. Both proteins are required for the bidirectional transport of early endosomes and peroxisomes, but they differently affect their distribution. We found that KIN2 associates with some peroxisomes, and observed a low frequency of peroxisome-early endosome co-transport. Finally, we show that the GTPase RAB5B is required for the distribution and motility of early endosomes but not of peroxisomes, suggesting independent transport systems for these organelles in P. anserina. Our findings reveal a major role for KIN2 and HOOK1 in organelle dynamics during polarized cell growth.