Studies on Peroxisome Motility in the Model Fungal System Ustilago maydis

Peroxisomes are ubiquitous organelles found in almost all eukaryotes. They are sensitive to changes in cellular homeostasis and involved in various metabolic processes. Deficiencies in peroxisome function cause severe neurological problems. Here I report, investigation of peroxisome motility and its relation to peroxisomal functions in the fungal model system Ustilago maydis. Peroxisomes are mostly motile in Ustilago maydis. Motile peroxisomes show different motility patterns: short-range pulse type movements and long range bidirectional motility. Motility behaviour is not static as oscillating peroxisomes may start long-range motility. Here, I present evidence that long-range bidirectional peroxisome motility is an energy driven process and is essential for homogeneous distribution of peroxisomes. Similar to early endosomes and endoplasmic reticulum, microtubule motors kinesin-3 and dynein are responsible for long-range peroxisome transport. In addition to using the same molecular motors for transport, early endosomes, endoplasmic reticulum and peroxisomes have the same transport velocity. Interestingly, motile peroxisomes and endoplasmic reticulum tubules co-localize with early endosomes. Functional investigation of early endosome mutants, Δrab5a and Yup1ts has revealed a novel transport mechanism where endoplasmic reticulum and peroxisomes hitch hike on early endosomes. Additionally, I report functional characterization of an AAA-ATPase, um05592, which has high homology to human protein NP_055873. Altogether these results reveal molecular mechanism of peroxisome transport in Ustilago maydis. Similarities in transport machinery illustrate Ustilago maydis as a model system to study peroxisome function in mammalian cells