Studies on nuclear migration and cell morphogenesis in the dimorphic fungus Ustilago maydis

Ustilago maydis is a dimorphic fungus with a yeast-like form and a filamentous form, and both are characterized by extensive nuclear movements. This makes Ustilago a model organism for understanding the link between cell morphogenesis and nuclear migration. Lis1 is a microtubule plus-end tracking protein conserved in eukaryotes and is required for nuclear migration and spindle positioning. In this study, I have characterized the homologue of the human LIS1 gene in Ustilago, and demonstrate, for the first time in fungi, that lis1 is essential for cell viability. Using a conditional null mutation I also show that lis1 is necessary for nuclear migration, cell morphogenesis, septum positioning, cell wall integrity, and microtubule organization. I also generated conditional null mutations for other putative nuclear migration genes, num1 and nudC. In addition, I further characterized the morphologically similar Deltatea4 mutant phenotype, confirming that Tea4 is required for normal cell morphogenesis and septum positioning.