Septins are a highly conserved family of
GTP-binding proteins involved in multiple cellular functions, including cell division and morphogenesis. Studies of
septins in fungal cells underpin a clear correlation between
septin-based structures and fungal morphology, providing clues to understand the molecular frame behind the varied morphologies found in fungal world.
METHODOLOGY/PRINCIPAL FINDINGS: Ustilago maydis genome has the ability to encode four
septins. Here, using loss-of-function as well as GFP-tagged alleles of these
septin genes, we investigated the roles of
septins in the morphogenesis of this basidiomycete fungus. We described that
septins in U. maydis could assemble into at least three different structures coexisting in the same cell: bud neck collars, band-like structures at the growing tip, and long
septin fibers that run from pole to pole near the cell cortex. We also found that in the absence of
septins, U. maydis cells lost their elongated shape, became wider at the central region and ended up losing their polarity, pointing to an important role of
septins in the morphogenesis of this fungus. These morphological defects were alleviated in the presence of an osmotic stabilizer suggesting that absence of
septins affected the proper formation of the cell wall, which was coherent with a higher sensitivity of
septin defective cells to drugs that affect cell wall construction as well as exocytosis. As U. maydis is a phytopathogen, we analyzed the role of
septins in virulence and found that in spite of the described morphological defects,
septin mutants were virulent in corn plants.
CONCLUSIONS/SIGNIFICANCE: Our results indicated a major role of
septins in morphogenesis in U. maydis. However, in contrast to studies in other fungal pathogens, in which
septins were reported to be necessary during the
infection process, we found a minor role of
septins during corn
infection by U. maydis.