The role of MODA, the Aspergillus nidulans homologue of Cdc42p, in hyphal morphogenesis

Date of Completion

January 2002


Biology, Molecular|Biology, Genetics|Biology, Cell




Hyphal growth in filamentous fungi such as Aspergillus nidulans involves polarized cell surface expansion that is associated with a highly asymmetric actin cytoskeleton. Mutants defective in the establishment and/or maintenance of hyphal polarity have been identified and characterized; however, the molecular mechanisms underlying polarized hyphal morphogenesis are still poorly understood. Studies in budding and fission yeast have identified Cdc42p, a Rho-type GTPase, as a central component in the regulation of the actin cytoskeleton that is necessary for polarized growth. While the genetic analysis of polarity establishment and maintenance have focused mostly in the yeasts, the general mechanisms controlling cell polarity establishment are likely to be conserved between the yeasts and filamentous fungi. ^ We have identified and cloned modA (morphogenesis d&barbelow;efective), the A. nidulans homologue of CDC42. MODA is a functional homologue of Cdc42p that is able to complement the S. cerevisiae cdc42-1 mutant. Overexpression of the constitutively active modAG14V allele results in germlings that polarize with a wide germ tube. Double mutant analysis of modA G14V overexpression with other polarity defective mutants indicates that genetically modA acts upstream of or in parallel with the mutants examined. ^