Identification and characterization of genes required for hyphal morphogenesis in the filamentous fungus Aspergillus nidulans

In the filamentous fungus Aspergillus nidulans, germination of an asexual c onidiospore results in the formation of a hyphal cell. A key feature of spo re germination is the switch from isotropic spore expansion to polarized ap ical growth. Here, temperature-sensitive mutations are used to characterize the roles of five genes (sepA, hypA, podB-podD) in the establishment and m aintenance of hyphal polarity. Evidence that suggests that the hypA, podB, and sepA genes are required for multiple aspects of hyphal morphogenesis is presented. Notably, podB and sepA are needed for organization of the cytos keleton at sites of polarized growth. In contrast, podC and podD encode pro teins that appear to be specifically required for the establishment of hyph al polarity during spore germination. The role of sepA and the lod genes in controlling the spatial pattern of polarized morphogenesis in germinating spores is also described. Results obtained from these experiments indicate that the normal pattern of germ-tube emergence is dependent upon the integr ity of the actin cytoskeleton.