Morphogenesis is coordinated with nuclear division in germinating Aspergillus nidulans conidiospores

Germinating Aspergillus nidulans conidiospores switch to polarized apical g rowth following an initial period of isotropic expansion. At the same time, they re-enter the nuclear division cycle. The relationship between spore p olarization and nuclear division was investigated by testing the effect of cell cycle inhibitors and temperature-sensitive cell cycle mutations on spo re morphogenesis. On rich media, it was found that spore polarization is de layed if completion of the first mitosis is blocked. The observed delay may be dependent upon the activity of the mitosis-promoting NIMA kinase. An ad ditional mechanism appears to prevent polarization as the spore progresses through its first S phase. In contrast, on poor media, spore polarization d oes not require completion of the first mitosis. These observations suggest that spore morphogenesis is influenced by cell cycle signals in a growth-d ependent manner.