GENETIC REQUIREMENTS FOR INITIATING ASEXUAL DEVELOPMENT IN ASPERGILLUS-NIDULANS

Conidiation in the filamentous ascomycete Aspergillus nidulans require s activation of brlA, a well-characterized transcriptional regulator o f genes that are induced specifically during asexual development. We h ave isolated and characterized developmental mutations in six loci, de signated fluG, flbA, flbB, flbC, flbD, and flbE, that result in defect ive development and reduced brlA expression. These mutants grow indete rminately to produce masses of aerial hyphae resulting in the formatio n of cotton-like colonies with a ''fluffy'' morphology. The results of growth and epistasis tests involving all pairwise combinations of flu ffy mutations indicate complex hierarchical relationships among these loci. We discuss these genetic interactions and propose that there are multiple mechanisms for activating brlA.