DOMINANT MUTATIONS AFFECTING BOTH SPORULATION AND STERIGMATOCYSTIN BIOSYNTHESIS IN ASPERGILLUS-NIDULANS

The initiation of conidiophore development in the filamentous fungus A spergillus nidulans is a complex process requiring the activities of s everal genes including fluC, flbA, flbB, flbC, flbD, and flbE. Recessi ve mutations in any one of these genes result in greatly reduced expre ssion of the brlA developmental regulatory gene and a colony morpholog y described as fluffy. These fluffy mutants have somewhat diverse phen otypes but generally grow as undifferentiated masses of vegetative hyp hae to form large cotton-like colonies. In this paper we describe a ge netic screen to identify dominant mutations resulting in similar fluff y colony morphologies. We have identified 36 dominant fluffy mutant st rains and shown that 29 of these mutants have greatly reduced brlA exp ression as compared to wild-type. In addition, we have found that 19 o f these mutants are not only developmentally altered but also fail to produce the toxic, carcinogenic, secondary metabolite sterigmatocystin . At least three of the mutants isolated result from dominant activati ng mutations in fadA which encodes the Get subunit of a heterotrimeric G-protein. Another of the mutants results from a dominant interfering mutation in brlA. We discuss the approaches taken to characterize the se potentially important regulators of growth, development and seconda ry metabolism.