hymA (hypha-like metulae), a new developmental mutant of Aspergillus nidulans.

Asexual fruiting body development in Aspergillus nidulans requires a precise spatial and temporal coordinated expression of many genes. Insertional mutagenesis was used to isolate and characterize a new mutant of A. nidulans in which hyphal growth was slightly reduced and conidiophore development was specifically blocked at the metula stage. In contrast to the uninucleate metulae of the wild-type, in the mutant these structures were elongated, multinucleate and septate. Further differentiation and production of phialides by a budding-like process was not observed. The mutant metulae thus resembled hyphae rather than metulae and the gene was therefore named hypha-like metulae (hymA). The hymA gene was mapped to linkage group VI. The integrated vector was rescued with border sequences from the integration site. The border sequences were used to isolate a cosmid from a wild-type library which was subcloned to a 5 kb fragment able to complement the mutation in trans. This fragment encoded a 1.8 kb transcript expressed in hyphae and throughout development. It is proposed that hymA is involved in budding processes, and is required for the formation of metulae and for their further differentiation.