Isolation and molecular characterization of the Aspergillus nidulans wA gene.

The walls of Aspergillus nidulans conidia contain a green pigment that protects the spores from damage by ultraviolet light. At least two genes, wA and yA, are required for pigment synthesis: yA mutants produce yellow spores, wA mutants produce white spores, and wA mutations are epistatic to yA mutations. We cloned wA by genetic complementation of the wA3 mutation with a cosmid library containing nuclear DNA inserts from the wild-type strain. The wA locus was mapped to an 8.5-10.5-kilobase region by gene disruption analysis. DNA fragments from this region hybridized to a 7500 nucleotide polyadenylated transcript that is absent from hyphae and mature conidia but accumulates during conidiation beginning when pigmented spores first appear. Mutations in the developmental regulatory loci brlA, abaA, wetA and apsA prevent wA mRNA accumulation. By contrast, yA mRNA fails to accumulate only in the brlA- and apsA- mutants. Thus, the level of wA transcript is regulated during conidiophore development and wA activation requires genes within the central pathway regulating conidiation.