| Understanding the mechanisms controlling asexual development (conidiation) in the filamentous ascomycete Aspergillus nidulans requires the knowledge of how regulatory factors interact with structural genes involved in the formation of the asexual apparatus, the conidiophore, and asexual spores, the conidia. Most of gene expression during conidiophore development is controlled by the sequential expression of three regulatory genes, ;The walls of A. nidulans conidia contain a green pigment that protects the spores from ultraviolet light. Two genes, yA and wA, encode enzymes in the central pigment synthesis pathway. wA mutants produce white spores and yA mutants produce yellow spores. wA mutations are epistatic to yA mutations when only conidial color is scored. However, the enzymatic product of yA, conidial laccase, accumulates in the conidial wall of wA mutants, implying that the observed epistasis is due to the absence of a synthetic intermediate in wA-strains. Thus, it was proposed that the product of wA converts a colorless precursor to a yellow pigment intermediate that is subsequently converted to the mature green form by yA-encoded laccase. This work focused on the characterization of the wA gene to understand its function in spore formation and the mechanisms controlling its expression during conidiation.;The wA gene was cloned by complementation. wA mRNA is absent from hyphae and mature conidia but accumulates during conidiation beginning with the appearance of pigmented spores, indicating its expression is localized to conidiophore cells. The wA gene codes for a polyketide synthase that synthesizes the yellow pigment intermediate from a colorless precursor. wA mRNA accumulates in wild type conidiating colonies but mutations in the develpmental regulatory loci brlA, abaA and wetA prevent its accumulation. Forced expression of wetA induces wA transcription, indicating that wetA is necessary and sufficient for wA expression. No direct interaction between the WetA protein and the wA promoter could be detected; however a novel wetA-homologous transcript was detected in hyphae. Detection of this novel mRNA suggests the wetA locus is complex, consisting of overlapping transcription units. Further analysis will be required to understand these transcripts' role in regulating gene expression, particularly wA expression. |
