Expression of asexual developmental regulator gene abaA is affected in the double mutants of classes I and II chitin synthase genes, chsC and chsA, of Aspergillus nidulans.

The chsA and chsC encode classes II and I chitin synthases, respectively, of the filamentous fungus Aspergillus nidulans. The DeltachsA DeltachsC double mutants (DeltaAC mutants) show defects in asexual development: a striking reduction in the number of conidiophores and aberrant conidiophore morphology. Here, we examined the involvement of regulatory genes for asexual development (brlA, abaA, and medA) in the conidiation defects of the DeltaAC mutants. Spatial expression patterns of brlA, abaA, and medA in conidiophores of the wild-type strains and DeltaAC mutants were examined by in-situ staining using a reporter gene; expression of either gene was detected at abnormal sterigmata in the DeltaAC mutants as well as at normal ones in the wild-type strain. However, abaA expression was not prominent at a subset of conidiophores developing long chains of aberrant sterigmata, suggesting that induction of the abaA expression was retarded in the DeltaAC mutants. Based on these results and those previously presented, possible mechanisms involved in the conidiation defects are discussed.