The chsA gene from Aspergillus nidulans is necessary for maximal conidiation

A fragment from the open reading frame of the cloned chsA gene from Aspergillus nidulans was deleted and replaced with the argB gene. The resulting construct was used to replace the wild-type chsA gene in an argB deletion strain. The growth and morphology of the vegetative hyphae from the resulting chsA disruptant strain were indistinguishable from those of a wild-type strain but the chitin content of the hyphae from the disruptant was reduced to approximately 90% of that of wild-type. The disruptant showed reduced ability to produce the asexual spores (conidia) that are formed by differentiated aerial hyphae called conidiophores. The ability to form undifferentiated aerial hyphae was not impaired in the disruptant. The conidiophores and conidia produced by the disruptant were indistinguishable from those of wild-type. Conidium formation by the disruptant grown on a variety of media was reduced to about 30% of the wild-type. A chsE null strain did not show a defect in conidiation but a strain in which both chsA and chsE were inactivated produced about 3% of the conidia of wild-type. That finding supports the hypothesis that chsA and chsE encode a partially redundant function necessary for conidiophore development.