THE PLANT CELL, Vol 2, Issue 8 731-739, Copyright © 1990 by American Society of Plant Biologists
abaA Controls Phialide Differentiation in Aspergillus nidulans
T. C. Sewall, C. W. Mims and W. E. Timberlake
Department of Plant Pathology, University of Georgia, Athens, Georgia 30602
Aspergillus nidulans is an ascomycetous fungus that reproduces asexually by
forming multicellular conidiophores and uninucleate spores called conidia.
Loss of function mutations in the abacus A (abaA) regulatory locus result
in formation of aberrant conidiophores that fail to produce conidia.
Wild-type conidiophores form two tiers of sterigmata. The first tier,
metulae, divide to produce the second tier, phialides. Phialides are
sporogenous cells that produce conidia through a specialized apical budding
process. We have examined conidiophore development in an abaA- strain at
the ultrastructural level. The results showed that in the mutant metulae
produce supernumerary tiers of cells with metula-like, rather than
phialide-like, properties. Temperature shift experiments with an abaA14ts
strain demonstrated that abaA+ function induced phialide formation by the
aberrant abacus cells and was continuously required for maintenance of
phialide function. In the absence of abaA+ activity, metulae simply
proliferated and later developmental steps never occurred. We conclude that
abaA+ directs the differentiation of phialides and is continuously required
for maintenance of their function.
