Neurospora crassa ASM-1 complements the conidiation defect in a stuA mutant of Aspergillus nidulans.

Aspergillus nidulans StuA and Neurospora crassa ASM-1 are orthologous APSES (ASM-1, PHD1, SOK2, Efg1, StuA) transcription factors conserved across a diverse group of fungi. StuA and ASM-1 have roles in asexual (conidiation) and sexual (ascospore formation) development in both organisms. To address the hypothesis that the last common ancestor of these diverse fungi regulated conidiation with similar genes, asm-1 was introduced into the stuA1 mutant of A. nidulans. Expression of asm-1 complemented defective conidiophore morphology and restored conidia production to wild type levels in stuA1. Expression of asm-1 in the stuA1 strain did not rescue the defect in sexual development. When the conidiation regulator AbaA was tagged at its C-terminus with GFP in A. nidulans, it localized to nuclei in phialides. When expressed in the stuA1 mutant, AbaA::GFP localized to nuclei in conidiophores but no longer was confined to phialides, suggesting that expression of AbaA in specific cell types of the conidiophore was conditioned by StuA. Our data suggest that the function in conidiation of StuA and ASM-1 is conserved and support the view that, despite the great morphological and ontogenic diversity of their condiphores, the last common ancestor of A. nidulans and N. crassa produced an ortholog of StuA that was involved in conidiophore development.