The acetyltransferase GcnE is part of the SAGA complex which regulates fungal gene expression through acetylation of chromatin. Target genes of the histone acetyltransferase GcnE include those involved in secondary metabolism and asexual development. Here, we show that the absence of GcnE not only abrogated conidiation, but also strongly impeded vegetative growth of hyphae in the human pathogenic fungus Aspergillus fumigatus. A yeast two-hybrid screen using a Saccharomyces cerevisiae strain whose tRNA molecules were specifically adapted to express A. fumigatus proteins identified two unprecedented proteins that directly interact with GcnE. Glutamine synthetase GlnA as well as a hypothetical protein located on chromosome 8 (GbpA) were identified as binding partners of GcnE and their interaction was confirmed in vivo via bimolecular fluorescence complementation. Phenotypic characterization of gbpA and glnA deletion mutants revealed a role for GbpA during conidiogenesis and confirmed the central role of GlnA in glutamine biosynthesis. The increase of glutamine synthetase activity in the absence of GcnE indicated that GcnE silences GlnA through binding. This finding suggests an expansion of the regulatory role of GcnE in A. fumigatus.
Keywords: Aspergillus fumigatus; Bimolecular fluorescence complementation assay; Glutamine synthetase GlnA; Histone acetyltransferase GcnE; Yeast two-hybrid system.