title: Expression and specificity profile of the major acetate transporter AcpA in Aspergillus nidulans.
abstract: AcpA has been previously characterized as a high-affinity transporter essential for the uptake and use of acetate as sole carbon source in Aspergillus nidulans. Here, we follow the expression profile of AcpA and define its substrate specificity. AcpA-mediated acetate transport is detected from the onset of conidiospore germination, peaks at the time of germ tube emergence, and drops to low basal levels in germlings and young mycelia, where a second acetate transporter is also becoming apparent. AcpA activity also responds to acetate presence in the growth medium, but is not subject to either carbon or nitrogen catabolite repression. Short-chain monocarboxylates (benzoate, formate, butyrate and propionate) inhibit AcpA-mediated acetate transport with apparent inhibition constants (Ki) of 16.89±2.12, 9.25±1.01, 12.06±3.29 and 1.44±0.13mM, respectively. AcpA is also shown not to be directly involved in ammonia export, as proposed for its Saccharomyces cerevisiae homologue Ady2p. In the second part of this work, we search for the unknown acetate transporter expressed in mycelia, and for other transporters that might contribute to acetate uptake. In silico analysis, genetic construction of relevant null mutants, and uptake assays, reveal that the closest AcpA homologue (AN1839), named AcpB, is the 'missing' secondary acetate transporter in mycelia. We also identify two major short-chain carboxylate (lactate, succinate, pyruvate and malate) transporters, named JenA (AN6095) and JenB (AN6703), which however are not involved in acetate uptake. This work establishes a framework for further exploiting acetate and carboxylate transport in filamentous ascomycetes.
authors.affiliation: Centre of Molecular and Environmental Biology (CBMA), Department of Biology, University of Minho, Campus de Gualtar, Braga 4710-057, Portugal.
authors.forename: Joana
authors.initials: J
authors.lastname: Sá-Pessoa
authors.affiliation: Faculty of Biology, Department of Botany, University of Athens, Panepistimioupolis, Athens 15781, Greece.
authors.forename: Sotiris
authors.initials: S
authors.lastname: Amillis
authors.affiliation: Centre of Molecular and Environmental Biology (CBMA), Department of Biology, University of Minho, Campus de Gualtar, Braga 4710-057, Portugal. Electronic address: mcasal@bio.uminho.pt.
authors.forename: Margarida
authors.initials: M
authors.lastname: Casal
authors.affiliation: Faculty of Biology, Department of Botany, University of Athens, Panepistimioupolis, Athens 15781, Greece. Electronic address: diallina@biol.uoa.gr.
authors.forename: George
authors.initials: G
authors.lastname: Diallinas
mesh_terms: D000085:Acetates / Q000378:metabolism*; D064751:Ammonium Compounds / Q000378:metabolism; D001233:Aspergillus nidulans / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D025282:Mycelium / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D000085:Acetates; D064751:Ammonium Compounds
keywords: Acetate; Carbon catabolism; Filamentous fungi; Germination; Specificity