Transcriptome analysis of nitrate assimilation in Aspergillus nidulans reveals connections to nitric oxide metabolism.
Nitrate is a dominant form of inorganic nitrogen (N) in soils and can be efficiently assimilated by bacteria, fungi and plants. We studied here the transcriptome of the short-term nitrate response using assimilating and non-assimilating strains of the model ascomycete Aspergillus nidulans. Among the 72 genes positively responding to nitrate, only 18 genes carry binding sites for the pathway-specific activator NirA. Forty-five genes were repressed by nitrate metabolism. Because nirA(-) strains are N-starved at nitrate induction conditions, we also compared the nitrate transcriptome with N-deprived conditions and found a partial overlap of differentially regulated genes between these conditions. Nitric oxide (NO)-metabolizing flavohaemoglobins were found to be co-regulated with nitrate assimilatory genes. Subsequent molecular characterization revealed that the strongly inducible FhbA is required for full activity of nitrate and nitrite reductase enzymes. The co-regulation of NO-detoxifying and nitrate/nitrite assimilating systems may represent a conserved mechanism, which serves to neutralize nitrosative stress imposed by an external NO source in saprophytic and pathogenic fungi. Our analysis using membrane-permeable NO donors suggests that signalling for NirA activation only indirectly depends on the nitrate transporters NrtA (CrnA) and NrtB (CrnB).
Schinko
Thorsten
T
Fungal Genetics and Genomics Unit, Department of Applied Genetics and Cell Biology, Austrian Institute of Technology and BOKU University Vienna, Muthgasse 18, 1190 Vienna, Austria.
Berger
Harald
H
Lee
Wanseon
W
Gallmetzer
Andreas
A
Pirker
Katharina
K
Pachlinger
Robert
R
Buchner
Ingrid
I
Reichenauer
Thomas
T
Güldener
Ulrich
U
Strauss
Joseph
J
D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism; D001233:Aspergillus nidulans / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism
D027321:Anion Transport Proteins; D005656:Fungal Proteins; D000091285:Nitrate Transporters; D009566:Nitrates; D009569:Nitric Oxide; D009572:Nitrite Reductases; D050901:Nitrate Reductase