Nitric oxide (NO), and its role in signalling, has been extensively studied in mammals and to some extent
in plants. However, little is known about the role of NO in fungi and how it is synthesized in these
organisms. Recently, we reported that NO production in A. nidulans is coupled to conidiation and requires
a functional nitrate reductase (NR) gene (niaD) that is upregulated under these conditions even in the
presence of the repressing nitrogen source ammonium. NO levels influence the balance between
conidiation and sexual reproduction.
Here we report that NO levels are also modulated by light, a general environmental cue and a regulator of
fungal development. The light-dependent modulation of nitric oxide levels involves NO catabolism by the
mitochondrial flavohemoglobin fhbB, and agaA, an arginase that controls the intracellular concentration of
the NO precursor arginine. Addition of arginine to the cultures provokes a transient increase of the
production of NO. However, analogues of arginine did not affect the production of NO. Mutants in the
urea cycle genes show differences in NO levels compared to the wild type strain. Taken together our
findings indicate that light-dependent developmental processes in A. nidulans interfere with nitric oxide
metabolism which – in addition to nitrate reduction - is modulated by enzymes of the urea cycle.
Reference: Marcos AT, Ramos MS, Marcos JF, Carmona L, Strauss J, Cánovas D. Nitric oxide synthesis
by nitrate reductase is regulated during development in Aspergillus. Mol Microbiol (2016) 99:15-33.
Full conference title:
- Asperfest 14 (2017)