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SESSION 1: FUSARIUM – GENETICS, GENOMICS AND SYSTEMS BIOLOGY
Molecular network of nitrate sensing and assimilation
in Fusarium fujikuroi
A. Pfannmüller 1 , P. Wiemann 1,2 , B. Tudzynski 1
1 Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität Münster,
Schlossplatz 8, Münster, Germany ; 2 Department of Medical Microbiology and Immunology, University
of Wisconsin-Madison, WI, United States
E-mail: a_pfan02@uni-muenster.de
The phytopathogenic ascomycete Fusarium fujikuroi produces a broad spectrum
of interesting secondary metabolites, including the agriculturally applied plant
hormone gibberellic acid (GA3), the red pigment bikaverin and the fungal toxin
fusarin C. The biosynthesis of these three secondary metabolites depends greatly
on the amount and quality of the available nitrogen source. At high nitrogen
concentrations, the biosynthesis of gibberellins and bikaverin are repressed on
the transcriptional level, while fusarin C genes are repressed at nitrogen
starvation conditions. Because of this impact on secondary metabolism, the
detailed understanding of the nitrogen sensing and regulatory network in
F. fujikuroi is of great interest.
Previous work has shown that F. fujikuroi is able to sense the availability of
ammonium by the ammonium-transporter MepB and the glutamine synthetase
GS. However, it is not known if nitrate is sensed as a separate nitrogen source or
+
after its metabolization to NH4 and glutamine. Therefore, we analyzed
orthologues of the Aspergillus nidulans nitrate-specific activator NirA, the nitrate
reductase NiaD and the nitrate transporter NrtA, to gain more insights on the
nitrate sensing and assimilation process in F. fujikuroi. We show the impact of
FfNirA on the expression of certain nitrate-assimilatory genes and its subcellular
localization depending on the nitrogen availability and the activity of putative
nitrate sensors. Since the deletion of ffnirA, but not ffniaD led to a deregulation
effect on secondary metabolism under nitrate sufficient conditions, we are
investigating the putative role of FfNrtA as a nitrate transceptor and screen for
additional FfNirA-controlled genes that might be involved in the nitrate sensing of
F. fujikuroi.
Keywords: Fusarium fujikuroi, secondary metabolism, nitrate, sensing
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