The nitrate assimilation model system Aspergillus nidulans: Genetic, genomic and proteomic approaches to understand nitrate signalling.

Rational: This project aims to improve our understanding of the molecular regulation of nitrate utilization. Nitrate is heavily used in agriculture but has proven health risks for humans. The better understanding of underlying regulatory mechanisms has the potential to improve also the efficacy of the more than 100 million tons of nitrogen fertilizers applied anually worldwide. Description: The common soil fungus Aspergillus nidulans has proven to be one of the most advanced model organism to study the molecular basis of nitrate assimilation and a wealth of information is available on the main regulators governing the genes responsible for this process. In this project we plan to extend our knowledge to the molecular switches signalling the presence or absence of nitrate from the environment through to the cell nucleus. For this purpose we intend to employ genetic screens with engineered Aspergillus strains carrying reporter constructs which are indicating the function of a signalling process. In a second work package, the transcriptional response of nitrate induction on a whole genome level will be analyzed by differential display techniques and by the appplication of microarray-based transcriptome analysis. Thirdly, the whole detectable protein complement of Aspergillus will be analyzed for the response to nitrate. It is anticipated that some proteins will appear or disappear in response to the stimulus and some will undergo specific modifications which modulate their activity. These changes will be monitored by the application of Two-Dimensional protein separation techniques combined with mass spectometry and bioinformatics tools which alltogether allow the identification of the nitrate responsive protein(s). The results from our studies will unravel new signalling pathways responding to nitrate in a simple eukaryote fungus. Many of these pathways are genetically conserved between fungi and plants and a better understanding of this pathway could help to increase the efficacy of nitrogen fertilizers and hence reduce the considerable health threat related to consumption of nitrate by humans.