Role of Ustilago Nit2 in nitrogen utilization

The basidiomycete Ustilago maydis is the causal agent of corn smut disease and induces tumor formation during biotrophic growth in its host plant maize. The Usilago maydis genome harbors a homolog to the GATA transcription factors Nit2 and AreA that act as global regulators of nitrogen catabolite repression in filamentous model fungi Neurospora crassa and Aspergillus nidulans, respectively. We aimed at resolving the role of the Ustilago maydis Nit2 homolog for the utilization of complex nitrogen sources and pathogenicity. Sporidia of the indicated Ustilago maydis strains were grown overnight in ammonium minimal medium (Holliday, 1976) and samples for total RNA extraction were taken 2h after transfer to minimal medium lacking any nitrogen source (-N) during the exponential growth phase to assess those genes that are regulated in response to nitrogen starvation. The solopathogenic strain SG200 (control) and deletion mutants of UmNit2 were studied in two independent experiments. The (Target of Nit2) UmTon1 deletion mutant was examined in one experiment only. All mutants were generated in the SG200 background. Per strain and experiment, three biological replicate samples were analyzed (except for only two biological replicates for the Nit2 mutants in the second experiment).