Regulators for Ustilago maydis mig gene expression during pathogenic development

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The corn pathogen Ustilago maydis requires its host plant maize for development and completion of its sexual life cycle. We have identified the Ustilago maydis genes mig1 and mig2 that show a plant specific expression profile. The mig2 genes are organized in a cluster comprising five highly homologous genes, designated mig2-1 to mig2-5. In the promoters of the mig2-1 and mig2-5 genes distinct negatively- and positively cis-acting regions have been mapped. In particular, a highly conserved 40bp region has been identified in the mig2-5 promoter that is absolutely required for gene activation during the biotrophic growth phase. In this proposal we wish to delineate the respective consensus sequences and to isolate the transcriptional regulator(s) from U. maydis that bind(s) to this region by a biochemical approach based on gel retardation analysis and a yeast one-hybrid screen. The gene(s) encoding the binding activity will be analysed and U. maydis mutants deleted in identified mig2 activator genes will be generated to investigate their impact on mig gene regulation and pathogenicity. Furthermore, identified mig2 activator genes will be expressed under control of an inducible promoter to assess whether overexpression is sufficient to trigger mig gene expression during axenic growth. If successful, conditional activator strains will be exploited to screen for additional target genes by microarray analysis.