Regulation des Mais-induzierten mig2-Genclusters in Ustilago maydis
Der Erreger des Maisbeulenbrands, Ustilago maydis, induziert die Entwicklung von Tumoren bei der Maispflanze. Die pathogene Entwicklung von U. maydis beginnt mit der Fusion zweier kompatibler haploider Sporidien. Das entstehende dikaryotische Filament penetriert die Pflanzenoberfläche und proliferie...
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| Format: | Doctoral Thesis |
| Language: | German |
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Philipps-Universität Marburg
2004
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| Online Access: | PDF Full Text |
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The phytopathogenic fungus Ustilago maydis causes smut disease in its host plant maize. Pathogenic development starts with the fusion of two compatible haploid sporidia resulting in dikaryotic hyphae, which is infectious. U. maydis proliferates within plant tissue and triggers the formation of tumors on aerial parts. The U. maydis mig2 gene cluster comprises five highly homologous genes identified by a differential display approach. All genes display a pronounced plant specific expression profile, suggesting co-regulation. In order to identify cis-regulatory elements the promoter of the strongest differentially expressed gene, mig2-5, was subjected to a detailed mutation analysis. A 350 bp mig2-5 promoter fragment contained all elements sufficient to confer differential promoter activity. Further analysis of this region, fused to the green fluorescent protein (GFP) reporter gene, allowed dissecting core promoter elements (TATA-like and Inr elements), which strongly contribute to high-level promoter activity, from elements conferring inducible expression in planta. In particular, the presence of several 5-CCA-3 motifs within a 70 bp stretch of the mig2-5 promoter was decisive for inducible promoter activity. On this basis an artificial promoter was reconstituted whose inducible activity specifically relied on multiple CCA motifs. Based on sequence comparison and mutation analysis within the critical 70 bp region, the 5'-CCAMC-3' consensus motif was derived representing a potential binding motif for the putative mig2-5 activator. In addition, a novel mig2 homologous gene, mig2-6, was identified that despite the fact that it is unlinked from the mig2 cluster displayed the strongest differential expression profile among mig2 genes. Comparative sequence analysis including the mig2-6 promoter revealed an over-representation of the consensus motif 5-MNMNWNCCAMM-3 in all mig2 promoter sequences. This hypothesized that promoter strength correlates with number and arrangement of this consensus element as well as with the existence of conserved core promoter elements. Finally, potential mig2 activator candidate genes could be narrowed down based on their predicted recognition motifs.