KINGDOM EUMYCOTA Phylum 3 - DIKARYOMYCOTA Subphylum ...

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Ustilago maydis (corn smut) shows an alternation between a saprophytic yeast phase and a parasitic (obligately!) filamentous phase. Casselton, LA and Olesnickcy, NS 1998 Microbiology and Molecular Biology Reviews 62: 55-70.
Key points: -Corn smut is caused by Ustilago maydis -A promycelium = a 4 celled smut basidium -The monokaryon is a haploid saprophyte yeast (yeast cells are here called sporidia). -Not until mating and the formation of dikaryon does this fungus become a obligate parasite on corn. There are 2 mating type loci, each with different “jobs”. -Dimorphism means two forms: yeast + hyphae -The haploid dikaryon is the obligate, biotrophic parasitic phase. It is filamentous hyphae. - To reproduce, a diploid forms that in turn forms teliospores. -Teliospores form basidia (= promycelia). Switch from saprophytic growth by budding to filamentous and pathogenic development regulated by the multi-allelic b-mating type locus that encodes 2 unrelated homeodomain proteins bE and bW. The combination of the alleles forms heterodimer that controls pathogenicity genes as a transcriptional regulator. - Bolker M. 2001. Microbiology 147:1395-1401. - Steinberg, G. and Perez-Martin, J. (2008) Ustilago maydis, a new fungal model system for cell biology. Trends Cell Biol., 18, 61-67.
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Page 3: 3 characteristics of Ustilaginales

KINGDOM EUMYCOTA Phylum 3 - DIKARYOMYCOTA Subphylum ...

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