Ustilago maydis

U. maydis is a basidiomycetes that cause smut disease on its host plants maize and the maize predecessor teosinte. The most prominent feature of U. maydis is its ability to cause galls filled with black spores on all aerial parts of the plant. U. maydis became a prominent fungal pathogen model as it can be grown saprophytically like yeast but infects as a true specialized biotroph its host plant. It is amendable to genetic manipulation and the whole molecular toolbox to study various aspects of fungal biology has been developed.

 

Life cycle: After mating and formation of a dikaryotic filament, U. maydis forms a penetration structure on the leaf surface, a so-called appressorium. Previously it has been shown that hydrophobicity and hydroxyl- fattyacids are the two cues that induce this developmental program. RNAseq, microarray-studies and mass-spectrometric analyses of different developmental stages of U. maydis indicate, that filament formation and appressoria formation on the host plant maize induce expression of a number of genes encoding putative secreted protein effectors. Their expression is spatially and temporally controlled. (Lanver et al 2018) (Skibbe et al. 2010). The U. maydis genome encoded for several hundred candidate effector genes of which only very few have been so far functionally characterized. We developed a systematic EFFECTOMICs approach to reveal new effector functions efficiently.

Powdery mildews

Blumeria graminis is an obligate biotrophic Ascomycete fungus that causes powdery mildew disease (PM) on a number of grass species. Several formae speciales (ff.spp.) of B. graminis can be distinguished by their specific host range. B. graminis f. sp. hordei (barley PM) normally infects only barley and B. graminis f.sp. tritici (wheat PM) normally infects only wheat. The massive and simultaneous spore production, airborne proliferation and the ability of sexual reproduction puts B. graminis in the highest pathogen risk class (McDonald & Linde, 2002, Euphytica 124:163).

 

Barley and powdery mildew as a model system

Barley and the barley PM are a well-established model system to study obligate biotrophic grass- fungal pathogen interactions and plant immunity. The epiphytic hyphal growth on leaf or stem surfaces with interaction limited to the epidermal layer of cells allows easy visualization of host cellular processes and fungal development. The cell-autonomous nature of the host defense against PM makes the system very well suited for single-cell experiments including transient induced gene silencing (TIGS) or transient gene overexpression (TOX). The extreme host specificity of the fungus allows studies of nonhost resistance and cross-validation experiments for instance with barley/wheat PM and wheat/barley PM. The genome of both species has been fully sequenced.