The Ustilago hordei–Barley Interaction is a Versatile System for Characterization of Fungal Effectors

Abstract

Obligate biotrophic fungal pathogens, such as Blumeria graminis and Puccinia graminis, are amongst the most devastating plant pathogens, causing dramatic yield losses in many economically important crops worldwide. However, a lack of reliable tools for the efficient genetic transformation has hampered studies into the molecular basis of their virulence or pathogenicity. In this study, we present the Ustilago hordei–barley pathosystem as a model to characterize effectors from different plant pathogenic fungi. We generate U. hordei solopathogenic strains, which form infectious filaments without the presence of a compatible mating partner. Solopathogenic strains are suitable for heterologous expression system for fungal virulence factors. A highly efficient Crispr/Cas9 gene editing system is made available for U. hordei. In addition, U. hordei infection structures during barley colonization are analyzed using transmission electron microscopy, showing that U. hordei forms intracellular infection structures sharing high similarity to haustoria formed by obligate rust and powdery mildew fungi. Thus, U. hordei has high potential as a fungal expression platform for functional studies of heterologous effector proteins in barley.

A conserved enzyme of smut fungi facilitates cell-to-cell movement in the plant bundle sheath

“…1,3-β-glucans are well described elicitors, inducing basal defense responses such as callose (another 1,3-β-glucan) deposition at infection sites (Wanke et al ., 2020; Wanke et al ., 2021; Chandrasekar et al ., 2022). Recently, we performed immune gold labelling of 1,3-β-glucans on U. hordei infected barley leaf sections; subsequent TEM analysis revealed a strong accumulation of 1,3-β-glucans at the biotrophic interface (Ökmen et al ., 2021). Thus, one could hypothesize that Erc1 hydrolyzes 1,3-β-glucans to prevent the accumulation and subsequent recognition of these DAMP molecules at the biotrophic interface (Fig.…”

“…The CRISPR/Cas9-HF (high fidelity) gene editing system was used to knockout the Erc1 gene in the U. hordei as described in Ökmen et al . (2021).…”

Smuts to the Power of Three: Biotechnology, Biotrophy, and Basic Biology

“…Application of CRISPR/Cas9 is also possible for Ustilago hordei , a smut fungus forming intracellular structures with high similarity to haustoria of obligate rust fungi. B. Ökmen and coworkers developed a solopathogenic strain and suggest its use for the functional study of heterologous rust effector proteins [ 5 ]. In contrast, L. Plücker and coworkers suggest development of a model of the Brassicaceae smut fungus Thecaphora thlaspeos that can infect Arabidopsis thaliana .…”

An Endoglucanase Secreted by Ustilago esculenta Promotes Fungal Proliferation

“…There are diverse strategies existed, e.g., hemibiotroph fungi such as Magnaporthe oryzae and Colletotrichum species possess melanized appressorium with extremely high turgor pressure, which converts to mechanical pressure to help with going through the plant cuticle and plant cell wall [ 11 , 12 ]. Biotrophs such as U. maydis and U. hordei have non-melanized appressorium and facilitate penetration of the cuticle and plant cell wall by secretion of plant cell wall degrading enzymes (CWDEs) and mechanical force [ 13 , 14 ]. U. esculenta is unable to form structures such as appressorium, therefore secretion of CWDEs is most likely the prime strategy to enter into the plant cytoplasm.…”