The Ustilago hordei-Barley Interaction Is a Versatile System for Characterization of Fungal Effectors.

Bilal Ökmen,Ulla Neumann,Gunther Doehlemann,Daniela Schwammbach,Guus Bakkeren

doi:10.3390/jof7020086

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.

Highlights

Plant pathogens have evolved different types of pathogenic lifestyles with their hosts, including obligate biotrophic, biotrophic, hemibiotrophic, and necrotrophic
It has been found that compared to biotrophic pathogens, necrotrophs and hemibiotrophs have more plant cell wall degrading enzymes, secondary metabolites, and toxins in order to kill their host cells during the infection and feed on nutrients released from dead host cells [6,7,8]
The requirement of mating for the induction of pathogenic development implies that genetic mutations always need to be made in both compatible U. hordei strains, which presents an obvious drawback of the system, for larger scale analyses

Summary

Introduction

Plant pathogens have evolved different types of pathogenic lifestyles with their hosts, including obligate biotrophic, biotrophic, hemibiotrophic, and necrotrophic. Recent genome and transcriptome analyses of a wide range of phytopathogens have provided new insights into the effector inventories of pathogens with different pathogenic lifestyles [1,2,3,4,5]. It has been found that compared to biotrophic pathogens, necrotrophs and hemibiotrophs have more plant cell wall degrading enzymes, secondary metabolites, and toxins in order to kill their host cells during the infection and feed on nutrients released from dead host cells [6,7,8]. While many effectors from different facultative biotrophs, hemibiotrophs, and necrotrophs have been functionally characterized, there is still limited mechanistic insight into effectors of obligate biotrophic filamentous pathogens

Methods

Results

Conclusion