Conditional gene expression reveals stage‐specific functions of the unfolded protein response in the Ustilago maydis–maize pathosystem

Summary Ustilago maydis is a model organism for the study of biotrophic plant–pathogen interactions. The sexual and pathogenic development of the fungus are tightly connected since fusion of compatible haploid sporidia is prerequisite for infection of the host plant, maize (Zea mays). After plant pe...

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Bibliographic Details
Published in:Molecular plant pathology 2020-02, Vol.21 (2), p.258-271
Main Authors: Schmitz, Lara, Kronstad, James W., Heimel, Kai
Format: Article
Language:English
Subjects:
Analysis
Cassettes
Chromatin
conditional gene expression
Control systems
Corn
Deletion mutant
Fungi
Gene expression
Genetic engineering
Genetic research
Genomes
Health aspects
Host plants
Infection
Infections
Localization
Mutants
pathogenicity
Penetration
Protein folding
Proteins
Robust control
Technical Advance
Transcription factors
unfolded protein response
Ustilago
Ustilago maydis
Zea mays
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Summary:Summary Ustilago maydis is a model organism for the study of biotrophic plant–pathogen interactions. The sexual and pathogenic development of the fungus are tightly connected since fusion of compatible haploid sporidia is prerequisite for infection of the host plant, maize (Zea mays). After plant penetration, the unfolded protein response (UPR) is activated and required for biotrophic growth. The UPR is continuously active throughout all stages of pathogenic development in planta. However, since development of UPR deletion mutants stops directly after plant penetration, the role of an active UPR at later stages of development remained to be determined. Here, we established a gene expression system for U. maydis that uses endogenous, conditionally active promoters to either induce or repress expression of a gene of interest during different stages of plant infection. Integration of the expression constructs into the native genomic locus and removal of resistance cassettes were required to obtain a wild‐type‐like expression pattern. This indicates that genomic localization and chromatin structure are important for correct promoter activity and gene expression. By conditional expression of the central UPR regulator, Cib1, in U. maydis, we show that a functional UPR is required for continuous plant defence suppression after host infection and that U. maydis relies on a robust control system to prevent deleterious UPR hyperactivation. A new expression system enabling the analysis of stage‐specific gene functions in Ustilago maydis reveals the continuous requirement of the unfolded protein response for biotrophic growth in planta.
ISSN:1464-6722
1364-3703
DOI:10.1111/mpp.12893