Universität zu Köln

Schurack, Selma (2021). Mechanisms of quantitative disease resistance in the maize - Ustilago maydis interaction. PhD thesis, Universität zu Köln.

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Abstract

The biotrophic pathogen Ustilago maydis causes smut disease on maize (Zea mays) and induces the formation of tumours on all aerial parts of the plant. Unlike in other biotrophic interactions, no gene-for-gene interactions have been identified in the maize-U. maydis pathosystem. Thus, maize resistance to U. maydis is considered a polygenic, quantitative trait. In this study, the molecular mechanisms that underlie the interaction of U. maydis with maize lines of quantitatively different resistance levels were investigated. This aimed at elucidating whether the fungus’ virulence strategy is adapted to different host genotypes and at identifying host processes involved in quantitative disease resistance (QDR) to U. maydis. Based on quantitative scoring of disease symptoms in 26 maize lines, an RNA-Seq analysis of six U. maydis-infected maize lines of highly distinct resistance levels was performed. In accordance with the complex nature of QDR, the different maize lines showed specific responses of diverse cellular processes to U. maydis infection. On the fungal side, 406 genes were differentially expressed between maize lines, of which 102 encode predicted effector proteins. Furthermore, correlation analysis of co-expressed U. maydis genes to the susceptibility levels of the different maize lines suggested differences in host nutrient availability as well as cell wall composition to be involved in QDR to U. maydis. On the host side, expression of genes related to cell division or photosynthesis was correlated with low or high resistance levels, respectively. Based on the enrichment of predicted effector genes in differentially expressed U. maydis genes, U. maydis CRISPR/Cas9 knock-out mutants for selected maize line-specific effector sets were generated to investigate, if and how U. maydis effectors are adapted to the host genotype. Infections of different maize lines with the fungal mutants identified effectors with quantitative, maize-line-specific virulence functions. RNA-Seq revealed auxin-related processes as a possible target for one of those effectors, UMAG_02297. To identify genetic loci contributing to QDR to U. maydis in maize seedlings, a QTL mapping experiment using a population derived from a cross of two maize lines with highly distinct U. maydis resistance was performed in the field. Preliminary data identified one QTL on chromosome 9 that contributes to heavy tumour formation. Taken together, this study showed that both transcriptional activity and virulence function of fungal effectors are modified according to the infected maize line, which provides new insights into the molecular mechanisms underlying the quantitative interaction of U. maydis and maize.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Schurack, Selma selma.schurack@web.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-356753
Date:	2021
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Botanical Institute
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language Ustilago maydis UNSPECIFIED quantitative disease resistance UNSPECIFIED plant microbe interactions UNSPECIFIED
Date of oral exam:	16 February 2021
Referee:	Name Academic Title Doehlemann, Gunther Prof. Dr. Zuccaro, Alga Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/35675