Universität zu Köln

Werner, Janina ORCID: 0000-0002-6421-4783 (2024). A smut hybrid provides insights into the regulation of effector genes contributing to tumor formation of Ustilago maydis. PhD thesis, Universität zu Köln.

All available versions of this item

• A smut hybrid provides insights into the regulation of effector genes contributing to tumor formation of Ustilago maydis. (deposited 16 May 2025 08:27) [Currently Displayed]

PDF Dissertation_Janina Werner_June2024_KUPS.pdf Download (12MB)

Abstract

The smut fungi infect economically important crops such as barley, sorghum, wheat, and maize. The majority of the smuts infect their host systemically, replacing the inflorescences with teliospores. An example is Sporisorium reilianum, which can infect maize (S. reilianum f. sp. zeae) and sorghum (S. reilianum f. sp. reilianum) to cause head smut disease. In contrast, Ustilago maydis, the prime model organism of the smuts and a close relative of S. reilianum, can form distinct tumors locally at infection sites on both, maize leaves and inflorescences. U. maydis and S. reilianum have similar genomes and infect the same host, Zea mays, providing a promising basis for interspecific hybridization. The objective of this study was to elucidate the molecular mechanisms underlying the different disease progressions observed in U. maydis and S. reilianum. An exchange of the mating type genes between the species resulted in the generation of a recombinant hybrid using the mating type system of S. reilianum (rUSH). rUSH successfully colonized maize and displayed an S. reilianum-like phenotype without the formation of teliospores. RNA sequencing (RNA seq) was employed to provide insights into the gene expression levels in the binuclear recombinant hybrid strain, which revealed 218 differentially expressed one-to-one effector orthologues in rUSH with three distinct gene expression patterns: cis-, trans- and hybrid-specific expression. Within these patterns, several downregulated U. maydis effector genes were identified mainly residing in gene clusters previously associated with virulence. Therefore, I postulated that U. maydis effector genes being downregulated in the non-tumor-forming rUSH may play a role in tumor formation. To test this hypothesis, infection assays were performed with knock-out mutants of the respective effector genes. This resulted in the identification of two novel U. maydis virulence factors with a role in tumor formation. As a next step, transcription factors (TFs) that are activated during host infection by U. maydis were overexpressed in rUSH to elucidate whether this could lead to a shift towards the U. maydis phenotype. Strikingly, the overexpression of the conserved TF Hdp2 of U. maydis and S. reilianum induced tumor formation in maize seedlings. The utilization of RNA-seq facilitated the identification of five TFs and 41 U. maydis effector genes regulated directly or indirectly by Hdp2. Thus, using rUSH as a tool to investigate the regulation of effector orthologue expression between the two species resulted in the identification of novel virulence factors and the identification of a key TF for tumor formation of U. maydis. Future studies aim to elucidate additional elements downstream of Hdp2 to unravel the underlying mechanism of U. maydis induced tumorigenesis.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Werner, Janina jwerne24@uni-koeln.de orcid.org/0000-0002-6421-4783 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-750916
Date:	2024
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 Sporisorium reilianum UNSPECIFIED hybrid UNSPECIFIED
Date of oral exam:	19 September 2024
Referee:	Name Academic Title Döhlemann, Gunther Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/75091