Universität zu Köln

Kraege, Anton ORCID: 0000-0002-4741-5671 (2026). Functional and Evolutionary Characterization of Antimicrobial Effectors Secreted by Verticillium dahliae to Shape Host Microbiota. PhD thesis, Universität zu Köln.

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Abstract

Plants are continuously colonized by diverse microbial communities, collectively known as the plant microbiota, which inhabit all parts of the plant including roots, shoots, and leaves. The assembly of these communities is shaped by both environmental factors, such as soil properties and microbial pools, and host-derived factors, including root exudates that attract or repel specific taxa. Together with their host, these microbes form a functional unit known as the holobiont, in which host and microbial activities are tightly interconnected. The microbiota contributes to plant health by protecting against pathogens, for instance through direct antagonism or by stimulating host defences. Under pathogen attack, plants can recruit beneficial microbes from the bulk soil to enhance protection, a process termed the “cry for help” response. Research over recent years has shown that plant pathogens have evolved sophisticated strategies to overcome not only plant immune responses, but also microbiota-mediated defences. Many pathogens secrete antimicrobial effector proteins that manipulate host-associated microbial communities to facilitate disease development. In this thesis research I aimed to investigate the functional and evolutionary roles of antimicrobial effectors in shaping plant–microbe interactions and promoting pathogen success. During my doctoral research, I investigated the functional and evolutionary roles of antimicrobial effectors in shaping plant–microbe interactions and pathogen success. We first characterized the Verticillium dahliae effector Av2, demonstrating that it suppresses the plant’s “cry for help” recruitment of antagonistic Pseudomonas bacteria, providing the first evidence that pathogens can actively undermine microbiota-mediated host defences. We then examined the effector Ave1, revealing that it perturbs host-associated microbial communities across natural soils and that its contribution to fungal virulence is strongly influenced by the composition of the soil microbiota, highlighting the context-dependent interaction between effectors, microbial communities, and pathogen success. Expanding to an evolutionary perspective, we developed an antimicrobial activity predictor and, revealed that antimicrobial effector repertoires in filamentous fungi are larger and more conserved than previously recognized. Additionally, we found that many fungal effectors with immunomodulatory functions possess conserved antimicrobial activity, supporting the idea that ancient antimicrobial molecules were repeatedly co-opted as immunomodulators during fungal adaptation to plant-associated niches. Focusing on the cerato-platanin effector family in V. dahliae, structural clustering revealed four effectors, including Ave1, with conserved antimicrobial activity in vitro, a trait maintained across fungi with diverse lifestyles. Together, these findings position antimicrobial effectors as ancient molecules that have been repeatedly co-opted by plant pathogens in the ongoing arms race between plants and pathogens.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Kraege, Anton anton.kraege@gmail.com https://orcid.org/0000-0002-4741-5671 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-800016
Date:	2026
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Botanical Institute
Subjects:	Natural sciences and mathematics Agriculture
Uncontrolled Keywords:	Keywords Language Plant microbe UNSPECIFIED Antimicrobial UNSPECIFIED Verticillium UNSPECIFIED
Date of oral exam:	9 March 2026
Referee:	Name Academic Title Thomma, Bart Prof./ Principal Investigator de Jonge, Ronnie Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/80001