Universität zu Köln

Eichfeld, Ruben ORCID: 0000-0001-6190-4482 (2025). Function of chitinases from beneficial root endophytes during fungal antagonism and host-immune evasion. PhD thesis, Universität zu Köln.

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Abstract

Microorganisms from all domains of life are ubiquitous inhabitants of plants growing in natural environments. Stable multi-kingdom consortia of plant-associated microbial communities, the plant microbiota, convey several beneficial functions to their host plant, including protection from pathogens. Both, the colonization of host tissue as well as competition with other microbes, including pathogens, partially relies on the secretion of microbial effector proteins. While effector proteins that target host-plant components have been extensively studied, antimicrobial effectors involved in microbiota interactions and host protection represent an emerging field of research. Beneficial root endophytic fungi from the order Sebacinales, especially Serendipita indica and Serendipita vermifera utilize a plethora of effector proteins to colonize host plants and additionally restrict the proliferation of pathogens in the rhizosphere. Thus, they are excellent models to study the role of antimicrobial effector proteins in plant-beneficial fungi. In this thesis, we analyze the transcriptome of S. indica and S. vermifera during host plant colonization and confrontation with microbes, including the hemi-biotrophic fungal pathogen Bipolaris sorokiniana. We define distinct effector categories based on transcriptional profiles. We identify and characterize a secreted GH18-CBM5 chitinase, SiCHIT as one antimicrobial effector protein that contributes to antagonism against B. sorokiniana, recapitulating the plant-protective function of S. indica and S. vermifera. Moreover, we demonstrate that loss of the CBM5 domain diminishes antifungal activity while enabling the emergence of an effector function during plant colonization. A paralogous GH18 chitinase, SiCHIT2, lacking the CBM5 domain contributes to the evasion of chitin-triggered immunity during host plant colonization. Remarkably, reintroducing the CBM5 domain into this chitinase restores antifungal activity. This exemplifies how domain reshuffling drives functional transitions in the evolution of effector proteins. Finally, I review classical and recent literature on the roles of chitinases as microbial effector proteins across different ecological niches and emphasized different structural variations as drivers of functional adaptations. Overall, this work advances the understanding of antimicrobial effector proteins and their evolution by integrating functional, evolutionary, and ecological perspectives. It highlights how beneficial fungi use chitinases as effectors for niche protection and host immune modulation and which structural rearrangements underlie the evolutionary trajectories of functional effector diversification.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Eichfeld, Ruben ruben.eichfeld@gmail.com https://orcid.org/0000-0001-6190-4482 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-793660
Date:	2025
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 Chitinase English Endophytic fungi English Plant immunity English
Date of oral exam:	5 December 2025
Referee:	Name Academic Title Zuccaro, Alga Prof. Dr Thomma, Bart Prof. Dr
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79366