Universität zu Köln

Wanke, Alan ORCID: 0000-0002-8932-1809 (2023). Innate sensing of β-glucans in plants: insights into the role of host β-glucanases and fungal cell surface glycans in plant-fungal interactions. PhD thesis, Universität zu Köln.

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Abstract

As plants constantly interact with living organisms from all kingdoms of life, they deploy receptor-based surveillance systems to assess their immediate surroundings and adapt accordingly. Glycans, a major component of cell surfaces in microbes and plants, represent a central class of ligands for these receptors, enabling plants to effectively interpret their biotic environment. Upon enzymatic attack, hydrolytically released fragments inform the host about putative invaders and self-damage. Moreover, some microbes actively secrete glycan-based molecules as symbiotic messenger to initiate host symbiotic programs. In most cases, it is not the perception of a single molecule but rather the continuous integration of an array of signals, creating a complex and intertwined signaling network that shapes the host response. Fungal cell wall β-glucans represent an important class of glycans in plant-fungal interactions. Although it has long been known that β-glucans can elicit plant immunity, our understanding of the molecular principles underlying this process has been hindered by technical challenges. With the recent advances in glycan biochemistry and plant immunity research, new tools and resources emerged to readdress the fundamental questions underpinning innate sensing of β-glucans in plants. To establish a comprehensive literature-based foundation for this thesis, we conducted an extensive review of our current understanding on the impact of glycans in various plant-microbial interactions (Chapter 2). Furthermore, we spotlight how the use of secreted fungal lectins as microscopic probes can advance our view on fungal cell wall architectures. Based on recent literature and our own microscopic observations, we present a three-layer cell wall model for plant-associated fungi. We performed a systematic study on the perception of short-chain and long-chain β-glucans in different plants which revealed striking species-specific differences in β-glucan perception based on β-glucan polymer length (Chapter 3). We demonstrate that perception of these two classes of β-glucan substrates is mediated by different receptor systems, unveiling a previously unknown, CERK1-independent glucan perception pathway in plants. Although recent studies emphasized the presence of a β-glucan-rich extracellular polysaccharide matrix surrounding fungal hyphae, only little is known on the function of this outer most cell wall layer. In Chapter 4, we isolated cell walls from the root mutualistic fungus Serendipita indica and the hemibiotrophic pathogen Bipolaris sorokiniana, separating the outer, amorphous polysaccharide matrix from the rigid inner cell wall core. We show that these two layers are separate but interconnected compartments with distinct glycomic and proteomic signatures. Moreover, we demonstrate that fungi hijack the host hydrolytic machinery to release an antioxidative β-glucan decasaccharide from their extracellular polysaccharide matrix to facilitate plant colonization. This mechanism represents a conserved strategy in phylogenetically distant fungi with different plant-associated lifestyles. In Chapter 5, we applied a proteomic pull-down approach with biotinylated laminarin to identify host components involved in β-glucan-mediated immunity pathways. This identified a GH81-type β-1,3-endoglucanase that acts a tissue-independent compatibility factor for mutualistic and pathogenic fungi. Overall, the findings presented in this thesis contribute several novel aspects with regards to fungal cell wall architecture as well as the processing and perception of β-1,3-glucans by plants. These concepts not only directly impact our understanding of plant-fungal interactions, but furthermore highlight the role of glycans in the context of complex microbial communities.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Wanke, Alan alan.wanke@slcu.cam.ac.uk orcid.org/0000-0002-8932-1809 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-701958
Date:	23 February 2023
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 Life sciences
Uncontrolled Keywords:	Keywords Language plant English fungi English cell wall English symbiosis English glucan English pattern-triggered immunity English carbohydrate English bacteria English immunity English
Date of oral exam:	2 June 2023
Referee:	Name Academic Title Zuccaro, Alga Prof. Dr. Thomma, Bart Prof. Dr. Riemer, Jan Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/70195