Universität zu Köln

Yu, Dongli (2022). A novel regulatory mechanism of the plant TIR immune signaling. PhD thesis, Universität zu Köln.

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Abstract

Plant defense against microbial pathogens is mainly realized by pattern-triggered immunity (PTI) mediated by pattern recognition receptors (PRRs) at the cell surface, and effectortriggered immunity (ETI) mediated by nucleotide-binding leucine-rich repeat (NLR) immune receptors inside cells. Based on their N-terminal domains, plant NLRs can be divided into two categories: CC-NLRs (CNLs) with a coiled-coil (CC) domain and TIR-NLRs (TNLs) with a toll/interleukin 1 receptor (TIR) domain. Specific recognition of pathogen effectors induces oligomerization of NLRs, termed resistosomes, to transduce plant immune signaling. CNLs are able to form pentameric resistosomes upon activation and function as calcium (Ca2+)-permeable channels in the plasma membrane. Whether TNLs form resistosomes in response to pathogen infection remained an open question, although the TIR domain in TNLs has NADase activity that is required for TNL-mediated immunity. NADase activity, although essential, is not sufficient for TIR-triggered immune responses in plants, suggesting that other components may be required for TIR-mediated signaling. In my dissertation, I employed multiple approaches including biochemistry and structural biology to address these questions. The thesis contains three parts: In the first part, I present multiple lines of evidence showing that the Arabidopsis TNL RPP1 (for recognition of Peronospora parasitica 1) forms a tetrameric resistosome upon recognition of the cognate Hyaloperonospora arabidopsidis effector ATR1. Biochemical and structural data are summarized revealing the mechanism underlying the requirement of the RPP1 resistosome formation for NADase activity. The data from this study define the mechanism of direct effector recognition by a TNL, and demonstrate that the assembly of RPP1 resistosomes is required for TIR-encoded NADase activity and RPP1 function. In the second part, I describe biochemical evidence that TIR domain proteins also exhibit 2′,3′-cAMP/cGMP synthetase activity with RNA and probably DNA (RNA/DNA) as substrates. Then I present functional data supporting the physiological relevance of the synthetase activity in TIR-mediated immune responses. Structural data on a TIR domain protein bound by its dsDNA substrate are described, and the mechanisms of how TIR domain proteins encode both NADase and synthetase activities and how the two activities may act together to mediate TIR signaling are discussed. The data presented in this part reveal a novel enzymatic activity of plant TIR domain proteins and establish a role of 2′,3′-cAMP/cGMP in plant immunity. In the last section of my thesis, I describe experiments testing whether the RNase-like effector proteins associated with haustoria (RALPH effectors) have RNase activity.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Yu, Dongli dyu@mpipz.mpg.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-643746
Date:	22 November 2022
Place of Publication:	Cologne
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Außeruniversitäre Forschungseinrichtungen > MPI for Plant Breeding Research
Subjects:	Natural sciences and mathematics Life sciences
Uncontrolled Keywords:	Keywords Language plant immunity English NLRs English TIRs English 2′,3′-cAMP/cGMP synthetases English bifunctional enzymes English 2′,3′-cAMP/cGMP phosphodiesterases English
Date of oral exam:	12 September 2022
Referee:	Name Academic Title Chai, Jijie Professor Behrmann, Elmar Professor Schulze-Lefert, Paul Professor
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/64374