Universität zu Köln

Moormann, Jannis ORCID: 0000-0002-4059-2480 (2025). Cysteine in signaling and plant pathogen response. PhD thesis, Universität zu Köln.

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Abstract

Beyond their role as building blocks of proteins, amino acids serve a variety of additional functions in plants. Since plants are sessile organisms, they need to identify and properly deal with a plethora of adverse environmental circumstances. Amino acids are known to be implicated in plant stress responses in different ways. While some aspects are already well understood, many remain elusive to date. Here, we reviewed the recent research progress on amino acids in plant-microbe interactions (chapter 2). There, we explored how specialized metabolites and amino acid transporters shape the plant microbiome and elaborated on how amino acids impact plant immunity. Furthermore, we aimed to elucidate the role of cysteine in signaling and plant pathogen response (chapter 3). To that end, we set up a liquid culture approach in which Arabidopsis thaliana seedlings were incubated with 1 mM cysteine for 24 hours. Subsequent shotgun proteome analysis revealed that elevated cysteine levels are interpreted as a biotic threat by the plant. Consistent with this, cysteine both primed adult Arabidopsis plants against infection with the hemibiotrophic leaf pathogen Pseudomonas syringae (Pst) and its levels increased in response to Pst infection. Comparing proteome responses of cysteine-treated and Pst-infected plants revealed potential mediators of the cysteine-induced defense response. Unlike other amino acids, cysteine can be synthesized in multiple subcellular compartments by different O-acetylserine(thiol)lyase (OASTL) isoforms. Here, we found that the lack of mitochondrial OASTL-C renders Arabidopsis plants more susceptible to infection with Pst. Remarkably, mitochondria allow for the complete oxidation of cysteine facilitated by a four-step enzymatic process. This is the only pathway to degrade cysteine without producing sulfide, which becomes toxic in high concentrations. However, the first enzyme catalyzing the transamination of cysteine is unknown. Here, we aimed to identify the missing aminotransferase to complete the mitochondrial cysteine degradation pathway (chapter 4). Thus, we established mass spectrometry-based thermal proteome profiling (TPP) with mitochondrial fractions to find novel proteins binding or interacting with cysteine. Consequently, selected candidate proteins were produced in Escherichia coli and purified using immobilized metal affinity- and size exclusion chromatography. Strikingly, alanine aminotransferase 1 and aspartate aminotransferase 1 showed activity using cysteine as an amino donor. Moreover, both enzymes were able to complete the mitochondrial cysteine degradation pathway in vitro. The findings in this dissertation expand our understanding of cysteine as an infochemical in the plant pathogen response, highlight the importance of plant mitochondria for biotic stress adaptation and suggest potent targets for future research in plant immunity. Additionally, we present a powerful tool to identify novel protein metabolite interactions and, thereby, further our knowledge about the mitochondrial cysteine metabolism.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Moormann, Jannis jannis.moormann@gmx.de https://orcid.org/0000-0002-4059-2480 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-791500
Date:	2025
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 cysteine English pathogen response English arabidopsis English
Date of oral exam:	26 September 2025
Referee:	Name Academic Title Hildebrandt, Tatjana Prof Dr Doehlemann, Gunther Prof Dr
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/79150