Universität zu Köln

Katzy, Philipp Michael (2025). Identification of signaling peptides involved in immune responses in Zea mays. PhD thesis, Universität zu Köln.

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Abstract

The phytohormone salicylic acid (SA) plays a crucial role in regulating plant immunity, particularly against biotrophic pathogens. SA modulates a variety of molecular processes including the transcriptional regulation of pathogenesis-related (PR) genes and the activation of apoplastic proteases. So far, neither early responses within the first 24 hours are described in maize nor have serine hydrolases, an important class of apoplastic proteases, been implicated in SA-induced responses. Thus, the first part of this study focused on profiling and identifying active SHs after SA treatments. A significant increase in the activity of SHs was observed 3 hours upon SA treatment and three activated subtilases: ZmSBT7, ZmSBT1.9 and ZmSBT4, were identified. So far, their role in maize immunity has not been elucidated. However, orthologs of these subtilases were shown to be involved in resistance against biotrophic pathogens. As the activation of certain proteases was demonstrated to result in the release of signaling peptides (phytocytokines), the second aim of this study was to identify novel SA-related phytocytokines and elucidate their role in immunity. Numerous peptides were identified being uniquely present at 3 hours upon SA treatment. 14 peptides were selected as phytocytokine candidates (PC1 to PC14) of which six were found to induce PR-gene expression, indicating a role in SA signaling. Notably, the presence of two PCs modulated the virulence of Ustilago maydis, a biotrophic maize pathogen. PC13 was found to significantly reduce the virulence of U. maydis, while SIGGI (PC14) was observed to increase U. maydis virulence. Transcriptome analysis in response to SIGGI revealed its ability to induce genes involved in ubiquitination, proteolysis and SA-biosynthesis pointing to a potential role in modulating protein homeostasis and SA signaling. In contrast, PC13 triggered the upregulation of genes associated with programmed cell death (PCD), hypersensitive response (HR) and negative regulation of the jasmonic acid (JA) signaling pathway. This suggests that PC13 may influence the balance between defense mechanisms potentially by modulating the SA-JA crosstalk. In conclusion, this study shows an early increase in serine hydrolase activity, specifically subtilases, upon SA treatments. These subtilases could likely release potential phytocytokines to modulate immune related hormonal pathways. These results deepen our knowledge about proteases and substrates involved in the plant immune system.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Katzy, Philipp Michael philippkatzy@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-800966
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 Plant Sciences English Plant Immunity English phytocytokines English
Date of oral exam:	24 March 2025
Referee:	Name Academic Title Döhlemann, Gunther Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/80096