Phytocytokines are endogenous signaling peptides that act as key regulators of plant immunity by amplifying and modulating defense responses, particularly within salicylic acid (SA)-associated pathways. Originally described as damage-associated molecular patterns (DAMPs), they are now recognized as actively regulated signals that fine-tune immune responses. Despite their importance in plant–pathogen interactions, the molecular mechanisms governing their activation, processing, and spatial release remain poorly understood.

In my PhD project, I investigated how the maize phytocytokine Zip1 (1) is processed from its precursor PROZIP1 to generate a bioactive signal (2). Building on earlier work demonstrating apoplastic cleavage by papain-like cysteine proteases (PLCPs), I showed that PROZIP1 undergoes intracellular processing at the endoplasmic reticulum by the type II metacaspase ZmMC9, generating a C-terminal fragment (Ct-PROZIP1). This step licenses PROZIP1 for unconventional secretion via an ER–Golgi-independent route, linking intracellular proteolysis to extracellular signaling and establishing intracellular proteolytic licensing as a key principle in phytocytokine activation. Following secretion, Ct-PROZIP1 is further processed in the apoplast by PLCPs and other proteases, contributing to signal modulation and turnover rather than primary activation. In parallel, I established a quantitative ELISA-based approach enabling sensitive detection of the phytocytokine Zip1 in plant tissues (3), and showed that multiple maize phytocytokines modulate pro-survival host responses and pathogen resistance (4).

As a postdoctoral researcher, I aim to establish a mechanistic framework for phytocytokine biogenesis across plant systems, including proteolytic networks, trafficking routes, and unconventional secretion pathways. By combining biochemical, cell biological, and proteomic approaches, this work seeks to define general principles of peptide-mediated communication and to enable targeted strategies for improving plant disease resistance through mechanistically guided manipulation.

(1) Ziemann, S., van der Linde, K., Lahrmann, U., Acar, B., Kaschani, F., Colby, T., ... & Doehlemann, G. (2018). An apoplastic peptide activates salicylic acid signalling in maize. Nature Plants, 4(3), 172–180.
(2) Koenig, M., Sorger, Z., Kakanj, P., Dewes, P., Mantz, M., Perrar, A., ... & Doehlemann, G. (2025). Processing and release of the maize phytocytokine Zip1. bioRxiv, 2025-06.
(3) Koenig, M., Sorger, Z., Keh, S. P. Y., Doehlemann, G., & Misas Villamil, J. C. (2025). Quantitative detection of the maize phytocytokine Zip1 utilizing ELISA. Journal of Experimental Botany, 76(2), 299–311.
(4) Koenig, M., Moser, D., Leusner, J., Depotter, J. R., Doehlemann, G., & Misas Villamil, J. (2023). Maize phytocytokines modulate pro-survival host responses and pathogen resistance. Molecular Plant-Microbe Interactions, 36(9), 592–604.

Dr. Maurice König

University of Cologne

CEPLAS / Institiute for Plant Sciences
Chair of Terrestrial Microbiology
Zülpicher Straße 47a
D-50674 Cologne

Tel:  +49 221-470-4572
Fax: +49 221-470-7406
Mail: mkoeni23@uni-koeln.de