2025: Best Master Thesis

Alexander Mandel's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at University of Cologne in the year 2025 with the title:

Functional characterisation of TIR-catalysed immunostimulatory small molecule pRib-AMP in Arabidopsis thaliana 

This thesis uncovered the transcriptional and systemic plant responses upon exogenous treatment with the immunostimulatory small molecule pRib-AMP, laying the groundwork for the use of a naturally derived compound, capable of eliciting broad-spectrum resistance in dicot and potentially monocot crops.

This thesis provides new evidence that exogenous plant application of pRib-AMP is sufficient to induce EDS1-PAD4-ADR1-dependent transcriptional reprogramming, leading to strong resistance responses. Furthermore, root application of pRib-AMP leads to systemic immune responses, including root growth inhibition, suggesting cellular uptake of the molecule for immunity. 

Recognition of pathogen effectors by plant intracellular Toll/interleukin-1 nucleotide-binding leucine-rich repeat (TIR-NLR) receptors leads to production of immunostimulatory small molecules such as pRib-AMP, binding to the Enhanced Disease Susceptibility 1 (EDS1)-Phytoalexin Deficient 4 (PAD4) immune receptor complex, resulting in downstream immune responses. As binding of pRib-AMP to EDS1-PAD4 was previously only demonstrated in vitro, the aim of this thesis was to functionally characterise the molecule and its signalling in planta. Therefore, a collaboration with the Kath-Schorr chemistry lab at the University of Cologne was established, to chemically synthesise pRib-AMP, allowing immune transcriptional analysis of effector-triggered immunity (ETI)-signalling pathway mutants, using RT-qPCR. Analysis of immunity-related transcripts revealed that exogenously applied pRib-AMP acts via the EDS1-PAD4-Activated Disease Resistance 1 (ADR1), but not the EDS1-Senescence Associated Gene 101 (SAG101)-N Requirement Gene 1 (NRG1) signalling node in a dose- and time-dependent manner. Furthermore, it was demonstrated by mutant analysis that the recognition of exogenous pRib-AMP is not mediated by cell surface receptors, that confer pattern-triggered immunity (PTI) responses, suggesting cellular uptake of the molecule. In the second part of the thesis, systemic plant responses after synthetic pRib-AMP treatment were assessed, using root growth assays. Those assays revealed dose- and EDS1-PAD4-dependent primary root growth inhibition. Moreover, those experiments could identify a sub-maximal dose which does not lead to macroscopic growth effects, but still induces immune transcriptional reprogramming. This sub-maximal dose of pRib-AMP could be used in future experiments to prime Arabidopsis thaliana but also economically relevant crops against a broad range of biotrophic pathogens, due to the conservation of the EDS1-PAD4 complex and the binding site for pRib-AMP in both dicot and monocot plants.

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Alexander Mandel conducted this work at the Max Planck Institute for Plant Breeding Research in the working group of Prof. Jane Parker.