Fakultäten der Universität Bonn

Signaling Components Shaping Arabidopsis Defense and Susceptibility in Nematode Interactions

2026-04-15T00:00:00Z

Signaling Components Shaping Arabidopsis Defense and Susceptibility in Nematode Interactions Letia, Sharon Plant-parasitic nematodes (PPNs) are roundworms distinguished by a spear-like stylet at the anterior end of their body, which they use to mechanically damage host cells and facilitate entry. This stylet also serves as a conduit for effectors, proteins that manipulate and modify host biology and it ultimately functions as a siphon to extract nutrients from the host after successful establishment. PPN-associated diseases result in substantial economic losses, estimated at over 150 billion USD annually. Given their economic significance, considerable research has focused on developing management strategies such as chemical treatments, the use of resistant and tolerant varieties, and cultural practices like flooding and crop rotation. However, current PPN management options have significant drawbacks, including the ecological harm caused by chemical controls and the breakdown of resistance in previously resistant crop cultivars. Therefore, there is a pressing need to further investigate the complex interactions between hosts and PPNs to gain mechanistic insights. Such understanding is crucial for developing novel, effective, and sustainable management solutions.

This thesis therefore investigates two major axes of nematode defense, focusing on host susceptibility factors and molecular signaling mechanisms. First, we reveal that Ascaroside#18, a nematode-derived molecular pattern, triggers a unique leucine-rich repeat receptor NILR1-independent defence, distinct from classical pattern-triggered immunity (PTI). Unlike typical PTI, ascr#18-associated resistance acts without causing reactive oxygen species bursts or growth inhibition and operates independently of the peroxisomal β-oxidation pathway. Transcriptomic profiling shows that defense is mediated by downregulation of auxin transport and signaling genes, ultimately suppressing susceptibility to cyst nematodes without activating classical defense pathways. Reduced auxin influx carrier AUX1 and downstream auxin-responsive genes SAUR69 and IAA27 coincide with impaired nematode feeding cell development, highlighting the critical role of auxin signaling as a susceptibility factor.

Secondly, work on heterotrimeric G-protein signaling delineates the role of extra-large G-proteins XLG2 and XLG3 as central susceptibility factors induced downstream of cytokinin (CK) signaling. These factors promote nematode parasitism, as demonstrated by Arabidopsis xlg123 mutant lines showing reduced susceptibility to both cyst and root-knot nematode infection, with reduced nematode fitness and impaired feeding structures. XLG2 and XLG3 expression is shown to be CK-dependent, establishing a mechanistic link between hormone signaling and G-protein-mediated susceptibility pathways in host-pathogen interactions.

Collectively, these findings underscore the importance of susceptibility factor modulation via auxin and cytokinin-linked signaling components in nematode defense. The thesis integrates novel insights into how plant immunity can be enhanced by reducing susceptibility, rather than by solely activating classical immune responses. This mechanistic knowledge opens new directions for crop engineering to achieve durable, broad-spectrum nematode resistance.

Deutsch-britische Forschungszusammenarbeit auf supranationaler Ebene nach dem Beitritt des Vereinigten Königreichs zur Europäischen Gemeinschaft

2026-04-15T00:00:00Z

Deutsch-britische Forschungszusammenarbeit auf supranationaler Ebene nach dem Beitritt des Vereinigten Königreichs zur Europäischen Gemeinschaft Wekerle, Anke Die europäische Forschungsförderung stellt seit den 1980er Jahren einen zentralen Pfeiler der Europäischen Integration dar. Mit den Forschungsrahmenprogrammen (FRP) hat die Europäische Union ein supranationales Instrument etabliert, das die Förderung exzellenter Forschung unabhängig von nationaler Herkunft zum Ziel hat. Der Austritt des Vereinigten Königreichs aus der Europäischen Union ("Brexit") markiert jedoch eine tiefgreifende Zäsur für dieses Politikfeld, da Großbritannien nicht nur zu den größten Beitragszahlern und Nutznießern der europäischen Forschungsförderung zählte, sondern auch als zentraler Verfechter des Exzellenzprinzips galt.
Die vorliegende Arbeit untersucht die Auswirkungen des Brexits auf die europäische Forschungsförderung mit besonderem Fokus auf die deutsch-britische Forschungszusammenarbeit auf supranationaler Ebene. Im Zentrum steht die Frage, inwieweit der Ausschluss britischer Akteure aus den formalen Entscheidungsprozessen der EU, insbesondere aus den Programmausschüssen und Komitologieverfahren, zu Veränderungen bei der Vergabe von Forschungsmitteln unter Exzellenzkriterien geführt hat. Methodisch basiert die Untersuchung auf einer vergleichenden qualitativen Fallstudienanalyse der Forschungspolitiken des Vereinigten Königreichs und der Bundesrepublik Deutschland, ergänzt durch eine Auswertung von Primär- und Sekundärquellen sowie einschlägiger Programmdaten der Europäischen Kommission.
Die Ergebnisse zeigen, dass der Brexit die institutionelle Balance innerhalb der europäischen Forschungspolitik verschoben hat. Während das Exzellenzprinzip weiterhin normativ verankert bleibt, haben sich Machtverhältnisse und Einflussmöglichkeiten in den Entscheidungsstrukturen verändert. Deutschland übernimmt zunehmend eine gestaltende Rolle innerhalb der EU-27, während Großbritannien trotz seiner Assoziierung an Horizont Europa dauerhaft von der formalen Mitgestaltung ausgeschlossen bleibt. Die Arbeit kommt zu dem Schluss, dass die langfristige Sicherung exzellenter Forschung in Europa maßgeblich von der starken institutionellen Stabilität der EU-Forschungsförderung und der strategischen Ausgestaltung der Beziehungen zu assoziierten Drittstaaten abhängt.; European research funding has constituted a central pillar of European integration since the 1980s. Through the Framework Programmes for Research and Innovation, the European Union has established a supranational instrument aimed at promoting scientific excellence irrespective of national origin. The withdrawal of the United Kingdom from the European Union ("Brexit"), however, represents a profound rupture in this policy field, as the UK was not only one of the largest contributors to and beneficiaries of European research funding, but also a key advocate of the excellence principle.
This dissertation examines the impact of Brexit on European research funding, with a particular focus on German–British research cooperation at the supranational level. The core research question addresses whether and to what extent the exclusion of British actors from formal EU decision-making processes—especially programme committees and comitology procedures—has led to changes in the allocation of research funding under excellence-based criteria. Methodologically, the study employs a comparative qualitative case study approach, analysing the research policy frameworks of the United Kingdom and the Federal Republic of Germany.
The findings indicate that Brexit has altered the institutional balance within European research policy. While the excellence principle remains normatively embedded in the EU’s research funding architecture, power relations and influence within decision-making structures have shifted. Germany has assumed an increasingly prominent role within the EU-27, whereas the United Kingdom, despite its association with Horizon Europe, remains structurally excluded from formal agenda-setting and governance. The dissertation concludes that the long-term sustainability of excellence-based research funding in Europe will depend on the great and stable institutional stability of EU research governance and the strategic design of partnerships with associated third countries.

Root growth and belowground interactions and plasticity of field crops

2026-04-14T00:00:00Z

Root growth and belowground interactions and plasticity of field crops Hadir, Sofia Understanding the growth of roots and belowground interactions of field crops constitutes a pathway to enhancing the performance of field crops. Global challenges related to climate change and a growing population are driving a more rational use of agricultural inputs to reduce soil and water ressources degradation. Roots play a central role in this process, as shown by research that has provided valuable insights into their development, functions, diversity, and adaptations to the environmental conditions.
To contribute to this understanding, the present thesis aims to investigate the root growth and interactions occuring in intercropping systems as well as the effects of nutrient omission on root traits of field crops.
For intercropping, a field experiment was conducted using one faba bean cultivar and two spring wheat cultivars sown at three sowing densities, defining three intercropping designs. Destructive root coring was conducted (0–100 cm) in the intercrops and sole crops at two development stages. FTIR spectroscopy was used to discriminate the species' root masses. In intercrops, sowing density affected more than the cultivar choice the root growth and belowground interactions. The highest sowing density led to a decrease of root biomass and more competitive interaction between faba bean and winter wheat. The lowest sowing densities promoted deeper root growth of wheat. Regarding the cultivar choice, the early root growth in depth and in density of one spring wheat cultivar lowered faba bean root growth. The findings highlight the importance of plant density and root co-occurrence in belowground interactions of intercrops.
To investigate the nutrient availability's effects on root growth and plasticity, root and shoot sampling was conducted in 2019 for sugar beet, 2019/20 and 2020/21 for winter wheat and 2021/2022 for winter rye at the long-term fertilizer experiment (LTFE) Dikopshof. Various fertilizer treatments were chosen in the three studies including: fully fertilized including manure (m) and supplemental mineral fertilizer (s) (NPKCa+m+s), fully fertilized without manure (NPKCa), N omitted (_PKCa), and P omitted (N_KCa) for winter rye and additionally lime omitted (NPK_) and no fertilization for winter wheat and sugar beet. N availability affected root morphology and plasticity: N omission reduced root growth in winter rye and winter wheat, with stage-specific effects on root diameter, root length density and P omission significantly impacts root traits of field crops, demonstrating the plasticity of root systems in adapting to nutrient-limited conditions. Sustained Ca and K omission affected to a less extent root morphological traits. The Results found in this thesis suggest that nutrient availability as well as intercropping system may affect the root growth and plasticity of field crops. However, the responses are species specific, and affected by growth stage. The results provide valuable insights into potential root traits that can be considered in breeding programs and agronomically relevant insights that serve to design sustainable cropping systems.

Photoswitchable Ligands Enable Thermodynamic Disequilibration of Metal-Organic Assemblies

2026-04-14T00:00:00Z

Photoswitchable Ligands Enable Thermodynamic Disequilibration of Metal-Organic Assemblies Notheis, Maximilian Johannes Living organisms need a constant supply of energy to sustain life. The molecular reason for this can be found in the operating mechanism of biological systems that perform extraordinary functions like absorbing nutrients and distributing them across the organism, self-healing, movement, and reproduction. These intricate biological systems do not reside in the thermodynamic minimum. Instead, a constant energy supply is needed to sustain meta-stable states far away from the thermodynamic minimum. The innate energy of these states is harnessed to perform work, enabling the complex behaviors of living organisms.
A fundamental understanding of how to access and sustain meta-stable states in artificial systems and materials is a step towards extending life-like behaviors to inanimate objects, opening numerous perspectives from more sustainable self-repairing materials to medical applications in targeted drug release. Systems making use of phase boundaries to stabilize meta-stable states such as dynamic droplets and nanocrystals have recently been described in literature. However, the systematic use of dynamic and reversible metal-ligand interactions to stabilize meta-stable states remains an underexplored approach.
This dissertation establishes light-driven reaction networks, specifically energy ratchets, as a foundational mechanism to accumulate meta-stable states in self-assembled metal-organic structures. Furthermore, it explores how the innate energy of the meta-stable state can be harnessed in enabling macroscale spatio-temporal control over nanoscale chemical transformations.
Initial work focused on the design, synthesis and investigation of photoresponsive building blocks. Firstly, a family of novel twelve-membered macrocyclic azobenzenes was investigated, yielding new insights on using backbone flexibility to tune photochromic properties. Secondly, a reliable gram‑scale synthesis of 2,8-dihalogenated diazocine was established. This was followed by selective, stepwise Suzuki couplings to access asymmetrically functionalized diazocine building blocks that combine a large geometry change during switching with favorable photochemical properties.
A one-pot sub-component self-assembly using one of the tailor-made building blocks resulted in selective formation of high-fidelity, low-symmetry, heterobimetallic helicates. The final structure contains two distinct coordination sites, enabling quantitative formation of self-sorted Fe/Zn and Zn/Co heterobimetallic helicates. The precise metal distribution is enabled by a complex reaction network during self-assembly that amplifies differences in metal-ligand bond strength and exchange kinetics. This separates the metals into the two coordination sites as a result of kinetic and thermodynamic factors.
Investigating the photoresponsive behavior of the helicates revealed a light-driven energy-ratchet mechanism. Photoisomerization of the diazocine units transiently reshapes the assemblies' energy landscape, enabling rapid reconfiguration of the initial structure into a mixture of metastable isomeric states. These become kinetically trapped upon back-isomerization, enabling the accumulation of meta-stable high-energy atropisomers. Continuous white-light irradiation operates the energy ratchet autonomously by exciting both switching transitions simultaneously. This amplifies a minor photostationary state into a dominant, long-lived meta-stable diastereomer. Additionally, operation of the ratchet accelerates regioselective metal-cation exchange (Zn₂L → ZnFeL), providing spatiotemporal control over selective metal ion capture.
Nature shows us that complex behavior is a result of complex systems. The incorporation of energy ratchets into metal-organic cages elevates them into a realm of complexity that is usually reserved for enzymes. These results pave the way towards larger photoresponsive cages for molecular machines that operate under out‑of‑equilibrium conditions, thus enabling life-like behaviors such as controlled catalysis, active transport, or macroscale directed movement.