Decoding Nodules – The spatiotemporal hormonal regulation of tissue-specific nodule initiation in Medicago truncatula

This thesis investigates how early nodule development in Medicago truncatula is spatially and temporally regulated, focusing on hormonal control and high-resolution transcriptomics. It reveals that auxin accumulation during early nodulation is driven by coordinated local biosynthesis and polar transport, establishing gradients required for nodule initiation. In parallel, ethylene signaling is dynamically reprogrammed: its responsiveness shifts to outer root tissues, where distinct biosynthesis genes differentially regulate infection and restrict improper nodule formation.
To resolve these processes at higher resolution, optimized single-cell and single-nucleus RNA sequencing approaches were developed, enabling detailed mapping of root cell states. Integration of these datasets identified candidate transcription factors involved in pericycle competence, though functional analyses suggest complex or redundant roles.
Overall, this work provides new insights into how hormonal signaling, and gene regulation are spatially coordinated to control symbiotic organogenesis, advancing understanding and the potential to improve nitrogen-fixing interactions in agriculture, with the aim of reducing the reliance on energy-intensive, synthetic fertilizers.