"Groundbreaking" ability of the root: how to cope with soil's hardness

This thesis investigates how Arabidopsis thaliana roots adapt to increasing mechanical resistance in their growth medium, simulating the effects of soil compaction. Compacted soil poses a major agricultural challenge by restricting root growth, thereby reducing water and nutrient uptake, which can impact plant health and crop yields. This research aims to understand both the anatomical changes and the molecular mechanisms that enable Arabidopsis roots to penetrate and grow within dense substrates, focusing on adaptive root growth strategies and cell wall dynamics. Through a specialized agar-based growth setup that controls for mechanical stress, it was found that Arabidopsis roots undergo a series of changes in response to increased substrate hardness. These adaptations include reductions in root meristem size, slower cell cycle progression, and enhanced cell elongation in the cortex and epidermis. Further analysis identified the AHK3-ARR1-ARR12 cytokinins signalling pathway as a key regulator of these adaptations, promoting cell wall remodelling via activation of EXPANSINS and proton pumps such as AHA2. This pathway’s activity increases with medium hardness, enabling roots to elongate more effectively in response to mechanical stress. Additionally, cell wall softening was shown to be a targeted adaptation that facilitates deeper root penetration in harder media. These findings highlight the complex hormonal and cellular responses that equip plants to navigate compact soils, providing potential strategies for engineering crop resilience. The research also suggests future directions in developing computational models and bio-inspired robots capable of mimicking these adaptive growth strategies for applications in agricultural engineering.