Mechanisms and mechanics of lateral root initiation

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Lateral roots (LR) are post-embryonically formed from few founder cells located deep into the main root of Arabidopsis. LR formation is an auxin-induced, robust, self-organizing process that requires that abutting pairs of founder cells to radially expand before they divide asymmetrically. Failure to execute these steps accurately results in formation of aberrant LRs. Results obtained during the first funding phase suggest a link between the arrangement of founder cells in pairs, distribution of auxin, the radial expansion of the founder cells and lateral root initiation. However, the mechanisms responsible for the synchronous and mirror-imaged radial expansion of both LR founder cells on each side of the shared wall remain elusive. Here, we propose to decipher these mechanisms with a particular focus on mechanics. We will use live imaging and targeted manipulation of cells properties such as auxin content, cell wall mechanics and apoplasmic pH together with mechanical modelling to understand how the interface between two founders necessary and sufficient for LR initiation. We will unravel how is the synchronous radial expansion triggered. As well as the role played by modification of the extracellular pH induced by auxin in this process. This project will reveal how the coordinated modifications of elemental cell properties is leveraged by development as a robust trigger for morphogenesis of a new organ.