Thesis defense: Stéphanie Afonso
Root hair (RH) growth is a highly polarized process that requires the continuous and coordinated delivery of new plasma membrane and cell wall components to the growing tip through exocytosis. However, despite its fundamental importance, how exocytosis contributes quantitatively and functionally to RH growth, and in particular to the regulation of cell wall extensibility, remains poorly understood. In addition, the mechanisms that regulate exocytic activity in space and time during RH elongation are still not fully elucidated. Several models have been proposed to explain how this extensibility is controlled, including the “expanding beam”, “pectate exchange”, and “biomechanical hot spot” models. These models highlight different roles for exocytosis, from supplying new wall material required for expansion, to regulating growth through feedback mechanisms and contributing to the formation of locally extensible domains. Together, they suggest that exocytosis may play a central role in coupling cell wall mechanics with polarized RH growth. In this thesis, I used mutant analysis combined with pharmacological treatments to study rapid responses of Arabidopsis thaliana RHs grown in microfluidic chambers, aimed at investigating the contribution of exocytosis to RH growth, with a particular focus on understanding how changes in exocytic activity affect the capacity of the cell wall to expand. A second major objective was to identify and characterize the cellular and molecular mechanisms that underlie exocytosis during RH growth, and to determine how these regulatory processes are integrated with the machinery controlling polarized tip growth.
Director: Kalina Haas, "Physiology of plant cell wall assembly, remodelling, and expansion" phyWALL team, INRAE, IJPB, Versailles
Co-supervision:
> Alexis Peaucelle, "Physiology of plant cell wall assembly, remodelling, and expansion" phyWALL team, INRAE, IJPB, Versailles
> Heman Höfte, "Physiology of plant cell wall assembly, remodelling, and expansion" phyWALL team, INRAE, IJPB, Versailles
Jury members
> Fernanda De Carvalho-Niebel (Rapportrice) - CNRS, "Laboratoire des interactions plantes - microbes - environnement" LIPME, Castanet-Tolosan
> Martin Potocký, (Rapporteur) - IEB, Czech Academy of Sciences, République tchèque
> Alex Costa (Examinateur) - Université de Milan, Département Bioscience, Italie
> Hannes Kollist (Examinateur) - INRAE, "Institute of Plant Sciences Paris-Saclay"IPS2, Gif-sur-Yvette
> Sebastien Thomine (Examinateur) - CNRS, "Institute for Integrative Biology of the Cell", I2BC, Gif-sur-Yvette
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
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