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PhD defense of Marion Louveaux

Marion Louveaux will defend her PhD

Contribution of mechanical stress to cell division plane orientation at the shoot apical meristem of Arabidopsis thaliana

on Friday Oct. 2nd at 14h30 in the Salle des Thèses.

Abstract

Morphogenesis during primary plant growth is driven by cell division and elongation. In turn, growth generates mechanical stress, which impacts cellular events and channels morphogenesis. Mechanical stress impacts the orientation of division plane in single animal cells ; this remains to be fully demonstrated in plants. Currently, cell geometry is proposed to be the main factor determining plane orientation in symmetric divisions : cell divide along one the shortest paths. This geometrical rule was tested on tissues with rather isotropic shapes or growth and the corresponding molecular mechanism remains unknown, although it could involve tension within the cytoskeleton. To address these shortcomings, we developed a pipeline to analyze cell divisions in the different domains of the shoot apical meristem of Arabidopsis thaliana. We computed the probability of each possible planes according to cell geometry and compared the output to observed orientations. A quarter of the cells did not follow the geometrical rule. Boundary domain was enriched in long planes aligned with supracellular maximal tension lines. Computer simulations of a growing tissue following a division rule that relies on tension gave the most realistic outputs. Mechanical perturbations of local stress pattern, by laser ablations, further confirmed the importance of mechanical stress in cell division. To explore the role of microtubules in this process, we developed a microindenter-based protocol to quantify the cytoskeletal response to mechanical stress. This protocol was tested and validated in the katanin and spiral2 mutants, in which the response to stress is delayed or promoted respectively.

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