Our team is studying the role of mechanical signals in plant development.

More specifically, we are addressing the following questions:
 Pattern of mechanical signals
 Transduction of mechanical signals
 Targets of mechanical signals
 Developmental implications of mechanical signals
 New tools

We are also involved in science-society projects, notably on the environmental question sustainability and in several art-science projects.

Check out what our past members are about!

Pattern of mechanical signals

We contributed to generate cell-based, mechanical models of floral morphogenesis (1)(2)(3). This is an important building block to predict patterns of mechanical stresses in growing tissues, and thus identify potential targets of such mechanical signals.

To validate the predicted stress patterns, we developed an original method, based on cell-cell adhesion defects to detect and quantify tensile stress intensity and direction in aerial tissues (4). For instance (left panel), transverse cracks (bright propidium iodide staining) in hypocotyls of the qua1-1 mutant, perturbed in pectin synthesis, reveal the presence of longitudinal growth-derived stress in the epidermis.

Transduction of mechanical signals

We started to investigate the molecular features of mechanotransduction pathways at the cell cortex. We had previously shown that microtubules align with maximal tensile stress. Using a biosensor for Phosphatidylinositol 4,5-bisphosphate (PIP2), we revealed the accumulation of PIP2 in meristem boundaries, a site under highly anisotropic stresses (see left, PIP2 heatmap at the shoot apical meristem) and further showed its induction after mechanical perturbations (5).

Tension causes membrane thinning, which in turn can lead to channel opening. In collaboration with Gwyneth Ingram, we contributed to show a role of the Defective Kernel 1 (DEK1)-dependent calcium channel activity in epidermis specification (6).

In addition to these regulators, we proposed that microtubules may align with tensile stress by default (7), meaning that membrane composition, channels or receptor-like kinase would rather have a modulating role in that response.

Targets of mechanical signals

In past work, we showed that cortical microtubules align along maximal tensile stress directions, thereby reinforcing cell walls through the guidance of cellulose deposition (8,9). Cortical microtubules also guide the orientation of the next division plane (through the preprophase band). Combining modeling and experiments, we formally showed that tensile stress prescribes cell division plane orientation (10).

Beyond the cell cortex, we started to analyze the impact of mechanical signals on gene expression. We found that the expression of key transcription factors (CUC3 and STM) is in part under mechanical control ((11), see left: STM induction after compression).

The nexus between mechanical signals at the cell cortex and gene expression may involve different pathways. We identified a coupling between the mechanical modification of cell walls and the expression of wall remodelers (12). More recently, we started to analyze the role of nucleus deformation in gene expression (in prep).

Developmental implications of mechanical signals

We unraveled a role of microtubule dynamics and response to stress in organ initiation (13) in organ shape robustness (14), in organ growth arrest (15) and in organ flatness (submitted).

Introducing “mechanical shielding”: Growth heterogeneity may distort final organ shapes (left). However, as adjacent cells respond to mechanical conflicts (notably by reinforcing their walls through microtubule reorientations, right), they locally buffer growth heterogeneities, thereby contributing to the reproducibility of final organ shapes. Adapted from (11).

Through collaborations, and using cotyledon jigsaw puzzle-shaped pavement cells as model systems, we identified a role of the microtubule response to stress in maintaining cell shapes (16), while proposing a role of tensile stress in initiating the waviness of anticlinal walls (17).

Conversely, we contributed to show that complex cell shape can keep stress levels low (Right: after treatment with the microtubule depolymerizing drug oryzalin, cell walls become weaker. Meristematic cells increase their size and the largest cells finally explode (stars) (18)).

From a screen for touch-insensitive plants, Liz Haswell identified a mutant in the RNA Polymerase-associated factor 1 complex (Paf1c), a central regulator of transcription. Touch being a form of mechanical perturbation, we contributed to characterize the mutant’s response to stress (19).

Interestingly, we found that Paf1c-dependent transcription contributes to the robustness of phyllotaxis (20) and flower termination (accepted ; see left: in the Paf1c mutant, a new inflorescence with secondary carpels (arrows) emerges from a silique (arrowhead)). Although at this stage it remains difficult to link mechanosensing with these phenotypes, these results open the possibility for crosstalks between transcriptional noise, mechanotransduction and floral patterning.

New tools

We generated resources in the form of expression maps for cell wall-related remodelers at the shoot apical meristem (12). We are currently building a gene atlas of the flower (in prep).

We adapted atomic force microscopy to probe wall stiffness on living plant tissues (21). We also adapted microindentation techniques to quantify the microtubule response to compression (22).

We are developing light sheet microscopy for plant aerial organs, adapting a set-up developed by Phaseview® in the frame of a CIFRE/ANRT contract (in prep).

Last, we developed several image analysis tools, including a cell separation analysis tool (23), a microtubule orientation analyzer (FibrilTool, 24) and a cell segmentation tool (SurfCut, 25).

Sustainability

A short presentation on lab sustainability (FASEB conference, July 2019, in english):

A short presentation on the anthropocene (APM Singapore, May 2019, in french):

A short presentation on the new roles of researchers in the anthropocene (RDP lab meeting, Feb. 2020, in english):

Seven steps to make travel to scientific conferences more sustainable:
https://www.nature.com/articles/d41586-019-02747-6

Check out:
http://anthropocene-curriculum.org
http://institutmichelserres.ens-lyon.fr
https://labos1point5.org/

Art-science

Vahan Soghomonian
http://www.ens-lyon.fr/evenement/campus/fytolit-skhole-exposition-de-vahan-soghomonian

COAL: la table et le territoire
https://www.projetcoal.org/coal/2018/05/13/r%C3%A9sidence-selfood/

Tiphaine Calmettes
http://agenda-pointcontemporain.com/la-melee-ecole-normale-superieure-de-lyon/

Xu Yi "Résonance végétale"
http://xuyi.fr/oeuvres/51

Past members and their teams

Stève de Bossoreille:
Epithelial differentiation and morphogenesis in Drosophila (LBMC, Lyon, France)
http://www.ens-lyon.fr/LBMC/equipes/epithelial-differentiation-and-morphogenesis-in-drosophila

Benoit Landrein:
Mechanical signals in seed development (RDP, Lyon, France)
http://www.ens-lyon.fr/RDP/spip.php?rubrique15&lang=en#projMECA

Pascale Milani:
Bioméca (Lyon, France)
http://www.bio-meca.com/Qui_Sommes_Nous/

Thomas Stanislas:
Plasma Membrane and Mechano-Perception in Plant Development (Univ. Tuebingen, Germany)
https://uni-tuebingen.de/en/faculties/faculty-of-science/departments/interdepartmental-centres/center-for-plant-molecular-biology/res/developmental-genetics/stanislas/

Magalie Uyttewaal:
Spatial control of cell division (IJPB, Versailles, France)
https://www-ijpb.versailles.inra.fr/fr/bc/equipes/cyto/index.html

Stéphane Verger:
Mechanics and Dynamics of Cell to Cell Adhesion in Plants (SLU, Umea, Sweden)
https://www.upsc.se/researchers/5435-verger-stephane-mechanics-and-dynamics-of-cell-to-cell-adhesion-in-plants.html

References

1. F. Boudon et al., A computational framework for 3D mechanical modeling of plant morphogenesis with cellular resolution. PLoS Comput. Biol. 11 (2015)
2. O. Ali, J. Traas, Force-Driven Polymerization and Turgor-Induced Wall Expansion. Trends Plant Sci. 21, 398–409 (2016).
3. H. Oliveri, J. Traas, C. Godin, O. Ali, Regulation of plant cell wall stiffness by mechanical stress: a mesoscale physical model. J. Math. Biol. 78, 625–653 (2019).
4. S. Verger, Y. Long, A. Boudaoud, O. Hamant, A tension-adhesion feedback loop in plant epidermis. eLife. 7 (2018)
5. T. Stanislas et al., A phosphoinositide map at the shoot apical meristem in Arabidopsis thaliana. BMC Biol. 16, 20 (2018).
6. D. Tran et al., A mechanosensitive Ca2+ channel activity is dependent on the developmental regulator DEK1. Nat. Commun. 8, 1009 (2017).
7. O. Hamant et al., Are microtubules tension sensors? Nat Commun. 10, 2360 (2019)
8. O. Hamant et al., Developmental patterning by mechanical signals in Arabidopsis. Science. 322, 1650-5 (2008).
9. M. Uyttewaal et al., Mechanical stress acts via katanin to amplify differences in growth rate between adjacent cells in Arabidopsis. Cell. 149:439-51 (2012)
10. M. Louveaux, J.-D. Julien, V. Mirabet, A. Boudaoud, O. Hamant, Cell division plane orientation based on tensile stress in Arabidopsis thaliana. Proc. Natl. Acad. Sci. U. S. A. 113, E4294-4303 (2016).
11. B. Landrein et al., Mechanical stress contributes to the expression of the STM homeobox gene in Arabidopsis shoot meristems. eLife. 4, e07811 (2015).
12. A. Armezzani et al., Transcriptional induction of cell wall remodelling genes is coupled to microtubule-driven growth isotropy at the shoot apex in Arabidopsis. Dev. Camb. Engl. 145 (2018)
13. M. Sassi et al., An auxin-mediated shift toward growth isotropy promotes organ formation at the shoot meristem in Arabidopsis. Curr. Biol. CB. 24, 2335–2342 (2014).
14. N. Hervieux et al., Mechanical Shielding of Rapidly Growing Cells Buffers Growth Heterogeneity and Contributes to Organ Shape Reproducibility. Curr. Biol. CB. 27, 3468–3479.e4 (2017).
15. N. Hervieux et al., A Mechanical Feedback Restricts Sepal Growth and Shape in Arabidopsis. Curr. Biol. 26, 1019–1028 (2016)
16. A. Sampathkumar et al., Subcellular and supracellular mechanical stress prescribes cytoskeleton behavior in Arabidopsis cotyledon pavement cells. eLife. 3 (2014)
17. M. Majda et al., Mechanochemical Polarization of Contiguous Cell Walls Shapes Plant Pavement Cells. Dev. Cell. 43, 290–304.e4 (2017).
18. A. Sapala et al., Why plants make puzzle cells, and how their shape emerges. eLife. 7 (2018)
19. G. S. Jensen, K. Fal, O. Hamant, E. S. Haswell, The RNA Polymerase-Associated Factor 1 Complex Is Required for Plant Touch Responses. J. Exp. Bot. 68, 499–511 (2017).
20. K. Fal et al., Phyllotactic regularity requires the Paf1 complex in Arabidopsis. Dev. Camb. Engl. 144, 4428–4436 (2017).
21. P. Milani et al., In vivo analysis of local wall stiffness at the shoot apical meristem in Arabidopsis using atomic force microscopy. Plant J. 67, 1116-23 (2011)
22. M. Louveaux, S. Rochette, L. Beauzamy, A. Boudaoud, O. Hamant, The impact of mechanical compression on cortical microtubules in Arabidopsis: a quantitative pipeline. Plant J. Cell Mol. Biol. 88, 328–342 (2016).
23. S. Verger, G. Cerutti, O. Hamant, An Image Analysis Pipeline to Quantify Emerging Cracks in Materials or Adhesion Defects in Living Tissues. Bio-Protoc. 8, e3036 (2018).
24. A. Boudaoud et al., FibrilTool, an ImageJ plug-in to quantify fibrillar structures in raw microscopy images. Nat. Protoc. 9, 457–463 (2014).