Skip to main content

Mechanical signals in plants: from cellular mechanisms to growth coordination and patterning

Periodic Report Summary 2 - MECHANODEVO (Mechanical signals in plants: from cellular mechanisms to growth coordination and patterning)

In “On growth and forms” (1917), D’Arcy Thompson stresses the inevitable interactions between physics and biology. Thanks to ongoing developments in live imaging and modeling, this field of study has been rejuvenated: the relation between mechanics and shape changes can now be addressed more comprehensively, notably in plants in which morphogenesis is mainly determined by cell walls. In the ERC MechanoDevo project, we propose to identify the plant mechanotransduction pathways and investigate their role in development, mainly using the shoot apical meristems (containing the plant stem cell) and sepal (the outermost floral organ) in Arabidopsis as experimental systems.

Within the reporting period, five results stand out:

1/ A central and largely unanswered question in development is « how do organs know when to stop growing ? ». Here we identified an organ-shape sensing mechanism that partly addresses that question: differential growth in the developing sepal triggers a large scale mechanical conflict, which in turn leads to microtubule-dependent wall stiffening and thus growth restriction, in a negative feedback ultimately leading to growth arrest (Hervieux et al., 2016 Curr. Biol.).

2/ Organ shapes are reproducible despite high heterogeneity at the cell level, raising the question of how such heterogeneities are filtered out during development. We identified a mechanism that buffers growth heterogeneity through the mechanical isolation of fast growing cells (via microtubule-driven wall reinforcement) in epithelia (Hervieux et al., submitted).

3/ Since Errera (1886), cell division plane orientations in plants were thought to depend on cell geometry. Here we provide evidence that plant cells divide along maximal tension instead, which not only depends on cell geometry, but also on differential growth and tissue curvature (Louveaux et al., 2016 PNAS).

4/ Plants respond to touch and wind, notably by becoming stiffer and shorter. We identified Paf1c as the first regulator of this response (Jensen et al., in press in J. Exp. Bot.).

5/ STM is a homeobox gene which is essential for the maintenance of shoot apical meristems, and its expression is a defining marker of meristematic identity. We found that STM promoter is mechanosensitive and that tissue folding at the meristem prescribes a stress pattern that in turn adds robustness to STM expression pattern (Landrein et al., 2015 eLife).

In addition, we developed quantitative tools to relate mechanical stress to cell responses (e.g. using a microindenter in Louveaux et al., 2016 Plant J. or mathematical tools in Tsugawa et al., 2016 Biophys. J.) and we identified several putative mechanosensors as well as novel targets of mechanical signals (unpublished). Beyond the interactions with physicists, mathematicians and modelers, the results obtained in this project also fuel new interdisciplinary collaborations within the art and humanities communities where questions of feedback and suboptimality find an intriguing echo.