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Biophysique et Développement

Disciplines Biology
Research fields Biophysics, Vegetal biology, Developmental biology
Supporting organisms ENS de Lyon, CNRS, INRA
Geographical location ENS de Lyon (Campus Charles Mérieux)
Team leader Arezki Boudaoud


Team Biophysique et développementOur team is interested in understanding how the interplay between gene regulatory networks, hormone signalling and biophysical mechanisms results in the emergence of organs. We will focus our efforts on the Arabidopsis shoot apical meristem (SAM), which contains a population of dividing, undifferentiated stem cells that is maintained for the life of the plant. Founder cells on the flanks of the SAM give rise to flowers, which themselves give rise to organs such as sepals, petals, stamens and carpels. For clarity, we use the term inflorescence meristem (IM) to include the SAM and the flower.

Although extensive genetic analyses have helped identify a highly conserved network of genes involved in patterning the SAM and in the control of floral identity within emerging primordia (Krizek and Fletcher, 2005), the mechanisms that determine the positioning of these organs are not fully understood. The accepted scenario is that phyllotaxis and floral symmetry are regulated by cell-cell signalling (e.g. by peptides, hormones or lipids), with the plant hormone auxin almost certainly being a key player, though direct evidence is extremely limited in the flower (Nemhauser et al., 1998). In addition, we have recently showed that mechanical signals are required for certain morphogenetic events, such as boundary formation (Hamant et al., 2008). Thus organ initiation in the flower might be regulated by a feed-forward mechanism involving signalling as well as physical forces.

More generally, how cell-based regulation translates into multi-cellular complex forms remains largely unknown in any organism, and yields a central challenge in developmental biology. Although the study of individual genes or molecules has been extremely fruitful in identifying gene function, the morphogenetic role of these genes remains elusive, mainly because they do not control geometry directly, but only indirectly through the biochemical and biophysical properties of the cell. An integrated understanding of cell structure and mechanics is thus essential (e.g. Farge, 2003 ; Kasza et al., 2007).

It is clear that organs are shaped via coordinated growth of the plant. Two parameters – growth rate and growth anisotropy – are sufficient to characterise shape changes (Coen et al., 2004 ; Erickson, 1976 ; Chopard et al., unpublished data). On the one hand, it is believed that plant cell growth is driven by internal turgor pressure (up to 10 bars), and limited by the ability of the cell wall to yield to this pressure. Wall loosening and the associated growth rate are controlled by a large number of cellular processes (Cosgrove, 2005). On the other hand, growth anisotropy is determined by the direction of the highly oriented cellulose microfibrils that are embedded in the cell wall. This architecture depends mainly on the cytoskeleton : in particular, cortical microtubules (MTs) are thought to guide the movement of cellulose synthase complexes (Paredez et al., 2006) and thus to indirectly control growth anisotropy. Two of our main aims are to quantify growth and understand its genetic regulation.