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Keywords : Arabidopsis thaliana - cellulose - FT-IR microspectrocopy -pectin - herbicides - cell elongation

Doctoral school affiliation : ED145 "Sciences du Végétal" Université Paris 11-Orsay

Contacts :

Institut Jean-Pierre Bourgin, UMR1318 INRA-AgroParisTech
Bâtiment 2
INRA Centre de Versailles-Grignon
Route de St-Cyr (RD10)
78026 Versailles Cedex France

tél : +33 (0)1 30 83 30 00 - fax : +33 (0)1 30 83 33 19


Group leader
Herman Höfte

Senior scientist

Martine Gonneau
Research Scientist
Organization, traffic and regulation of cellulose synthesis machinery

Samantha Vernhettes
Senior scientist

Organization, traffic and regulation of cellulose synthesis machinery

Thierry Desprez
Engineer

Geoffroy Lescure
Engineer
from 9/1/13 to 8/7/14

 

Grégory Mouille
Senior scientist
Cell adhesion, pectin biosynthesis

Marjolaine Martin
Technician

Salem Chabout
Technician

Stéphane Verger
PhD student
from 1/10/11 to 30/09/14

Julien Sechet
Engineer
from 2/1/14 to 30/11/14

Julien.Sechet@versailles.inra.fr


Summary :


coupe transversale
Plant cells are surrounded by a ligno-cellulosic cell wall, which is at the same time sufficiently strong to withstand the stresses exerted by the high turgor pressure of the protoplast and sufficiently plastic for cell expansion to occur. The cell wall of growing cells (primary wall) consists primarily of a complex network of polysaccharides. Besides their key role in growth, development and the interaction with the abiotic and biotic environment of the plant, cell wall polymers have an enormous economic importance: they determine the mechanical and textural properties of food and contribute to its nutritional value. In addition, cell wall composition and architecture determine mechanical properties of wood, paper and textile. Finally, cell walls constitute an essential and  renewable source of molecules and energy. Despite their importance, the mechanisms of the synthesis, transport and assembly of wall polymers remain poorly understood as well as the link between cell wall modifications, its mechanical properties and cell growth. To understand better these processes at the level of a growing organ, we combine molecular genetics, biochemistry and cytology on the model plants Arabidopsis  thaliana for dicots and Brachypodium distachyon for the grasses. As a model system for the study of growth, we use the Arabidopsis dark-grown hypocotyl (Refrégier et al., 2004; Pelletier et al., 2010). Numerous mutants affected in the growth of this organ are also perturbed in cell wall deposition. The study of such mutants has led to the identification of genes involved in cellulose or pectin synthesis as well as genes controlling wall homeostasis during cell expansion.




Main Results :


Cellulose :

Cellulose is synthesized from hexameric complexes in the plasma membrane of terrestrial plants and Charophycean algae.  We have shown that :

    • The cellulose synthase complex (CSC) contains three distinct cellulose synthase isoforms. CESA1 and 3 are essential, whereas CESA6 is partially redundant with 3 other isoforms (CESA2, 5 and 9) in different cell types and developmental stages (Desprez et al., 2007; Bischoff et al., 2011)
    • GFP-tagged CSCs migrate in the plasma membrane propelled by the glucan polymerization (Desprez et al., 2007; Crowell et al., 2009)
    • Microtubules modulate the CSC insertion pattern, trajectories and velocity in the plasma membrane and internalization, but are not essential for the insertion or the mobility in the membrane per se (Crowell et al., 2009; Bischoff et al., 2011)
    • Phosphorylation of at least one isoform (CESA5) controls the mobility of CSC in the plasmamembrane through the interaction with microtubules. The red/farred light photoreceptor phytochrome regulates directly or indirectly this interaction (Bischoff et al., 2011)
    • CSC are targets for the herbicide isoxaben: mutations in CESA3 or CESA6 confer resistance to isoxaben (Desprez et al., 2002; Desprez et al., 2007)
    • The membrane-bound endoglucanase KOR is also required for cellulose synthesis and is part of the CSC. The exact role in cellulose synthesis remains to be determined (Robert et al., 2005)
    • A secreted protein similar to a basic chitinase (POM1) (Mouille et al., 2003) and a membrane protein with a putative glycosyl transferase domain (Pagant et al., 2002) are also required for cellulose synthesis.

    Figure 1: Monitoring cellulose deposition in real time using GFP-labeled cellulose synthase complexes. The surface of an epidermal cell expressing GFP-labeled CESA3 is shown (left panel). Punctae correspond to individual CSC in the plasma membrane. A time projection (middle panel) shows the trajectories of the GFP-tagged complexes while they churn out the cellulose microfibrils. These microfibrils are visualized at the most recent cell wall surface using Field Emission Scanning Electron Microscopy (right panel). 


    Pectins :

    Pectins are acidic polysaccharides present in terrestrial plants and Charophytes. They contain galacturonic acid and are synthesized in the Golgi in a highly methylesterified form. In the cell wall, enzymatic de-methylesterification controls the spatial and temporal variation in physicochemical properties of the cell wall. This controls numerous biological processes such as cellulose deposition, secondary cell wall assembly, cell growth and adhesion, phyllotaxis, fertilization, fruit maturation, responses to pathogens and abiotic stresses, etc.

    To gain insights into the role of pectin in growth, cell-cell adhesion, wall hydration and plant development, we are studying suppressors of mutants with reduced homogalacturonan synthesis (Bouton et al., 2002; Mouille et al., 2007; Ralet et al., 2008). In this context our objectives are: i) Understanding the control of de-methylesterification ? What is the role of the large families of  pectin methylesterases (PME) and PME inhibitors(PMEI); ii) Understanding the impact of de-methylesterification on pectin metabolism and the mechanical properties of the wall through the use of Atomic Force Microcopy (AFM) and iii) dissecting the role of pectin-mediated  feedback signaling (Hematy et al., 2007; Hematy and Hofte, 2008; Wolf et al., 2012a)

    Coordination between cell wall synthesis and cell elongation :

    One of the most intriguing questions in plant biology is how the cell wall can be at the same time strong and extensible.  We are using the Arabidopsis hypocotyl to study the role of cell wall modification in growth control. We have identified a cell wall integrity signaling networks including sugar-binding receptors that signal either growth arrest through the activation of ROS accumulation (Hematy et al., 2007; Hematy and Hofte, 2008; Wolf et al., 2012a) or growth promotion through pectin de-methylesterification through the promotion of brassinosteroid signaling (Wolf et al., 2012b).

     

    Movie: Kinematic analysis of Arabidopsis hypocotyl growth. A seedling growing in infrared light is shown. The growing zone is visualized by colors representing the strain rate (from red to blue: from fast to slow) (Renaud Bastien).

     



Selected Publications :

Geshi N., Johansen J.N., Dilokpimol A., Rolland A., Belcram K., Verger S., Kotake T., Tsumuraya Y., Kaneko S., Tryfona T., Dupree P., Scheller H.V., Hofte H., and Mouille G. 2013. A galactosyltransferase acting on arabinogalactan protein glycans is essential for embryo development in Arabidopsis. The Plant journal doi: 10.1111/tpj.12281

Wolf, S., Mravec, J., Greiner, S., Mouille, G., and Hofte, H. (2012). Plant Cell Wall Homeostasis is Mediated by Brassinosteroid Feed-back Signalling. Current Biology 18, 1732-7.

Wolf, S., Hematy, K., and Hofte, H. (2012). Growth control and cell wall signaling in plants. Annu Rev Plant Biol 63, 381-407.

Bischoff V, Desprez T, Mouille G, Vernhettes S, Gonneau M, Hofte H. 2011. Phytochrome regulation of cellulose synthesis in Arabidopsis. Current Biology, 21 : 1821-1827.

Peaucelle A, Braybrook SA, Le Guillou L, Bron E, Kuhlemeier C, Hofte H. 2011. Pectin-induced changes in cell wall mechanics underlie organ initiation in Arabidopsis. Current Biology, 21 : 1720-1726.

Crowell EF, Timpano H, Desprez T, Franssen-Verheijen T, Emons AM, Hofte H, Vernhettes S. 2011. Differential regulation of cellulose orientation at the inner and outer face of epidermal cells in the Arabidopsis hypocotyl. Plant Cell 23: 2592-605

Pelletier S, Van Orden J, Wolf S, Vissenberg K, Delacourt J, Assoumou Ndong Y, Pelloux J, Bischoff V, Urbain A, Mouille G, Lemonnier G, Renou JP, Hofte H. (2010) A role for pectin de-methylesterification in a developmentally-regulated growth acceleration in dark-grown arabidopsis hypocotyls. New Phytologist 188, 726-39

The International Brachypodium Initiative, (Including Mouille, G., Hematy, K., Hofte, H.) (2010). "Genome sequencing and analysis of the model grass Brachypodium distachyon." Nature 463: 763-768.

Crowell, E.F., Bischoff, V., Desprez, T., Rolland, A., Stierhof, Y.D., Schumacher, K., Gonneau, M., Hofte, H. and Vernhettes, S. (2009) Pausing of Golgi bodies on microtubules regulates secretion of cellulose synthase complexes in Arabidopsis. Plant Cell, 21, 1141-1154.

Peaucelle, A., Louvet, R., Johansen, J.N., Hofte, H., Laufs, P., Pelloux, J. and Mouille, G. (2008) Arabidopsis phyllotaxis is controlled by the methyl-esterification status of cell-wall pectins. Current Biology, 18, 1943-1948.

 

All publications since 2008
 


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