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Press release.
11/12/2008
How plants take shape
INRA - ENS Lyon - CNRS
A team of French, American and Swedish scientists, led by researchers from INRA-Lyon, and in collaboration with ENS-Lyon, CNRS and the Université Claude Bernard Lyon I, has just uncovered a fundamental mechanism in plant morphogenesis (1). Their interdisciplinary efforts combining experimentation and computer models showed that the physical forces generated by growing plant tissue determine the orientation of cell cytoskeletons (2). This in turn controls the shape of the cells and, to a large extent, plant shape itself. Their findings are published in the 12 December 2008 issue of Science.
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One of the major themes of developmental biology is understanding how genetic regulation networks relate to the shape of multicellular organisms. Genes indirectly control tissue geometry by affecting the chemical and mechanical properties of individual cells. Conversely, tissue properties may also affect gene activity. The challenge was unravelling the dialogue between genes and shapes. The INRA-led team has just made a breakthrough in the area while studying the meristem (3) of Arabidopsis, a flowering plant commonly used in plant biology.
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Modelling mechanical constraints in the epiderm of the meristem after ablation of a cell.
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Taken together, the varying growth rates of meristem cells create different stress areas in the tissues. These areas arise from the mechanical pressure exerted by cells on one another. Using computer models that have been validated by many experimental tools, the researchers showed that microtubules – major components of the cytoskeleton - orient themselves parallel to the direction of the forces. Cells thus react to mechanical stress. Microtubules orient the deposit of cellulose fibrils in the cell wall, giving cells both their rigidity and a preferred growth axis. Consequently, through the organisation of microtubules in every individual cell, tissues can change shape, bend, and take characteristic patterns in the Arabidopsis meristem. In return, growing shapes also generate mechanical constraints that condition microtubule organisation.
More generally, these findings fall under an ongoing paradigm shift in developmental biology. Researchers no longer view embryonic development as a process controlled strictly by genetics, but rather, one that has multiple interacting levels. The team has demonstrated that meristem morphogenesis is an emergent phenomenon coming from the behaviour of individual cells resisting mechanical stress. Nonetheless, this is not the only mechanism at work in plant morphogenesis. It occurs alongside chain reactions induced by auxin, a hormone essential to the formation of plant organs. Understanding how these two mechanisms dovetail to form fully-differentiated tissues and structures is now a field open to researchers.
These results are the fruit of close collaboration between biologists, physicists and computer modelling specialists. The recent entry of dynamic models in the area of plant biology now makes it possible to study complex phenomena that take place during morphogenesis. The virtual plant tissues that were created for the study may ultimately help make current plant models – used chiefly by agronomists – more realistic.
(1) Development of form and structure in an organism.
(2) Network of protein polymers that confer mechanical properties to a cell. There are three types: intermediate filaments, actin filaments, and microtubules.
(3) The meristem is the actively growing part of a plant. It is made up of stem cells that can divide, and is the origin of all plant organs (plants, leaves, fruits, etc.).
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Arabidopsis: research's indispensable model plant
In the 1980s, the international scientific community decided to focus its efforts on Arabidopsis thaliana, a plant with a small genome and several advantages owing to its ease of cultivation in the laboratory, its rapid development, and its prolific nature. INRA has contributed to the flourishing body of knowledge about the plant with its large collection of Arabidopsis mutants in Versailles, thanks to an original method that is now used the world over.
Today, the full Arabidopsis genome has been sequenced. Most of the genes have been identified and localised, and researchers are working on discovering the function of each gene. The study of Arabidopsis has helped speed up the acquisition of plant knowledge in general, opening up new research possibilities and agricultural applications. Recent years have been marked by the success of INRA scientists.
They have contributed to deciphering hidden functions such as the mechanisms behind the epigenetic regulation of gene expression, the role of plant hormones, how meiosis takes places, cellulose synthesis in cell walls, how plant shape is regulated and how plant organs are formed, from leaves and roots to flowers and seeds.
These scientists have uncovered the regulation of metabolic pathways, including for sulphur, flavonoids and oilseed, and described the mechanisms behind plant resistance to salt. Researchers have also discovered disease-fighting mechanisms, such as resistance to the viral disease sharka, Salmonella plant infections or plant sensitivity to aphids. |
>Reference:
Developmental patterning by mechanical signals in Arabidopsis
Science, 12 December 2008
Olivier Hamant 1,2,7, Marcus Heisler 3,7, Henrik Jönsson 4,7, Pawel Krupinski 4, Magalie Uyttewaal 1,2, Plamen Bokov 5,6, Francis Corson 5, Patrik Sahlin 4, Arezki Boudaoud 5, Elliot M. Meyerowitz 3, Yves Couder 6, Jan Traas 1,2
1.INRA, Plant Reproduction and Biology, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
2.Université Claude bernard Lyon I, CNRS, Ecole Normale Supérieure de Lyon, 46 Allée d’Italie, 69364 Lyon Cedex 07, France
3.Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
4.Computational Biology and Biological Physics Group, Department of Theoretical Physics, Lund University, S-221 00 Lund, Sweden
5.Statistical Physics Laboratory, Ecole Normale Supérieure, 24, rue Lhomond ; 75231 Paris Cedex 05, France
6.MSC, Université Denis-Diderot Paris 7, 10, rue Alice Domont et Léonie Duquet; 75013 Paris, France
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
Contacts :
Press contacts
INRA Press Service: Sylvie Colleu, tel +33 (0)1 42 75 91 69
ENS de Lyon Press Service: Joëlle Pornin, tel.: +33(0)4 72 72 89 77
CNRS Press Service: Laetitia Louis, tel. +33 (0)1 44 96 51 37
Université Paris Diderot: Nadège Cauchois, tel +33 (0)1 57 27 83 39
Scientific contacts
- Jan Traas
Joint INRA-CNRS-ENS Research Unit for Plant Reproduction and Development, Lyon-Univ. Claude Bernard Lyon I
tel: +33 (0)4 72 72 86 14 / 86 01 ou +33 (0)6 33 58 62 69
email: jan.traas@ens-lyon.fr
- Olivier Hamant
Joint INRA-CNRS-ENS Research Unit for Plant Reproduction and Development, Lyon-Univ. Claude Bernard Lyon I
tel: 04 72 72 89 81 / 86 13
email: olivier.hamant@ens-lyon.fr
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