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Press release.
18/12/2008
INRA researchers discover genes for compound leaf formation
Although the wide, lobed geranium leaf bears little resemblance to the shamrock's leaflets, researchers from INRA-Versailles and their counterparts at Oxford University have discovered that the same genes are behind their formation. Their work will be published in the 19 December 2008 issue of SCIENCE. The researchers demonstrated the importance of the NAM/CUC3 gene family in the leaflet and serration development so common in dicotyledons.
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Unlike monocotyledons, like wheat or tulip, which have simple leaves, dicots have more diverse leaf shapes, often composed of several leaflets - 3 in the shamrock, and as many as 5 to 7 in horse chestnut trees. Leaflets form on the edges of the new leaf in the earliest stages of its development. They become distinct when cell growth slows down in the boundary domains separating them.
Researchers focused on the NAM/CUC3 gene family, which codes for transcription factors that they suspected of playing a role in leaflet formation. For one, these genes are involved in the development of boundary domains separating the leaves when they begin to grow from stems. Moreover, a previous study had already observed the involvement of a NAM/CUC3 gene in the formation of the model plant Arabidopsis thaliana's serrated leaf margin. The scientists first studied the expression of NAM/CUC3 genes during leaf development in plants that were distantly related from an evolutionary standpoint but had leaflets, such as columbine (Ranunculacaea), tomato (Solanacaea), cardamine (Brassicacaea) and pea (Fabacaea). They found that these genes were expressed in boundary domains surrounding the young leaflets, and that this expression preceded leaflet emergence. Inhibiting the expression of these genes provided proof of their importance. Without them, leaf development was abnormal. Serrated edges disappeared, leaflets were fused, and leaflet numbers decreased.
The characteristic columbine leaf (Aquilegia caerulea) loses its three leaflets when NAM/CUC3 genes are inhibited.
Photo © Science/AAAS, INRA.
The results allowed the authors to propose a general model of leaflet and serration formation in leaves. Transcription factors encoded by NAM/CUC3 genes slow growth in the boundary domains along the leaf margin, leading to the formation of indentations. Meanwhile, they activate the formation of neighbouring leaflets and induce factors that in turn activate the expression of NAM/CUC3 genes, a positive feedback loop needed to maintain the new tissue. "The development of boundary domains that stimulate adjacent units at the same time has already been observed in animals," says Patrick Laufs, "in fly wing formation or brain development, for instance. We see here a similar mechanism in plant and animal tissue development." He also suggests that the same model and the same players may also be at work in the formation of new leaves and flowers in the shoot apical meristem.
Reference:
A conserved molecular framework for compound leaf development
Science, 19 December 2008
Thomas Blein 1, Amada Pulido 1, Aurélie Vialette-Guiraud 1, Krisztina Nikovics 1, Halima Morin 1,2, Angela Hay 3, Ida Elisabeth Johansen 4, Miltos Tsiantis 3, Patrick Laufs 1
1 Laboratoire de Biologie Cellulaire, Institut Jean-Pierre Bourgin, INRA, 78026 Versailles Cedex, France
2 Plateforme de Cytologie et d’Imagerie Végétale, Institut Jean-Pierre Bourgin, INRA, 78026 Versailles Cedex, France
3 Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
4 Department of Genetics and Biotechnology, University of Aarhus, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
Sylvie Colleu, tel +33 (0)1 42 75 95 55 or presse@inra.fr
Contacts :
Scientific Contacts
Patrick Laufs
Cell Biology Unit
INRA Versailles-Grignon
Tel: +33 (0)1 30 83 30 14 or +33 (0)1 30 83 30 11
or +33 (0)6 17 93 58 13
email: Patrick.Laufs@versailles.inra.fr
Thomas Blein
Cell Biology Unit
INRA Versailles-Grignon
Tel: 01 30 83 30 14 ou 33 (0)1 30 83 30 11
email: thomas.blein@versailles.inra.fr
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