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Press release.
22/10/2009
A genetic mutation at the origin of the development of female flowers in the melon
A team of INRA researchers in Evry (Joint Research Unit for Plant Genomics, INRA-CNRS-Evry University) has recently identified the genetic mechanism by which a male flower becomes female in the melon. Most flowering plants have hermaphrodite flowers possessing both male and female organs. However, more than 4000 species, including melon, develop unisexual flowers, only male or female. The researchers have recently identified the mechanism by which these unisexual flowers are formed. They have identified a gene implicated in controlling the formation of female organs.
The study of genes governing sex determinism in the melon is of major agronomic importance. It could lead to better yield by favouring the formation of female flowers at the origin of fruit production. The results are published online on the site of the journal NATURE.
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The sex determinism of the melon is governed by two genes, andromonoecy (A) and gynoecy (G). The multiple interactions between them result in a distribution of different sexual types. Thus depending on the genetic mixing occurring at each generation, the plants can bear male flowers and female flowers, or bear male flowers and hermaphrodite flowers, or bear female flowers only, or hermaphrodite flowers.
Sex determinism in melon leads to the development of unisexual or hermaphrodite flowers from a bisexual flower primordium. In a previous publication, the researchers characterised the A gene which codes for an enzyme which is active during the development of female flowers and implicated in the synthesis of ethylene, a hormone known to modify sex determinism. They showed that a mutation in this A gene, acquired during evolution, led to the inactivation of the enzyme and the development of male organs in the female flowers and therefore of hermaphrodite flowers.
After having studied the natural variations of the genomic region responsible for gynoecy (plants bearing female flowers only) in 500 melon varieties from all parts of the world, the researchers publish today their results which explain the formation of female flowers in melon and more broadly the ballet of interactions between the A and G genes at the origin of sex determinism in melon (see diagram below). The scientists show here that a mutation close to the G gene, found in one of the varieties collected, leads to epigenetic modifications1 and represses the expression of this gene, thus enabling the formation of female organs. The inhibition of the expression of the A gene by the G gene is in turn lifted and the male organs do not develop. A female flower is formed.
These results are of major agronomic importance, as a greater production of female plants (at the origin of fruit formation) improves yield. They make it possible to envisage the control of flower development in melon, and also in other species. This research also sheds light on the original epigenetic mechanisms involved in the evolution of plants.
1 An epidgenetic mutation is a mutation which does not change the DNA sequence. In this specific case, the mutation is caused by the insertion of a transposable element. These elements are mobile DNA sequences present in all living organisms. Their ability to move in the genome can lead to genetic mutations or epigenetic modifications of the expression of neighbouring genes.
Diagram summing up the interaction between the A and G genes at the origin of the formation of male and female sexual organs in melon flowers. In the first case, the G gene inhibits the expression of the A gene, thus enabling the development of the male organs and preventing the development of the female sexual organs. A male flower is thus formed.
In the second case, the non expression of the G gene enables the expression of the A gene. As it has not mutated, it prevents the development of male organs. A female flower is thus formed.
In the third case, the A gene is mutated. It is thus no longer opposed to the development of male sexual organs. Moreover, the G gene is not expressed, which leads to the development of female organs. A hermaphrodite flower is thus formed.
Reference:
A transposon-induced epigenetic change leads to sex determination in melon. Antoine Martin1, Christelle Troadec1, Adnane Boualem1, Mazen Rajab1, Ronan Fernandez1, Halima Morin2, Michel Pitrat3, Catherine Dogimont3 and Abdelhafid Bendahmane1.
Nature, 22 October 2009, vol.461, doi :10.1038/nature08498.
1INRA-CNRS, UMR1165, Unité de Recherche en Génomique Végétale, 2 rue Gaston Crémieux,
F-91057 Evry, France.
2Plateforme de Cytologie et d’Imagerie Végétale, Institut Jean Pierre Bourgin, INRA, 78026 Versailles Cedex, France.
3INRA, UR 1052, Unité de Génétique et d’Amélioration des Fruits et Légumes, BP 94, F-84143 Montfavet, France.
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
Contacts :
Scientific contacts:
Abdelhafid Bendahmane
Tel: 33 (0)1 60 87 45 02 or bendahm@evry.inra.fr
Antoine Martin
Tel: 33 (0)1 60 87 45 23 or amartin@evry.inra.fr
INRA-CNRS-University of Evry Joint Research Unit for Plant Genomics
Versailles-Grignon Research Centre
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