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Press release.
18/02/2011
Can plants give up sex?
A research team at INRA Versailles-Grignon, working with colleagues from the U.S. and India, has proven for the first time that a sexual plant can produce clonal seeds which are genetically identical to the mother plant. Most plants – cultivated species in particular – reproduce sexually. Certain plant species, however, produce seeds differently through an asexual process called apomixis. Progeny obtained this way are identical clones to their mother. Introducing apomixis in cultivated plant species would be revolutionary, making it possible to clone and propagate any plant of agricultural interest. The results of this study were published 18 February in the advance online edition of the journal SCIENCE.
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Apomixis – the cloning of plants through seeds – results from changes to two steps in the process of sexual reproduction: the formation of gametes which carry all the genetic information of the mother plant instead of half (2n chromosomes rather than n), and the initiation of embryogenesis without pollination (i.e. without the genetic information of the father plant).
The first component of apomixis can be introduced in Arabidopsis using MiMe or dyad mutants, previously obtained by the teams of Raphaël Mercier (INRA, France) and Imran Siddiqi (CSIR, India). The 2n-chromosome gametes produced by these mutants normally play a role in sexual reproduction. The progeny thus obtained by fertilisation carry double the number of chromosomes (4n instead of 2n) and are therefore different to the mother plant which has 2n chromosomes.
Producing progeny that is wholly identical to the mother plant requires the second component of apomixis: embryonic development without fertilisation by male gametes. This process was recently identified in a GEM (1) line of Arabidopsis by the team of Simon Chan (University of California, Davis, United States). GEM chromosomes are usually eliminated when crossed. When GEM is crossed as male, a part of the progeny carry only maternal chromosomes; when crossed as female, a part of the progeny carry only paternal chromosomes.
INRA Versailles-Grignon and CSIR researchers combined both components of apomixis (MiMe or dyad on one hand, GEM on the other). This work demonstrated that clonal seeds wholly identical to the mother or father plant can effectively be obtained by crossing MiMe and dyad plants to the GEM line.
When MiMe is crossed as female to GEM used as a male plant, for example, 34% of the resultant progeny carry only maternal chromosomes and are identical to the mother. Inversely, when MiMe is crossed as male to GEM as female, 42% of resultant progeny are identical to the father. A maternal MiMe clone was also crossed to GEM to obtain a second generation. Here, 24% of progeny were identical to their mother and grandmother, demonstrating that clonal propagation through seed is possible for several generations.
These results demonstrate that clonal reproduction can be introduced in a sexual plant by modifying just a few genes, and constitute a proof of principle for the development of apomixis in cultivated plants.
The advantages of apomixis in agriculture
Apomixis is a specific type of reproduction observed in more than 400 species of wild plants. The progeny of a plant that reproduces by apomixis are genetically identical to the mother plant. By contrast, progeny obtained by sexual reproduction carry original genetic information that is a mixture of part of the father’s genome and part of the mother’s. Almost all cultivated plants produce seeds as a result of sexual reproduction, and not by apomixis. The apomictic reproduction of a cultivated species would be an extremely efficient means of obtaining and propagating new, elite varieties to meet the needs of consumers and producers. Indeed, the most interesting plants, that combine a large number of traits, often have a complex genetic composition. Because sexual reproduction mixes genetic information at each generation, their progeny do not retain targeted traits. However, the progeny of these same plants obtained by apomixis could conserve these traits and be reproduced and distributed endlessly. Apomixis has not yet been introduced in species of major agricultural interest.
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1 GEM stands for “Genome Elimination induced by a Mix of CENH3 variants”
Reference:
Synthetic clonal reproduction through seeds. SCIENCE, 18 February 2011 : 876. DOI:10.1126/science.1199682
Mohan P. A. Marimuthu1, Sylvie Jolivet2, Maruthachalam Ravi3, Lucie Pereira2, Jayeshkumar N. Davda1, Laurence Cromer2, Lili Wang3, Fabien Nogué2, Simon W. L. Chan3, Imran Siddiqi1 & Raphaël Mercier2
1 Centre for Cellular & Molecular Biology CSIR, Uppal Road, Hyderabad 500007. India
2 Institut Jean-Pierre Bourgin. UMR1318. INRA. Route de Saint Cyr. 78026 Versailles Cedex France
3 Department of Plant Biology, University of California, Davis. 1 Shields Ave, Davis, CA 95616. USA
For more information on the MiMe line, see the press info item: “MIME, a plant line producing pollen grains and ovules that are genetically identical to the parent plant”.
Associated patent:
Synthetic clonal reproduction through seeds
INRA and UC Davis
USA 61/418,792
1st December 2010
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
Contacts :
Raphaël Mercier
tel.: 33 (0)1 30 83 39 89 or raphael.mercier@versailles.inra.fr
Institut Jean-Pierre Bourgin
INRA Versailles-Grignon.
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