Lab equipment. © INRA, William Beaucardet

Green biotechnologies: paving new paths for agriculture

Mutations

Mutations, sometimes occurring spontaneously, are a source of genetic diversity. Mutagenesis is a tool for creating new varieties and understanding how genomes work. 

Mutations to create new varieties 

Mutagenesis is a tool for creating new varieties © LEPINIEC Loïc
Mutagenesis is a tool for creating new varieties © LEPINIEC Loïc
Thanks to mutagenesis, new genetic varieties of a species can be created. Mutagenesis accelerates a natural process by increasing the frequency of mutations. Most genome mutations go by undetected (synonymous mutations), and some are immediately ruled out from the process because they are either unexploitable or harmful (e.g. albinism).

Mutagenesis was used on a very large scale between the 1950s and 1980s to promote diversity in many species.

More than 2,000 varieties were created from natural or induced mutations (source: FAO/IAEA, 2000).

 

Mutation, a means of studying genomes

Provoking a mutation in a gene allows scientists to inhibit the gene’s function, and thereby learn what the function of a given gene is. Now that the genomes of several plants are known to science, (Arabidopsis thaliana, rice, poplar, Medicago truncatula, vine), the challenge now is to attribute a role to these genes and identify those that can bring agronomic benefits.

A large number of varieties obtained from mutations of Arabidopsis thaliana was created by INRA in Versailles. With some 55,000 independent mutants, the entire genome of the plant, statistically speaking, is covered: a gene has a 75-80% chance of being affected by a mutation. Moreover, the desired method of mutation is chosen by inserting a label (a T-DNA), which allows the gene in question to be marked and isolated using molecular genetic methods.

A major discovery with mutant Arabidopsis: imitating apomixis

By combining several mutations, a team of INRA researchers in Versailles has proven that it is possible to obtain seeds from a sexed plant that are genetically identical to the mother plant, a process that exists naturally in certain plant species.
The discovery consisted of two steps: first, obtaining a mutant by combining three mutations of Arabidopsis, capable of producing pollen grains with 2n chromosomes that are identical to the cells of the mother plant (the MIME mutant, cf 1 & 2). The second step consisted of identifying a mutant capable of developing an embryo from these 2n pollen grains without fertilisation (cf 2 & 3).
These findings, published in Science magazine (cf. 4), show that reproduction by cloning is possible in sexed plants by modifying only a few genes.

Applying such reproduction, known as apomixis, to crop plants would be revolutionary, for it would allow for the reproduction of any elite variety, including hybrids. According to Raphael Mercier: “Despite their agronomic performance, hybrids have a major drawback for farmers, because the seeds have to be bought each year. Farmers cannot sow the seeds they reap because if hybrids crossbreed, genetic mixing will prevent the same hybrid from being produced. A different progeny will be produced and the initial properties will be lost over generations. A hybrid that can reproduce itself would remove these obstacles; it is a goal that scientists the world over have been striving to reach for years. Hybrids that can adapt to all sorts of environments can be produced quickly and affordably. Apomixis is often cited as the technology of choice for developing countries.” 

This was a fortuitous discovery that came about during fundamental research:
“At first, we were trying to understand the mechanism of meiosis by using mutants to identify the genes involved. The idea of imitating apomixis only came later.”

(1) d’ Erfurth, I.et al.2009. Turning meiosis into mitosis. PLoS Biology 7, e1000124
(2) Ravi, M., Marimuthu, M.P. a, Siddiqi, I. 2008. Gamete formation without meiosis in Arabidopsis. Nature 451, 1121-4
(3) Ravi, M., Chan, S.W.L. 2010. Haploid plants produced by centromere-mediated genome elimination. Nature 464, 615-8.
(4) Marimuthu, M.P. aet al. 2011. Synthetic clonal reproduction through seeds. Science (New York, N.Y.)331, 876.

Contact(s)
Scientific contact(s):

Associated Centre(s):
Versailles-Grignon