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Stabilisation of polyploid forms

Stabilisation of polyploid forms

Research

Context and Issues

  • Polyploidy is the process that gives rise to organisms with multiple complete sets of chromosomes; this genome duplication is recognized as a major evolutionary process generating biodiversity at the origin of several crops
  • The elucidation of the structural and functional mechanisms involved in the stabilization of polyploid species such as bread wheat and oilseed rape will allow the optimal use of the progenitor diversity in breeding programmes

Objectives

• To understand how a new species as oilseed rape can occur from the initial crosses between diploids. We are focusing on (1) the impact of diploid genotype, (2) the method of synthetic production on structural and functional mechanisms responsible of meiosis regularity and fertility

 
• In bread wheat, identify structural, genetic and epigenetic modifications in neo-hexaploid and neo-tetraploid synthetics 

Methodology

In oilseed rape, synthetic forms are produced by crosses between different diploid progenitors. Somatic doubling or production of unreduced gametes is used to produce oilseed rape synthetic. Their selfing progeny are analysed for their meiotic stability, their fertility, their genomic structure and their functional regulation.

In bread wheat, hexaploid synthetics are developed through hybridization between tetraploid wheats and Ae. tauschii. Embryo culture is required and F1 chromosome doubling is most often spontaneous. In order to better identify modifications of the A and B genomes in the synthetics, AB tetraploid components of two synthetics were extracted and compared to the tetraploid parents of these synthetics.

Main Results

In oilseed rape, numerous structural modifications occur from the first meiosis but their frequency and the size of rearrangements depend on the way of production (Szadkowsky et al. 2010, 2011). The meiosis remains unstable even in advanced selfing generations. Functional regulation takes place from first hybridization (Albertin et al 2006; Książczyk et al. 2011) but without burst of transposable activation (Sarilar et al. 2013). The impact of self incompatibility present in diploid progenitors and of allogamy on the stabilization of meiosis is under study.

In bread wheat, stability of the synthetic allohexaploids was shown to depend on the considered genotypes of both AB and D genome progenitors, where few combinations compare to the natural wheat allohexaploid in terms of regularity of meiosis and euploidy. Aneuploidy represents the only structural change observed in these synthetic allohexaploids, as no apparent DNA sequence elimination or rearrangement was observed when analysing euploid plants with molecular markers, developed from expressed sequence tags (ESTs) as well as simple sequence repeat (SSR) and transposable element sequences (Chagué et al. 2010; Mestiri et al. 2010).

Additive expression was shown to represent the majority of expression regulation in the synthetic allohexaploids, where expression for more than c. 93% of transcripts was equal to the mid-parent value. 

Tetraploids (AABB) extracted from synthetic wheats and present-day bread wheats are presently studied to find out genome modifications occurring in the short and the long terms.

Partners

  • UMR URGV Evry, France
  • Genoscope Evry, France
  • GenOuest IRISA/INRIA, Rennes, France
  • GenScale, IRISA/INRIA, Rennes, France
  • UMR génétique végétale, Moulon, France
  • UMR IJPB Versailles, France
  • UMR EcoBio, Université de Rennes I, France
  • Academy of Sciences, Brno, Czech Republic
  • University of York, UK
  • University of Giessen, Deutschland
  • University of Alger, Algeria

Funding and Support

ANR Biodiversité (2006-2008) (PI : M. Ainouche): Effet de la polyploïdie sur la biodiversité et l’évolution du génome des plantes

ANR PLOID-PLOID-WHEAT (2011-2015) (PI : B. Chalhoub):Unraveling bases of polyploidy and aneuploidy responses in flowering plants, using the wheat ploid model

ERA CAPS Evo-Genapus (2014-2016) (PI : Bancroft): Evolution of genomes: structure-function relationships in the polyploid crop species Brassica napus

France Génomique PolySuccess (2014- ): (PI A.M. Chèvre): How a polyploid becomes a new species, Brassica model

Recent publications on the topic

Albertin W., Balliau T., Brabant P., Chèvre A.M., Eber F., Malosse C., Thiellement H., 2006. Numerous and rapid non-stochastic modifications of gene products in newly synthesized Brassica napus allotetraploids. Genetics 173: 1101-1113.

Chagué V., Just J., Mestiri I., Balzergue S., Tanguy A.M., Huneau C., Huteau V., Belcram H., Coriton O., Jahier J., Chalhoub B. 2010. Genome-wide gene expression changes in genetically stable synthetic and natural wheat allohexaploids. New Phytologist 187: 1181-1194 

Jenczewski E., Chevre A.M., Alix K., 2013. Chromosomal and Gene Expression Changes in Brassica Allopolyploids. In Polyploid and hybrid genomics. (eds Z. J. Chen and J. A. Birchler), John Wiley & Sons, Inc., Oxford, UK. DOI

Książczyk T.*, Kovarik A.*,  Eber F., Huteau V., Khaitova L., Tesarikova Z., Coriton O., Chèvre A.M. 2011 Epigenetic silencing precedes rDNA loci rearrangements during the stabilization of a polyploid species Brassica napus. Chromosoma 120: 557-571 

Mestiri I., Chagué V., Tanguy A.M., Huneau C., Huteau V., Belcram H., Coriton O., Chalhoub B., Jahier J. 2010. Newly synthesized wheat allohexaploids display progenitor-dependent meiotic stability and aneuploidy but structural genomic additivity. New Phytol 186 : 86-101. 

Sarilar V., Martinez Palacios P., Rousselet A., Ridel C., Falque M., Eber F., Chèvre A.M., Joets J., Brabant P., Alix K., 2013. Allopolyploidy has a moderate impact on restructuring at three contrasting transposable element insertion sites in resynthesized Brassica napus allotetraploids. New Phytologist 198: 593-604

Szadkowski E., Eber F., Huteau V.,  Lodé M.,  Huneau C., Belcram H. , Coriton O., Manzanares-Dauleux M.J., Delourme R., King G.J. , Chalhoub B., Jenczewski E., Chèvre AM. 2010. The first meiosis of resynthesized Brassica napus, a genome blender. New Phytologist 186 : 102-112

Szadkowski E., Eber F., Huteau V., Lodé M., Coriton O.,Jenczewski E., Chèvre AM. 2011.  Polyploid formation pathways have an impact on genetic rearrangements in resynthesized Brassica  napus. New phytologist 191: 554-894