Structure et dynamique du génome des cultivars modernes de canne à sucre (Saccharum spp) ; apports du marquage moléculaire (RFLP)

Les cultivars de canne à sucre résultent de croisements interspécifiques complexes, réalisés au début du siècle, entre quelques clones de l'espèce domestiquée S. officinarum (2n=80) et de l'espèce sauvage apparentée, S.spontaneum (2n=40 à 128), et sont hautement polyploïdes, aneuploïdes. Environ 80% de leur génome provient de S officinarum et seulement 20 % de S. spontaneum. La compréhension de cette structure génétique conditionne le raisonnement efficace des programmes d'amélioration. Dans ce but, différentes études ont été conduites à l'aide de marqueurs RFLP: (1) diversité au sein d'un ensemble représentatif de S. officinarum et de cultivars issus principalement de deux stations de sélection; (2) ségrégation de marqueurs dans la descendance d'un cultivar; (3) recherche de déséquilibres de liaison parmi les principaux cultivars utilisés à 1'lle Maurice. Il en ressort que la création des cultivars a largement exploité la grande diversité observée chez S. officinarum et l'a enrichie d'une composante importante issue de S. spontaneum. Celle-ci contribue notamment à une différenciation variétale en fonction du lieu de création. Une compartimentation relative est maintenue par des appariements préférentiels entre chromosomes d'une même espèce. Le recours massif à quelques hybrides interspécifiques semble avoir instauré un déséquilibre de liaison, qui subsiste entre locus très liés parmi les cultivars modernes, et se trouve particulièrement visible avec les marqueurs issus de S. spontaneum. Ces résultats orientent l'utilisation des marqueurs moléculaires en appui à l'amélioration variétale. (Résumé d'auteur

Orthologous comparison in a gene-rich region among grasses reveals stability in the sugarcane polyploid genome

Modern sugarcane (Saccharum spp.) is an important grass that contributes 60% of the raw sugar produced worldwide and has a high biofuel production potential. It was created about a century ago through hybridization of two highly polyploid species, namely S. officinarum and S. spontaneum. We investigated genome dynamics in this highly polyploid context by analyzing two homoeologous sequences (97 and 126 kb) in a region that has already been studied in several cereals. Our findings indicate that the two Saccharum species diverged 1.5-2 million years ago from one another and 8-9 million years ago from sorghum. The two sugarcane homoeologous haplotypes show perfect colinearity as well as high gene structure conservation. Apart from the insertion of a few retrotransposable elements, high homology was also observed for the non-transcribed regions. Relative to sorghum, the sugarcane sequences displayed colinearity, with the exception of two genes present only in sorghum, and striking homology in most non-coding parts of the genome. The gene distribution highlighted high synteny and colinearity with rice, and partial colinearity with each homoeologous maize region, which became perfect when the sequences were combined. The haplotypes observed in sugarcane may thus closely represent the ancestral Andropogoneae haplotype. This analysis of sugarcane haplotype organization at the sequence level suggests that the high ploidy in sugarcane did not induce generalized reshaping of its genome, thus challenging the idea that polyploidy quickly induces generalized rearrangement of genomes. These results also confirm the view that sorghum is the model of choice for sugarcane. (Résumé d'auteur

Orthologous Comparison In A Gene-rich Region Among Grasses Reveals Stability In The Sugarcane Polyploid Genome.

Modern sugarcane (Saccharum spp.) is an important grass that contributes 60% of the raw sugar produced worldwide and has a high biofuel production potential. It was created about a century ago through hybridization of two highly polyploid species, namely S. officinarum and S. spontaneum. We investigated genome dynamics in this highly polyploid context by analyzing two homoeologous sequences (97 and 126 kb) in a region that has already been studied in several cereals. Our findings indicate that the two Saccharum species diverged 1.5-2 million years ago from one another and 8-9 million years ago from sorghum. The two sugarcane homoeologous haplotypes show perfect colinearity as well as high gene structure conservation. Apart from the insertion of a few retrotransposable elements, high homology was also observed for the non-transcribed regions. Relative to sorghum, the sugarcane sequences displayed colinearity, with the exception of two genes present only in sorghum, and striking homology in most non-coding parts of the genome. The gene distribution highlighted high synteny and colinearity with rice, and partial colinearity with each homoeologous maize region, which became perfect when the sequences were combined. The haplotypes observed in sugarcane may thus closely represent the ancestral Andropogoneae haplotype. This analysis of sugarcane haplotype organization at the sequence level suggests that the high ploidy in sugarcane did not induce generalized reshaping of its genome, thus challenging the idea that polyploidy quickly induces generalized rearrangement of genomes. These results also confirm the view that sorghum is the model of choice for sugarcane.50574-8