| Summary: | <p>Abstract</p> <p>Background</p> <p>The role of gene duplication in the structural and functional evolution of genomes has been well documented. Analysis of complete rice (<it>Oryza sativa</it>) genome sequences suggested an ancient whole genome duplication, common to all the grasses, some 50-70 million years ago and a more conserved segmental duplication between the distal regions of the short arms of chromosomes 11 and 12, whose evolutionary history is controversial.</p> <p>Results</p> <p>We have carried out a comparative analysis of this duplication within the wild species of the genus <it>Oryza</it>, using a phylogenetic approach to specify its origin and evolutionary dynamics. Paralogous pairs were isolated for nine genes selected throughout the region in all <it>Oryza </it>genome types, as well as in two outgroup species, <it>Leersia perrieri </it>and <it>Potamophila parviflora</it>. All <it>Oryza </it>species display the same global evolutionary dynamics but some lineage-specific features appear towards the proximal end of the duplicated region. The same level of conservation is observed between the redundant copies of the tetraploid species <it>Oryza minuta</it>. The presence of orthologous duplicated blocks in the genome of the more distantly-related species, <it>Brachypodium distachyon</it>, strongly suggests that this duplication between chromosomes 11 and 12 was formed as part of the whole genome duplication common to all Poaceae.</p> <p>Conclusion</p> <p>Our observations suggest that recurrent but heterogeneous concerted evolution throughout the <it>Oryza </it>genus and in related species has led specifically to the extremely high sequence conservation occurring in this region of more than 2 Mbp.</p>
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