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Genetics |
Genome Evolution and Speciation Laboratory. CNRS UMR 6553 University of Rennes 1 Campus Scientifique de Beaulieu, Bât. 141 35042 Rennes Cedex (France)
ABSTRACT
The origin of polyploid Bromus species of section Genea was investigated using molecular data. This group of annual species native from the Old-World is composed of three diploids, two tetraploids, one hexaploid, and one octoploid. Molecular cloning, sequencing, and phylogenetic analyses were performed on several accessions per species. We used the low copy nuclear gene Waxy, repeated rDNA spacers ITS1 and ITS2 and chloroplast spacers trnT-trnL and trnL-trnF. Our analyses revealed four different lineages involved in the parentage of the polyploids and confirmed their reticulate origin. Three of these lineages are closely related to the diploid species B. sterilis, B. tectorum, and B. fasciculatus. The fourth lineage could not be related to any diploid according to the available data. Our data gave insights on the origin of all the polyploids of section Genea, and chloroplast data allowed us to identify the maternal lineages. The Waxy gene was the most informative regarding origin of the polyploids. The Waxy copies duplicated by polyploidy appear selectively maintained in the polyploid species. No sequence heterogeneity was encountered in the ITS region, where concerted evolution seems to have occurred toward either maternal or paternal repeats. These results provide new information about the origin and molecular evolution of these polyploids and will allow a more accurate taxonomic treatment of the concerned species, based on their evolutionary history.
Key Words: allopolyploidy • Bromus • gene duplication • molecular phylogeny • Poaceae • Waxy
Received for publication 17 September 2007. Accepted for publication 6 February 2008.
FOOTNOTES
1 The authors thank L. Gicquiaud, M. A. Esnault, R. Amirouche, K. Tielbörger, C. Lampei, L. Janeway, L. Ahart, K. Schierenbeck, and A. M. Chèvre for collecting Bromus samples and F. Ebert for assistance in flow cytometry analyses. This work was funded by UMR CNRS 6553 Ecobio, University of Rennes 1 and the ANR "Polyploidy and Biodiversity" collaborative research project.
2 Author for correspondence (e-mail: malika.ainouche{at}univ-rennes1.fr), phone: +33 2 23 23 51 11, fax: +33 2 23 23 50 47
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