Evidence that rice, and other cereals, are ancient aneuploids

Klaas Vandepoele1, Cedric Simillion2, Stephane Rombauts and Yves Van de Peer
1klpoe@gengenp.rug.ac.be, University of Gent, VIB dep. Plant Systems Biology; 2cesim@gengenp.rug.ac.be, University of Gent, VIB dep. Plant Systems Biology

Detailed analyses of the genomes of several model organisms revealed that large-scale gene or even entire genome duplications have played a prominent role in the evolutionary history of many eukaryotes. Recently, strong evidence has been presented that the genomic structure of the dicotyledonous model plant species Arabidopsis thaliana is the result of multiple rounds of entire genome duplications. Here, we analyze the genome of the monocotyledonous model plant species rice (Oryza sativa), for which a draft of the genomic sequence has recently been published. We show that a substantial fraction of all rice genes, i.e. about 15%, are found in duplicated segments. Dating of these block duplications, their non-uniform distribution over the different rice chromosomes, and comparison with the duplication history in Arabidopsis suggest that rice is not an ancient polyploid as previously suggested, but has experienced the duplication of one or large part of one chromosome in its evolutionary past, approximately 70 million years ago. This date predates the divergence of most of the cereals and relative dating by phylogenetic analysis indeed shows that the duplication event is shared by most, if not all, of them.