Duplication and DNA segmental loss in the rice genome: implications for diploidization

Large-scale duplication events have been recently uncovered in the rice genome, but different interpretations were proposed regarding the extent of the duplications. Through analysing the 370 AAb genome sequences assembled into 12 chromosomes of Oryza sativa subspecies indica, we detected 10 duplicated blocks on all 12 chromosomes that contained 47% of the total predicted genes. Based on the phylogenetic analysis, we inferred that this was a result of a genome duplication that occurred c. 70 million years ago, supporting the polyploidy origin of the rice genome. In addition, a segmental duplication was also identified involving chromosomes 11 and 12, which occurred c. 5 million years ago. Following the duplications, there have been large-scale chromosomal rearrangements and deletions. About 30-65% of duplicated genes were lost shortly after the duplications, leading to a rapid diploidization. Together with other lines of evidence, we propose that polyploidzation is still an ongoing process in grasses of polyploidy origins.