Rice genome approaches completion

01/25/05



Child dressed in traditional Han suit, wanting to share his fully cooked rice genome with the rest of the world, after reserving a small portion for himself. Photography by Lei Xu and Fang Chen, Beijing Institute of Genomics. Child model: Wensen Cai.
Click here for a high resolution photograph.

A large group of scientists led by the Beijing Institute of Genomics has published in the freely-available online journal PLoS Biology a much improved, near-complete genome analysis of the indica and japonica subspecies of Oryza sativa, which are eaten in India and China, and Japan, respectively. The analysis team, led by Gane Ka-Shu Wong, provides important insights into the evolution of rice.

The key to the improvement in the genome sequence analysis is that the researchers have used the combined DNA sequence data from the two subspecies to facilitate the sequence assembly. The result is a nearly 1,000-fold increase in contiguity for the two genome sequences relative to the existing sequence data.

The researchers have used their improved genome sequence to investigate the evolutionary history of rice. Central to evolution is the development of new functions through mutation of existing genes. But when mutations occur in functional genes, the result is rarely beneficial, so it is thought that evolution is more likely to proceed first by duplicating existing genes and then experimenting on the "backup" copy of the gene.

Wong and colleagues report that there is evidence in the rice DNA sequences for a whole-genome duplication event just before the grasses diverged from other flowering plants, about 5570 million years ago. This genome duplication may have played a role in the origin of the grasses, which then spread rapidly across the world to provide important sources of food that, among other things, possibly influenced human evolution.

Analysis of the rice genomes also indicates that there is massive ongoing duplication of individual genes. These individual gene duplications provide a continuous source of raw material for gene genesis and very likely contribute to the differences between members of the grass family. Now the challenge is to use the rice sequences as a basis for detailed genetic analyses of additional cereal crops and for the development of improved strains of not only rice, but wheat, maize, and other important food crops.

Source: Eurekalert & others

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