Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

Frequent Gene Movement During The Evolution Of Grass Genomes

Jinsheng Lai¹ , Jianxin Ma² , Zuzana Swigonova¹ , Jeffrey L. Bennetzen² , Joachim Messing¹

¹  Waksman Institute, Rutgers University, Piscataway, NJ 08854

²  Department of Genetics, University of Georgia, Athens, Georgia, 30602

A general conservation of gene content and order, although with many exceptions, has been reported for several loci from different grass species. To obtain a larger data set including a whole-genome duplication (WGD) event, we have sequenced large genomic fragments from five different loci of known duplicated regions in the maize genome and the orthologous regions from sorghum and aligned them with the orthologous regions from rice, representing a total of 4 Mb of genomic DNA. We found that at least one of the two copies was lost for nearly half of the duplicated genes of the orthologous maize regions. The residual orthologous genes for all four genomes demonstrated that the two progenitors of maize and the progenitor of sorghum split about 11.9 million years ago (mya), and that maize was formed by WGD as recently as 4.8 mya. Pair-wise comparison between all three species indicated that at least 14% of the genes within the aligned regions violate collinearity. Based on the complete rice genome sequence, we found that most of the noncollinear genes from maize and sorghum were present in the rice genome but in other chromosomal positions. Therefore, it appears that a large number of genes have moved to new chromosomal locations, mostly as single gene events, over the last 50 million years or less and that massive gene loss occurred in maize as part of its diploidization process after a WGD event.