Synteny among grass genomes inferred from large sequence comparisons

The grass family, comprising more than 10 000 members, includes several agronomical important species such as wheat, maize, rice and sorghum. Cereal genomes are composed of homologous sequences, inherited from a common ancestor. Homologs include orthologs (present in different species and produced by speciation) and paralogs (present within an organism and produced by gene duplication). Moreover, comparative mapping of cereal genomes, based on hybridization experiments (RFLP), has revealed extensive conservation of gene content (synteny) and gene order (colinearity) despite huge differences in genome sizes of grass species [1]. Rice has emerged as a model for comparing cereal genome structure and the international rice genome project is on the way to finish its complete sequencing. Consequently, scientists involved in the study of a particular cereal genome could learn much from syntenic relationships established with rice genome. In order to study these relationships, we developed a global comparison method using information derived from EST sequencing and leading to the cross-species clustering of homologs.