Retrotransposon-related DNA sequences in the centromeres of grass chromosomes

Several distinct DNA fragments were subcloned from a sorghum (Sorghum bicol or) bacterial artificial chromosome clone 1.3116 that was derived from a ce ntromere. Three fragments showed significant sequence identity to either Ty 3/gypsy- or Ty1/copia-like retrotransposons. Fluorescence in situ hybridiza tion (FISH) analysis revealed that the Ty1/copia-related DNA sequences are not specific to the centromeric regions. However, the Ty3/gypsy-related seq uences were present exclusively in the centromeres of all sorghum chromosom es. FISH and gel-blot hybridization showed that these sequences are also co nserved in the centromeric regions of all species within Gramineae. Thus, w e report a new retrotransposon that is conserved in specific chromosomal re gions of distantly related eukaryotic species. Mie propose that the Ty3/gyp sy-like retrotransposons in the grass centromeres may be ancient insertions and are likely to have been amplified during centromere evolution. The pos sible role of centromeric retrotransposons in plant centromere function is discussed.