Characterization of chromosome ends on the basis of the structure of TrsA subtelomeric repeats in rice (Oryza sativa L.).

Subtelomeres contain species-specific repetitive sequences. We characterized rice chromosome ends on the basis of the structure of TrsA, a subtelomeric repetitive sequence of rice. Among the 24 chromosome arms, TrsA was arrayed in tandem on the ends of five: 5L, 6S, 8L, 9L, and 12L. TrsA sequences were arranged in discrete clusters of 3-106 copies in a chromosome-specific manner, instead of being distributed uniformly throughout the subtelomeric regions. The clusters were located at the distal-most end of the sequenced region in 5L, 6S, 8L, and 9L, but in 12L expressed genes were present distal to the clusters. Thus, rice subtelomeres are composed of discrete clusters of a TrsA-rich region and a gene-rich region with high transcriptional activity. Intra-chromosomal duplications have resulted in a striking degree of variation in the number and distribution of TrsAs, suggesting that the areas near the ends of the chromosomes are dynamic and variable.