Retrotransposon BARE-1 and its role in genome evolution in the genus Hordeum

The replicative retrotransposon life cycle offer's the potential for explos ive increases in copy number and consequent inflation of genome size. The B ARE-I retrotransposon family of barley is conserved, disperse, and transcri ptionally active, To: assess the role of BARE-I in genome evolution, we det ermined the copy number of its integrase, its reverse transcriptase, and it s long terminal repeat (LTR) domains throughout the genus Hordeum, On avera ge, BARE-1 contributes 13.7 x 10(3) full-length copies, amounting to 2.9% o f the genome. The number increases with genome size. Two LTRs are associate d with each internal domain in intact retrotransposons, but surprisingly, B ARE-I LTRs were considerably more prevalent than would be expected from the numbers of intact elements, The excess in LTRs increases as both genome si re and BARE-I genomic fraction decrease.: Intrachromosomal homologous recom bination between LTRs could explain the excess, removing BARE-1 elements an d leaving behind solo LTRs, thereby reducing the complement of functional r etrotransposons in the genome and providing at least a partial "return tick et from genomic obesity,".