Loss and recovery of Arabidopsis-type telomere repeat sequences 5 '-(TTTAGGG)(n)-3 ' in the evolution of a major radiation of flowering plants

Fluorescent in situ hybridization and Southern blotting were used for showi ng the predominant absence of the Arabidopsis-type telomere repeat sequence (TRS) 5 '-(TTTAGGG)(n)-3 ' (the 'typical' telomere) in a monocot clade whi ch comprises up to 6300 species within Asparagales. Initially, two apparent ly disparate genera that lacked the typical telomere were identified. Here, we used the new angiosperm phylogenetic classification for predicting in w hich other related families such telomeres might have been lost. Our data r evealed that 16 species in 12 families of Asparagales lacked typical telome res. Phylogenctically, these were clustered in a derived clade, thereby ena bling us to predict that the typical telomere was lost, probably as a singl e evolutionary event, following the divergence of Doryanthaceae ca. 80-90 m illion years ago. This result illustrates the predictive value of the new p hylogeny, as the pattern of species lacking the typical telomere would be c onsidered randomly placed against many previous angiosperm taxonomies. Poss ible mechanisms by which chromosome end maintenance could have evolved in t his group of plants are discussed. Surprisingly, one genus, Ornithogalum (H yacinthaceae), which is central to the group of plants that have lost the t ypical telomere, appears to have regained the sequences. The mechanism(s) b y which such recovery may have occurred is unknown, but possibilities inclu de horizontal gene transfer and sequence reamplification.