The enormous sequence heterogeneity of telomerase RNA (TR) subunits has thus far complicated their characterization in a wider phylogenetic range. Our recent finding that land plant TRs are, similarly to known ciliate TRs, transcribed by RNA polymerase III and under the control of the type-3 promoter, allowed us to design a novel strategy to characterize TRs in early diverging Viridiplantae taxa, as well as in ciliates and other Diaphoretickes lineages. Starting with the characterization of the upstream sequence element of the type 3 promoter that is conserved in a number of small nuclear RNAs, and the expected minimum TR template region as search features, we identified candidate TRs in selected Diaphoretickes genomes. Homologous TRs were then used to build covariance models to identify TRs in more distant species. Transcripts of the identified TRs were confirmed by transcriptomic data, RT-PCR and Northern hybridization. A templating role for one of our candidates was validated in Physcomitrium patens. Analysis of secondary structure demonstrated a deep conservation of motifs (pseudoknot and template boundary element) observed in all published TRs. These results elucidate the evolution of the earliest eukaryotic TRs, linking the common origin of TRs across Diaphoretickes, and underlying evolutionary transitions in telomere repeats.

Boyce Thompson Institute Cornell University Ithaca NY 14853 USA

Department of Cell Biology and Radiobiology Institute of Biophysics of the Czech Academy of Sciences Brno CZ 61265 Czech Republic

Institute of Experimental Botany of the Czech Academy of Sciences Prague CZ 16000 Czech Republic

Laboratory of Functional Genomics and Proteomics NCBR Faculty of Science Masaryk University Brno CZ 61137 Czech Republic

Mendel Centre for Plant Genomics and Proteomics CEITEC Masaryk University Brno CZ 62500 Czech Republic

References provided by Crossref.org