title: Transitions between the Arabidopsis-type and the human-type telomere sequence in green algae (clade Caudivolvoxa, Chlamydomonadales).
abstract: Telomeres are nucleoprotein structures that distinguish native chromosomal ends from double-stranded breaks. They are maintained by telomerase that adds short G-rich telomeric repeats at chromosomal ends in most eukaryotes and determines the TnAmGo sequence of canonical telomeres. We employed an experimental approach that was based on detection of repeats added by telomerase to identify the telomere sequence type forming the very ends of chromosomes. Our previous studies that focused on the algal order Chlamydomonadales revealed several changes in telomere motifs that were consistent with the phylogeny and supported the concept of the Arabidopsis-type sequence being the ancestral telomeric motif for green algae. In addition to previously described independent transitions to the Chlamydomonas-type sequence, we report that the ancestral telomeric motif was replaced by the human-type sequence in the majority of algal species grouped within a higher order clade, Caudivolvoxa. The Arabidopsis-type sequence was apparently retained in the Polytominia clade. Regarding the telomere sequence, the Chlorogonia clade within Caudivolvoxa bifurcates into two groups, one with the human-type sequence and the other group with the Arabidopsis-type sequence that is solely formed by the Chlorogonium species. This suggests that reversion to the Arabidopsis-type telomeric motif occurred in the common ancestral Chlorogonium species. The human-type sequence is also synthesized by telomerases of algal strains from Arenicolinia, Dunaliellinia and Stephanosphaerinia, except a distinct subclade within Stephanosphaerinia, where telomerase activity was not detected and a change to an unidentified telomeric motif might arise. We discuss plausible reasons why changes in telomeric motifs were tolerated during evolution of green algae.
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265, Brno, Czech Republic.|Faculty of Science, and CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-62500, Brno, Czech Republic.
authors.forename: Jana
authors.initials: J
authors.lastname: Fulnečková
authors.affiliation: Department of Biology and Ecology, Life Science Research Centre & Institute of Environmental Technologies, Faculty of Science, University of Ostrava, Chittussiho 10, CZ-71000, Ostrava, Czech Republic.
authors.forename: Tereza
authors.initials: T
authors.lastname: Ševčíková
authors.affiliation: Institute of Soil Biology, Biology Centre Academy of Sciences of the Czech Republic, v.vi., Na Sádkách 7, CZ-37005, České Budějovice, Czech Republic.
authors.forename: Alena
authors.initials: A
authors.lastname: Lukešová
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 135, CZ-61265, Brno, Czech Republic. evin@ibp.cz.|Faculty of Science, and CEITEC - Central European Institute of Technology, Masaryk University, Kamenice 5, CZ-62500, Brno, Czech Republic. evin@ibp.cz.
authors.forename: Eva
authors.initials: E
authors.lastname: Sýkorová
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics*; D001483:Base Sequence; D004275:DNA, Ribosomal / Q000235:genetics; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D017422:Sequence Analysis, DNA; D019098:Telomerase / Q000235:genetics*; D016615:Telomere / Q000235:genetics*; D059506:Telomere Shortening / Q000235:genetics; D016823:Volvocida / Q000235:genetics*
chemical_list: D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D019098:Telomerase
keywords: 18S rDNA phylogeny; Green algae; TRAP; Telomerase activity; Telomere evolution