Origin, Diversity, and Evolution of Telomere Sequences in Plants

Abstract

Telomeres are basic structures of eukaryote genomes. They distinguish natural chromosome ends from double-stranded breaks in DNA and protect chromosome ends from degradation or end-to-end fusion with other chromosomes. Telomere sequences are usually tandemly arranged minisatellites, typically following the formula (T x A y G z) n. Although they are well conserved across large groups of organisms, recent findings in plants imply that their diversity has been underestimated. Changes in telomeres are of enormous evolutionary importance as they can affect whole-genome stability. Even a small change in the telomere motif of each repeat unit represents an important interference in the system of sequence-specific telomere binding proteins. Here, we provide an overview of telomere sequences, considering the latest phylogenomic evolutionary framework of plants in the broad sense (Archaeplastida), in which new telomeric sequences have recently been found in diverse and economically important families such as Solanaceae and Amaryllidaceae. In the family Lentibulariaceae and in many groups of green algae, deviations from the typical plant telomeric sequence have also been detected recently. Ancestry and possible homoplasy in telomeric motifs, as well as extant gaps in knowledge are discussed. With the increasing availability of genomic approaches, it is likely that more telomeric diversity will be uncovered in the future. We also discuss basic methods used for telomere identification and we explain the implications of the recent discovery of plant telomerase RNA on further research about the role of telomerase in eukaryogenesis or on the molecular causes and consequences of telomere variability.

Composition and Function of Telomerase—A Polymerase Associated with the Origin of Eukaryotes

“…[22,38,46]. Unlike insects, even the unusual plant telomeric sequences characterized so far are synthesized by telomerases using TRs with corresponding template regions [19,43,44,47].…”

Step-by-Step Evolution of Telomeres: Lessons from Yeasts

“…In most flowering plants, telomeric sequences are very similar (5′-TTTAGGG-3′) ( Richards and Ausubel 1988 ; Richards et al. 1992 ; Shippen and McKnight 1998 ; Peška and Garcia 2020 ) or even identical to the vertebrate motif (e.g., several species belonging to the order Asparagales or Zostera marina ) ( Sýkorová, Lim, Kunická, et al. 2003 ; Sýkorová et al.…”

Origin and Fates of TERT Gene Copies in Polyploid Plants

“…When telomerase is not active, telomeres become shortened, and their function in the protection of chromosomes is disrupted. The extreme evolutionary success of telomerase-based mechanisms of telomere maintenance is illustrated by current findings in plants (reviewed in [ 14 ]). Even among apparent exceptions in telomere sequences, in plant genera Allium (Asparagales) and Cestrum (Solanales) [ 15 , 16 , 17 , 18 ], recent research has revealed that novel, unusual telomere DNA sequences are synthesized by telomerase [ 16 , 18 , 19 ] and not by alternative mechanisms as had been suggested previously (reviewed in [ 20 ]).…”

“…Even among apparent exceptions in telomere sequences, in plant genera Allium (Asparagales) and Cestrum (Solanales) [ 15 , 16 , 17 , 18 ], recent research has revealed that novel, unusual telomere DNA sequences are synthesized by telomerase [ 16 , 18 , 19 ] and not by alternative mechanisms as had been suggested previously (reviewed in [ 20 ]). Moreover, we recently demonstrated that changes in the template region of the telomerase RNA subunit directed the observed evolutionary transitions in telomere DNA sequences [ 14 , 21 , 22 ]. In contrast to the RNA subunit, the protein subunit TERT is evolutionary well conserved and possesses a central reverse transcriptase domain essential for its catalytic function [ 23 , 24 ].…”