Telomerase RNAs in land plants

Abstract

To elucidate the molecular nature of evolutionary changes of telomeres in the plant order Asparagales, we aimed to characterize telomerase RNA subunits (TRs) in these plants. The unusually long telomere repeat unit in Allium plants (12 nt) allowed us to identify TRs in transcriptomic data of representative species of the Allium genus. Orthologous TRs were then identified in Asparagales plants harbouring telomere DNA composed of TTAGGG (human type) or TTTAGGG (Arabidopsis-type) repeats. Further, we identified TRs across the land plant phylogeny, including common model plants, crop plants, and plants with unusual telomeres. Several lines of functional testing demonstrate the templating telomerase function of the identified TRs and disprove a functionality of the only previously reported plant telomerase RNA in Arabidopsis thaliana. Importantly, our results change the existing paradigm in plant telomere biology which has been based on the existence of a relatively conserved telomerase reverse transcriptase subunit (TERT) associating with highly divergent TRs even between closely related plant taxa. The finding of a monophyletic origin of genuine TRs across land plants opens the possibility to identify TRs directly in transcriptomic or genomic data and/or predict telomere sequences synthesized according to the respective TR template region.

Evolutionary and biochemical analyses reveal conservation of the Brassicaceae telomerase ribonucleoprotein complex

“…155confirming the findings inFajkus et al 2019.156 Double knockout of TER1 and TER2 does not decrease telomere length. (A) Two 157 Atter1 mutants were created using either CRISPR-Cas9 nuclease or nickase.…”

Human-like telomeres in Zostera marina reveal a mode of transition from the plant to the human telomeric sequences

“…The assembly was performed as stranded RNA-seq with paired-end fastq datasets. Putative TR from Z. marina were found out using blast with published orthologs 10,18,19 .…”

“…For the discovery of unusual telomeric sequences in Cestrum and Allium (well-known genera for their ornamental and crop plants, respectively), which had remained enigmatic for decades, the availability of NGS data and bioinformatics tools have been crucial, together with molecular cytogenetics 8 . The finding of unusual telomeric sequences have had a great scientific impact, for instance, the exceptionally long Allium sequence motif 9 was further utilized as bait for the identification of bona fide telomerase RNAs (TRs) in plants 10 .…”

“…Finally, we utilized our recent finding of plant telomerase RNA in plants 10 to obtain independent evidence of the newly found telomeric sequences in Z. marina , by analysing its genomic and transcriptomic data. Telomerase RNA is an essential part of the telomerase ribonucleoprotein complex, carrying the template region to produce telomeric DNA by reverse transcription.…”

“…Moreover, a combination of the available genomic data from Alismatales with the recent breakthrough of the discovery of plant telomerase RNA10,18,19 have led us to the astonishing conclusion that the template region in plant telomerase RNA is a very dynamic element, with unexpectedly variable borders, even in species with the same telomere sequence. The finding of two distinct telomerase RNA paralogs within several of the Alismatales genomes analysed, including the Z. marina genome assembly, offers an answer to how plants are able to change their telomeres.…”