Variability of interstitial telomeric-like repeats in Mediterranean weedy species

A telomere is the region of DNA that marks the end of a chromosome. The protect the ends of the chromosome, and stop one chromosome from fusing with another. So finding something that looks like a telomere in the middle of a chromosome would be odd – but it happens. And no one knows exactly why.

Although interstitial occurrence of telomeric repeat motifs (ITR) has been reported in the genome of a few organisms, the striking level of polymorphism found by Rosata et al. within a single species has not been described before. Rosata and colleagues investigate whether a comparable pattern of dynamism found for another repetitive element, interstitial 45S rDNA sites, in the genus Anacyclus (Asteracea), is linked to ICT and both have the same underlying causes.

Cariograms showing inter- and intrapopulation site number variation of interstitial telomeric repeats (ITRs) in Anacyclus clavatus.
Cariograms showing inter- and intrapopulation site number variation of interstitial telomeric repeats (ITRs) in Anacyclus clavatus. Telomeric sites and ITRs are shown as red fluorescent signals and the chromosomes are counterstained with 4, 6-diamidino-2-phenylindole (DAPI) (blue colour). Representative individuals from Salobreña (A, D), Carchuna (B) and Altea (C) populations are shown. (A) Four ITR sites; (B) six sites; (C) nine sites; (D) 14 sites. Scale bars: 10 µm.

This study provides hints that ancient Robertsonian translocations or the amplification of terminal 45S rDNA sites can be involved in the patterns found for both repetitive families, although a wide survey across Asteraceae is needed for a conclusive answer.

While the regions studied are tiny, the effects could be big if you use ITRs to examine plant evolution. The authors say: “Our results suggest caution for those studies using ITRs as markers of species’ phylogenetic relationships without a thorough sampling.”

Further reading

Rosato, M., Álvarez, I., Feliner, G. N., & Rosselló, J. A. (2018). Inter- and intraspecific hypervariability in interstitial telomeric-like repeats (TTTAGGG)n in Anacyclus (Asteraceae). Annals of Botany, 122(3), 387–395. https://doi.org/10.1093/aob/mcy079

Rosato, M., Álvarez, I., Feliner, G.N., & Rosselló, J. A. (2017). High and uneven levels of 45S rDNA site-number variation across wild populations of a diploid plant genus (Anacyclus, Asteraceae). PLOS ONE, 12(10), e0187131. https://doi.org/10.1371/journal.pone.0187131