14. Aug. 2023
A group of plant scientists from CEITEC Masaryk University and the Institute of Biophysics of the Czech Academy of Sciences (CAS) led by Jiri Fajkus, Petr Fajkus and Vratislav Peska made a fascinating discovery about plant DNA and how evolution has shaped plant telomeres. The results of their study were recently published in the international science journal New Phytologist and could have significant implications for the future of crop plant breeding.
In the intricate world of DNA, a vital mechanism called telomerase safeguards the ends of our chromosomes, ensuring the stability of our genetic material. Telomeres are the physical ends of chromosomes. They are usually composed of short, tandemly arranged DNA repeats. Their DNA sequence is determined by a short region in the RNA subunit of a complex enzyme called telomerase. Telomere functions are largely dependent on proteins that associate with telomeres. Therefore, telomerase, telomeric DNA and associated proteins represent a complex, finely tuned and functionally conserved mechanism that ensures genome integrity by protecting and maintaining chromosome ends.
Any changes in this mechanism can put an organism's survival at risk. Surprisingly, throughout evolution, some plants have developed unique and unusual DNA sequences at their chromosome ends, thanks to innovative adaptations in telomere maintenance. At the heart of this mechanism lies telomerase RNA (TR), which guides the synthesis of telomeric DNA. Mutations in TR can change telomere DNA and disrupt its recognition by telomere proteins, thereby leading to a collapse of their end-protective and telomerase recruitment functions. This may result in the death of the organism.
Michal Zavodnik, Jiri Fajkus, Petr Fajkus, Vratislav Peska and their colleagues sought a plausible solution to this enigma. “The process was very challenging because, on the one hand, preventing deleterious complications in telomere functions naturally constrains telomere diversity. On the other hand, telomere DNA and telomerase RNAs show a considerable evolutionary divergence in plants. We used a unique approach and proposed a possible explanation for how telomerase RNA genes and telomere DNA have evolved and changed throughout the history of life on Earth,” explains Petr Fajkus.
Using a combination of advanced computer analysis and wet lab experiments, scientists have explored how these changes occur. Instead of starting with experimental findings, they systematically looked at a wide range of plant species with available genomic data. This allowed them to identify plants with unusual telomeres and the corresponding telomerase RNAs responsible for their synthesis. They streamlined the research process by focusing their experimental work only on the positive findings.
Through their investigations, the researchers found plants with multiple copies of the telomerase RNA gene (TR paralogs) capable of creating various telomeres. “We proposed that the formation of unusual telomeres might be linked to the occurrence of these TR paralogs, which can accumulate mutations with less risk. Multiple copies of the TR gene can safeguard the telomere function because it doesn´t rely on a single gene but is shared among all copies. This scenario aligns with the concept of adaptive evolution,” added shared first author of the study Michal Zavodnik.
In this case, mutations in genes coding for telomere-binding proteins seem to favour the development of novel telomere variants, making them successful in the long run. Through experimental analysis, the research team confirmed the presence of diverse telomere transitions in plants with predicted unusual telomeres, corresponding to the different TR paralogs with varied template regions.
This research study provides a solution to the mystery of unusual telomeres in plants. “Instead of viewing unusual telomeres as exceptions, we see them as a result of an ongoing battle among duplicated TR genes that frequently mutate and evolve. This process minimises the risk of losing viability, as our hypothesis suggests. This updated perspective on telomere evolution sheds light on how new species emerge and how plants can be crossbred or undergo meiotic segregation, “explains Jiri Fajkus.
Telomere DNA is now seen as a product of the intricate and dynamic evolution of TRs. This ground-breaking research presents fascinating ways in which plants have evolved to safeguard their genetic material, providing us with a deeper understanding of the secrets hidden within the world of DNA. The findings could have significant implications for crop plant breeding.
This work is mainly the outcome of our GAČR-EXPRO project, which is the collaborative project between Masaryk University and the Institute of Biophysics of the Czech Academy of Sciences. Therefore, the key members of the team (both shared first authors, Michal Zavodnik and Petr Fajkus) and all three corresponding authors (Jiri Fajkus, Vratislav Peska and Petr Fajkus) were from these institutions. The other collaborating institutions were the Institute of Experimental Botany CAS (David Kopecky), Potato Research Institute Havlickuv Brod, s.r.o. (Jiri Ptacek), Institut Botanic de Barcelona (Sonia Garcia), University of Portsmouth (Steven Dodsworth) and Instituto Tecnologico del Putumayo (Andres Orejuela).