Effects of cycloastragenol on telomere/telomerase system of Arabidopsis thaliana

The aging process affects most living organisms, from unicellular yeast to multicellular mammals and plants. In complex organisms, the aging process is associated with the length of telomeric repeat sequences at the end of DNA. The length of telomeres shortens with each cell division, therefore limits proliferation of cells to a finite number, which is explained as telomere loss hypothesis. Accordingly, the length of telomeres are regulated by the telomerase activity which synthesizes the repeats at the end of chromosome in most eukaryotes. In this regard, loss of telomerase activity or its tissue limited expression is implicated in aging process. Although the process of aging, is quite different amongst plants and animals, telomere biology is essentially the same. Cycloastragenol (CAG) is a triterpenoid saponin compound which is synthesized by some Astragalus species. Studies have shown that CAG has a wide range of bioactivity, including telomerase activation, telomere elongation, anti-inflammatory and anti-oxidative properties. While clinical studies have demonstrated that CAG activates human telomerase, no study has been conducted to investigate its effect on the plant telomere/telomerase system. In this study, in order to test whether CAG has an effect on plants, 1 µM and 10 µM CAG were tested on all in vitro grown plant and callus tissues of a model plant Arabidopsis thaliana. Results revealed that CAG caused an increase in the transcript levels of TER1, CTC1, TRB1, POT1a, TAC1, BT2 which act as positive regulators on the telomere/telomerase system together with the TERT gene encoding the catalytic subunit of telomerase in A.thaliana. While CAG application resulted in 2 cm increase in height and a decrease in chlorophyll amount, no remarkable effect on callus growth index was observed. Furthermore, an increase in cell proliferation was observed in plant root cells due to the increased CAG dose. These results suggest that CAG might have a role as a telomerase activator in plants as well as in humans, and it led us to conclude that increased activity in the telomere/telomerase system might create a positive effect on cell proliferation.