Dorothy Shippen

Areas of Expertise

• Telomeres
• Telomerase
• RNP structure function
• Chromosome biology

Professional Summary

Telomeres cap the ends of eukaryotic chromosomes and play essential roles in conferring genome stability. The critical function of telomeres was demonstrated in plants 80 years ago by the pioneering work of Barbara McClintock. A half-century later, our lab developed Arabidopsis thaliana as a powerful comparative model for elucidating fundamental aspects of telomere biology. Our research employs biochemical, genetic, genomic, proteomic, and molecular evolution strategies to elucidate the origin and function of telomere-related proteins and RNAs in plants.

Telomere biology in plants

The stability of eukaryotic genomes derives in part from telomeres, the nucleoprotein caps on chromosome termini. Telomeric DNA is maintained by telomerase, a reverse transcriptase that continually replenishes telomeric DNA using a catalyst TERT and an integral long noncoding RNA, TR, as a template. Mis-regulation of telomerase is linked to stem cell disease and tumorigenesis in humans. Our work has revealed that plants are much more tolerant of genome instability, particularly telomere dysfunction than mammals. One major thrust of our research is to provide a deeper understanding of the evolution and regulation of telomere-related factors and their mechanisms for safeguarding genome integrity. More recently, we have begun to examine the impact of oxidative stress on various facets of telomere biology.

E. V. Shakirov, J. J.-L. Chen and D. E. Shippen, D.E. Plant telomere biology: the green solution to the end-replication problem. Plant Cell 34, 2492-2504 (2022).

Identification and characterization of the telomerase RNA subunit in the plant kingdom

The predominant structure models for telomerase derive from the vertebrate and ciliate enzymes. We recently identified TR from A. thaliana and, working with collaborators from Arizona State University, developed a robust secondary structure model for plant TR that provides an evolutionary bridge for the highly divergent TR molecules studied to date. TERT and TR are common to all telomerases, but the accessory subunits of the enzyme complex are unique to each particle. A current focus in the lab is the comprehensive identification of telomerase-associated factors and the acquisition of a 3D structure for plant telomerases to uncover both novel mechanisms and unifying principles for this essential enzyme.

J. Song, D. Logeswaran, C. Castillo-Gonzalez, Y. Li, S. Bose, B. B. Aklilu, Z. Ma, A. Polkhovskiy, J. J. Chen, D. E. Shippen, The conserved structure of plant telomerase RNA provides the missing link for an evolutionary pathway from ciliates to humans. Proc. Natl. Acad. Sci. USA 116, 24542–24550 (2019).

Telomeres and their relationship to oxidative stress

Telomeres have been heralded as both a sentinel and elicitor of physiological stress, but recent studies indicate that telomere proteins are also regulated by, and engage, the oxidative stress response pathway. We are currently investigating non-telomeric functions of telomerase and Protection of Telomeres 1, an essential highly conserved telomere end-binding protein. We discovered that only one of the two Arabidopsis POT1 paralogs are required for telomere maintenance. The second POT1 protein (POT1b) is required to modulate ROS levels across many different organs during development.

In collaboration with colleagues at NASA, Ohio University and Colorado State University, we are also investigating the impact of the space environment on plant telomeres and telomerase. We found that telomerase activity is strongly induced by abiotic stressors, most notably spaceflight conducted on the International Space Station, without triggering telomere elongation. In addition, we discovered that telomerase activity levels are inversely correlated with genome oxidation, suggesting that telomerase may have a redox-protective function in Arabidopsis. In the next decade NASA aspires to establish a colony on the moon, which will require lunar farming for sustained agriculture. The capacity to grow plants with the in-situ substrate of lunar regolith would be highly advantageous. We found that Arabidopsis can grow for multiple generations in lunar regolith simulant if the substrate is pre-washed with an antioxidant cocktail. However, plant fitness declines progressively, genome oxidation is increased, telomerase enzyme activity declines and telomeres shorten each generation. Without a remedy, telomere shortening will ultimately lead to genome instability and loss of plant viability. Current studies focus on elucidating why telomeres shorten in lunar regolith simulant and on defining ways that this problem can be circumvented.

B. Barbero Barcenilla and D. E. Shippen, Back to the future: The intimate and evolving connection between telomere-related factors and genotoxic stress. J. Biol. Chem. 294, 14803–14813 (2019).

B.B. Barcenilla, A.D. Meyer*, C. Castillo-González*, P. Young, J. H. Min, C. Phadke, J. Song, E. Land, E. Canaday, I. Y. Perera, S. M. Bailey, R. O. Aquilano, S. Wyatt and D. E. Shippen, Arabidopsis telomerase takes off: uncoupling telomerase activity from telomere length maintenance in space. Nature Comm. 14, 7854 (2023) *Equal contribution.

B.B. Barcenilla, I. Kundel*, E. Hall*, N. Hilty, P. Ulianich, J. Cook, J. Turley, M. Yerram, J. H. Min, C. Castillo-González and D. E. Shippen, Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant. Submitted. *Equal contribution.

Publications

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