Characterization of telomerase RNP in Arabidopsis thaliana

Abstract

Telomeres are critical for the integrity of eukaryotic genomes. They function to protect chromosome ends from DNA damage surveillance and inappropriate repair. Telomeres are maintained by the specialized ribonucleoprotein complex telomerase. Without telomerase, telomere shortening would ultimately lead to compromised genome stability and cellular senescence. Therefore, telomerase function is necessary for extension of the proliferative capacity of the cell. In this dissertation, we describe the characterization of core components of telomerase ribonucleoprotein complex in the flowering plant, Arabidopsis thaliana. We find that dyskerin, one of the core telomerase components in humans is also conserved in Arabidopsis telomerase. Arabidopsis dyskerin associates with the telomerase RNP in an RNA-dependent manner and is required for telomere length maintenance in this organism. We also describe the characterization of another core telomerase component, the telomerase RNA subunits (TERs). Unexpectedly, we uncovered two distinct TER subunits that share a region of high identity. The two TERs named TER1G7 and TER5G2, based on their chromosomal positions, display differences in their expression levels and their association with telomere-related proteins. Both TERs can serve as templates for telomerase in vitro. Through genetic analyses, we show a templating function for TER1G7 in vivo and a novel role for TER5G2 as a negative regulator of telomerase. Finally, the presence of TER genes in other plant species was investigated and evidence for duplication of TER genes in plants closely related to Arabidopsis was obtained. We also show evidence for a template mutation in Asparagus TER that could lead to variant repeats in this organism. In summary, the studies presented in this dissertation reveal that Arabidopsis telomerase shares both similarities and differences with other telomerase RNPs, making it an exciting model system for study of telomere biology.