Song, Xiangyu (2010-05). Telomere Protection and Maintenance in Arabidopsis thaliana. Doctoral Dissertation. Thesis uri icon

abstract

  • Telomeres are the physical ends of linear chromosomes in eukaryotes. Telomeres not only protect chromosome ends from being recognized as double-strand breaks but also maintain the chromosome terminal sequences. These processes involve a number of telomere-related proteins. A major challenge in the field is to elucidate the full constitution of telomere-associated proteins and to understand how different protein complexes are regulated at chromosome termini. Here, I report the identification and characterization of STN1 (Suppressor of cdc thirteen, 1), CTC1 (Conserved Telomere maintenance Component 1) and TEN1 (Telomeric pathways in association with Stn1, 1) in Arabidopsis. CTC1/STN1/TEN1 (CST) forms a trimeric complex that specifically associates with telomeres. Loss of any component of the CST induces catastrophic telomere loss, disrupted telomere end architecture, and massive chromosome end-to-end fusions. Thus, CST plays an essential role in chromosome end protection. I also show that CST function at telomeres is independent of a previously characterized capping complex KU70/KU80, and that ATR is responsible for a checkpoint response in plants lacking CTC1/STN1. Additionally, I present data showing that Arabidopsis POT1a (Protection Of Telomere 1, a) has evolved as a telomerase recruitment factor. Unlike POT1 in other eukaryotes which binds and protects ss telomeric DNA, AtPOT1a interacts with telomerase RNA (TER). Based on an evolutionary analysis, we found that the POT1a lineage is under positive selection in the Brassicaceae family in which Arabidopsis belongs. Mutations of two positive selection sites significantly reduce POT1a?s activity in vivo. These data suggest POT1a is under pressure to evolve from a telomeric DNA binding protein to a TER binding protein. I also discovered that POT1a interacts with the novel telomere capping protein CTC1 in vitro and in vivo. Thus, I hypothesize that POT1a acts as a telomerase recruitment factor linking this enzyme to the chromosome termini via interacting with TER and CTC1. Finally, I dissected the functional domains of POT1a and demonstrated that both the N-terminus and the C-terminus of POT1a are required for its function in vivo. In summary, my work has uncovered several new and essential telomereassociated proteins that provide new insight into mechanisms of chromosome end protection and maintenance.
  • Telomeres are the physical ends of linear chromosomes in eukaryotes. Telomeres
    not only protect chromosome ends from being recognized as double-strand breaks but
    also maintain the chromosome terminal sequences. These processes involve a number
    of telomere-related proteins. A major challenge in the field is to elucidate the full
    constitution of telomere-associated proteins and to understand how different protein
    complexes are regulated at chromosome termini.
    Here, I report the identification and characterization of STN1 (Suppressor of cdc
    thirteen, 1), CTC1 (Conserved Telomere maintenance Component 1) and TEN1
    (Telomeric pathways in association with Stn1, 1) in Arabidopsis. CTC1/STN1/TEN1
    (CST) forms a trimeric complex that specifically associates with telomeres. Loss of any
    component of the CST induces catastrophic telomere loss, disrupted telomere end
    architecture, and massive chromosome end-to-end fusions. Thus, CST plays an
    essential role in chromosome end protection. I also show that CST function at
    telomeres is independent of a previously characterized capping complex KU70/KU80,
    and that ATR is responsible for a checkpoint response in plants lacking CTC1/STN1.
    Additionally, I present data showing that Arabidopsis POT1a (Protection Of
    Telomere 1, a) has evolved as a telomerase recruitment factor. Unlike POT1 in other eukaryotes which binds and protects ss telomeric DNA, AtPOT1a interacts with
    telomerase RNA (TER). Based on an evolutionary analysis, we found that the POT1a
    lineage is under positive selection in the Brassicaceae family in which Arabidopsis
    belongs. Mutations of two positive selection sites significantly reduce POT1a?s activity in
    vivo. These data suggest POT1a is under pressure to evolve from a telomeric DNA
    binding protein to a TER binding protein. I also discovered that POT1a interacts with the
    novel telomere capping protein CTC1 in vitro and in vivo. Thus, I hypothesize that
    POT1a acts as a telomerase recruitment factor linking this enzyme to the chromosome
    termini via interacting with TER and CTC1. Finally, I dissected the functional domains of
    POT1a and demonstrated that both the N-terminus and the C-terminus of POT1a are
    required for its function in vivo.
    In summary, my work has uncovered several new and essential telomereassociated
    proteins that provide new insight into mechanisms of chromosome end
    protection and maintenance.

publication date

  • May 2010