Telomere-associated proteins in Arabidopsis thaliana
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Telomeres comprise the physical ends of chromosomes. Essential functions of telomeres include protecting the terminus from being recognized as a DNA doublestrand break and facilitating the complete replication of the physical end of the DNA. Telomere functions are mediated by a large array of telomere-associated proteins. Mutations in telomere-related genes cause immediate telomere dysfunction, activation of DNA damage response, and accumulation of end-to-end chromosome fusions. In addition, changes in telomere complex composition may affect the ability of the telomerase enzyme to maintain telomeres in vivo. Here, we describe the characterization of telomere-associated proteins in the flowering plant, Arabidopsis thaliana. Using a bioinformatics approach, we identified twelve proteins with sequence similarity to vertebrate duplex telomere DNA binding proteins TRF1 and TRF2. We showed that, like their vertebrate counterparts, some of the Arabidopsis TRFL (TRF-LIKE) proteins can homodimerize and bind telomeric DNA in vitro, indicating that Arabidopsis encodes a large family of double-strand telomeric DNA binding proteins. We have also characterized three Arabidopsis POT1 proteins whose homologs in yeast and vertebrates associate with the single-stranded portion of telomeric DNA. Unexpectedly, we found that unlike POT1 protein in other organisms, Arabidopsis AtPOT1a protein associates with telomeres only in the S phase of the cell cycle and is a physical component of the active telomerase RNP complex, providing positive telomere length regulation. Our data implicated AtPOT1b, another Arabidopsis POT1 protein, in chromosome end protection. Finally, we showed that Arabidopsis thaliana has evolved a third POT1 protein, AtPOT1c, which contributes to both telomere length regulation and telomerase activity, and maintenance of the structure of the chromosome terminus. Thus, Arabidopsis has evolved a set of POT1 proteins that make distinct and novel contributions to telomere biology. Finally, we describe the identification and characterization of a novel Arabidopsis protein CIT1 (Critical for Integrity of Telomeres 1), and show that CIT1 deficiency leads to an immediate and profound telomere dysfunction and chromosome end deprotection. Altogether, these data provide new insight into plant telomereassociated factors and significantly improve our understanding of the overall architecture and evolution of telomeric complex in Arabidopsis.
Surovtseva, Yulia V. (2008). Telomere-associated proteins in Arabidopsis thaliana. Doctoral dissertation, Texas A&M University. Available electronically from