title: POT1a and components of CST engage telomerase and regulate its activity in Arabidopsis.
abstract: Protection of Telomeres 1 (POT1) is a conserved nucleic acid binding protein implicated in both telomere replication and chromosome end protection. We previously showed that Arabidopsis thaliana POT1a associates with the TER1 telomerase RNP, and is required for telomere length maintenance in vivo. Here we further dissect the function of POT1a and explore its interplay with the CST (CTC1/STN1/TEN1) telomere complex. Analysis of pot1a null mutants revealed that POT1a is not required for telomerase recruitment to telomeres, but is required for telomerase to maintain telomere tracts. We show that POT1a stimulates the synthesis of long telomere repeat arrays by telomerase, likely by enhancing repeat addition processivity. We demonstrate that POT1a binds STN1 and CTC1 in vitro, and further STN1 and CTC1, like POT1a, associate with enzymatically active telomerase in vivo. Unexpectedly, the in vitro interaction of STN1 with TEN1 and POT1a was mutually exclusive, indicating that POT1a and TEN1 may compete for the same binding site on STN1 in vivo. Finally, unlike CTC1 and STN1, TEN1 was not associated with active telomerase in vivo, consistent with our previous data showing that TEN1 negatively regulates telomerase enzyme activity. Altogether, our data support a two-state model in which POT1a promotes an extendable telomere state via contacts with the telomerase RNP as well as STN1 and CTC1, while TEN1 opposes these functions.
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, United States of America.
authors.forename: Kyle B
authors.initials: KB
authors.lastname: Renfrew
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, United States of America.
authors.forename: Xiangyu
authors.initials: X
authors.lastname: Song
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, United States of America.
authors.forename: Jung Ro
authors.initials: JR
authors.lastname: Lee
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, United States of America.
authors.forename: Amit
authors.initials: A
authors.lastname: Arora
authors.affiliation: Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas, United States of America.
authors.forename: Dorothy E
authors.initials: DE
authors.lastname: Shippen
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D032461:Chromosomes, Plant; D046912:Multiprotein Complexes / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism; D059505:Telomere Homeostasis; D034501:Telomere-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C544991:CTC1 protein, Arabidopsis; D002868:Chromosomal Proteins, Non-Histone; D046912:Multiprotein Complexes; D009687:Nuclear Proteins; C528256:POT1A protein, Arabidopsis; C534225:STN1 protein, Arabidopsis; C585248:TEN1 protein, Arabidopsis; D034501:Telomere-Binding Proteins; C528255:TERT protein, Arabidopsis; D019098:Telomerase