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Molecular and Cellular Biology, September 2005, p. 7725-7733, Vol. 25, No. 17
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.17.7725-7733.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The Arabidopsis Pot1 and Pot2 Proteins Function in Telomere Length Homeostasis and Chromosome End Protection

Eugene V. Shakirov, Yulia V. Surovtseva, Nathan Osbun, and Dorothy E. Shippen^*

Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, Texas 77843-2128

Received 29 April 2005/ Accepted 20 May 2005

Pot1 (protection of telomeres 1) is a single-stranded telomere binding protein that is essential for chromosome end protection and telomere length homeostasis. Arabidopsis encodes two Pot1-like proteins, dubbed AtPot1 and AtPot2. Here we show that telomeres in transgenic plants expressing a truncated AtPot1 allele lacking the N-terminal oligonucleotide/oligosaccharide binding fold (P1N) are 1 to 1.5 kb shorter than in the wild type, suggesting that AtPot1 contributes to the positive regulation of telomere length control. In contrast, telomere length is unperturbed in plants expressing the analogous region of AtPot2. A strikingly different phenotype is observed in plants overexpressing the AtPot2 N terminus (P2C) but not the corresponding region in AtPot1. Although bulk telomeres in P2C mutants are 1 to 2 kb shorter than in the wild type, these plants resemble late-generation telomerase-deficient mutants with severe growth defects, sterility, and massive genome instability, including bridged chromosomes and aneuploidy. The genome instability associated with P2C mutants implies that AtPot2 contributes to chromosome end protection. Thus, Arabidopsis has evolved two Pot genes that function differently in telomere biology. These findings provide unanticipated information about the evolution of single-stranded telomere binding proteins.

E.V.S. and Y.V.S. contributed equally to this work.

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