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Molecular and Cellular Biology, March 2007, p. 1706-1715, Vol. 27, No. 5
0270-7306/07/$08.00+0     doi:10.1128/MCB.02059-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Telomere Rapid Deletion Regulates Telomere Length in Arabidopsis thaliana

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

Received 3 November 2006/ Returned for modification 2 December 2006/ Accepted 11 December 2006

Telomere length is maintained in species-specific equilibrium primarily through a competition between telomerase-mediated elongation and the loss of terminal DNA through the end-replication problem. Recombinational activities are also capable of both lengthening and shortening telomeres. Here we demonstrate that elongated telomeres in Arabidopsis Ku70 mutants reach a new length set point after three generations. Restoration of wild-type Ku70 in these mutants leads to discrete telomere-shortening events consistent with telomere rapid deletion (TRD). These findings imply that the longer telomere length set point is achieved through competition between overactive telomerase and TRD. Surprisingly, in the absence of telomerase, a subset of elongated telomeres was further lengthened, suggesting that in this background a mechanism of telomerase-independent lengthening of telomeres operates. Unexpectedly, we also found that plants possessing wild-type-length telomeres exhibit TRD when telomerase is inactivated. TRD is stochastic, and all chromosome ends appear to be equally susceptible. The frequency of TRD decreases as telomeres shorten; telomeres less than 2 kb in length are rarely subject to TRD. We conclude that TRD functions as a potent force to regulate telomere length in Arabidopsis.

Published ahead of print on 22 December 2006.

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