Key message Prolonged hypomethylation of DNA leads to telomere truncation correlated with increased telomere recombination, transposon mobilization and stem cell death. Abstract Epigenetic pathways, including DNA methylation, are crucial for telomere maintenance. Deficient in DNA Methyla- tion 1 (DDM1) encodes a nucleosome remodeling protein, required to maintain DNA methylation in Arabidopsis thaliana. Plants lacking DDM1 can be self-propagated, but in the sixth generation (G6) hypomethylation leads to rampant transposon activation and infertility. Here we examine the role of DDM1 in telomere length homeostasis through a longitudinal study of successive generations of ddm1-2 mutants. We report that bulk telomere length remains within the wild-type range for the first five generations (G1–G5), and then precipitously drops in G6. While telomerase activity becomes more variable in later generation ddm1-2 mutants, there is no correlation between enzyme activity and telomere length. Plants lacking DDM1 also exhibit no dysregulation of several known telomere-associated transcripts, including TERRA. Instead, telomere shortening coincides with increased G-overhangs and extra-chromosomal circles, consistent with deletional recombination. Telomere shortening also correlates with transcriptional activation of retrotransposons, and a hypersensitive DNA damage response in root apical meristems. Since abiotic stresses, including DNA damage, stimulate homologous recombination, we hypothesize that telomere deletion in
Plant Cell Reports – Springer Journals
Published: Feb 1, 2018
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