| Aging is associated with the functional decline of organs, and results in agedependent differences in stress-sensitivity. Younger animals are more sensitive to mutagenic insults than adults, whereas in plants, the transition to reproductive growth is the most stress-sensitive.;Here, we show a role of reduced H3K9 trimethylation and corresponding genomic instability in the aging rat thymus and in senescence of human fibroblasts. A similar reduction of SUV39H1 expression was observed in response to ionizing radiation (IR), which correlated with the induction of senescence.;In plants exposed to IR during the transition to reproductive growth, histone methyltransferases were up-regulated, which correlated with reduced transcription of transposable elements.;This difference in response may be reflected in the differences in life cycles. Whereas plants rely on the survival and genome integrity of meristematic cells for their reproductive success, in mammals, limiting the cell division in cells that have incurred damage may be crucial. |
