The Response to Telomeric Instability in Arabidopsis

The ends of linear eukaryotic chromosome are "hidden" in nucleoprotein structures called telomeres and loss of the telomere structure causes inappropriate "repair", leading to severe karyotypic and genomic instabilility. Little is known of the signalling of dysfunctional plant telomeres and we have thus analysed the roles of the two DNA damage signalling kinases ATM and ATR. We found that plants activate a strong ATM- and ATR-dependent DNA damage response at uncapped telomeres. However, although unprotected telomeres are recognised as damaged DNA in Arabidopsis through activation of ATM and ATR, processing of these chromosome ends is clearly not dependent upon activation of the ATM and ATR signalling. Interestingly, ATM and ATR kinases both contribute to genomic stability by activating a DNA damage signal, the transduction of which induces death of genetically damaged stem cells. Our  data thus provide a clear biological illustration of the action of programmed cell death (PCD) induced by ATM/ATR-dependent surveillance of genome integrity in maintaining genome stability through elimination of genetically unstable cells.