Increased telomere length and hypersensitivity to DNA damaging agents in an Arabidopsis KU70 mutant

We have identified a putative homologue of the KU70 gene (AtKU70) from Arabidopsis thaliana. In order to study its function in plants we have isolated an A.thaliana line that contains a T-DNA inserted into AtKU70. Plants homozygous for this insertion appear normal and are fertile. In other organisms the KU70 gene has been shown to play a role in the repair of DNA damage induced by ionising radiation (IR) and by radiomimetic chemicals such as methylmethane sulfonate (MMS). We show that AtKU70(–/–) plants are hypersensitive to IR and MMS, and thus the AtKU70 gene plays a similar role in DNA repair in plants as in other organisms. The KU70 gene also plays a role in maintaining telomere length. Yeast and mammalian cells deficient for Ku70 have shortened telomeres. When we studied the telomeres in the AtKU70(–/–) plants we found unexpectedly that they were significantly longer (>30 kb) than was found in wild-type plants (2–4 kb). We propose several hypotheses to explain this telomere lengthening in the AtKU70(–/–) plants.