A new hyperrecombinogenic mutant of Nicotiana tabacum

We have isolated a hyperrecombinogenic Nicotiana tabacum mutant. The mutati on, Hyrec, is dominant and segregates in a Mendelian fashion. In the mutant , the level of mitotic recombination between homologous chromosomes is incr eased by more than three orders of magnitude. Recombination between extrach romosomal substrates is increased six- to ninefold, and intrachromosomal re combination is not affected. Hyrec plants were found to perform non-homolog ous end joining as efficiently as the wild type, ruling out the possibility that the increase in homologous recombination is due to a defect in end jo ining. In addition, Hyrec plants show significant resistance to gamma-irrad iation, whereas UV resistance is not different from the wild type. This sug gests that homologous recombination can be strongly up-regulated in plants. Moreover, Hyrec constitutes a novel type of mutation: no similar mutant wa s reported in plants and hyperrecombinogenic mutants from other organisms u sually show sensitivity to DNA damaging agents. We discuss the insight that this mutant provides into understanding the mechanisms of recombination pl us the potential application for gene targeting in plants.