Reactivation of somatic instability in an inactive Mutator stock by treatment of seed with gamma rays

Chromosome breakage, DNA damaging agents, and stress have been previously implicated as agents that may stimulate the activity of heretofore cryptic transposable elements. To test whether DNA damage--and the DNA repair following such treatments--could influence the activity of the Mutator system the following experiment was carried out. Colorless seed carrying a cryptic mutable bz2 allele recovered from a Mutator parent was selected; the DNA of the bz2-mu1 parent plant was shown to contain mainly modified copies of Mu elements as evidenced by poor HinfI digestion of the Mu element DNA. Seed were treated with gamma radiation from a 137Cs source, planted and crossed by bz2 tester. The radiation did not reduce seed germination. Control experiments of this lineage involving >30,000K have yielded no somatically unstable kernels when the OFF line was used as female parent. Although smut considerably reduced the yield in the gamma plot, 3 of 1,104K were spotted and one 5K purple ear sector was found. These results suggest that DNA damage can reactivate an OFF line. Molecular tests are underway to examine the state of the Mu elements in general and the Mu element presumed to be at bz2-mu1 in the reactivated lines. The experiment will be repeated with a larger population this summer and with higher, calibrated dosages of gamma irradiation. Facilities for these experiments were provided by Dr. M. Christianson.

Virginia Walbot

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