Isolation and characterization of ultraviolet light hypersensitive mutants of Arabidopsis thaliana.

Abstract

UV resistance mechanisms have been extensively studied in bacteria, fungi, and mammalian cells, but little is known about these mechanisms in plant cells. We have developed a genetic screen to help identify mutant Arabidopsis plants that are hypersensitive to the damaging effects of UV light. Six mutants, designated uvh1 through uvh6, were isolated by this screening procedure. The uvh mutants, which behave as single recessive traits, form six complementation groups. Although isolated as hypersensitive to UV-C light wavelengths, all of the uvh mutants are also hypersensitive to small fluences of UV-B wavelengths that do not affect wild type plants. UV-induced damage in the uvh mutants could be reduced or eliminated by subsequent exposure to light containing photoreactivating wavelengths, suggesting that the damage is pyrimidine dimers. One of the mutants, uvh1, was shown not to be defective in protection of chloroplast and nuclear DNA from UV-induced damage, suggesting that the defect in uvh1 may be in repair or toleration of UV-induced damage. Further analysis revealed that levels of UV-induced DNA damage removal were the same in chloroplast and nuclear DNA of uvh1 and wild type plants. uvh1 was more sensitive than wild type to the rosette-inhibiting effects of ionizing radiation, suggesting a possible defect in recombinational repair in uvh1, however, the frequency of meiotic recombination was normal in uvh1. In a collaborative study with Dr. E. Signer, Department of Biology, Massachusetts Institute of Technology, uvh1 was shown to be defective in T-DNA integration, suggesting a defect in non-homologous genetic recombination. As a first step in isolating the gene by map-based cloning, genetic and RFLP mapping techniques were used to localize the uvh1 mutation to a region of chromosome 3.