Genetic characterization ofuvh6, an Arabidopsis mutant hypersensitive to UV light and high temperature.

Abstract

Five Arabidopsis mutants were previously identified in a genetic screen to isolate UV hypersensitive (uvh) mutants. In this work, these mutants were further characterized. Each uvh phenotype was due to a single, recessive Mendelian trait, and complementation analysis suggested that each mutant defined a separate locus. To examine the tissue specificity of UV hypersensitivity, the UV sensitivity of leaf and root tissues of the five uvh mutants and wild-type plants were compared. Two of the mutants, uvh1 and uvh3, had root UV hypersensitivity comparable to that of uvr1, another Arabidopsis mutant identified in a genetic screen that examined sensitivity of root tissue to UV light. Sensitivity to an additional treatment, ionizing radiation, which causes a different type of DNA damage was also compared between the five uvh mutants and wild-type plants by irradiating seeds. Three of the five mutants, uvh1, uvh3 and uvh5 were hypersensitive to both ionizing radiation and UV light. Although hypersensitivity to both DNA damaging agents has been observed in other organisms, such as the rad6 epistasis group of yeast, these are the only plant mutants described with this pattern of sensitivity. uvh6 and uvh3 also had unique phenotypes that were observed under normal laboratory growth conditions. By comparing the above properties, the five uvh mutants were all phenotypically unique. The uvh6 mutant had a tissue-specific UV hypersensitivity and several additional properties including reduced chlorophyll levels, altered chloroplast anatomy, temperature sensitivity and alterations in the regulation of heat shock proteins. For these reasons, the uvh6 mutant was selected for detailed characterization. Analysis of revertants of the uvh6 phenotype indicated that all these properties resulted from a single mutation. The uvh6 mutation mapped near position 27 ± 6 on chromosome one. Several of the properties of the uvh6 mutant at room temperature were observed in wild-type plants grown at elevated temperatures. On the basis of the properties of the uvh6 mutant, a possible model of UVH6 function is proposed. In this model, the UVH6 protein participates in a developmental program that decreases cellular stress resulting from exposure to high temperatures.