AtRAD1, a plant homologue of human and yeast nucleotide excision repair endonucleases, is involved in dark repair of UV damages and recombination

Plants are unique in the obligatory nature of their exposure to sunlight an d consequently to ultraviolet (UV) irradiation. However, our understanding of plant DNA repair processes lags far behind the current knowledge of repa ir mechanisms in microbes, yeast and mammals, especially concerning the uni versally conserved and versatile dark repair pathway called nucleotide exci sion repair (NER). Here we report the isolation and functional characteriza tion of Arabidopsis thaliana AtRAD1, which encodes the plant homologue of S accharomyces cerevisiae RAD1, Schizosaccharomyces pombe RAD16 and human XPF , endonucleolytic enzymes involved in DNA repair and recombination processe s. Our results indicate that AtRAD1 is involved in the excision of UV-induc ed damages, and allow us to assign, for the first time in plants, the dark repair of such DNA lesions to NER. The low efficiency of this repair mechan ism, coupled to the fact that AtRAD1 is ubiquitously expressed including ti ssues that are not accessible to UV light, suggests that plant NER has othe r roles. Possible 'UV-independent' functions of NER are discussed with resp ect to features that are particular to plants.