Genotoxin resistance properties of transgenic tobacco plants expressing bacteriophage T4 DenV and Saccharomyces cerevisiae Apn1 proteins.

We have examined whether the resistance to genotoxic agents can be altered in transgenic plants by introducing heterologous DNA repair enzymes. Transformation of tobacco tissue produced two lines of plants, one expressing bacteriophage T4 UV endonuclease (DenV) and the other expressing Saccharomyces cerevisiae apurinic-apyrimidinic endonuclease and 3'-diesterase (Apn1). Some of the transformants were subsequently crossed, with the expectation that Apn1 activity might complement DenV activity in hybrid plants. Apn1 transgenotes behaved similarly to control plants upon exposure to UV-C light, oxidizing agents, or alkylating agents, as measured by chlorophyll bleaching. This is in contrast to plants expressing DenV activity, which have been previously shown to exhibit varying degrees of sensitivity to UV-C light and the alkylating agent dimethyl sulfate. APN1/denV hybrid plants were more sensitive to UV-C light than were parental lines, but reproducibly displayed enhanced resistance to dimethyl sulfate. These data indicate that repair processes are an important component of natural protective systems in tobacco, because exogenous repair genes compromised the natural resistance of denV-transformed plants. In the hybrid plants, the two proteins appeared to act in concert, potentiating the effects of UV damage but enhancing the resistance to alkylation damage.