Extracellular Serratia marcescens nuclease is an extremely active enzyme which non specifically degrades RNA and DNA. Its antiviral activity was previously shown both in animals and in plants when applied exogenously. Transgenic tobacco plants (Nicotiana tabacum L. cv. SR1) expressing S. marcescens chi meric, mutant, and intracellular mutant nuclease gene variants were regenerated and challenged with tobacco mosaic virus. The transgenic plants exhibited a higher level of resistance to the virus infection than the control non transgenic plants. The resistance was evidenced by the delay of the appearance of mosaic symptoms and the retarded accumulation of viral antigen. Thus, these results reveal that modulations of both extracellular nuclease activity and intracellular RNA/DNA binding can protect plants against viral diseases.

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