Tomato Yellow Leaf Curl Virus (TYLCV) is a monopartite-genome geminivirus transmitted by whiteflies. The capsid protein of the virus is the only known protein that serves as a component of the viral coat. The gene that encodes the capsid protein driven by the cauliflower mosaic virus 35S promoter was cloned into an Agrobacterium Ti-derived plasmid. Tomato plants, sensitive to the disease, were transformed with the TYLCV capsid protein gene. The gene was transcribed in all transgenic plants. These transgenic Fl plants were inoculated with TYLCV using whiteflies fed on TYLCV-infected plants. The transgenic plants' response to inoculation was of two kinds: (i) behavior like non-transformed tomato; or (ii) expression of delayed disease symptoms and recovery from the disease with increasingly more resistance upon repeated inoculation. Transformed plants that were as sensitive to inoculation as were the non-transformed plants, expressed the capsid protein gene at the RNA level only. All the transformed plants that recovered from the disease expressed the TYLCV capsid protein as detected by western blot analysis. Using sequence analysis of the amino acid sequence of the capsid protein, a nuclear localization signal (NLS) have been identified at the N-terminal part of this protein. The functional activity of this NLS and its importance in the resistance of the transgenic plants is now being studied.