Principles and background for the construction of transgenic plants displaying multiple virus resistance.

We investigated the possibility of reconstructing the 2'-5' oligoadenylate (2-5A) pathway into the plant kingdom to achieve multiple virus resistance. Differently phosphorylated 2-5A trimers and tetramers inhibited TMV RNA translation in cell-free systems. In wheat germ extracts the most potent inhibitors were nonphosphorylated forms of 2-5A. Triphosphorylated forms of 2-5A were deposphorylated and hydrolysed in plant extracts. Since we could not detect homologous DNA to mammalian 2-5A synthetase cDNA in tobacco or potato, we cloned rat 2-5A synthetase cDNA and transformed it by the Agrobacterium-mediated mechanism into tobacco and potato. Transformed tobacco plants were resistant to PVS infection and propagation of PVX was reduced. In transgenic potatoes tolerance to PVX and, in one transgenic clone, also to PVY was observed.