REPLICASE-MEDIATED RESISTANCE TO POTATO-VIRUS-Y IN TRANSGENIC TOBACCOPLANTS

Nicotiana tabacum 'Turkish Samsun NN' plants were transformed with nuc lear inclusion b (NIb) gene sequences of potato virus Y, O strain (PVY O). The full-length construct included an additional in-frame initiati on codon contiguous to the putative N-terminal amino acid codon and a stop codon replacing the C-terminal amino acid codon. Of 13 independen tly transformed lines, four yielded 37 (out of 100) plants in the R(1) generation that were resistant to PVYO infection. Progeny of 13 out o f 15 of R(1) plants tested expressed resistance in the R(2) generation . Conversely, 30 independently transformed tobacco lines expressing es sentially the same sequence but deleted for the Gly-Asp-Asp (GDD) moti f were not resistant. Two other constructs encoding either the 5'-dele ted or 3'-truncated NIb gene, but harboring the GDD motif, conferred r esistance to PVYO in some tobacco plants. Despite the high level of nu cleotide and amino acid identity shared by strains PVYO and PVYN for t he NIb gene, PVYN replication was found in all PVYO-resistant plants. However, plants of one R(2) line showed reduced PVYN replication.