HIGH-RESISTANCE TO PLUM POX VIRUS (PPV) IN TRANSGENIC PLANTS CONTAINING MODIFIED AND TRUNCATED FORMS OF PPV COAT PROTEIN GENE

Two modified plum pox virus (PPV) coat protein (CP) gene constructs, d esigned to reduce putative biological risks associated with heteroenca psidation, were integrated into Nicotiana benthamiana plants. The firs t one contained a deletion of the nucleotides encoding for the DAG ami no acid triplet involved in virus aphid-transmission. In the second on e, the first 420 nucleotides of the PPV CP gene were removed. We prese nt here the analysis and the selection throughout the generations of P PV-resistant transgenic lines containing these constructs. In most of the lines, a recovery phenotype was observed and was associated with a down-regulation of the transgene products (RNA or protein). We also d escribe two lines that were highly resistant to PPV. This immunity was correlated with a high number of transgene copies (at least three) an d with low or undetectable transgene RNA levels. No heterologous prote ction was observed against other potyviruses. These characteristics in dicate that the described resistance against PPV was RNA-mediated and can be classified as a `sense suppression' or homology-dependent resis tance. Moreover, the production of a highly resistant line containing the PPV CP gene with one third of its 5' end deleted indicated that th is region is not necessary to trigger the plant resistance mechanism(s ).