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, designed to reduce putative biological risks associated with heteroen capsidation, were integrated into Nicotiana benthamiana plants. The first one contained a deletion of the nucleotides encoding for the DAG amino acid triplet involved in virus aphid-transmission. In the second one, the first 420 nucleotides of the PPV CP gene were removed. We present here the analysis and the selection throughout the generations of PPV-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 describe two lines that were highly resistant to PPV. This immunity was correlated with a high number of transgene copies (at least three) and with low or undetectable transgene RNA levels. No heterologous protection was observed against other potyviruses. These characteristics indicate that the described resistance against PPV was RNA-mediated and can be classified as a 'sense suppression' or homology-dependent resistance. Moreover, the production of a highly resistant line containing the PPV CP gene with one third of its 5 end deleted indicated that this region is not necessary to trigger the plant resistance mechanism(s)