ABSTRACT
The aphid transmissibility of seven Plum pox virus (PPV) isolates and the amino acid sequences of their coat proteins were analysed. Two aphid transmissible isolates PPV-A and PPV-P contained the DAG amino triplet, while DAL or NAG replaced this triplet in the coat proteins of non-aphid transmissible isolates. In addition, a sequence of 15 or 17 amino acids was deleted in the coat proteins of PPV-P48, PPV-P45 and PPV-II/7. Helper components with Mr. of 52 kDa were successfully purified from N. benthamiana plants inoculated with aphid transmissible and non-aphid transmissible isolates. The helper components of two coat-proteins-defective isolates mediated aphid transmission of non- coat-protein defective isolates, indicating that the helper components were biologically active.