Partial epitope mapping of Alfalfa mosaic virus and the effect of coat protein gene mutation on aphid transmission

Epitope mapping with seventy-one overlapping octapeptides representing the whole sequence of Alfalfa mosaic virus (AMV) coat protein (CP) (strain S) was done using monoclonal antibodies. In total, five monoclonal antibodies identified 5 epitopes, at different sites along the amino acid sequence of AMV coat protein. Four MAbs each reacted with a single epitope, while one MAb bonded with peptides on two widely separated parts of the coat protein. A full length DNA copy of RNA 3 of AMV strain S in a pBS plasmid was used as a template for mutation and transcription. Both before and after modification, the RNA 3 of this strain was inoculated to Nicotiana tabacum transgenic P12 plants and AMV particles were purified. Strain S of AMV produced systemic symptoms in N. tabacum transgenic P12 plants. It was suggested that MAb-2 was effective in blocking insect transmission of AMV. Epitope-2 which play an important role in transmission is recognized by MAb-2. To further investigate the interaction between epitope-2 and transmission of AMV mutation of the amino acids of epitope-2 was made in the appropriate coding regions of the coat protein of AMV strain S. These changes were (i) a phenylalanine to tyrosine and (ii) asparagine to glutamine. The mutation of asparagine to glutamine had no effect on the transmission of AMV by M. persicae, but the mutation of phenylalanine to tyrosine gave a significant reduction (P = 0.02) in aphid transmissibility. This indicated that the phenylalanine residue at position 67 of the AMV coat protein was involved in transmission.