Partial Epitope Mapping of Alfalfa mosaic Virus and the Effect of Coat Protein Gene Mutation on Aphid Transmission

Abstract

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