Immunodetection and subcellular localization of the proteins encoded by ORF 3 of grapevine viruses A and B

Polyclonal antisera were raised to Escherichia coli-expressed ORF3 products (putative movement proteins) of Grapevine virus A (GVA) and Grapevine virus B (GVB) (genus Vitivirus), and used for their immunodetection in infected plants. Western blot analysis of subfractionated cellular compartments showed that the distribution of both proteins was comparable to that of plant virus movement proteins, as they were transiently present in a crude membrane fraction and accumulated in a cell wall-enriched fraction. The GVA ORF3-encoded protein, but not the comparable GVB protein, was also present in large amount in a cytoplasmic soluble fraction. Intracellular immunogold labelling localized these proteins in the cell wall and plasmodesmata of infected cells and, especially for GVA, in association with cytoplasmic virus aggregates.