Immunodetection of the 33 K/92 K polymerase proteins in cymbidium ringspot virus-infected and in transgenic plant tissue extracts.

An antiserum was raised against the 33 K protein encoded by the 5' proximal gene of cymbidium ringspot tombusvirus RNA. This antiserum reacts specifically with the 33 K and 92 K proteins, which constitute the viral replicase, in CyRSV-infected Nicotiana benthamiana plants and in transgenic plants transformed with the full-length replicase gene. In inoculated leaves of infected plants, synthesis of the 33 K/92 K proteins stops ten days after inoculation, whereas in newly produced systemically infected leaves there was continuous production of these proteins. In transgenic plants, both proteins were detected showing that readthrough of the termination codon of the 33 K protein does not depend on the presence of the replicating virus. The subcellular localization of the 33 K/92 K proteins is similar in infected and transgenic plants. No correlation was found between the level of expression of integrated virus gene and level of resistance to the challenging virus.