In situ localization of the non-structural protein P25 encoded by beet necrotic yellow vein virus RNA 3.

The in situ localization of the non-structural protein P25 encoded by beet necrotic yellow vein virus (BNYVV) RNA 3 and of the BNYVV coat protein (CP) was studied by immunoelectron microscopy in infected leaf and root cells of Chenopodium murale and C. quinoa. The CP was detected in the cytoplasm of all cell types except xylem, sieve elements, and companion cells. P25 was detected in the cytoplasm and nuclei of the same cell types. The intensity of CP labelling varied depending upon the stage of infection of the cell, whereas the P25 labelling intensity was similar in newly infected cells and in cels at later stages of infection. These results suggest that P25 may be synthesized at an earlier stage of infection than CP. Its presence in the nuclei of newly infected cells may be related to the reported effect of P25 on leaf symptom development.