Viroplasms of an Aphid-transmissible Isolate of Cauliflower Mosaic Virus Contain Helper Component Activity

Abstract

SUMMARY Aphid transmission experiments with the transmissible isolate Cabbage B and the non-transmissible isolate Campbell of cauliflower mosaic virus (CaMV), using different combinations of purified viruses, viroplasms and cellular fractions, revealed that helper component (HC) activity for CaMV transmissibility was associated only with the viroplasm preparations of the transmissible isolate. In electrophoretic analyses of purified virions, viroplasms and cellular fractions from plants infected with both CaMV isolates as has already been described, a PI 8 polypeptide in the purified viroplasm preparations from the transmissible CaMV isolate was the only difference between the two isolates. These results suggest that the purified viroplasms of transmissible CaMV isolates contain the HC in a functional form, and that the P18 polypeptide is the active HC for CaMV aphid transmissibility or a part of it.