Role of viral coat protein and plant binding component(s) in the transmission of plant viruses by leaf-feeding beetles

The role of coat protein and plant binding component(s) in the transmission of plant viruses by leaf-feeding beetles was studied. Virus particles were reassembled in vitro from the coat protein of the cowpea strain of southern bean mosaic virus (CP-SBMV), a beetle-transmissible virus, with the RNA of the cowpea strain of tobacco mosaic virus (CP-TMV), a non-beetle-transmissible virus. The reassembled virus particles were indistinguishable in shape and size from those of the native CP-SBMV when examined with the electron microscope. Reassembled particles were infectious when inoculated on a systemic and local lesion host for CP-TMV, but not infectious when inoculated on a systemic and local lesion host for CP-SBMV. Mexican bean beetles, Epilachna varivestis, and bean leaf beetles, Cerotoma trifurcata, transmitted CP-TMV after acquisition of reassembled virus. These results indicate that the transmission of plant viruses by leaf-feeding beetles is determined by coat protein characteristics.;Translocation studies of virus particles from the stems of Black Valentine bean showed that virus particles of two non-beetle-transmissible viruses (CP-TMV and tobacco ringspot nepovirus) did not translocate but virus particles of two beetle-transmissible viruses (SBMV and bean pod mottle comovirus) translocated into the trifoliolate leaves and growing point. Evidence is presented that inability of non-beetle-transmissible viruses to translocate is not due to a lower concentration of virus or a slower translocation time.;Two non-beetle-transmissible viruses, TRSV and CP-TMV, were used in studies to identify plant components that bind to these viruses and not to the beetle-transmissible SBMV and BPMV. An extra protein band was detected by SDS-PAGE when purified TRSV or CP-TMV was mixed with a crude leaf extract or cell wall extract, pelleted by ultracentrifugation, and then analyzed by SDS-PAGE electrophoresis. This protein band was not present in purified virus preparations or in preparations of SBMV and BPMV similarly exposed to crude plant extracts. The 17 kDa putative binding protein for CP-TMV and TRSV in Black Valentine bean extracts was also detected by virus overlay of protein blots.