THE SATELLITE RNA OF BARLEY YELLOW DWARF VIRUS-RPV IS SUPPORTED BY BEET WESTERN YELLOWS VIRUS IN DICOTYLEDONOUS PROTOPLASTS AND PLANTS

The subgroup Il luteovirus barley yellow dwarf virus-RPV (BYDV-RPV) ac ts as a helper virus for a satellite RNA (satRPV RNA). The subgroup II luteovirus beet western yellows virus (BWYV) and the ST9-associated R NA (ST9a RNA], a BWYV-associated RNA that encodes a polymerase similar to those of subgroup I luteoviruses, were assayed for their ability t o support replication of satRPV RNA. SatRPV RNA was replicated in toba cco protoplasts in the presence of BWYV RNA or a mixture of BWYV plus the ST9a RNA, but not in the presence of ST9a RNA alone. ST9a RNA stim ulated BWYV RNA accumulation which,in turn,increased the accumulation of satRPV RNA. SatRPV RNA was encapsidated in BWYV capsids primarily a s circular monomers, which differs from the linear monomers found in B YDV (RPV + PAV] particles. SatRPV RNA was transmitted to Capsella burs a-pastoris plants by aphids only in the presence of BWYV and ST9a RNA. SatRPV RNA reduced accumulation of both BWYV helper and ST9a nonhelpe r RNAs in plants but did not affect symptoms. The replication of satRP V RNA only in the presence of subgroup II luteoviral RNAs but not in t he presence ct RNAs with subgroup I-like polymerase genes, in both mon ocotyledonous and dicotyledonous hosts, suggests that the specificity determinants of satRPV RNA replication are contained within the polyme rase genes of supporting viruses rather than in structural genes or ho st plants. (C) 1997 Academic Press.