REPLICATION OF WILD-TYPE AND MUTANT CLONES OF SATELLITE TOBACCO MOSAIC-VIRUS IN NICOTIANA-BENTHAMIANA PROTOPLASTS

RNA transcribed from cloned satellite tobacco mosaic virus (STMV) cDNA replicated in Nicotiana benthamiana protoplasts when co-inoculated wi th tobacco mild green mosaic virus (TMGMV) genomic RNA, but degraded w hen inoculated alone. STMV genomic RNA extracted from wild-type virion s replicated in protoplasts when co-inoculated with TMGMV, tobacco mos aic virus (TMV) or tomato mosaic virus (ToMV), Transcripts from clones of two STMV coat protein (CP) mutants accumulated to the same level a s wild-type transcripts in protoplasts when co-inoculated with TMGMV, whereas a third mutant accumulated to detectable levels in some, but n ot all, experiments. These results confirm that STMV RNA requires help er virus for replication, and that the helper specificity exhibited by cloned STMV reflects a specific requirement for the TMGMV replicase, It also demonstrates that the low accumulation of STMV CP mutants obse rved previously in whole plants cannot be attributed to inefficient RN A replication.