EVIDENCE THAT ORF-1 AND ORF-2 ARE THE ONLY VIRUS-ENCODED REPLICASE GENES OF CYMBIDIUM RINGSPOT TOMBUSVIRUS

The 33-kDa and its 92-kDa readthrough protein genes (open reading fram es (ORF-s) 1 and 2) of cymbidium ringspot tombusvirus (CyRSV) were int roduced into Nicotiana benthamiana plants. Protoplasts derived from tr ansgenic plants expressing the first two ORFs were inoculated with in vitro transcripts of defective interfering (pi) RNA, The efficient rep lication of input DI RNA, which is incapable of autonomous replication , confirmed the biological activity of the expressed viral replicase. In addition, in vitro transcripts of a genomic RNA deletion mutant clo ne encoding only ORFs 1 and 2 were able to replicate on their own and could support the replication of CyRSV DI RNAs in N. benthamiana proto plasts. (C) 1994 Academic Press, Inc.