A single amino acid substitution in the ORF1 of cymbidium ringspot virus determines the accumulation of two satellite RNAs

Tombusviruses may support the replication of satellite (sat) RNAs. In particular, two satRNAs, sat L and Cymsat RNAs, are replicated by carnation Italian ringspot (CIRV) and tomato bushy stunt (TBSV) virus, but not by cymbidium ringspot virus (CymRSV) in vitro transcripts unless they contain a poly(A) tail at the 3′ end. Conversely, the replication of both satRNAs was supported by virus particles or viral RNA of the original CymRSV inoculum even in the absence of the poly(A) tail. Sequence and mutational analyses revealed that the full-length infectious CymRSV clone contains one relevant sequence variation in the ORF 1-encoded protein (p33) compared with the original inoculum, i.e. a Ser19 TCC codon instead of a Phe19 TTC codon, which inhibited the replication of sat L and Cymsat RNAs. It is suggested that this amino acid is contained in a domain essential for the replication of some subviral RNAs.