Cucumber mosaic virus satellite RNA (strain Y): analysis of sequences which affect systemic necrosis on tomato.

The location of a sequence within the Y satellite RNA of cucumber mosaic virus (CMV) that confers the ability to induce necrosis on tomato plants has been analysed using chimeric satellite RNAs. These recombinant RNA molecules contained parts of the Y (necrogenic) and Ra (benign) satellite RNAs and were inoculated into tomato plants together with CMV helper virus. From the composition of the recombinant satellite RNAs that induced necrosis it was concluded that, of the nucleotides which differ between Y and Ra satellite RNAs, those affecting necrosis are on the 3' side of nucleotide 259. The composition of satellite RNAs that failed to induce necrosis implies that at least some of the necrogenic positions are on the 3' side of nucleotide 311. The symptoms induced by mutated forms of Y and Ra satellite RNAs showed that nucleotide spacing between positions 322 and 323 and sequence identity at one or more of nucleotides 318, 323 or 325 affects the necrogenic potential of Y satellite RNA. The effect of a frameshifting mutation in Y satellite RNA and the location of the necrogenic sites relative to open reading frames in other satellite RNAs suggested that necrosis is not caused by polypeptides encoded in satellite RNA.