Long-distance RNA-RNA interactions and conserved sequence elements affect potato virus X plus-strand RNA accumulation

Conserved octanucleotide sequences located upstream of two major potato vir us X (PVX) subgenomic RNAs (sgRNAs), as well as elements in the 5' end of t he genome, affect accumulation of sgRNA, To determine if complementarity be tween these sequences is important for PVX RNA accumulation, we analyzed th e effects of mutations within these elements and compensatory mutations in a tobacco protoplast system and in plants. Mutations in the 5' nontranslate d region (NTR mutants) that reduced complementarity resulted in lower genom ic RNA (gRNA) and sgRNA levels, whereas mutations to the octanucleotide ele ments affected only the corresponding sgRNA levels. However, for both the N TR and octanucleotide mutants, the extent of reductions in RNA levels did n ot directly correlate with the degree of complementarity, suggesting that t he sequences of these elements are also important. Mutants containing chang es in the NTR and compensatory changes in one of the octanucleotide element s restored levels of gRNA and the other sgRNA species with an unaltered oct anucleotide element to those of wild-type. Although compensatory changes si gnificantly increased levels of the sgRNA species with the modified octanuc leotide element, levels were not restored to those of wild-type, Our data i ndicate that long distance RNA-RNA interactions and the sequences of the in teracting elements are required for PVX plus-strand RNA accumulation.