The chlorosis-induction domain of the satellite RNA of cucumber mosaic virus: identifying sequences that affect accumulation and the degree of chlorosis.

A number of satellite RNAs of cucumber mosaic virus (CMV) can induce chlorosis in either tobacco or tomato. A region containing the chlorosis domain was delimited, and one nucleotide position (153) regulating chlorosis induction as well as the nucleotide position (149) controlling the host specificity for chlorosis were identified. A cDNA clone of the B5-sat RNA was modified by site-directed mutagenesis to identify other nucleotides affecting chlorosis itself, as well as the extent of chlorosis and the helper virus-strain specificity for chlorosis. Four nucleotides conserved in chlorosis-inducing satellite RNAs (positions 127, 148, 149, 158) as well as two nucleotides within the chlorosis-induction domain that vary among chlorosis-inducing satellite RNAs (170, 171) were altered. Only substitutions at nucleotide positions 127 and 171 did not affect expression of the chlorosis phenotype. Alteration of position 148 affected satellite RNA accumulation. The pleiotropic effects of various sequences within the chlorosis-induction domain are discussed relative to particular sequence contexts in different chlorosis-inducing RNAs.