The Chlorosis-Induction Domain of the Satellite RNA of Cucumber Mosaic Virus: Identifying Sequences That Affect Accumulation and the Degree of Chlorosis. Lee Zhang. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. Chung Mo Kim, and Peter Palukaitis. Department of Plant Pathology, Cornell University, Ithaca, NY 14853 U.S.A. MPMI 7:208-213. Accepted 29 December 1993. This article is in the public domain and not copyrightable. ll may be (freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994.

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 arc discussed relative to particular sequence contexts in different chlorosis-inducing RNAs.