Increased Viral Yield and Symptom Severity Result from a Single Amino Acid Substitution in the Turnip Yellow Mosaic Virus Movement Protein. Ching-Hsiu Tsai. Department of Agricultural Chemistry, Program in Genetics, Oregon State University, Corvallis 97331 U.S.A. Theo W. Dreher(1,2). (1)Department of Agricultural Chemistry, Program in Genetics, and (2)Center for Gene Research and Biotechnology, Oregon State University, Corvallis 97331 U.S.A. MPMI 6:268-273. Accepted 15 January 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993.

Turnip yellow mosaic virus is a positive-strand RNA virus that produces light green or yellow-green mosaic symptoms in Chinese cabbage plants. We have characterized a strain that produces nearly uniform yellow-green chlorosis in systemically infected Chinese cabbage leaves. The increased symptom severity is due to the single nucleotide substitution U1888-->C, which results in a tyrosine to histidine substitution in the movement protein encoded by ORF-69. Coding by the overlapping ORF-206 is not affected. The mutation results in fourfold higher accumulations of viral products in systemically infected Chinese cabbage leaves but does not affect viral replication in isolated protoplasts. These results suggest that the increased viral yield and symptom severity result from improved viral spread in the host plant. These effects were specific to Chinese cabbage, since neither viral yield nor symptoms in turnips were affected by the U1888-->C mutation.