MAPPING OF HOST-RANGE RESTRICTION OF THE RAKKYO STRAIN OF TOBACCO MOSAIC-VIRUS IN NICOTIANA-TABACUM CV BRIGHT YELLOW

The rakkyo strain (TMV-R) and the common strain (TMV-U1) of tobacco mo saic virus exhibit distinct host range differences. TMV-R infects rakk yo plants. a monocot host that TMV-U1 is unable to infect. However, TM V-R causes only latent infection in Nicotiana tabacum cv. Bright Yello w (BY) in inoculated leaves, whereas TMV-U1 infects BY systemically an d induces mosaic symptoms. Complete nucleotide sequencing of the TMV-R genomic RNA revealed amino acid changes in the 130K/180K replicase pr oteins, the 30K protein, end the coat protein and nucleotide changes i n the 5' and 3' noncoding regions compared to TMV-U1. To identify vira l components involved in determination of differences in host range, w e have mapped determinants for the differential infection phenotype in BY plants by constructing chimeric Viruses between the two strains in the present study. Examination of the infection phenotypes of the 14 constructed chimeric viruses in BY showed that determinants defining t he differential infection phenotype in BY reside in the 130K/180K repl icase proteins and the 3' noncoding region. Cognate combination of the 130K/180K replicase proteins and the 3' noncoding region of TMV-U1 or igin is required to produce systemic infection in BY plants. (C) 1996 Academic Press, Inc.