A DISEASE SYNDROME ASSOCIATED WITH EXPRESSION OF GENE-VI OF CAULIMOVIRUSES MAY BE A NONHOST REACTION

Gene VI of cauliflower mosaic virus (CaMV), which specifies a protein (P62) found in virus-induced inclusion bodies, has been implicated as a major determinant for host range and disease induction. In this study, gene VI of two strains of CaMV, CM1841 and D4, and gene VI of one strain of figwort mosaic virus (FMV) were used to transform tobacco (Nicotiana tabacum) and Datura inoxia and to evaluate the potential of this gene for disease induction. Tobacco, which is not a host for either CaMV or FMV, developed generalized chlorosis or a prominent chlorotic mottling after transformation with gene VI of either virus. D. inoxia is not a host for CaMV but is systemically susceptible to FMV. It developed a prominent chlorotic mottling syndrome after transformation with gene VI of CaMV, but no symptoms after transformation with gene VI of FMV. In both tobacco and D. inoxia plants that express gene VI of CaMV and tobacco plants that express gene VI of FMV, a positive correlation between the level of gene VI-encoded protein accumulation and disease was found. These experiments and those done previously with transformation of Nicotiana edwardsonii, with gene VI of both viruses, suggest that a low level of gene VI-encoded protein is sufficient to cause chlorosis or chlorotic mottling in plants that are not systemic hosts, but not in plants that are systemic hosts for these viruses.