Host range control of cauliflower mosaic virus.

Studies with recombinant genomes of cauliflower mosaic virus (CaMV) strains D4, CM1841, and Cabb-B have shown that a host range determinant of CaMV is encoded within the first half of region VI, a gene which codes for P62, an inclusion body protein. In order to further study the host specificity of CaMV, a fourth CaMV strain, W260, was chosen that has a host range that is intermediate between D4 and CM1841. To determine which portion of the W260 genome controls systemic spread, recombinant viruses made between this strain and CM1841 and D4 were tested for their ability to systemically infect several solanaceous plants (Datura stramonium, Nicotiana edwardsonii, and Nicotiana bigelovii). The first half of gene VI specified the type of local lesions and systemic spread of recombinant strains in D. stramonium. In N. edwardsonii, it was found that the first half of gene VI controlled the type of local lesion formed but systemic spread was dependent on the whole of gene VI. In N. bigelovii the number of genes that determined systemic spread of CaMV varied with the strain of CaMV. Systemic spread of D4 in N. bigelovii was dependent on the first half of gene VI. In contrast, systemic spread of W260 in the same host was dependent on the whole of gene VI and another locus which mapped within genes I-V. Consequently, it appears that other viral proteins may interact with P62 or that P62 may function well in some hosts only in compatible forms of other viral proteins.