THE EXPRESSION OF A CHIMERIC CAULIFLOWER MOSAIC-VIRUS (CAMV-35S) PEA VICILIN GENE IN TOBACCO

A gene encoding the 7S pea seed protein vicilin was modified for general expression in transgenic tobacco by fusion of the cauliflower mosaic virus 35S enhancer to the promoter region of the gene. The 7S seed protein was accumulated in leaves, stems, roots, seeds and callus but the level of expression varied widely in the different organs. Vicilin per unit of total soluble protein was higher in younger (upper) leaves (0.01%) than in older (lower) leaves (0.001%) indicating that vicilin was less stable than the average leaf protein. The vicilin in tobacco leaves was cleaved preferentially at or near one of the two post-translational cleavage sites used in pea seeds and in a manner very similar to that which occurs in tobacco seeds with either the unmodified vicilin gene or the 35S-vicilin construct. Leaf vicilin was also assembled into a normal 7S oligomer. These results indicate that a seed protein gene can be modified for expression in most organs of a transgenic host and that expression proceeds with a high level of fidelity. Minor variations in expression were related to selective cleavage of the polypeptide chain and to the production of two mRNA size classes instead of one. The fact that the seed protein was moderately stable in the heterologous environment augurs well for the engineered expression of other seed protein genes in transgenic hosts.