Differential expression of the rolA plant oncogene and its effect on tobacco development

The rolA gene not only provokes the abnormal traits of wrinkled leaves, shortened internodes, and deficient root growth in tobacco, but also induction of roots in leaf disks in hormone-free medium. The rolA mRNA is most abundant in the stem of transgenic tobacco, accumulating at fivefold and 50-fold lower levels in the leaf and the root, respectively. Promoter deletion mutants were constructed and the rolA-induced abnormal traits were exploited to identify promoter regulatory regions. The removal of specific promoter domains provokes the appearance of new patterns of rolA transcripts in leaves, stems and roots. These new patterns are correlated with the disappearance of specific abnormal trait, thereby identifying three functional domains. Domain A includes a mosaic motif composed of a putative GT-2 binding site and DUE-NDE elements. This domain positively regulates rolA gene expression in the leaf and negatively regulates it in the stem and root. Domains B and C, which contain sequences homologous to the OCS enhancer and to ASF-1 binding sites, respectively, generally activate the rolA gene expression in all tissues. The possible function of these elements on the regulation of the rolA gene is discussed.