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 mRN A is most abundant in the stem of transgenic tobacco, accumulating at fivefold and 50-fold lower levels in the leaf and the root, respective ly. Promoter deletion mutants were constructed and the rolA-induced ab normal traits were exploited to identify promoter regulatory regions. The removal of specific promoter domains provokes the appearance of ne w patterns of rolA transcripts in leaves, stems and roots. These new p atterns are correlated with the disappearance of specific abnormal tra it, thereby identifying three functional domains. Domain A includes a mosaic motif composed of a putative GT-2 binding site and DUENDE eleme nts. This domain positively regulates rolA gene expression in the leaf and negatively regulates it in the stem and root. Domains B and C, wh ich contain sequences homologous to the OCS enhancer and to ASF-1 bind ing sites, respectively, generally activate the rolA gene expression i n all tissues. The possible function of these elements on the regulati on of the rolA gene is discussed.