LEVELS AND LOCATION OF EXPRESSION OF THE AGROBACTERIUM-TUMEFACIENS PTIA6 IPT GENE PROMOTER IN TRANSGENIC TOBACCO

The location of gene expression of the Agrobacterium tumefaciens ipt g ene promoter in transgenic tobacco plants was examined using the beta- glucuronidase (GUS) reporter gene. Expression of GUS was detected in e very organ and most cell types examined. The highest levels of GUS act ivity were found in roots. To further examine the transcriptional basi s of this broad expression pattern, deletions in the 5' noncoding regi on of the gene were translationally fused to two promoterless reporter genes, encoding the enzymes chloramphenicol acetyl transferase (CAT) and beta-glucuronidase (GUS). Reporter enzyme assays revealed the exis tence of an upstream segment required for maximal promoter function, t he 5' end of which is between -442 and -408 of the P(ipt) ATG codon. T his upstream segment is required for maximal levels of GUS expression in roots, but not in other organs, and a tobacco suspension-cultured c ell line. The implications of broad ipt expression on the process of c rown gall tumorigenesis are discussed.