A Mutational and Transcriptional Analysis of a Tumor Inducing Plasmid of Agrobacterium tumefaciens

Abstract

The large tumor inducing (Ti) plasmids (Zaenen et al., 1974) of Agrobacterium tumefaciens are the causitive agents of gall tumors on dicotylendonous plants. The plant cell transformation is brought about by the stable integration of a portion of the bacterial Ti-plasmid into plant nuclear DNA (Chilton et al., 1978a; Thomashow et al., 1980a; Thomashow et al., 1980b; Lemmers et al., 1981; Chilton et al., 1980; Yadav et al., 1980). Transformed plant cells are characterized by the following properties: the ability to grow in azenic culture without an exogenous supply of the plant hormones auxin and cytokinin (Braun, 1958) and the synthesis of unusual amino acids called opines (Petit et al., 1968; Menage and Morel, 1964; Goldman et al., 1968; Goldman et al., 1969; Fermin and Fenwick, 1978). The transferred plasmid DNA (T-DNA) is transcribed, (Drummond et al., 1978; Yang et al., 1979; Gelvin et al., 1981; Ledeboer, 1978; Gurley et al., 1979) influences the levels of plant hormones, and directs the synthesis opines (Bomhoff et al., 1976; Montoya et al., 1977; Kemp et al., 1979; Hack and Kemp, 1980; Guyon et al., 1980) in transformed plant cells. Thus, crown gall tumorigenesis is a model system for the study of the mechanism by which a bacterial plasmid transforms a eukaryotic cell causing a neoplastic disease.