T-DNA of the Agrobacterium Ti and Ri Plasmids as Vectors
Crown gall and hairy root disease are incited by Agrobacterium tumefaciens strains carrying large virulence plasmids (Zaenen et al., 1974; Van Larebeke et al., 1974, 1975; Watson et al., 1975; White & Nester, 1980a). These are groups of related plasmids and have been designated Ti (tumor-inducing) and Ri (root-inducing) plasmids (Sciaky et al., 1978; Chilton et al., 1982), based on morphology of the infected plant tissue. The pathogenic bacteria genetically transform the host plant cells by an unknown mechanism that results in incorporation of a specific part of the virulence plasmid into the host plant genome (Chilton et al., 1977, 1982; White et al., 1982). This foreign DNA element, called T-DNA (transferred DNA), is covalently joined to host plant nuclear DNA (Chilton et al., 1980; Willmitzer et al., 1980; Yadav et al., 1980; Zambryski et al., 1980). T-DNA contains genes that function in the transformed plant cells, producing polyadenylated transcripts (Drummond et al., 1977; Gelvin et al., 1981, 1982; Gurley et al., 1979; Willmitzer et al., 1981, 1982; Bevan and Chilton, 1982). The morphology of tumor cells is affected when specific transcripts are inactivated by transposon insertion mutagenesis (Ooms et al., 1981; Garfinkel et al., 1981; Leemans et al., 1982). The auxin and cytokinin autotrophy of tobacco crown gall tumor cells can be eliminated individually by specific T-DNA mutations (Barton et al., 1982; Binns et al., 1982). An additional genetic function encoded by T-DNA is the synthesis by tumor tissue of novel metabolites, called opines, catalyzed by enzymes encoded by mapped T-DNA genes (Holsters et al., 1980; Garfinkel et al., 1981; Murai and Kemp, 1982; Schröder et al., 1981). Because the opines serve as specific catabolic substrates for the inciting Agrobacterium strain (Petit et al., 1970; Tepfer and Tempé, 1981), the transformation of thehost plant cells can be rationalized as an example of genetic engineering by a prokaryotic organism.
KeywordsHairy Root Agrobacterium Tumefaciens Crown Gall Homo Arginine Crown Gall Tumor
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