T-DNA of a crown gall teratoma is covalently joined to host plant DNA

Agrobacterium tumefaciens strains containing tumour-inducing (Ti) plasmids incite cancerous growths called crown galls when inoculated into wounded dicotyledonous plants. Tumour tissue can be cultured axenically in vitro, and exhibits a transformed phenotype in the absence of the inciting bacterium. Transformed cells grow autonomously, are auxin and cytokinin autotrophic in vitro and synthesize opines, novel amino acid derivatives dictated by Ti plasmid genetic information. A small segment of the Ti plasmid, termed T-DNA is maintained in axenic tumour cells. Mitochondrial and chloroplast DNA from a crown gall teratoma are free from T-DNA, whereas nuclear DNA contains T-DNA in amounts similar to that in total tumour cell DNA. T-DNA appears to be attached to what is presumably plant DNA in the crown gall tumour cell: Southern blot analysis of tumour DNA digested with restriction endonucleases reveals T-DNA fragments that are not fully homologous to Ti plasmid DNA. We report here the isolation by molecular cloning of a 'border fragment' T-DNA and flanking plant DNA from the crown gall teratoma BT37 and show that T-DNA is covalently joined to a repeated DNA element of the tobacco nuclear genome.