Agrobacterium tumefaciens mutants affected in crown gall tumorigenesis and octopine catabolism

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Abstract
Mutants of A. tumefaciens which affect virulence or the ability to catabolize octopine were isolated after Tn5[transposon 5]-induced mutagenesis. Of 8900 colonies tested, 7 mutants with Tn5 insertions in a specific region of the Ti plasmid unable to catabolize octopine were isolated. Thirty-seven mutants affected in tumorigenesis resulted from insertions in the Ti plasmid and the Agrobacterium chromosome. Of these mutations, 12 were chromosomal and 25 mapped on the plasmid. Twenty-three mutations were mapped within a 20 Mdalton region, which is distinct from the Ti plasmid sequences found stably integrated into the plant cell genome (T-DNA). Included in these were mutants that were either avirulent or produced tumors with unusual morphologies. Three mutants contained insertions in the T-DNA. These 3 mutants incited tumors which synthesized octopine but had an altered morphology due to either extensive proliferation of shoots or roots from the tumor callus. Three additional mutants not caused by Tn5 contained mutations in the Ti plasmid.