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Agrobacterium tumefaciens. Characteristics Plant parasite that causes Crown Gall Disease Encodes a large (~250kbp) plasmid called Tumor-inducing (Ti) plasmid Portion of the Ti plasmid is transferred between bacterial cells and plant cells T-DNA (Tumor DNA ). Agrobacterium tumefaciens.
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Agrobacterium tumefaciens • Characteristics • Plant parasite that causes Crown Gall Disease • Encodes a large (~250kbp) plasmid called Tumor-inducing (Ti) plasmid • Portion of the Ti plasmid is transferred between bacterial cells and plant cells T-DNA (Tumor DNA)
Agrobacterium tumefaciens • T-DNA integrates stably into plant genome • Single stranded T-DNA fragment is converted to dsDNA fragment by plant cell • Then integrated into plant genome • 2 x 23bp direct repeats play an important role in the excision and integration process
Agrobacterium tumefaciens • Tumor formation = hyperplasia • Hormone imbalance • Caused by A. tumefaciens • Lives in intercellular spaces of the plant • Plasmid contains genes responsible for the disease • Part of plasmid is inserted into plant DNA • Wound = entry point 10-14 days later, tumor forms
Agrobacterium tumefaciens • What is naturally encoded in T-DNA? • Enzymes for auxin and cytokinin synthesis • Causing hormone imbalance tumor formation/undifferentiated callus • Mutants in enzymes have been characterized • Opine synthesis genes (e.g. octopine or nopaline) • Carbon and nitrogen source for A. tumefaciens growth • Insertion genes • Virulence (vir) genes • Allow excision and integration into plant genome
Auxin, cytokinin, opine synthetic genes transferred to plant Plant makes all 3 compounds Auxins and cytokines cause gall formation Opines provide unique carbon/nitrogen source only A. tumefaciens can use!
