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

Ti plasmid of A. tumefaciens

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!