Agrobacterium tumefaciens n Characteristics Plant parasite that causes

Agrobacterium tumefaciens n Characteristics • Plant parasite that causes Crown Gall Disease • Encodes a large (~250 kbp) plasmid called Tumorinducing (Ti) plasmid n Portion of the Ti plasmid is transferred between bacterial cells and plant cells T-DNA (Tumor DNA)

Agrobacterium tumefaciens üT-DNA integrates stably into plant genome üSingle stranded T-DNA fragment is converted to ds. DNA fragment by plant cell Then integrated into plant genome n 2 x 23 bp direct repeats play an important role in the excision and integration process n

Agrobacterium tumefaciens n n n Tumor formation = hyperplasia Hormone imbalance Caused by A. tumefaciens • Lives in intercellular spaces of the plant • Plasmid contains genes responsible for the disease n Part of plasmid is inserted into plant DNA n Wound = entry point 10 -14 days later, tumor forms

Agrobacterium tumefaciens n What is naturally encoded in T-DNA? • Enzymes for auxin and cytokinin synthesis n n Causing hormone imbalance tumor formation/undifferentiated callus Mutants in enzymes have been characterized • Opine synthesis genes (e. g. octopine or nopaline) n n 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

1. Auxin, cytokinin, opine synthetic genes transferred to plant 2. Plant makes all 3 compounds 3. Auxins and cytokines cause gall formation 4. Opines provide unique carbon/nitrogen source only A. tumefaciens can use!