Agrobacterium tumefaciens is a rod shaped Gram negative soil bacteria that has a 200kb plasmid called as Ti plasmid (tumor inducing plasmid) which is responsible for crown gall disease.
Ti Plasmid - is a large 200 kb plasmid
- It has 4 major regions
- T-DNA region or transfer DNA region which has genes for auxin, cytokinin and opine
- T-DNA region is integrated into the plant genome
- A left border and right border repeats
- An origin of replication (ori)
- Virulence region that has genes that mediate T DNA transfer
- Opine catabolism region that has genes for opine utilization
T-DNA region
T-DNA or transfer DNA is the region of Ti plasmid that is transferred and integrated into the plant genome.
- Auxin and cytokinin gene induces cell division and proliferation leading to the crown gall disease.
- Opine gene will synthesize opines like octopine, noopaline etc These are nutrients for the growth of bacteria.
- LB and RB are required for transfer.
| Genes in T-DNA | Function |
| iaaM (aux1, tms1) |
Auxin biosynthesis: codes for enzyme tryptophan-2-monooxygenase that converts tryptophan to indole -3-acetamide (IAM)
|
| iaaH (aux2, tms2) |
Encodes indole -3-acetamide hydrolase, that converts IAM to indole-3- acetic acid (auxin biosynthesis)
|
| Ipt |
Cytokinin biosynthesis; codes for enzyme isopentenyl transferase that catalyses formation of isopentenyl adeniene
|
| Nos |
Nopaline biosynthesis, codes for enzyme noplaine synthase that form nopaline from pyruvic acid and arginine.
|
| 24 bp left and right borders |
Site of endonuclese action during T-DNA transfer, This region is essential for T-DNA transfer
|