Ti plasmids of Agrobacterium

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

Ti plasmid

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)
Cytokinin biosynthesis; codes for enzyme isopentenyl transferase that catalyses formation of isopentenyl adeniene
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

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