Agrobacterium tumefaciens is a soil bacterium that can transfer DNA fragments called T-DNA into plant cells. It causes crown gall disease in susceptible plants like tomatoes and sunflowers by integrating T-DNA into the plant cell's genome. During Agrobacterium-mediated gene transfer, wounded plant cells produce signal molecules that activate virulence genes in Agrobacterium, causing it to synthesize single-stranded T-DNA. The T-DNA is then transferred into the plant cell nucleus where it integrates and expresses genes that promote tumor formation. This natural process allows for stable transformation of plant cells and regeneration of whole transgenic plants.

1. AGROBACTERIUM MEDIATED GENE TRANSFER
Transformation:
 Uptake of foreign DNA by plant cells or Altering the
genome of plant cells is called transformation and these techniques
are known as Transformation techniques.
Techniques for plant genetic transformation:
Indirect method :
 1.Agrobacterium mediated gene transfer
Direct method :
 1.Particle bombardment method (biolistics).
 2 .Electroporation .
 3. PEG ( Polyethylene glycol method ).
 4. Microinjection.
 5. Silicon carbide fibres.
Agrobacterium tumefaciens :
 It is a rod shaped ,Gram negative, wide-spread soil inhabiting
bacterium and has Ti(Tumor inducing) plasmid.
 This bacterium invades crops such as tomato , sunflower ,
brinjal and cotton and causes crown gall disease which is in
the form of tumerous growth .
 It is also has an ability to integrate new genetic material also
called T-DNA or Transfer DNA into the plant cell

2.  It is also called “Natural Genetic Engineer”.
Crown gall disease:
Structure :
Ti plasmid :
 A Ti plasmid or tumour inducing plasmid is a plasmid that often
,but not always is apart of the genetic equipment that
Agrobacterium tumefaciens

3. Agrobacterium tumefaciens use to transduce its genetic material to
plants
Agrobacterium mediated gene transfer steps:

4.  Wounded plant cell produced actosyringone
 Acetosyringone is a small molecule and it is one of the plant derived
compounds that induce vir(virulence) genes.
 Virulence proteins synthesize the single stranded T-DNA ( Transfer
DNA).
 Then, Single stranded T-DNA only intermediate and transfer to
plant cells .This T-DNA complex import to nucleus and integrated.
 After integrating to the nucleus T-DNA have auxin , cytokinin ,
opines enzymes .First cytokinin and auxin synthesized promotes to
the tumor formation in Agrobacterium infected plant cells.
Important Requirements:
 The explants of the plant must produce phenolic compounds
(e.g.acetosringone) for activation of virulence genes
 Transformed cells/Tissues should be capable to regenerate into
whole plants.
Advantages :
 This is a natural method of gene transfer.
 Agrobacterium can conveniently infect any explant
(cells/tissues/organs)
 Even large fragments of DNA can be efficiently transferred.
 Stability of transferred DNA is reasonably good.
 Transformed plants can be regenerated effectively.

5. Limitations:
 There is a limitation of host plants for Agrobacterium , since many
crop plants (monocotyledons e.g. cereals ) are not infected by it. In
recent years, virulent strains of Agrobacterium that can infect a wide
range of plants have been developed.
 The cells that regenerate more efficiently are often difficult to
transform. E.g. embryonic cells lie in deep layers which are not easy
targets for Agrobacterium.