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Agrobacterium Mediated Gene Transfer

Updated on November 24, 2013

In the soil, a 'natural genetic engineer' is present and is a bacterium called Agrobacterium tumefaciems. From the time immemorial, this little bacterium transfer a gene fragment called T-DNA (transfer DNA) that lies in Ti (tumor inducing) plasmid into the plant genome. Bacteria transfers a specific gene segment to the plant genome without any outside intervention. We are exploiting bacteria's ability by placing our gene of interest in the place of bacterial Transfer DNA.

Crown gall disease caused by Agrobacterium tumefaciens
Crown gall disease caused by Agrobacterium tumefaciens

What is Agrobacterium tumefaciens?

Agrobacterium tumefaciens is a Gram negative, rod shaped soil bacterium that invade many dicot plants and causes crown gall disease by a naturally evolved 'genetic engineering' process.

The causative agent of crown gall disease is a plasmid called as tumor inducing plasmid or Ti plasmid.A part of the plasmid called as transfer DNA (T-DNA) is transferred from the bacterium to the plant cells and later gets integrated into the plant genome.The T DNA has genes for auxin, cytokinnin and opines. Expression of auxin and cytokinnin induces cell division leading to crown gall or tumor formation in the site.

Why bacteria transfers its T-DNA?

The T-DNA of Ti plasmid has genes for auxin, cytokinin and opine. Opine is a growth promoting nutrient for the infecting bacterium. As cytokinin and auxin promotes cell division and tumor formation, bacterium utilizes these cells as a factory for the production of opines.

Ti  Plasmid
Ti Plasmid | Source

The mechanism of gene transfer by Agrobacterium

The Ti plamid has

  • a transfer DNA (T-DNA): The region that is transferred and integrated into the plant genome
  • a 24 bp left and right repeats or (T-DNA borders): essential sequence for gene transfer
  • an origin of replication,
  • a virulence region (vir region): has genes that mediated gene transfer
  • an opine catabolism region: has genes for utilization of opines synthesised by the plant cells

Essential requirements for T-DNA transfer

  1. T-DNA borders are essential for gene transfer
  2. vir region mediated transfer of T-DNA into the plant genome.

Agrobacterium tumefaciens Mediated Gene Transfer
Agrobacterium tumefaciens Mediated Gene Transfer

How we exploit the gene transfer capability of Agrobacterium?

The major fact that allowed the use of Ti plasmid as our gene transfer carrier is

'Any gene fragment of suitable size if placed between T-DNA borders will be transferred and integrated into the plant genome. The only requirement is vir region and T-DNA borders'.

So we can replace the T-DNA with our gene of interest. If T-DNA borders and vir region are present it will be transferred and integrated into the plant genome irrespective of the gene sequence. The process of replacing T-DNA (tumor causing gene) with our gene of interest is called as 'disarming'. The plasmid with our gene of interest in the place of T-DNA is called as 'disarmed plasmids'.

This video will help you a lot in getting into the details of Agrobacterium mediated gene transfer in plants.


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    • teaches12345 profile image

      Dianna Mendez 4 years ago

      This is really an interesting post and so well done. Who would have thought gene gransfer would be fascinating? Thanks for the education.

    • conradofontanilla profile image

      conradofontanilla 4 years ago from Philippines

      Gene transfer is now being used in gene therapy in medicine. For example, the human gene that controls the production of the enzyme that induces the production of nitric oxide. This is cloned. Another gene that controls the production of protein envelop of a virus is also cloned. Then still another gene that controls the production of antibody that modifies the surface of cancer cell such that the protein envelop recognizes the cancer cell is also cloned. Now these three genes are put together; bound together by hydrogen bonds and sewn together by ligase enzyme. The result is recombinant DNA that is given like a vaccine to a person suffering from cancer. The human gene is carried by the protein coat that delivers it precisely to the surface of the cancer cell. Once incorporated in the chromosomes of the cancer cells the human genes will produce nitric oxide synthase that produces nitric oxide that kills cancer cell. That is gene therapy for cancer. I have three Hubs on gene therapy of cancer. This is a new cure for cancer better than chemotherapy. Unfortunately, it is still in the development stage for the market.

    • osaeoppongde profile image

      Deborah L. Osae-Oppong 4 years ago from Chicago, IL

      Great post! Gene transfer is a fascinating phenomenon! The fact that we have figured out how to exploit it is even more incredible!

    • thebiologyofleah profile image

      Leah Kennedy-Jangraw 4 years ago from Massachusetts

      Interesting stuff, I love examples found in nature that researchers have manipulated in the lab to work in their favor. For some reason in school I always thought plant biology was boring but it has provided biotechnology and drug discovery with some much.