What is Agrobacterium tumefaciens, and how is it used in plant transformation?

Agrobacterium tumefaciens is a soil-dwelling bacterium that has a natural ability to transfer part of its DNA into plant cells. Scientists have harnessed this unique property to use it as a tool for genetic engineering in plants.

Here’s a simple explanation of what it is and how it’s used in plant transformation:

1. Definition:
   Agrobacterium tumefaciens is a gram-negative bacterium that causes a plant disease known as crown gall, which results in tumor-like growths on infected plants. The bacterium transfers a piece of DNA called T-DNA from its Ti (tumor-inducing) plasmid into the plant cell, where it integrates into the plant genome.
2. Natural Mechanism:
   • In nature, Agrobacterium infects wounded plant tissues.
   • It attaches to the plant cells and transfers T-DNA into the plant’s genome.
   • This T-DNA causes the plant cells to divide uncontrollably and produce compounds that the bacteria use for growth.
3. Use in Genetic Engineering:
   Scientists have modified Agrobacterium to remove the tumor-causing genes from its Ti plasmid and replace them with desired genes (such as those for pest resistance, drought tolerance, or improved nutrition).
   • The modified bacterium then transfers this new DNA into the plant cell instead of tumor-causing genes.
   • The plant’s cells incorporate the new gene into their DNA, and the transformed cells are grown into complete plants through tissue culture.
4. Steps in Agrobacterium-Mediated Transformation:
   • The desired gene is inserted into a binary vector (plasmid) compatible with Agrobacterium.
   • The bacterium carrying this plasmid is co-cultivated with plant cells or tissues.
   • T-DNA carrying the target gene enters the plant cells.
   • Transformed cells are selected and regenerated into whole plants.
5. Advantages:
   • Efficient for many dicot plants (like tomato, tobacco, and soybean).
   • Produces stable and heritable gene expression.
   • Causes minimal damage to the plant genome compared to other methods.
6. Limitations:
   • Less effective in monocots (like rice, wheat, and maize), though modern techniques have improved this.
   • Requires sterile conditions and skilled handling in the lab.

In summary:
Agrobacterium tumefaciens acts as a natural genetic engineer of plants. In biotechnology, it is modified and used as a biological vector to introduce beneficial genes into plants, making it one of the most important tools in plant genetic transformation.