- Agrobacterium tumefaciens is a soil-dwelling, Gram-negative bacterium best known for its unique ability to transfer genetic material into plants. Belonging to the family Rhizobiaceae, it is a natural genetic engineer of the plant kingdom, capable of integrating a segment of its DNA into the host genome. This remarkable property has made A. tumefaciens both a significant plant pathogen in nature and an invaluable tool in agricultural biotechnology.
- In its natural context, Agrobacterium tumefaciens causes a plant disease called crown gall, characterized by tumor-like swellings at the junction of the root and stem. This occurs when the bacterium transfers a portion of its Ti plasmid (tumor-inducing plasmid) into the plant cell. Within this plasmid is a specific segment of DNA known as T-DNA, which integrates into the plant genome. The T-DNA contains genes that direct the plant to produce unusual compounds called opines, which the bacterium can metabolize as a unique nutrient source, and phytohormones that trigger uncontrolled cell division, leading to gall formation.
- The discovery of this natural DNA transfer mechanism in the mid-20th century revolutionized molecular biology. Scientists realized that by replacing the disease-causing genes on the T-DNA with genes of interest, Agrobacterium could be used as a vector for plant genetic engineering. This breakthrough laid the foundation for the creation of the first transgenic plants in the 1980s and remains one of the most widely used techniques for crop transformation today. The system allows stable integration of foreign genes into a plant’s genome, enabling the development of crops with traits such as pest resistance, herbicide tolerance, and enhanced nutrition.
- Beyond its role in plant transformation, Agrobacterium tumefaciens is an object of study in horizontal gene transfer and evolutionary biology. It demonstrates how bacteria can manipulate eukaryotic hosts by integrating foreign DNA, providing a natural example of cross-kingdom genetic exchange. Moreover, the bacterium’s ability to interact with plant defense systems has deepened understanding of plant–microbe interactions and host-pathogen relationships.
- In biotechnology, A. tumefaciens remains a cornerstone of agricultural innovation. It has been adapted for genetic modification not only of dicot plants like tomatoes and soybeans but also, with improved methods, for monocots such as maize and rice. Alternative transformation methods, like particle bombardment and CRISPR-Cas9 editing, have emerged, but Agrobacterium remains highly valued due to its efficiency and relatively low cost.
