Crown gall

Agrobacterium tumefaciens

Agrobacterium tumefaciens is a Gram-negative soil bacterium that is known for its ability to transfer a segment of its own DNA (transferred DNA or T-DNA) into the genomes of plants, leading to the formation of crown galls or tumors. This natural genetic transformation ability has made A. tumefaciens a valuable tool in genetic engineering and plant biotechnology. Here's an overview of Agrobacterium tumefaciens and its significance:

1. Pathogenicity:

  • Crown Gall Disease: A. tumefaciens causes a plant disease known as crown gall. The bacterium induces the formation of galls or tumors on the stems, roots, and sometimes, the crown of infected plants.

2. Mechanism of Genetic Transfer:

  • Ti Plasmid: A. tumefaciens carries a large circular DNA plasmid called the Ti (tumor-inducing) plasmid. This plasmid contains genes responsible for the synthesis of opines, which are amino acid and sugar derivatives that serve as nutrients for the bacterium.

  • Virulence (Vir) Genes: The bacterium uses a set of virulence (Vir) genes located on the Ti plasmid to transfer a segment of the T-DNA to the plant host.

  • T-DNA Integration: The T-DNA is transferred and integrated into the plant genome, leading to the formation of crown galls. The integrated T-DNA carries genes responsible for the synthesis of plant hormones, which contribute to gall development.

3. Importance in Genetic Engineering:

  • Transformation Tool: The natural transformation ability of A. tumefaciens has been harnessed for the genetic engineering of plants. Researchers use modified Ti plasmids to introduce desired genes into plant cells. This process is commonly known as Agrobacterium-mediated transformation.

  • Transgenic Plants: Agrobacterium-mediated transformation is widely used to create transgenic plants with desirable traits, such as insect resistance, herbicide resistance, or improved nutritional content.

4. Management of Crown Gall Disease:

  • Cultural Practices: Practices that promote plant health, such as proper irrigation, nutrition, and avoiding injuries to plant tissues, can reduce the susceptibility of plants to A. tumefaciens infection.

  • Use of Resistant Varieties: Some plant species or varieties are more resistant to crown gall disease. Planting resistant varieties can be an effective strategy.

  • Soil Treatments: Soil treatments with biological control agents or antagonistic organisms may help suppress the population of A. tumefaciens.

  • Elimination of Infected Plants: Removing and destroying plants with crown gall symptoms can help prevent the spread of the bacterium.

5. Applications in Research and Agriculture:

  • Crop Improvement: A. tumefaciens-mediated transformation is widely used in crop improvement programs to develop plants with enhanced traits, such as improved yield, resistance to diseases, and tolerance to environmental stresses.

  • Basic Research: The study of A. tumefaciens and its interaction with plants has contributed significantly to our understanding of molecular biology and host-pathogen interactions.