Agrobacterium Gene Transfer Method

Agrobacterium Gene Transfer Method

• Agrobacterium tumefaciens is a gram-negative bacterium, pivotal in plant transformation, and is the agent causing crown gall disease.
• This bacterium targets wounded plants by detecting amino acids, sugars, and organic acids released from them.
• It attaches to damaged plant tissue using a polar attachment mechanism.

Transformation Steps

• Initial attachment of Agrobacterium to plant tissue.
• Sensing plant signals induces the regulation of virulence genes.
• T-DNA and virulence proteins move from the bacterium into the plant cells.
• T-DNA and effector proteins are imported into the plant nucleus.
• Integration and expression of T-DNA occur within the plant genome.

Ti Plasmid

• The Ti plasmid is a circular DNA segment crucial for transformation.
• It has three key regions:
  • T-DNA region, which integrates into the plant genome.
  • Oncogene, responsible for tumor formation.
  • Virulence region containing 24 genes essential for bacterial infection and transformation.

Virulence Genes

• VirA: Senses acetosyringone, a plant signal.
• VirG: Acts as a transcriptional activator for virulence genes.
• VirB: Creates conjugation pores between bacterial and plant cells.
• VirD1: Cleaves substrate, facilitating T-DNA processing.
• VirE: Produces the gene transfer protein essential for T-DNA transport.
• VirC: Aids in the DNA transfer process.
• VirB11: Has ATPase activity that powers the DNA transfer mechanism.

Mode of Action

• Infected plant cells begin to divide, forming tumors.
• Tumors produce opine, an energy source exploited by Agrobacterium.
• The bacterium's entry into plants is enhanced by phenolic compounds like acetosyringone.
• Acetosyringone activates virulence factors in Agrobacterium.
• Virulence proteins synthesize single-stranded T-DNA, which is then transferred into plant cells.
• The T-DNA complex is imported into the nucleus and integrates randomly into plant chromosomes.
• This integration triggers synthesis of auxin and cytokinin, leading to tumor formation in infected plant cells.

This quiz explores the Agrobacterium tumefaciens gene transfer method, detailing its role in plant transformation and the process of how it integrates T-DNA into the plant genome. Understand the significance of the Ti plasmid and the molecular mechanisms involved in this transformation.