T DNA Transfer and integration

T DNA Transfer and integration

Signal induction to agrobacterium-

  • The wounded plant cell release certain chemicals phenolic compounds and sugars which are recognized as signals by agrobacterium.
  • The signal induced result in a sequence of biochemical events in Agrobacterium that helps in the transfer of T-DNA of T- Plasmid.

Attachment of Agrobacterium to plant cell

  • The Agrobacterium attached to plant cells through polysaccharides, particularly cellulose fibers produced by he bacterium. 
  • Several chromosomal virulence (chv) genes responsible for the attachment of bacterial cells to the plant cells have been identified.

Production of virulence protein

  • As the signal induction occurs in the Agrobacterium cells attached to the plant cells a series of events take place that result in the production of virulence protein
  • To start with signal induction by phenolics stimulate vir A which in turn activates (by phosphorylation) vir G. 
  • This induces expression of virulence genes of Ti plasmid to produce the corresponding virulence protein (D1, D2, E2, B etc.) 
  • Certain sugars (glucose galactose, xylose) that induce virulence genes have been identified.

Production of T- DNA strand

  • The right and left borders of T-DNA are recognized by vir D1/vir D2 proteins. 
  • These proteins are involved in the production single stranded T-DNA its protection and export to plant cells. 
  • The ss T-DNA gets attached to vir D2

Transfer of T-DNA out of Agrobacterium

  • The ss T-DNA –Vir D2 Complex in association with vir G is exported from the bacterial cell. Vir B products from the transport apparatus.

Transfer of T-DNA into plant cells and integration

  • The T-DNA vir D2 complex crosses the plant plasma membrane.
  • In the plant cells TDNA gets covered with vir E2. 
  • This covering protects the T-DNA from degradation by nucleases.
  • Vir D2 and Vir E2 interact with a variety of plant protein complex enters the nucleus through nuclear pore complex within the nucleus the T-DNA gets integrated into the plant chromosome through a process referred to illegitimate recombination.
  • This difference from the homologous recombination as it does not depend on the sequence similarity  
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