Ti-Plasmid

                                                           Introduction

 Agrobacterium tumefaciens is a rod shaped, gram negative Bacteria, soil born motile bacterium. This bacterium infects the parts of the plant which are in contact with soil. The genus Agrobacterium inclides four species of bacteria. They are A.tumefaciens, A.radiobacter, A.rubi, A.rhizogens. They  are pathogenic in nature and cause cancerous growth in the infected plant tissues. They infect the plants and cause tumberous growth in the infected portion. The induction of tumerous growth is due to the presence of a large sized plasmid named Ti Plasmid. Accourding to Zaenen et al. (1974) almost all the strain of A.tumefaciens contain Ti plasmid.

Agrobacterium is a bacterium which is used to produce transgenic plants because it contain tow kinds of vectors which are used in the transfer of genes of one plant to the genome of another plant:-

 1. Ti plasmid, 

 2. Ri plasmid,

                                                              Structure  

T-DNA carry genes for phytohormones, AND opine

Auxin:- The main function of auixn is to help plant grow. Auxin stimulates plant cell to elongate, and the apical meristem of a plant is one of the main places where auxin is produced.

Cytokinin:- Increased cell division by stimulating the process of mitosis. Increased formation of shoot and buds, as well as development of fruits and seeds.

Opin:- Nutritional source for agrobacteria and fall into different chemical grouping such as nopaline, Octopine, Mannopine, agrocinopine etc.

Vir genes:-

 Vir A:- Its a kinase portein in bacterial membrane. Act as receptor Phenolic compund relased by wounded plant.

Vir A and Vir G :- They expessed continuously respond to phenolic compund released by wounded plant.

Vir G :- Activate other vir gene (transcription gene factor)

Vir E/E2 :- Protect T-DNA against nuclease and target T-DNA to plant cell. Act as SSB protein (single standard binding protein).

Vir C :- Stimulate transfer/promotes high effciency T-stand Synthesis.

Vir D :- Responsible for virulence activity of bacterium.

Vir D1:- Topoisomerase helps virD2 to recognise and cleave within 25bp L.B sequence.

 Vir D2 :- Endonuclease ( vir D2 cut T-DNA right border, help to integration of T-DNA into host chromosome)

Vir D1 :- Prevent attack of exonuclease at 5' end of T-DNA, important for cutting phosphodiester bond.

Vir B/ Vir D4 :- ATP dependant linkage of  protein complex necessary for T-DNA transfer from bacterium of plant cell ( assemble into a secreation system which spns the inner and outer bacterial membrane.)

Vir D2/Vir E2 :- Have nuclear localization signal.

Vir F:- Plant cell cytosole, vib1protein.

                                                               Advantage

• Occure naturally in Bacteria.
• Have different restriction sites.
• Replication completely independent of Bacteria.
• Genes are easily inserted into plasmids.
• Easily transformed into bacteria.