Ti Plasmid

Ti plasmid is a circular plasmid that often, but not always, is a part of the genetic equipment that Agrobacterium tumefaciens and Agrobacterium rhizogenes use to transduce its genetic material to plants. The Ti plasmid is lost when Agrobacterium is grown above 28C. Such cured bacteria do not induce crown galls, i.e. they become avirulent. pTi and pRi share little sequence homology but are functionally rather similar. The Ti plasmids are classified into different types based on the type of opine produced by their genes. The different opines specified by pTi are octopine, nopaline, succinamopine and leucinopine.

The plasmid has 196 genes that code for 195 proteins. There is no one structural RNA. The plasmid is 206,479 nucleotides long, the GC content is 56% and 81 per cent of the material is coding genes. There are no pseudogenes.

The modification of this plasmid is very important in the creation of transgenic plants, but only in dicotyledon plants.

Virulence Region

Genes in the virulence region are grouped into the operons virABCDEFG , which code for the enzymes responsible for mediating transduction of T-DNA to plant cells.

• virA codes for a receptor which reacts to the presence of phenolic compounds such as acetosyringone, which leaks out of damaged plant tissues.
• virB encodes proteins which produce a pore/pilus-like structure.
• virC binds the overdrive sequence.
• virD1 and virD2 produce endonucleases which target the direct repeat borders of the T-DNA segment, beginning with the right border.
• virG activates vir-gene expression after binding to a consensus sequence, once it has been phosphorylated by virA .

References

• Schell J, Van Montagu M., The Ti-plasmid of Agrobacterium tumefaciens, a natural vector for the introduction of nif genes in plants?, Basic Life Sci. 1977;9:159-79.
• B.D.Singh, genetic enginnering and cloning.

1. ^ Scott E.Stachelt, Eugene W.Nester (1986). "The genetic and transcriptional organization of the vir region of the A6 Ti plasmid of Agrobacterium tumefaciens". The EMBO Journal 5 (7): 1445-1454 . http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1166964/ .  
2. ^ ^{a b c d e} Schrammeijer, B., Beijersbergen, A., Idler, K.B., Melchers, L.S., Thompson, D.V., Hooykaas, P.J.J. (2000). "Sequence analysis of the vir-region from Agrobacterium tumefaciens octopine Ti plasmid pTi15955". Journal of Experimental Botany 51 (347): 1167-1169 . http://jxb.oxfordjournals.org/cgi/content/full/51/347/1167 .  
3. ^ ^{a b c} Alexander N. Glazer, Hiroshi Nikaidō (2007). Microbial biotechnology: fundamentals of applied microbiology . Cambridge University Press. ISBN 0521842107.  

See also

• Mary-Dell Chilton
• Jeff Schell
• Marc Van Montagu