T DNA Transfer Process, DNA Synthesis, Endonuclease, Gene Products, Glucons, Cellulose Fibrils, Agrobacterium Chromosome

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	T DNA Transfer Process- An early event in the T-DNA: transfer process is the nicking of Ti plasmid at two specific sites, each between the third and fourth base of the bottom strand of each 25bp repeat. This initiates DNA synthesis from the nick in the right hand 25bp repeat sequence in 5' - 3' direction, thus is displacing a single T-DNA strand. This T-DNA single strand forms a complex with protein Vir E and gets transported to the plant nucleus. The vir D operon encodes an endonuclease that produces the nicks in the border sequences.
Several gene products of the vir B operon have been identified in the bacterial envelope, a location, which suggests that they may playa role in directing T -DNA transfer extracellularly. The functions of several other vir gene products are largely unknown.Apart from the role of Ti plasmid, the genes located on Agrobacterium chromosome also help in virulence. These genes are involved in the synthesis and secretion of glucons, cellulose fibrils and cell surface proteins. These loci are constitutively expressed and are also found in other soil bacteria associated with higher plants. Thus, these loci playa more general role in the virulence of Agrobacterium, and thus also in the Agrobacterium mediated gene transfer.