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Agrobactenu~ii (Zaenen et dl, 1974). Eventually, Chtltoli et al., (1977) found that the
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genes of TI plasrn~d were responsible for the synthes~s of op~nes which were necessary for
the progression of turiior w~tliout Ilie additton of growth liorniones They also found that
only 5% of the plarniid DNA war responsible for virulelicc (Chilton, 1978). Since then
many groups embarked upon exploring the lntr~cacies of the Agrobocieriuni and its abil~ty
to transforni the host cells.
2.1.2.1 Ti plnsltlid a ~ its ~ cllarncterislics
d
Many scientific groups in early 70s found that tlie TI plasmid, precisely part of it's
DNA is responsible for tlie tumorigenic nature of the infecting bacterium. Tile process of
identification of causal sequence for the tumorigenic activity was many folds expedited by
the d~scovery of Southern blot (Southern, 1975) and DNA sequencing metllods (Maxam
and Gilbert, 1977). Hooykaas, Schilperoot anti their associates found additional evidence
for the role of Ti plasmid III
tu~iior induction (Hooykaas et al., 1977). A detailed.
d~scription of eah-events In crown gall researcl! was provided by Shell et al., (1979). It
a? becatlie evident fiom Cliilton's experimelits thnt part of Ti DNA (termed as T-DNA)
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was transferred t ~ l k !$I. Transcriptio~i of tlie T-DNA was confirnied by northern
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blot experiments (Drunimond ct a]., 1977). All tile T-DNAs were found to be similar and
has a length of 23 kb flanked by alniost idelltical borders (Zambryski et al., 1980).
Spontaneous deletions studies rcvenled the gclietic componelits of tlie T-DNA and their
oncogcliic tiatuse was confirnied (Gelvin et al., 1981). Schilperoot atid colleagues revealed
many aspects of the T-DNA by inducing mutations and tracking tl~em down in the host
plant cells by transfortiling tile tobacco protoplasts (Hockcnia et al., 1984). By this time it
was also evident that a set of vir genes was involveti ill the transfer of T-DNA. It became
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