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Agrobacterium
1.
2. INTRODUCTION
Transformation – the process of obtaining
transgenic plants.
Transgenic plant – a plant with a foreign gene
(or genes) from another plant/animal that is
incorporated into its chromosome
3. Agrobacterium rhizogenes
A grobacterium rhizogenes is a Gram negative soil bacterium
that produces hairy root disease in dicotyledonous
plants.
A .rhizogenes induces the formation of proliferate multi-
branched adventitious roots at the site of infection; so
called ‘hairy roots’.
A.rhizogenes, the causative agent of hairy root
syndrome, is a common soil organism capable of
entering a plant through a wound and causing a
proliferation of secondary roots.
4. Ri plasmids
Ri plasmids are large (200 to greater than 800 kb) and
contain one or two regions of T-DNA and a vir (virulence)
region, all of which are necessary for hairy root
formation.
The Ri-plasmids are grouped into two main classes
according to the opines synthesized by hairy roots.
First, agropine-type strains induce roots to synthesise
agropine, mannopine and the related acids.
5. Second, mannopine-type strains induce roots to
produce mannopine and the corresponding
acids.
The agropine-type Ri-plasmids are very similar
as a group and a quite distinct group from the
mannopine-type plasmids.
6.
7. The genes responsible for hairy root
formation
The T-DNA of the agropine-type Ri-plasmid
consists of two separate T-DNA regions
designed the TL-DNA and TR-DNA (15 - 20
kb).These two fragments can be transferred
independently during the infection process.
The genes encoding auxin synthesis (tms1 and
tms2) and agropine synthesis (ags) have been
localised on the TR-DNA of the agropine type
Ri-plasmid.
The mannopine type Ri-plasmids contain only
one T-DNA that shares considerable DNA
8. rolA, rolB, and rolC play the most important role
in hairy root induction.
rolA is associated with internode shortening and
leaf wrinkling; rolB is responsible for protruding
stigmas and reduced length of stamens; rolC
causes internode shortening and reduced apical
dominance.
Although the TR-DNA is not essential for hairy
root formation it has been shown that the aux1
gene harbored in this segment provides to the
trasformed cells with an additional source of
auxin.
9. M e c h a n is m o f
A g r o b a c t e r iu m-p l a n t c e l l
in t e r a c t io n
One of the earliest stages in the interaction
between A grobacterium and a plant is the
attachment of the bacterium to the surface of the
plant cell.
A plant cell becomes susceptible to A grobacterium
when it is wounded.The wounded cells release
phenolic compounds, such as acetosyringone,
that activate the vir-region of the bacterial
plasmid.
The A grobacterium plasmid carries three genetic
components that are required for plant cell
10. The A grobacterium plasmid carries three genetic
components that are required for plant cell
transformation.
It has been shown that the A grobacterium plasmid
carries three genetic components that are
required for plant cell transformation.
The first component, the T-DNA that is
integrated into the plant cells, is a mobile DNA
element.
11.
12. The second one is the virulence area (vir), which
contains several vir genes.
These genes do not enter the plant cell but,
together with the chromosomal DNA (two loci),
cause the transfer of T-DNA. The third
component, the so-called border sequences (25
bp), resides in the Agrobacterium chromosome.
The mobility of T-DNA is largely determined by
these sequences, and they are the only cis
elements necessary for direct T-DNA processing.
13. ADVANTAGES
The hairy roots are grown in vitro in bioreactors
to study their soil interaction with other
pathogens like fungi and nematodes.
This technique has also led to the commercial
production of certain metabolic compounds that
the plant is known to secrete, especially in regard
to the medicinal plants that are difficult to
cultivate in sufficient quantities by other means.
The root cultures are also used for genetic
engineering.
