Download Lecture 13 Herbicide resistant plants Resistant plants have been

Lecture 13
Herbicide resistant plants
Resistant plants have been developed for the herbicide glyphosate, which is
environmentally friendly because it is readily degraded to non toxic compounds into soil.
It acts as an inhibitor of 5-enolpyruvyl shikimate 3-phosphate synthase (EPSPS), which is
an enzyme in the shikimate pathway. This enzyme plays an important role in the
synthesis of aromatic amino acids in bacteria and plants. An EPSPS encoding gene from
a glyphosate resistant strain of E.coli was isolated, put under the control of plant
promoter and transcription termination – polyadenylation sequences, and cloned into
plant cells.
Roundup Resistant Plants
Shikimic acid + Phosphoenol pyruvate
+ Glyphosate
Bacterial
EPSP synthase
RoundUp has no effect;
enzyme is resistant to herbicide
3-enolpyruvyl shikimic acid-5-phosphate
(EPSP)
With amino acids,
plant lives
NDSU
Aromatic
amino acids
Extension
Transgenic tobacco, petunia, tomato, potato and cotton plants that produce an
amount of the resistant E.coli EPSPS sufficiently, to replace the inhibited plant enzyme
are resistant to the effects of glyphosate treatment. Thus in these cases, the crop plant
would not be affected by glyphosate treatment whereas the weeds would be.
An example of resistance due to herbicide inactivation has been developed for
bromoxynil(3,5-dibromo-4 hydroxybenzonitrile), a herbicide that acts by inhibiting
photosynthesis. In this case, resistant plants were created, by the introduction of bacterial
gene that encodes the enzyme nitrilase, which can inactivate bromoxynil before the
herbicide can act. The gene for nitrilase was isolated from the soil bacterium Klebsielle
ozaenae and placed under the control of light regulated promoter from the small sub unit
of the enzyme ribulose biphosphate carboxylase before it was transferred to tobacco
plants. As expected, the transgenic plants expressed nitrilase activity in their shoots and
leaves but not in their roots, and were resistant to the toxic effects of the herbicide.
Fig 1.Detoxification of the herbicide bromoxynil by the enzyme nitrilase from
K.ozaenae
Table 1.Gene based herbicide resistance plants