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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