In this part, we will go through how one of the first ever herbicide resistant plant was generated. Its a very lucid diagrammatic version of the basic behind Roundup Ready Soybean.

1. Introduction to
Plant Biotechnology
Part 3
Roundup Ready Soybean
Somnath Mondal

2. What is Roundup?
• Roundup is a broad spectrum herbicide.
• Its active ingredient is Glyphosphate.
• Glyphosphate is an organo-phosphate compound.
• It inhibits the Shikimate Pathway and thus blocks the biosynthesis
of aromatic amino acids.
• Therefore, Roundup herbicide if sprayed on plants, glyphosphate
will inhibit the Shikimate Pathway in those plants.Somnath Mondal

3. Phospho Enol Pyruvate (PEP) + Erythrose-4-Phsophate (E4P)
3-deoxy-d-arabino-heptulosonate-7-phosphate
3-dehydroquianate
3-dehydro shikimate
shikimate
Shikimate-3-phosphate
5-enol pyruvylshikimate-3-phosphate
Chorismate
3-deoxy-d-arabino-heptulosonate-7-phosphate synthase
3-dehydroquianate synthase
3-dehydroquianate dehydratase
Shikimate-5-dehydrgenase
Shikimate kinase
5-enol pyruvylshikimate-3-phosphate synthase
(EPSPS)
Chorismate synthase
Shikimate Pathway:
Glyphosphate
Somnath Mondal

4. • Therefore, Glyphosphate inhibits the enzyme EPSPS.
• By inhibiting this enzyme, chorismate couldn’t be biosynthesised i.e
the precursor of aromatic amino acids like phenylalanine, tryptophan
and tyrosine in plants.
• That is why within hours of Roundup herbicide spray, weeds
stop growing, yellowing starts in couple of days & finally they
die.
• Now the question is weeds are affected by glyphosphate, but
why not crop plants?!
Somnath Mondal

5. 5-enol pyruvylshikimate-3-phosphate synthase (EPSPS)
Class I Class II
-Found in plants as well as in
bacteria
-Found only in some bacteria
-It is susceptible to micromolar
concentration of glyphosphate.
-It is resistant to glyphosphate
inhibition.
• 46 kD
• Two domains
 Hence, if Class II EPSPS gene can be incorporated into economically important
plants and expressed, they will be resistant to glyphosphate herbicide damage.
 Only the weeds of that field will be omitted.
Somnath Mondal

6. Vector Construct:
Ti Plasmid
Ti Plasmid
Bacterial
transfornation
Somnath Mondal

7. Somnath Mondal
Transcription Start Transcription Termination
mRNA
Translation
EPSPS tagged with Chloroplast
localization signal

8. Glyphosphate
Class 1 EPSPS
Class 2 EPSPS
-ve
+ve
• Therefore, in transgenic crops with additional
class 2 EPSPS will carry out Shikimate Pathway
normally & biosynthesise aromatic amino acids.
No chorismate
Chorismate
Somnath Mondal