Herbicide tolerance in transgenic petunia: resistance to glyphosate has been developed by transferring which gene?

Introduction / Context:
Glyphosate inhibits the shikimate pathway by targeting the enzyme EPSPS. Engineering glyphosate-tolerant crops typically involves introducing a glyphosate-insensitive EPSPS or overexpressing a bacterial version that is not inhibited by the herbicide.

Given Data / Assumptions:

• Glyphosate acts on EPSPS in the shikimate pathway.
• Different herbicides target different enzymes (ALS, ACCase).
• Petunia was among early models for herbicide-tolerance proof-of-concept.

Concept / Approach:
Resistance works when EPSPS no longer binds glyphosate effectively. This can be achieved by introducing a mutant EPSPS gene or a heterologous bacterial EPSPS that retains catalytic activity but is glyphosate-insensitive. ALS variants typically confer tolerance to sulfonylurea or imidazolinone herbicides, not glyphosate. ACCase variants relate to other herbicide classes.

Step-by-Step Solution:

Verification / Alternative check:
Commercial glyphosate-tolerant crops (e.g., Roundup Ready) use EPSPS variants or detox pathways such as GOX in some systems.

Why Other Options Are Wrong:

• B: ALS variants confer tolerance to sulfonylurea/imidazolinone herbicides.
• C: GS is not the primary glyphosate target.
• D: Incorrect—specificity matters.
• E: ACCase variants relate to ACCase-inhibiting herbicides, not glyphosate.

Common Pitfalls:
Assuming all herbicide-tolerance genes are interchangeable; each herbicide targets a specific enzyme.

Final Answer:
EPSPS (5-enolpyruvylshikimate-3-phosphate synthase) gene with a glyphosate-tolerant variant