In plant biotechnology, which gene product specifically detoxifies the herbicide bromoxynil in transgenic plants?

Introduction / Context:
Bromoxynil is a nitrile herbicide. When breeders engineer herbicide-tolerant crops, the key is to express an enzyme that inactivates the specific toxicant. Knowing which gene works on which herbicide is essential for correct trait design and for avoiding regulatory or stewardship errors.

Given Data / Assumptions:

• Bromoxynil contains a nitrile functional group.
• Engineered tolerance relies on enzymes that transform or sequester the active herbicide.
• Common detoxification genes include nitrilase (bxn), GSTs, and phosphinothricin acetyl transferase (bar/pat), each with distinct substrate specificity.

Concept / Approach:
Enzyme–substrate specificity determines herbicide tolerance. Nitrilases hydrolyze nitriles to corresponding acids and ammonia, directly targeting the nitrile group in bromoxynil. In contrast, GSTs catalyze glutathione conjugation, commonly used for chloroacetanilides and other classes, and phosphinothricin acetyl transferase detoxifies glufosinate (phosphinothricin) by acetylation, not bromoxynil.

Step-by-Step Solution:

Verification / Alternative check:
Classic bxn genes from soil bacteria confer bromoxynil tolerance; field and greenhouse data show survival of transformed plants after bromoxynil applications when nitrilase is expressed.

Why Other Options Are Wrong:

• B: GSTs aid detox for other herbicide classes; bromoxynil is not the primary target.
• C: Phosphinothricin acetyl transferase is specific to glufosinate, a different chemistry.
• D/E: Over-inclusive or incorrect; specificity matters in herbicide tolerance.

Common Pitfalls:
Assuming any generic “detox” enzyme works for all herbicides; overlooking functional group specificity leads to failed field tolerance.

Final Answer:
Nitrilase