Herbicide-resistance engineering in plants Which gene encodes the enzyme phosphinothricin acetyl transferase (PAT), widely used to confer resistance to the herbicide phosphinothricin (glufosinate)?

Introduction / Context:
Modern plant biotechnology frequently uses selectable marker genes that detoxify herbicides so transformed cells can survive tissue culture. One such marker is phosphinothricin acetyl transferase (PAT), which inactivates phosphinothricin (also known as glufosinate). Knowing the correct gene source is essential for understanding vector construction and regulatory dossiers.

Given Data / Assumptions:

• PAT enzymatically acetylates phosphinothricin, preventing its inhibition of glutamine synthetase.
• bar and pat are closely related bacterial genes used in plants.
• Different resistance genes target different herbicides (e.g., nitrilase for bromoxynil).

Concept / Approach:
The bar gene, originally identified in Streptomyces spp. (notably Streptomyces hygroscopicus), encodes PAT. A similar gene, pat, from Streptomyces viridochromogenes, is also used. These genes are placed under plant promoters to enable expression and selection on glufosinate-containing media.

Step-by-Step Solution:

Verification / Alternative check:
Plant transformation manuals and commercial trait descriptions consistently list bar/pat (Streptomyces origin) as the PAT-encoding genes for glufosinate resistance.

Why Other Options Are Wrong:

• gene bxn in Klebsiella pneumoniae: linked to bromoxynil resistance, not PAT for phosphinothricin.
• both (a) and (b): incorrect because (a) is wrong.
• none of these: incorrect because bar is correct.
• pat gene in Escherichia coli: pat used in plants is from Streptomyces viridochromogenes, not E. coli.

Common Pitfalls:
Confusing the herbicide targets (glufosinate vs. bromoxynil vs. glyphosate) and mixing up bar/pat with EPSPS or nitrilases.

Final Answer:
bar gene in Streptomyces spp.