Design of a plant transformation plasmid for Bt toxin Which statement best describes a necessary feature of a plasmid used to introduce the Bacillus thuringiensis (Bt) toxin gene into plant cells for transgenic expression?

Introduction / Context:
Engineering Bt crops requires expressing a bacterial insecticidal protein in plant tissues. Proper expression in plants depends on plant-compatible regulatory sequences, codon optimization, and transformation/selection strategies.

Given Data / Assumptions:

• Bt toxin genes originate from Bacillus thuringiensis.
• Plants use different promoters, introns, and polyadenylation signals than bacteria.
• Selectable markers (e.g., kanamycin resistance) are used in tissue culture but are not intended for field antibiotic resistance.

Concept / Approach:
A successful plant transformation vector positions the Bt coding sequence under a strong plant promoter (e.g., CaMV 35S for constitutive expression, or tissue-specific promoters) with plant terminators and often codon-optimized sequence. This ensures transcription/translation in the plant nucleus/cytoplasm. Tumor-inducing functions (opines) are removed in disarmed Ti vectors.

Step-by-Step Solution:

Verification / Alternative check:
Standard binary vectors (e.g., pBI121 derivatives) demonstrate plant promoters driving transgenes, validating this approach.

Why Other Options Are Wrong:

• Antibiotic resistance markers are for selection in culture, not agronomic antibiotic resistance.
• Opine synthesis is from oncogenic T-DNA; disarmed vectors lack these genes.
• Toxic vectors would kill transformants.
• Lack of selectable markers hinders recovery of true transformants.

Common Pitfalls:
Assuming bacterial promoters work efficiently in plants; they generally do not without plant regulatory elements.

Final Answer:
Carries a bacterial gene placed under a plant promoter and regulatory signals