120. A researcher wants to ectopically express protein X exclusively in the seeds of Arabidopsis. Which one of
the following promoters is most suitable for this purpose?
(1) CaMV 35S
(2) Maize ubiquitin
(3) Napin
(4) rd22

Detailed Explanation:

Question:
A researcher wants to ectopically express protein X exclusively in the seeds of Arabidopsis. Which one of the following promoters is most suitable for this purpose?

✅ Correct Answer: (3) Napin

Understanding Promoters and Ectopic Expression:

A promoter is a DNA sequence that controls when and where a gene is expressed. For ectopic expression, where a gene is expressed in a location where it’s not normally active, selecting the right promoter is crucial—especially if the goal is tissue-specific expression, like in seeds.

Why Napin Is the Right Choice:

The Napin promoter is derived from a seed storage protein gene and is:

• Highly active in seed tissues.

• Minimal or no activity in other plant tissues (like leaves, stems, roots).

• Widely used in plant genetic engineering for seed-targeted expression.

So, for seed-specific expression of protein X in Arabidopsis, Napin is the most precise and efficient promoter available.

Why the Other Options Are Less Suitable:

• (1) CaMV 35S:

  • A constitutive promoter from the Cauliflower Mosaic Virus.

  • Active in almost all plant tissues, not seed-specific.

• (2) Maize ubiquitin:

  • Also a strong constitutive promoter used in monocots like maize.

  • Not seed-specific, and not optimal for dicots like Arabidopsis.

• (4) rd22:

  • A stress-inducible promoter, activated by drought and dehydration stress.

  • Not seed-specific.

Conclusion:

For exclusive expression of a protein in Arabidopsis seeds, the Napin promoter is the most effective and specific choice. It ensures high levels of expression precisely where needed—in the seed—without off-target effects in other tissues.

✅ Correct Answer: (3) Napin