# DBT JRF 2022 — Question 81

Exam: DBT JRF 2022 · Section: B · Topic: Plant Biotechnology › Selectable Markers in Plant Transformation · Difficulty: Medium

## Question

Which one of the following is commonly used as a selection marker for developing transgenic plants?

## Options

- **A.** Green fluorescent protein
- **B.** ß-lactamase
- **C.** ß-galactosidase
- **D.** Hygromycin phosphotransferase

## Answer

Option D

## Explanation

Selectable marker for plant transformation — hygromycin resistance: In plant transformation (Agrobacterium-mediated or biolistic), a SELECTABLE MARKER gene is needed to identify successfully transformed cells/shoots. Hygromycin resistance gene (hpt, hygromycin phosphotransferase): • Encodes an enzyme that inactivates hygromycin B (an aminoglycoside antibiotic that inhibits translation in both prokaryotes and eukaryotes). • Transformed cells expressing hpt survive on hygromycin-containing selection medium. • Non-transformed cells die → only transformed cells grow into callus and then plants. Distractors: • GFP: A REPORTER gene (shows where expression occurs via green fluorescence), NOT a selectable marker — it doesn't confer any growth advantage on selective medium. • Other selectable markers include: nptII (neomycin/kanamycin resistance), bar (bialaphos resistance), PMI (phosphomannose isomerase, positive selection on mannose medium). Answer: Hygromycin phosphotransferase (hpt) gene confers antibiotic resistance for positive selection of transformed plants.

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