The neomycin phosphotransferase selectable marker inactivates (4) Kanamycin.

Correct option

• Neomycin phosphotransferase II (NPT II), encoded by the neo/nptII gene from Tn5, is an aminoglycoside 3′-phosphotransferase.

• It phosphorylates and thereby inactivates several aminoglycoside antibiotics, most prominently kanamycin (and also neomycin, G418 etc.).

• Transgenic plant cells expressing nptII survive and grow on kanamycin-containing medium, allowing selection.

Explanation of each option

1. Hygromycin

• Resistance to hygromycin B is conferred by a different enzyme, hygromycin B phosphotransferase (hpt/hph), not by neomycin phosphotransferase.

• NPT II does not efficiently detoxify hygromycin, so this is not the correct match.

2. Ampicillin

• Ampicillin is a β‑lactam antibiotic; resistance is typically provided by β‑lactamase (ampR), which hydrolyses the β‑lactam ring.

• Neomycin phosphotransferase does not act on β‑lactams, so it does not inactivate ampicillin.

3. Streptomycin

• Streptomycin is an aminoglycoside, but its common resistance determinants are specific streptomycin phosphotransferases or adenyltransferases (e.g., strA/strB), not the Tn5 nptII product used in most plant vectors.

• Standard plant transformation vectors with nptII are selected with kanamycin or G418, not streptomycin.

4. Kanamycin – Correct

• Kanamycin is an aminoglycoside efficiently phosphorylated and inactivated by neomycin phosphotransferase II.

• This makes kanamycin resistance via nptII one of the classic selectable marker systems in plant genetic engineering.

SEO-friendly introduction

In plant genetic engineering, the neo/nptII gene encoding neomycin phosphotransferase II is one of the most widely used selectable markers because it allows transformed cells to grow on medium containing the antibiotic kanamycin. By phosphorylating and inactivating kanamycin and related aminoglycosides, NPT II provides a reliable selection system, whereas other antibiotics such as hygromycin, ampicillin, or streptomycin require distinct resistance genes and are not inactivated by this enzyme.