The bar gene encodes phosphinothricin acetyltransferase (PAT), which detoxifies glufosinate ammonium (bialaphos or phosphinothricin), enabling selection of transformed plant cells under herbicide treatment.​

Option Analysis

hpt (Hygromycin Phosphotransferase): Encodes an enzyme that phosphorylates hygromycin B, conferring resistance to this antibiotic. Used for antibiotic-based selection in plant transformation, not herbicides.​

bar: Provides resistance to phosphinothricin-based herbicides like Basta by acetylation of the herbicide, preventing glutamine synthetase inhibition. Widely used as a herbicide tolerance selectable marker in crops like rice, wheat, and aspen.​

nptII (Neomycin Phosphotransferase II): Inactivates aminoglycoside antibiotics such as kanamycin, G418, or paromomycin by phosphorylation. Common for antibiotic selection, ineffective against herbicides.​

pmi (Phosphomannose Isomerase): Converts mannose-6-phosphate to fructose-6-phosphate, allowing transformed cells to utilize mannose as a carbon source. Positive selection system without antibiotics or herbicides.​

Introduction
Selectable marker genes for herbicide tolerance play a crucial role in plant genetic transformation, enabling efficient selection of transgenic cells during tissue culture. Among options like hpt, bar, nptII, and pmi, the bar gene stands out for conferring resistance to phosphinothricin-based herbicides, making it ideal for developing herbicide-tolerant crops. This guide explains each marker for competitive exams like CSIR NET Life Sciences.​

Herbicide Tolerance Markers
The bar gene, derived from Streptomyces hygroscopicus, encodes PAT that acetylates glufosinate, detoxifying it and allowing transformed plants to survive herbicide sprays. It has been successfully used in rice, Lotus japonicus, and wheat protoplast transformation, producing stable, heritable resistance. No other listed options (hpt, nptII, pmi) provide herbicide tolerance; they rely on antibiotics or metabolic selection.​

Antibiotic Resistance Markers

• hpt: Confers hygromycin B resistance by phosphorylation, blocking protein synthesis in non-transgenic cells.​

• nptII: Phosphorylates kanamycin or G418, widely used but limited to antibiotic selection in dicots and some monocots.​

Metabolic Selection Marker
pmi enables growth on mannose-supplemented media by isomerizing mannose-6-phosphate, starving non-transgenic cells without toxins. Preferred for marker-free systems but not herbicide-based.​