GATE 2022 BT Q.53: solution and answer

Official answer: A, C, DSource: Official answer key, GATE 2022 BT (IIT Kharagpur)

1. Agrobacterium tumefaciens naturally carries a Ti (tumor-inducing) plasmid whose T-DNA segment is transferred into and integrates with the plant cell genome; this natural gene-transfer mechanism is the most widely used vector-based method for plant transformation. Hence (A) is a valid method.

2. CaCl2-mediated plasmid uptake is the classical procedure for making bacterial cells (such as E. coli) chemically competent, relying on a brief heat shock to transiently destabilize the bacterial membrane so exogenous plasmid DNA can enter. It is a bacteria-specific technique and is not used to introduce genes into plant cells, which have a rigid cellulosic wall. Hence (B) is not a method used for plant cells.

3. Electroporation applies a short, high-voltage electric pulse to transiently create pores in the cell membrane, allowing DNA to enter. It is a standard direct-gene-transfer technique for plant protoplasts (cells with the wall removed or weakened). Hence (C) is a valid method.

4. The gene gun (biolistic or particle bombardment) method coats microscopic gold or tungsten particles with DNA and physically propels them through the plant cell wall and membrane, delivering DNA directly into cells or organelles such as chloroplasts. Hence (D) is a valid method.

5. Since the question is an MSQ asking which techniques can introduce foreign genes into plant cells, the valid methods are Agrobacterium-mediated transfer, electroporation, and the gene gun — options (A), (C), and (D) — while (B) is excluded as a bacteria-specific transformation method.