(A) P, S

(B) R, S

(C) P, R

(D) Q, S

Correct Answer

✅ Option (C): P and R

Detailed Explanation

Plant transformation involves Agrobacterium-mediated gene transfer and direct DNA delivery methods such as the biolistic (gene gun) method. Each statement is evaluated below.

Statement P

“Single-stranded nicks are made in T-DNA border repeats by the VirD1, VirD2 and VirD3 protein complex.”
✅ Correct

• During Agrobacterium-mediated transformation, the VirD1–VirD2 complex introduces site-specific single-strand nicks at the T-DNA border sequences.

• VirD2 remains covalently attached to the 5′ end of the T-strand, facilitating its transfer.

• VirD3 is associated with T-DNA processing.

✔ This statement is true.

Statement Q

“virA gene products form the export apparatus on the membrane for the transfer of T-DNA.”
❌ Incorrect

• VirA is a sensor kinase that detects phenolic compounds released by wounded plant cells.

• The export apparatus for T-DNA transfer is formed by VirB proteins and VirD4, not VirA.

✘ Hence, this statement is false.

Statement R

“Gold/Tungsten particles are used as microprojectiles in the biolistic method.”
✅ Correct

• The biolistic (gene gun) method uses gold or tungsten particles coated with DNA.

• These microprojectiles penetrate the plant cell wall and deliver DNA directly into the cell.

✔ This statement is true.

Statement S

“Acceleration of DNA-coated microprojectiles is carried out with compressed CO₂.”
❌ Incorrect

• Modern gene guns commonly use helium gas for accelerating microprojectiles.

• Compressed CO₂ is not the standard accelerating gas.

✘ Therefore, this statement is false.

Why Option (C) Is Correct

• P is correct (T-DNA nicking by Vir proteins)

• R is correct (gold/tungsten microprojectiles)

• Other options include at least one incorrect statement

✔ Hence, the correct answer is Option (C): P and R.

Quick Exam Memory Tips

• VirD1–VirD2 → T-DNA nicking

• VirB + VirD4 → T-DNA export

• Biolistic method → Gold/Tungsten particles

• Helium → Gene gun acceleration

Exam Relevance

🔹 Frequently asked in CSIR-NET Life Sciences
🔹 Important for plant biotechnology & genetic engineering
🔹 High-yield topic for matching and true/false MCQs