The correct combination is (2) A, C and D. Statements A, C and D are true; statement B is false.

Explanation of each statement

A. T-DNA of Agrobacterium contains oncogenes and opine synthesis genes – TRUE

• The T-DNA region carries two major classes of genes:

  • Oncogenes coding for enzymes that synthesize auxin and cytokinin, causing uncontrolled cell division.

  • Opine synthase genes (e.g., octopine synthase, nopaline synthase) that produce opines in transformed plant cells.​

• Hence statement A is correct.

B. All 8 operons present in vir region are essential for virulence – FALSE

• The vir region typically has eight operons: virA, virB, virC, virD, virE, virF, virG and virH.

• Six (virA, virB, virC, virD, virE, virG) are essential for efficient T-DNA transfer, while virF and virH are non‑essential but can broaden host range or improve efficiency.​

• Therefore it is wrong to say “all 8 operons” are essential.

C. CaMV 35S RNA promoter is a very strong constitutive promoter used in plant transformation – TRUE

• The cauliflower mosaic virus (CaMV) 35S promoter drives high, largely constitutive expression of transgenes in many dicot and several monocot species, and is the most widely used promoter in plant transformation vectors.​

• Thus statement C is correct.

D. Conjugative transfer (oriT or tra) region functions in conjugative transfer of the Ti plasmids – TRUE

• Ti plasmids possess an oriT/tra region that encodes relaxase and other transfer (tra) functions; together with trb genes, this region mediates conjugative transfer of Ti plasmids between Agrobacterium cells.​

• Therefore statement D is correct.

Option-wise evaluation

• (1) B, C and D – Incorrect because B is false.

• (2) A, C and D – Correct; all three statements accurately describe T-DNA gene content, CaMV 35S promoter use, and the oriT/tra region.

• (3) A, B and D – Incorrect due to B.

• (4) A, B and C – Incorrect due to B.

SEO‑oriented introduction (for article use)

In designing vectors for Agrobacterium-mediated plant transformation, it is important to know that the T-DNA carries oncogenes and opine synthase genes, the CaMV 35S promoter provides strong constitutive expression of transgenes, and the oriT/tra region controls conjugative transfer of the Ti plasmid between bacteria, whereas not all vir operons are absolutely required for virulence.