Agrobacterium‑mediated transformation in the lab does NOT require opine catabolism genes, so the correct answer is (4) opine catabolism genes.

Explanation of each statement

1. Host plant genes

• Plant transformation and T‑DNA integration depend on multiple host processes such as wound responses, nuclear import, DNA repair and integration.

• Without functional plant (host) genes, T‑DNA cannot stably integrate or be expressed, so host genes are always involved and cannot be considered “not required.”

2. Bacterial type IV secretion system

• The VirB/VirD4 type IV secretion system forms the transfer machinery and T‑pilus that export the T‑DNA–VirD2 complex and VirE2 into the plant cell.

• This system is indispensable for T‑DNA transfer; mutants lacking the type IV secretion system cannot deliver T‑DNA, so it is required for transformation.

3. vir genes

• vir genes encode proteins that process T‑DNA (nicking, coating, forming the T‑strand) and assemble the transfer apparatus.

• They are absolutely essential for generating and exporting T‑DNA; disarmed Ti plasmids used in binary vectors retain vir regions precisely because they are required.

4. Opine catabolism genes – NOT required (correct choice)

• Opine catabolism genes allow Agrobacterium to use opines produced by transformed tumors as carbon and nitrogen sources in nature.

• In laboratory plant transformation, the goal is gene transfer, not bacterial nutrition; bacteria are grown on rich media and do not need opine catabolism. These genes are routinely removed or left unused in disarmed Ti plasmids without affecting transformation efficiency.

Option-wise conclusion

• (1) (host plant genes) – essential, so wrong.

• (2) (type IV secretion system) – essential, so wrong.

• (3) (vir genes) – essential, so wrong.

• (4) (opine catabolism genes) – dispensable for lab transformation, so correct.

SEO‑oriented introduction (for article use)

Agrobacterium‑mediated plant transformation relies on vir genes, the bacterial type IV secretion system, and compatible host plant genes to process and transfer T‑DNA into the plant genome. In contrast, opine catabolism genes, which help Agrobacterium feed on opines in natural crown galls, are not needed under laboratory conditions, making them the correct “not required” choice in this multiple‑choice question.