Agrobacterium virulence genes — requirements for T-DNA processing and transfer During Agrobacterium-mediated transformation, which vir gene products are required for T-DNA processing and transfer into the plant genome?

Introduction / Context:
The virulence (vir) genes on the Ti plasmid coordinate sensing of plant signals, processing of T-DNA, pilus formation, coating of the T-strand, and transport into plant cells. Knowing which vir loci participate clarifies the orchestrated nature of the transfer machinery.

Given Data / Assumptions:

• Multiple vir operons exist (virA, virG, virB, virC, virD, virE, etc.).
• T-DNA transfer needs sensing, nicking/processing, coating, and a transport channel.
• The listed pairs are all known to contribute key functions.

Concept / Approach:

virA/virG sense phenolic inducers and activate vir transcription; virD (notably VirD2) nicks the right border to generate the T-strand; virE (VirE2) coats the single-stranded T-DNA; virB forms a type IV secretion system for transfer; virC enhances processing at borders. Therefore, multiple vir modules are essential, making ‘‘All of these’’ correct.

Step-by-Step Solution:

Verification / Alternative check:

Mutations in any of virA/G, virB, virC, virD, or virE reduce or abolish T-DNA transfer, confirming the necessity of the network.

Why Other Options Are Wrong:

Each individual pair alone is insufficient; the process needs coordinated action of several vir loci.

Common Pitfalls:

Overemphasizing a single vir gene (e.g., virD2) and overlooking the requirement for activation and transport modules.

Final Answer:

All of these