Nature of T-DNA integration — In plant tumor (crown gall) cells induced by Agrobacterium, what portion of the Ti plasmid is stably integrated into plant nuclear DNA?

Introduction / Context:
Crown gall formation is driven by the stable integration and expression of T-DNA genes in the plant genome. Distinguishing between transferred cargo (T-DNA) and bacterial machinery (vir region) is central to understanding and applying Agrobacterium-mediated transformation in plant biotechnology.

Given Data / Assumptions:

• T-DNA is delimited by left and right border repeats on the Ti plasmid.
• Vir genes act in trans to process and transfer T-DNA but are not themselves transferred.
• Plant tumor traits arise from T-DNA oncogenes and opine synthase genes.

Concept / Approach:
Only the DNA between the LB and RB is nicked, generated as a T-strand, and transferred to the plant nucleus for integration. The rest of the Ti plasmid remains in the bacterium. Hence, the correct statement is that only a specific, small T-DNA segment integrates.

Step-by-Step Solution:

Verification / Alternative check:
Binary vectors confirm that any gene placed between LB and RB can be transferred and integrated; sequences outside borders are not transferred.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming plasmid replication equals transfer; transfer is targeted and border-dependent.

Final Answer:
Only a small, specific T-DNA segment bounded by left/right borders.