Agrobacterium–plant interaction — In octopine-type Ti plasmids, the integrated T-DNA within the plant genome typically occurs as how many segments?

Introduction / Context:
Agrobacterium tumefaciens transfers a defined region of its Ti plasmid (T-DNA) into plant cells, where it integrates into the nuclear genome and drives tumor (crown gall) formation. Octopine-type Ti plasmids characteristically contain two T-DNA regions.

Given Data / Assumptions:

• Different Ti plasmid types (octopine vs nopaline) have different T-DNA organization.
• Octopine-type T-DNA is often found as two separate segments (TL and TR).
• These segments encode oncogenes and opine synthesis genes.

Concept / Approach:
Recall that “TL” (left) and “TR” (right) segments can integrate and express genes in plant cells. Their presence explains phenotypes and opine profiles in transformed tissues.

Step-by-Step Solution:

Verification / Alternative check:
Molecular mapping and restriction analyses of octopine Ti plasmids reveal separate TL and TR inserts.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing nopaline and octopine plasmid structures; always check plasmid type.

Final Answer:
Two segments (TL and TR).