Octopine-type Ti plasmids For octopine Ti plasmids, the right T-DNA segment (TR) is primarily required for which function?

Introduction / Context:
Ti plasmids differ in T-DNA organization. In octopine-type plasmids, T-DNA is typically split into two segments, TL and TR, each carrying distinct genetic modules that affect tumor development and opine metabolism. Knowing which segment encodes what is a classic detail tested in plant biotechnology.

Given Data / Assumptions:

• We are dealing with octopine Ti plasmids (not nopaline or agropine types).
• The T-DNA integrates into plant chromosomes and is expressed there.
• Different T-DNA segments encode oncogenes versus opine synthase genes.

Concept / Approach:
In octopine strains, the left segment (TL) carries the oncogenic genes that deregulate auxin and cytokinin synthesis, driving tumor formation. The right segment (TR) typically harbors the octopine synthase gene(s), enabling tumor tissues to synthesize the opine octopine, which Agrobacterium can catabolize. Conjugative transfer functions reside outside the T-DNA on plasmid transfer (tra/trb) regions and vir genes are bacterial and not plant-expressed.

Step-by-Step Solution:

Verification / Alternative check:
Molecular mapping and tumor metabolite profiling show octopine production driven by T-DNA-encoded octopine synthase, reinforcing that TR contributes opine metabolism rather than tumor initiation per se.

Why Other Options Are Wrong:

• Tumor formation: mainly TL in octopine plasmids.
• Conjugative transfer: plasmid transfer modules are outside T-DNA.
• All of these/vir in plant nucleus: contradict T-DNA organization and gene locations.

Common Pitfalls:
Confusing octopine and nopaline plasmids or assuming both TL and TR are interchangeable for oncogenesis. They have specialized roles.

Final Answer:
Enzymes for octopine biosynthesis (opine synthase expression)