T-DNA insertion pattern — Which statement about the genomic integration of T-DNA into plant nuclear DNA following Agrobacterium-mediated transfer is correct?

Introduction / Context:
Agrobacterium-mediated transformation delivers T-DNA into the plant nucleus, where it integrates into the host genome. Understanding the insertion pattern is essential for interpreting position effects, gene disruption risks, and transgene expression variability in transformants.

Given Data / Assumptions:

• T-DNA border sequences and Vir proteins mediate DNA transfer and integration.
• Host repair pathways (e.g., non-homologous end joining) are involved in integration.
• Insertions can be single or multiple, and orientation can vary.

Concept / Approach:
Empirical mapping of insertion sites in numerous transformants shows a quasi-random distribution across the nuclear genome, with certain biases (e.g., towards gene-rich regions) depending on species and protocol. There is no single, fixed locus for T-DNA insertion under standard methods.

Step-by-Step Solution:

Verification / Alternative check:
T-DNA flanking sequence recovery across large transformant populations (TAIL-PCR, genome walking) reveals broad genomic distributions with no single mandatory target site.

Why Other Options Are Wrong:

• Single or two specific sites: contradicted by extensive mapping data.
• “One site that may be random”: self-contradictory and incorrect in practice; multiple sites are observed across events.
• Chloroplast integration: standard Agrobacterium pathways target the nucleus; plastid transformation uses different methods.

Common Pitfalls:
Assuming precise targeting without engineered homology; site-specific integration requires specialized tools (e.g., CRISPR HDR), not standard Agrobacterium.

Final Answer:
Integration of T DNA can occur at many different, apparently random, sites in the plant nuclear DNA