T-DNA borders — identifying the incorrect statement about the direct repeats Regarding the short direct-repeat sequences that flank T-DNA on the Ti-plasmid, which statement is NOT true?

Introduction / Context:
T-DNA is delimited by short border repeats (about 25 base pairs) on the Ti plasmid. These border sequences are recognition elements for the virulence machinery. Clarifying what happens to the borders during transfer avoids common misconceptions.

Given Data / Assumptions:

• Right and left borders are highly conserved across Ti plasmid classes.
• VirD2 nicks at the right border to initiate a single-stranded T-strand.
• The transferred DNA corresponds primarily to the sequence between borders.

Concept / Approach:

Although the borders define T-DNA boundaries and are essential for processing, the transferred T-strand generally comprises the region between the borders. The border sequences themselves are not typically integrated as intact repeats in the plant genome; rather, processing occurs at or near these sites, and the internal region becomes integrated.

Step-by-Step Solution:

Verification / Alternative check:

Sequencing of T-DNA–plant junctions shows integration endpoints near but not composed of intact border repeats, supporting the conclusion.

Why Other Options Are Wrong:

Conservation between Ti types and importance in processing are correct; borders define processing boundaries through Vir protein recognition.

Common Pitfalls:

Equating ‘‘boundary definition’’ with ‘‘physical inclusion’’ of border repeats in the integrated T-DNA.

Final Answer:

These repeats are transferred intact into the plant genome along with T-DNA