Q.28
Which one of the following statements is CORRECT about Agrobacterium tumefaciens
mediated plant transformation?
(A) The marker gene for the selection of plant transformant is located outside the T-DNA
segment of the transformation plasmid
(B) The marker gene for the selection of bacterial transformant is located within the T-DNA
segment of the transformation plasmid
(C) Two T-DNA border sequences (left and right) are essential to design a binary vector
system
(D) In binary vector system, the vir genes and two T-DNA border sequences (left and right)
are present in the same transformation plasmid
Agrobacterium tumefaciens Mediated Plant Transformation: Correct Answer Revealed
Agrobacterium tumefaciens mediated plant transformation relies on T-DNA borders for efficient gene transfer in binary vectors. The correct statement identifies a key feature of this system used in genetic engineering.
Correct Answer
Option (C) is correct: Two T-DNA border sequences (left and right) are essential to design a binary vector system.
Binary vectors require these borders to define the T-DNA region transferred to the plant genome, enabling precise insertion of genes like selectable markers. Without both borders, VirD proteins cannot process and mobilize the DNA effectively.
Option A Explanation
Option (A) states the marker gene for plant transformant selection is outside the T-DNA segment, which is incorrect. Plant selectable markers, such as antibiotic resistance genes, reside within the T-DNA to integrate into the plant genome post-transfer.
Option B Explanation
Option (B) claims the bacterial transformant marker is within the T-DNA, but this is wrong. Bacterial selection markers like kanamycin resistance are on the plasmid backbone outside T-DNA, ensuring Agrobacterium survival without plant transfer.
Option D Explanation
Option (D) suggests vir genes and both T-DNA borders are on the same plasmid in binary systems, which is inaccurate. Binary vectors separate T-DNA borders on one plasmid from vir genes on a helper Ti plasmid for easier manipulation.
| Option | Statement Summary | Correct? | Reason |
|---|---|---|---|
| A | Plant marker outside T-DNA | No | Markers integrate via T-DNA |
| B | Bacterial marker inside T-DNA | No | Backbone location for bacteria |
| C | Two borders essential for binary | Yes | Defines transferable region |
| D | Vir genes and borders on same plasmid | No | Separate in binary system |
