Which of the following has been modified into a cloning vector that is no more pathogenic to plants but can still deliver genes of interest into a variety of plants?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Ti plasmid of Agrobacterium tumefaciens
Agrobacterium tumefaciens is a pathogen of several dicot plants. It transfers a piece of DNA called T-DNA into plant cells and turns them into a tumour. Its tumour inducing (Ti) plasmid has been modified into a cloning vector that no longer causes disease in plants but can still deliver genes of interest into many plants.
Option (1) pBR322 — Incorrect. pBR322 is a cloning vector of E. coli. It is used to clone genes in bacteria, not to deliver genes into plants.
Option (2) Disarmed retrovirus — Incorrect. Retroviruses have been disarmed too, but they are used to deliver genes into animal cells, not plants.
Option (3) Ti plasmid of Agrobacterium tumefaciens — Correct. The Ti plasmid of Agrobacterium tumefaciens is the modified, non-pathogenic vector for plants.
Option (4) Native plasmid of Salmonella typhimurium — Incorrect. The native plasmid of Salmonella typhimurium was used to make the first recombinant DNA. It is not a vector for plants.
NCERT Extract:
Cloning Vectors – “… For example, Agrobacterium tumifaciens, a pathogen of several dicot plants is able to deliver a piece of DNA known as ‘T-DNA’ to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen. … The tumor inducing (Ti) plasmid of Agrobacterium tumifaciens has now been modified into a cloning vector which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of our interest into a variety of plants. Similarly, retroviruses have also been disarmed and are now used to deliver desirable genes into animal cells.”