Question

The Ti plasmid and its T-DNA have been genetically modified for use as a vector for the insertion of recombinant DNA into plant chromosomes to prevent dicots from tumor diseases. The source of Ti plasmid is:

• A. Asparagus sp.
• B. Arthrobacter luteus
• C. Aspergillus niger
• D. Agrobacterium tumefaciens

Hint:

Think of Agrobacterium tumefaciens as "nature's genetic engineer." The name itself gives a clue: {tumefaciens} means "tumor-making," which refers to the crown gall disease caused by its \textbf{Ti} (Tumor-inducing) plasmid.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Ti (Tumor-inducing) plasmid is a natural plasmid used extensively in plant genetic engineering. The question asks for the natural source of this plasmid.
Step 2: Detailed Explanation:


The Ti plasmid is found in the soil bacterium Agrobacterium tumefaciens.

This bacterium is a plant pathogen that causes crown gall disease, which is characterized by the formation of tumors on plants, primarily dicots.

Agrobacterium naturally transfers a segment of its Ti plasmid, called the T-DNA (transfer DNA), into the plant's genome.

Scientists have exploited this natural gene transfer mechanism by "disarming" the Ti plasmid (removing the tumor-causing genes) and inserting a gene of interest into the T-DNA region. The modified Agrobacterium can then be used as a vector to deliver the desired gene into plant cells.

The other options are incorrect: Asparagus is a plant, Arthrobacter is a different soil bacterium, and Aspergillus is a fungus.

Step 3: Final Answer:
The source of the Ti plasmid is the bacterium Agrobacterium tumefaciens.