Question

Agrobacterium tumefaciens is frequently used as a vector to create transgenic plants. Under laboratory conditions Agrobacterium - mediated plant transformation does not require

• A. Host plant genes
• B. Bacterial type IV secretion system
• C. vir genes
• D. Opine catabolism genes

Hint:

Distinguish between the machinery for DNA transfer and the bacterium's reward. The vir genes and the Type IV secretion system are the machinery. Opine production (by the plant) and catabolism (by the bacterium) are the reward. For lab work, we only need the machinery, not the reward system.

Answer 1

The Correct Option is D

Step 1: Introduction
*Agrobacterium tumefaciens* naturally transfers a DNA segment (T-DNA) from its Ti plasmid into a plant's genome. This process is utilized in biotechnology to insert desired genes into plants. The question asks which component of the natural system is unnecessary in a laboratory setting.
Step 2: Component Analysis
Examine the roles of the following components in the transformation process:
1. Host plant genes: Wounded plant cells release chemical signals (e.g., acetosyringone) that initiate the process. Host plant gene expression is therefore required.
2. Bacterial type IV secretion system (T4SS): This bacterial "syringe" is essential for injecting the T-DNA complex into the plant cell.
3. vir genes: Located on the Ti plasmid, these "virulence" genes encode proteins vital for transformation. These proteins are responsible for sensing plant signals, processing T-DNA, and forming the Type IV secretion system. The *vir* genes are therefore essential.
4. Opine catabolism genes: In nature, T-DNA carries genes that cause the plant cell to produce opines. The Ti plasmid also contains opine catabolism genes that allow the bacterium to use these opines as food. This is advantageous for the bacterium in nature, but it's irrelevant for laboratory transformation. Scientists replace the opine synthesis genes with their gene of interest. Since no opines are produced, the bacterial catabolism genes are not required for successful gene transfer.
Step 3: Conclusion
Opine catabolism genes benefit the bacterium after a natural infection but are unnecessary for T-DNA transfer in a laboratory.