Q.What modification is done on the Ti plasmid of Agrobacterium tumefaciens to convert it into a cloning vector?

The Ti plasmid of Agrobacterium tumefaciens naturally transfers a segment of its DNA, known as T-DNA, into dicot plant cells, causing tumor formation due to specific tumor-inducing genes within this segment. To convert it into a cloning vector, these tumor-inducing genes present in the T-DNA region are removed. This modification disarms the plasmid, making it non-pathogenic while preserving its ability to deliver foreign DNA into plant cells. The desired gene can then be inserted into the modified T-DNA region, allowing its transfer and integration into the plant ge …

Agrobacterium tumefaciens is a fascinating bacterium, often referred to as nature's genetic engineer for plants. In its natural state, this soil bacterium causes a disease known as crown gall in many dicotyledonous plants. It achieves this by transferring a specific segment of its plasmid DNA, called T-DNA (Transfer DNA), into the host plant cells. Once inside the plant cell, this T-DNA integrates into the plant's genome, leading to the proliferation of cells and the formation of tumors, which are the characteristic galls. The genes within this T-DNA direct the plant cells to produce specific compounds (opines) that the bacterium uses as food.

The mechanism by which Agrobacterium transfers its T-DNA into plant cells is highly efficient and precise. This natural ability to deliver DNA into plant genomes makes the Ti (Tumor-inducing) plasmid an incredibly attractive tool for plant genetic engineering. However, for it to be useful as a cloning vector, its disease-causing properties must be eliminated.

The primary modification done on the Ti plasmid to convert it into a cloning vector involves removing the genes responsible for tumor formation. These undesirable genes are located within the T-DNA region of the plasmid.

Once these pathogenic genes are removed, the modified T-DNA region becomes a suitable site for inserting the gene of interest that a biotechnologist wishes to introduce into a plant. The rest of the Ti plasmid, including the vir (virulence) genes, is retained. The vir genes are crucial because they encode the proteins necessary for the processing and transfer of the T-DNA from the bacterium into the plant cell. They act in trans, meaning they can facilitate the transfer of any DNA flanked by the T-DNA border sequences, even if the vir genes themselves are not on the transferred DNA. …

Method 2 -- compare the wild-type and engineered plasmid as a before/after map