Q.Genetically modified tobacco plants were produced using Agrobacterium vectors. Which property of Agrobacterium helps in carrying nematode specific genes into the host plant ? (A) Infectious for monocot plant ; has Ti plasmid (B) Infectious for dicot plant ; has Ti plasmid (C) Infectious for plants and animals ; has Ti plasmids (D) Infectious for monocot and dicot plants ; has cry gene

Agrobacterium tumefaciens is a bacterium widely used as a natural genetic engineer for plants. It possesses a large plasmid called the Ti plasmid (Tumour-inducing plasmid), which contains a segment known as T-DNA. This T-DNA is naturally transferred and integrated into the genome of host plant cells.

Agrobacterium tumefaciens primarily infects dicotyledonous plants, causing crown gall disease. Scientists leverage this natural gene transfer mechanism by modifying the Ti plasmid: the tumour-inducing genes are removed, and desired genes, such as those providing resistance against nematodes, are inserted into the T-DNA region. This engineered *Agrobacterium …

Genetic modification in plants involves introducing new genes to confer desirable traits, such as resistance to pests or improved nutritional value. A crucial step in this process is the delivery of the desired gene into the host plant's cells. This is where vectors come into play, acting as carriers for the genetic material. Among the most effective and widely used natural vectors in plant biotechnology is the bacterium Agrobacterium tumefaciens.

Agrobacterium tumefaciens is a soil-dwelling bacterium renowned for its unique ability to naturally transfer a segment of its DNA into plant cells. This natural genetic engineering capability is the foundation of its utility in creating genetically modified plants. In nature, Agrobacterium causes a plant disease known as crown gall, characterized by tumor-like growths on the stems and roots of infected plants.

The key to Agrobacterium's gene transfer ability lies in a large plasmid it carries, called the Ti plasmid (Tumor-inducing plasmid). Within this Ti plasmid, there is a specific segment of DNA known as T-DNA (Transfer DNA). When Agrobacterium infects a plant, it transfers this T-DNA from its Ti plasmid into the host plant's genome. Once integrated, the genes on the T-DNA direct the plant cells to produce hormones that cause uncontrolled cell proliferation (leading to gall formation) and synthesize specialized compounds called opines, which the bacterium uses as a food source.

Scientists have ingeniously harnessed this natural mechanism for genetic engineering. By modifying the Ti plasmid, they can remove the tumor-inducing genes from the T-DNA, rendering the bacterium non-pathogenic. In place of these genes, the desired gene of interest – such as nematode-specific genes for resistance – is inserted into the T-DNA region. When this modified Agrobacterium infects a plant, it delivers the engineered T-DNA, now carrying the beneficial gene, into the plant's genome without causing disease. The plant cells then express this new gene, leading to the desired trait.