Question

Agrobacterium tumefaciens contains a large plasmid, which induces tumour in the plants. It is termed as
A. Ti plasmid
B. Ri plasmid
C. Recombinant plasmid
D. Shine- Dalgarno sequence

Answer 1

Tumor-producing Agrobacterium species are pathogenic and do not benefit the plant. It is a rod-shaped, Gram-negative soil bacterium. Causative symptoms are generated by the insertion of a small strain of DNA from a plasmid into the plant cell, which is incorporated at a semi-random location into the plant genome.

Complete answer:
To answer this question, first, we need to know about the Agrobacterium tumefaciens. Agrobacterium tumefaciens is a pathogen found in plants with the ability to carry oncogenic DNA segments bearing on a huge plasmid known as the Ti plasmid to be responsive to plant cells.

Now, let us find the solution from the option.
Agrobacterium tumefaciens is a plant pathogenic bacterium that bears Ti plasmid. It can deliver a specific segment of the tumor-inducing (Ti) plasmid into the nucleus of contaminated cells. When Ti plasmid transects the host plant, crown gall tumor is induced, transferring the T-DNA region. Those cells transfected with the T-DNA are induced to grow as well as to produce opine that the bacteria feed on. Agrobacterium rhizogenes is a Gram-negative soil borne bacterium, which causes hairy root disease.

The plasmid of A. rhizogenes is known as the Ri-plasmid (pRi). The pRi have extensive functional homology with the pTi. A clear segment of DNA of pRi is delivered to the plant genome, during infection, moderated by another segment on the plasmid the virulence (vir) region.

Recombinant plasmid is an engineered plasmid carrying gene of interest from a foreign source.

The sequence (AGGAGGU) present slightly upstream from the initiation sequence (AUG) on the messenger RNA of prokaryotes is complementary to the 16S ribosomal RNA and is referred to as the Shine-Dalgarno sequence. It recruits the ribosome to the mRNA to initiate protein synthesis.

Thus, the correct option is A. i.e. Ti plasmid.

Note: Ti plasmid bearing segment of Agrobacterium produces not only plant tumor but also generates many amino acid and sugar phosphate stimulates known as opines. The transformed plant cell releases opines, which can then be taken and catabolized for utilization as a nutrient by the contaminating bacterium. The Ti plasmid bears the genes for opine production by plant cells and also carries the metabolising genes.