Question

The Ti plasmid, is often used for making transgenic plants. This plasmid is found in

• A. Yeast as a 2 $\mu$m plasmid
• B. Azotobacter
• C. Rhizobium of the roots of leguminous plants
• D. Agrobacterium

Answer 1

The correct option is D Agrobacterium

Agrobacterium tumefaciens is a soil plant pathogenic bacterium that carries Ti plasmid which carries the genes that can induce tumor in plants. It can transfer a particular segment of the tumor-inducing (Ti) plasmid into the nucleus of infected cells. The transferred T-DNA is then integrated into the host genome and transcribed with it. This ability of Agrobacterium tumefaciens to transfer the T-DNA in host genome is explored in genetic engineering to transfer the desired DNA segment, carrying the gene of the interest, into genome of selected organisms. Azotobacter is a genus of aerobic soil bacteria that can "fix" atmospheric nitrogen. There are six species of Azotobacter. They do not carry the Ti plasmid and hence can induce tumor in plants. Four types of plasmid vectors have been developed from yeast. They are namely yeast episomal plasmids (YEps), yeast replicating plasmids (YRps), yeast centromere plasmids (YCps), and yeast artificial chromosomes (YACs). They all have unique restriction sites, can replicate in $E$. $coli$ at high copy number and employ specific markers but do not carry Ti plasmid and can not induce tumors in cells. Rhizobium of the roots of leguminous plants serves to fix atmospheric nitrogen and lives in a symbiotic relationship i.e. do not harm the host cell. Correct option is "D".