Q.45 Which of the following statement(s) is/are CORRECT about Agrobacterium
tumefaciens?
(A) It contains tumor inducing plasmid
(B) It causes crown gall disease in dicotyledonous plants
(C) It is a Gram-positive soil bacterium
(D) It is used in generating transgenic plants
Agrobacterium tumefaciens in Plant Biotechnology: Correct Statements and Key Facts
Agrobacterium tumefaciens is a soil bacterium renowned for its natural genetic engineering capabilities in plants. The correct statements from the given options are (A), (B), and (D).
Correct Options
Options (A), (B), and (D) are correct about Agrobacterium tumefaciens.
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(A) True: It contains a tumor-inducing (Ti) plasmid, a large extrachromosomal DNA molecule (~200 kb) with T-DNA that transfers to plant cells, inducing tumors.
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(B) True: It causes crown gall disease, forming tumor-like galls at plant crowns, primarily in dicotyledonous plants via Ti plasmid integration.
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(D) True: Disarmed Ti plasmids make it a key tool for generating transgenic plants by inserting desired genes into the T-DNA region for stable plant genome integration.
Incorrect Option
Option (C) is false.
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Agrobacterium tumefaciens is a Gram-negative (not Gram-positive) rod-shaped soil bacterium, distinguished by its thin peptidoglycan layer and outer membrane.
Biological Mechanism
Agrobacterium tumefaciens infects wounded dicot plants, transferring T-DNA from the Ti plasmid into the host nucleus via type IV secretion, where it expresses oncogenes causing galls and opines for bacterial nutrition. In biotechnology, tumor genes are removed, allowing gene-of-interest insertion for crops like Bt cotton. This system works best in dicots but has been engineered for monocots.
