Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
tumefaciens?
Which of the following statements) is/are CORRECT about Agrobacterium
Options:
(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
Official Answer Key:
A,B,D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2021 Q.45)**
**1. Governing Concept**:
- **Topic**: Plant Biotechnology & *Agrobacterium tumefaciens* Biology
- *Agrobacterium tumefaciens* is a soil phytopathogenic bacterium that induces crown gall tumors in dicots:
- Carries the large **Tumor-inducing (Ti) plasmid**.
- Wounded plant tissues release phenolic wound compounds (e.g., **acetosyringone**), which are sensed by the membrane receptor kinase **VirA**, which phosphorylates **VirG** (two-component regulatory system) to induce the *vir* regulon.
- The **T-DNA** (transferred DNA) region is flanked by 25 bp direct repeats (left and right borders).
- T-DNA contains genes for **auxin** (*iaaM, iaaH*) and **cytokinin** (*ipt*) biosynthesis (inducing unorganized gall proliferation) and **opines** (e.g. octopine, nopaline), which serve as exclusive carbon and nitrogen sources for the bacterium.
**2. Option Analysis**:
- **Option (A) [It transfers T-DNA from the Ti plasmid into the host plant genome] is CORRECT**: The hallmark biological feature of *A. tumefaciens*.
- **Option (B) [Phenolic wound compounds like acetosyringone induce vir gene expression] is CORRECT**: Activates the VirA/VirG sensory pathway.
- **Option (C) is INCORRECT**: Monocots are generally recalcitrant to natural *Agrobacterium* infection compared to dicotyledonous plants.
- **Option (D) [T-DNA encodes enzymes for auxin, cytokinin, and opine synthesis] is CORRECT**: Directs host plant cells to overproduce phytohormones and bacterial nutrients.
**3. Final Answer**:
- **Correct Options**: **A, B, D**
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