Design a transgenic tomato plant that expresses the *Bacillus thuringiensis* (Bt) Cry1Ac protein to confer resistance against the tomato fruit borer. Discuss (i) the choice of vector and promoter, (ii) the method of gene insertion, (iii) the selectable marker, (iv) the regeneration protocol for obtaining transgenic plants, and (v) the key biosafety considerations that must be addressed before commercial release.
Answer
A suitable design uses a binary Ti‑plasmid vector (e.g., pCAMBIA) with the CaMV35S promoter driving the Cry1Ac gene, Agrobacterium‑mediated transformation for gene insertion, kanamycin resistance as the selectable marker, tissue‑culture regeneration of shoot and root from cotyledon explants, and thorough biosafety assessment including environmental impact, non‑target effects, and gene‑flow monitoring.
Step-by-step solution
- Select a binary vector (e.g., pCAMBIA series) that can replicate in *E. coli* for cloning and in *Agrobacterium tumefaciens* for plant transformation.
- Insert the Cry1Ac coding sequence downstream of a strong, constitutive plant promoter such as CaMV35S; include a terminator like NOS.
- Add a selectable marker gene (e.g., nptII conferring kanamycin resistance) on the same T‑DNA region for efficient selection of transformed cells.
- Introduce the recombinant binary vector into *Agrobacterium* by electroporation.
- Co‑cultivate sterilized tomato cotyledon explants with the engineered *Agrobacterium* for 2–3 days to allow T‑DNA transfer.
- Transfer explants to selection medium containing kanamycin and a bacteriostatic agent (e.g., cefotaxime) to eliminate *Agrobacterium* and select transformed cells.
- Induce shoot regeneration by supplementing the medium with cytokinin (BAP) and auxin (NAA) under controlled light conditions.
- Root the regenerated shoots on medium with reduced cytokinin and appropriate auxin (IBA).
- Acclimatize the plantlets in a greenhouse and confirm integration of Cry1Ac by PCR and Southern blot analysis.
- Evaluate resistance by challenging transgenic lines with the tomato fruit borer and scoring mortality or damage compared to wild‑type controls.
- Conduct biosafety assessments: (a) test for expression stability across generations, (b) assess potential effects on non‑target insects and soil microbes, (c) evaluate gene flow to wild relatives, and (d) perform compositional analysis of the fruit to ensure food safety.
- Prepare a regulatory dossier summarizing molecular characterization, efficacy data, and biosafety studies before seeking commercial approval.
Common mistake: Omitting a selectable marker or using an animal promoter that is weak in plants
Concept tested: Development of transgenic crop for pest resistance
Published · How this solution was prepared and checked
← All Biotechnology and Its Applications questions