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Use of Ti and Ri as vectors

Introduction:

  • Ti (Tumor-inducing) plasmids from Agrobacterium tumefaciens and Ri (Root-inducing) plasmids from Agrobacterium rhizogenes are commonly used as vectors in plant genetic engineering.

  • They are modified to deliver foreign genes into plant cells, enabling the development of transgenic plants with desirable traits.


1. Why Ti and Ri Plasmids are Used as Vectors:

  • These plasmids naturally transfer a portion of their DNA (T-DNA) into the plant genome.

  • Scientists exploit this natural mechanism to introduce specific genes instead of the tumor or root-inducing genes.


2. Structure of Ti and Ri Plasmids for Vector Use:

  • T-DNA Region:

    • The T-DNA is modified to carry the desired gene.

    • Tumor-inducing (Ti) or root-inducing (Ri) genes are removed and replaced with foreign genes.

  • Vir (Virulence) Genes:

    • Essential for transferring the T-DNA into the plant cell.

    • Usually retained because they facilitate the T-DNA transfer process.

  • Selectable Marker Genes:

    • Added to identify transformed cells (e.g., antibiotic resistance).


3. Steps in Using Ti and Ri Plasmids as Vectors:

  1. Gene Insertion:

    • The desired gene is inserted into the T-DNA region of the plasmid.

  2. Transformation of Agrobacterium:

    • The modified plasmid is introduced back into Agrobacterium cells.

  3. Infection of Plant Tissues:

    • Plant tissues (e.g., leaves, stem, or callus) are infected with the transformed Agrobacterium.

  4. Integration into Plant Genome:

    • The Vir genes help transfer the T-DNA, containing the foreign gene, into the plant genome.

  5. Selection and Regeneration:

    • Transformed plant cells are selected using marker genes (e.g., antibiotic resistance).

    • The selected cells are regenerated into whole plants through tissue culture.


4. Applications of Ti and Ri Plasmid Vectors:

  1. Development of Transgenic Crops:

    • Introducing genes for pest resistance, herbicide tolerance, and enhanced nutrition.

    • Example: Bt cotton with a gene for insect resistance.

  2. Production of Pharmaceutical Proteins:

    • Plants engineered to produce vaccines or therapeutic proteins.

  3. Study of Gene Function:

    • Used in research to understand the role of specific genes in plants.

  4. Root Culture Studies (Ri Plasmid):

    • Ri plasmids are particularly useful for studying root development and producing valuable secondary metabolites in root cultures.


5. Advantages of Using Ti and Ri Plasmids as Vectors:

  • Efficient Gene Transfer: Natural ability to transfer DNA into plants.

  • Stable Integration: The foreign gene integrates into the plant genome and is passed on to the next generation.

  • Wide Host Range: Can be used with many different plant species.

  • Low Cost and Versatility: Easy to modify for different genes and traits.


6. Limitations:

  • Limited to Dicots: Agrobacterium naturally infects mainly dicotyledonous plants (e.g., tomatoes, potatoes). Monocots (e.g., wheat, rice) require special techniques.

  • Regulatory and Safety Concerns: Transgenic plants require extensive testing and regulatory approval.


Conclusion:

  • Ti and Ri plasmids are essential tools in plant biotechnology, acting as vectors for transferring foreign genes into plant genomes.

  • Their natural ability to integrate T-DNA into plants makes them ideal for developing transgenic crops with improved traits, contributing to advancements in agriculture and pharmaceutical production

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