Introduction:
Ti (Tumor-inducing) plasmids and Ri (Root-inducing) plasmids are naturally occurring plasmids found in Agrobacterium species.
These plasmids are widely used in genetic engineering to transfer genes into plants, making them essential tools in creating transgenic plants.
1. Ti Plasmid (Tumor-inducing Plasmid):
Found in Agrobacterium tumefaciens.
Responsible for causing crown gall disease in plants.
Key Features:
T-DNA (Transfer DNA):
A segment of the plasmid that gets transferred into the plant genome.
Contains genes responsible for tumor formation and opine production (nutrient source for bacteria).
Vir (Virulence) Genes:
Located outside the T-DNA.
Help in transferring the T-DNA into the plant cell.
Opine Catabolism Genes:
Enable the bacterium to utilize opines produced by the infected plant cells.
Border Sequences:
Mark the boundaries of the T-DNA.
Essential for precise T-DNA transfer.
Selectable Marker Genes:
Often modified to include genes for antibiotic resistance or herbicide tolerance for selecting transformed plants.
2. Ri Plasmid (Root-inducing Plasmid):
Found in Agrobacterium rhizogenes.
Causes the formation of hairy roots in plants.
Key Features:
T-DNA Region:
Contains genes responsible for inducing root formation.
Unlike the Ti plasmid, it promotes root growth instead of tumors.
Root-Inducing Genes (rol genes):
These genes (rolA, rolB, rolC, and rolD) regulate root development and growth.
Virulence (Vir) Genes:
Similar to Ti plasmid, involved in transferring T-DNA into the plant cell.
Opine Genes:
Control the production of specific opines in the transformed plant roots.
Border Sequences:
Define the region of T-DNA that gets integrated into the plant genome.
3. Differences between Ti and Ri Plasmids:
4. Importance in Genetic Engineering:
Gene Transfer Vectors:
Ti and Ri plasmids are modified to serve as vectors for transferring foreign genes into plants.
Transformation Efficiency:
High efficiency in integrating T-DNA into the plant genome.
Stable Integration:
Once integrated, the foreign gene remains stable across plant generations.
Conclusion:
Ti and Ri plasmids play crucial roles in plant genetic engineering.
Ti plasmids are mainly used for introducing genes into plants to produce transgenic crops, while Ri plasmids are valuable for studying root development.
Their ability to transfer genes makes them essential tools for crop improvement and biotechnology research.