Lesson 6 of 11 · 7 min
Plant and animal vectors, and competent hosts
NCERT §9.2.2 (iv), §9.2.3
Next door, the plant team is working with a soil bacterium that gives plants tumours. Kavya's own bench has a bucket of ice and a water bath set to 42°C.
The lesson in notes
In short
Methods of moving genes into plants and animals were learnt from bacteria and viruses. These pathogens deliver genes into eukaryotic cells and make the cells serve them.
Agrobacterium tumefaciens, a pathogen of several dicots, delivers a piece of DNA called T-DNA. The T-DNA turns normal plant cells into a tumour that makes chemicals the pathogen needs. Retroviruses turn normal animal cells cancerous.
The tumour-inducing (Ti) plasmid of Agrobacterium has been modified into a cloning vector. It no longer causes disease but still delivers chosen genes into many plants. Disarmed retroviruses deliver desirable genes into animal cells.
DNA is hydrophilic and cannot pass through cell membranes, so bacteria must first be made competent to take it up.
Cells are treated with a set concentration of a divalent cation, calcium for example, which helps DNA get in through pores in the cell wall more efficiently.
The cells are incubated with recombinant DNA on ice, placed briefly at 42°C (heat shock), and returned to ice. This lets them take up the DNA.
Micro-injection: recombinant DNA is injected directly into the nucleus of an animal cell.
Biolistics (the gene gun), used for plants: tiny particles of gold or tungsten, coated with DNA, are fired into the cells at high velocity.
Disarmed pathogen vectors transfer recombinant DNA into the cells they are allowed to infect.