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FIGURE 16.24 Expression of Genes on T-DNA

Survival of Agrobacteria in the plant requires space for them to grow and a carbon source to provide energy. The genes of the T-DNA region trick the plant cell into providing these factors. The genes for auxin and cytokinin are growth factors that induce the plant cells to grow at the site of infection, providing the space. The opine is a carbon source for the bacteria, providing a constant food supply.

Auxin Cytokinin

Auxin Cytokinin

Promotes Promotes plant cell plant cell growth division

Used as nutrient by

Agrobacterium

Promotes Promotes plant cell plant cell growth division

Used as nutrient by

Agrobacterium ferred into the plant are inserted in their place. In practice, Agrobacterium carrying an engineered Ti-plasmid is used to transfer genes of interest into plants using plant tissue culture.

In addition to inserting external genes into plants the Ti-plasmid system may be used for analysis of plant gene function. Insertion of T-DNA into the plant chromosome may disrupt a plant gene if insertion occurs into the coding sequence (or essential regulatory sequences). The model plant, Arabidopsis thaliana, has been used to generate a set of gene knockouts by random insertion of T-DNA. The locations of nearly 90,000 such insertions has been determined (as of 2003). These include insertions into about 22,000 of the estimated 29,500 genes of Arabidopsis. These insertions may be used to investigate the functions of the inactivated genes by comparing the knockout mutants with the parental wild type plant.

Many yeast strains contain a small multicopy plasmid, the "2 micron circle".

Flippase catalyses inversion of the DNA located between its recognition sites.

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