19.1.6: Arabidopsis Thaliana - A Model Organism

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Arabidopsis Thaliana has become to plant biology what Drosophila melanogaster and Caenorhabditis elegans are to animal biology. Arabidopsis is an angiosperm, a dicot from the mustard family (Brassicaceae). It is popularly known as thale cress or mouse-ear cress. While it has no commercial value - in fact is considered a weed - it has proved to be an ideal organism for studying plant development.

alt — Figure 19.1.6.1: *Arabidopsis Thaliana.* Photo courtesy of Nicole Hanley Markelz of the Plant Genome Research Outreach Program at Cornell University.

Some of its advantages as a model organism:

It has one of the smallest genomes in the plant kingdom: 135 x 10⁶ base pairs of DNA distributed in 5 chromosomes (2n = 10) and almost all of which encodes its 27,407 genes.
Transgenic plants can be made easily using Agrobacterium tumefaciens as the vector to introduce foreign genes.
The plant is small - a flat rosette of leaves from which grows a flower stalk 6–12 inches high.
It can be easily grown in the lab in a relatively small space.
Development is rapid. It only takes 5– 6 weeks from seed germination to the production of a new crop of seeds.
It is a prolific producer of seeds (up to 10,000 per plant) making genetics studies easier.
Mutations can be easily generated (e.g., by irradiating the seeds or treating them with mutagenic chemicals).
It is normally self-pollinated so recessive mutations quickly become homozygous and thus expressed.

Other members of its family cannot self-pollinate. They have an active system of self-incompatibility. Arabidopsis, however, has inactivating mutations in the genes — SRK and SCR - that prevent self-pollination in other members of the family.

However, Arabidopsis can easily be cross-pollinated to do genetic mapping and produce strains with multiple mutations.

Many of the findings about how plants work - described throughout these pages - were learned from studies with Arabidopsis.