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ARABIDOPSIS THALIANA, A MODEL FLOWERING PLANT
The model organism most widely used in plant genetics and molecular biology is the weed Arabidopsis thaliana, wild mustard weed or mouse ear cress (Fig. 1.22). Plant research has typically lagged behind research on humans, but there is extensive interest. Growing different crops to feed the world population is incredibly important, and much money is invested in research on the crops most used for food, such as rice, soybean, wheat, and corn. These plants have huge genomes, and most are polyploid—even hexaploid (such as wheat). Therefore, a model organism is essential to learn the basic biology of plants. Arabidopsis
has much the same responses to stress and disease as crop plants. Moreover, many genes involved in reproduction and development are homologous to those in plants with more complex genomes.
Arabidopsis has many convenient features. First, it is easily grown and maintained in a laboratory setting. The plant is small and grows to match its environment. If there is plenty of space and nutrients, the plant can grow to over a foot in height and width. If the environment is a small culture dish in a lab, the plant will grow about 1 cm in height and width. At either size, the plant forms flowers and seeds. An entire generation from seed to adult to seeds is finished in 6–10 weeks, which is relatively quick for a plant. (Note that for corn or soybeans, only one generation can occur in the span of a summer.) In Arabidopsis, many seeds are produced on each plant, so aiding genetic analysis. Much like yeast, Arabidopsis can be maintained in a haploid state.
Arabidopsis has a small genome for a plant, containing only five chromosomes with a total of 125 Mb of sequence. The genome was completely sequenced in 2000, allowing researchers to identify about 25,000 genes and important sequence features. Rice has also been sequenced and has an estimated 40,000 to 50,000 genes. This tops the number of predicted human genes, and so rice (and doubtless many other plants) may be more “advanced” than us lowly humans.
Plant research also relies on a model organism to study. Arabidopsis thaliana is used because of its size, ease of growth, and small genome.
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