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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