Arabidopsis Thaliana
Arabidopsis thaliana, common name thale cress or mouse ear cress, has revolutionized research in basic plant biology over the last 30 years. The number of research papers on this species grew from just a trickle before 1970 to more than 2000 in the year 2000. Arabidopsis research has impacted many other areas of research in molecular biology, cellular biology, pathogenesis, flower development, hormone physiology, gene regulation, population genetics and ecology. While Arabidopsis does not serve as a food source, results from research on the plant can be applied to other plants.
A member of the mustard family or Brassicaceae, Arabidopsis occurs globally in the northern hemisphere, generally in cold to moderate climates. Hundreds of ecotypes or strains have been collected from Asia, Europe, north Africa and north America. The most commonly used ecotypes are Columbia, Landsberg and Wf, sometimes in the erecta(ital) form with a dwarf, stocky appearance. Arabidopsis is a winter annual with a rosette growth habit -- in the vegetative state, its leaves are bunched around a short stem close to the ground. When the plant flowers, the stem rapidly elongates, or bolts, to a height of up to 40 cm, and produces clusters of small white flowers, each containing four petals. The fruit is a long, pod-like structure called a silique.
Arabidopsis has a number of features that make it an ideal or model research plant. Its small size means it's easy to grow in quantity even in limited space, including indoors under lights. From seed germination to seed set, the plant takes 6-8 weeks to mature, which means researchers can study several generations per year. Combined with the fact that it can be readily mutagenized, Arabidopsis is a good genetic system test subject
Arabidopsis thaliana, has a haploid set of only five chromosomes, with a small nuclear genome consisting of 125 million base pairs, relatively little repetitive DNA and few transposable elements (about 10%) compared to plants such as maize. The completed genome sequence, consisting of 25,498 genes, was announced in the December, 2000 issue of Nature.
The National Science Foundation recently launched Project 2010 to define the function of all of Arabidopsis' genes within this decade.
Despite its small size and trim genome, Arabidopsis does everything any other flowering plant does, which is why many plant biologists find it useful. Arabidopsis has other advantageous features. The small size of its organs means that certain morphological studies that would be impossible with larger plants can be done with Arabidopsis, such as visualization of microtubules in intact roots using fluorescence microscopy. Young roots have a simple internal anatomy that facilitates studies of meristem organization and pattern formation, with an epidermis, a two cell layered cortex including endodermis, single cell layer pericycle, and vascular cylinder. External root hairs occur in a pattern governed by the arrangement of underlying cortical cells. Unfortunately, Arabidopsis' diminutive size can also make it difficult to manipulate. Care must be taken in processing roots for cytology, and cross pollination is tedious as it requires emasculation of small flowers (the plant is self-fertile).
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