Arabidopsis thaliana (thale cress)
Thale cress hit the headlines in 2000, when this small garden weed became the first plant to have its genome sequenced.
Composite SEM image of dissected inflorescence of Arabidopsis thaliana, with different organs artificially coloured: pale green = perianth (sepals and petals); yellow = stamens; red = ovary (Image: P.J.Rudall)
thale cress, mouse ear cress
This species is common and widespread. It is not threatened and therefore rated by the IUCN as Not Evaluated (NE).
A pioneer of rocky ground, dunes, open sandy and calcareous habitats; also found in a wide range of disturbed habitats, including as a weed of gardens, waste ground and along railway lines.
About this species
Arabidopsis thaliana was the first plant to have its entire genome sequenced (in 2000), and is widely used in molecular and developmental biology as the archetypal angiosperm (flowering plant) model organism. The haploid chromosome number of A. thaliana is unusually small (n=5). The great wealth of different types of comparative data that have been compiled about this inconspicuous little plant make it immensely significant in every aspect of plant biology.
Geography & Distribution
This species occurs naturally throughout most of Europe to central Asia and is is also naturalised worldwide. It is abundant throughout the British Isles, except in the far north of Scotland, the Outer Hebrides and western Ireland. It grows on rocky ground, sand dunes and calcareous sites. It is especially common as a weed of gardens and waste ground, and often grows in the ballast of railway lines.
Arabidopsis thaliana is a small annual herb, which has basal leaves with short petioles (leaf stalks). The flowers are small, with four free, green, glabrous (hairless) sepals alternating with four free, white, spatulate petals. Each flower has six stamens (male organs), consisting of four median and two, longer, lateral stamens. The gynoecium (female part) is superior, and consists of two fused carpels, with locules separated by a false septum bearing about 50+ ovules. Nectaries are present at the stamen bases.
Used widely as a model in plant genetic studies (see sections below, 'First plant to have genome sequenced' and 'ABCs of flowers') and, futuristically, in space research (see 'Out of this world!'). In traditional medicine in India the leaves and flowers are used for treating asthma, throat and chest complaints.
Although this 'weed' would not be selected for cultivation by many gardeners, it has frequently been cultivated for scientific experiments. Thale cress has been grown for this reason at Wakehurst Place. For experimental use it is usual to grow the plants in a medium containing salts, sucrose and vitamins, rather than compost.
For any other purpose the species prefers open, light conditions in free-draining soil such as sand or sandy loam. The tiny seeds should be sown on the surface of the substrate. This can be carried out in autumn for plants that will flower the following March to June in the UK. As an annual, the plants will die and usually self-sow for the following year. Seed will survive in the soil for many years and plants are likely to reappear for a long time afterwards.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Number of seed collections stored in the Millennium Seed Bank: 1
Seed storage behaviour: Orthodox (the seeds of this plant survive being dried without significantly reducing their viability, and are therefore amenable to long-term frozen storage such as at the MSB)
Germination testing: Successful
First plant to have genome sequenced
The small garden weed Arabidopsis thaliana hit the headlines in 2000 when it became the first plant to have its genome sequenced. The landmark paper published in Nature magazine estimated the genome size of Arabidopsis to be about 125 Mb, based partly on new DNA sequencing data. Many scientists had previously estimated its genome size to be much larger. To resolve this discrepancy, scientists at Kew and Texas A & M University (USA) compared the genome size of Arabidopsis with the completely sequenced genome of the nematode worm Caenorhabdites elegans (c. 100 Mb) using flow cytometry (a technique for examining microscopic particles such as chromosomes). The results showed the genome size in Arabidopsis to be c. 157 Mb (about 25% larger than the estimate based partly on DNA sequencing). Extra DNA in unsequenced gaps is mainly composed of highly repeated (possibly junk) sequences but may also include some informational genes.
ABCs of flowers
Arabidopsis thaliana was important in the formulation of Coen and Meyerowitz’s influential ABC model of flower development published in Nature magazine in 1991. The ABC model used observations of laboratory-induced mutants of Arabidopsis and Antirrhinum with defects in floral organ development to show how different genes interact to regulate flower development. The model divides the genes into three classes, depending on which organs they regulate. Class A genes control sepals and petals, class B genes petals and stamens, and class C genes regulate stamens and carpels.
Out of this world!
Arabidopsis thaliana has the unique distinction of being the first plant to have undergone its complete lifecycle in space - from seed germination, flowering to setting seed - aboard the Mir space station in 1997.
Arabidopsis thaliana is also being used in experiments on the International Space Station to determine genes activated or in some way regulated by gravity. According to NASA this could have practical applications in agriculture (e.g. greater understanding of root and shoot architecture, and in understanding how plant growth is regulated in space). So, if our species was to colonise other planets in the future, our success might well owe a great deal to research undertaken on this tiny, and often overlooked, plant.
Seed longevity of this species
Kew’s collaborative research with Horticulture Research International and the Nottingham Arabidopsis Stock Centre has modelled the effects of moisture content and temperature on seed longevity in two ecotypes (subdivisions adapted to specific environmental conditions) of Arabidopsis thaliana. This study on the ‘lab-rat’ of the plant kingdom makes it possible to predict longevity under a range of storage conditions and to identify particularly short- or long-lived lines. The modelling process also advances the statistical understanding of how seed storage data should be analysed.
References & Credits
Asolkar, L.V., Kakkar, K.K. and Chakre, O.J. (1992). Second Supplement to Glossary of Indian Medicinal Plants with Active Principles Part – 1 (A-K) (1965-1981). Publications & Information Directorate (CSIR), New Delhi.
Bennett, M. (2003). Arabidopsis genome size. Kew Scientist. Issue 23: 3.
Coen, E. S. and Meyerowitz, E.M. (1991). The war of the whorls: genetic interactions controlling flower development. Nature 353: 31–37.
Harberd, N. (2006). Seed to Seed. The Secret Life of Plants. Bloomsbury, London.
Hay, F. (2003). Arabidopsis seed longevity. Kew Scientist. Issue 23: 3. Click here for the PDF.
Preston, C.D., Pearman, D.A. and Dines, T.A. (eds) (2002). New Atlas of the British and Irish Flora: An atlas of the vascular plants of Britain, Ireland, the Isle of Man and the Channel Islands. Oxford University Press, Oxford.
The Arabidopsis Genome Initiative (2000). Analysis of the genome sequence of the flowering plant Arabidopsis thaliana. Nature. 408: 796-815.
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