Arabidopsis thaliana
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| Arabidopsis thaliana (L.) Heynh. |
Arabidopsis thaliana, Thale Cress, or Mouse-ear Cress, a small flowering plant related to cabbage and mustard, is one of the model organisms for studying plant sciences, including genetics and plant development. It plays the role for agronomy that mouse and fruit fly (Drosophila) play in human biology.
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Model organism
Arabidopsis is not a plant with major agronomic significance, however, there are several advantages that resulted in it becoming a model organism for understanding the genetic, cellular and molecular biology of flowering plants.
Primarily the small size of the genome (125 Mb) made it useful for genetic mapping and ultimately more easy to sequence. The genome of Arabidopsis, consisting of five chromosomes, has been sequenced. The finished sequence was published in 2000 and represented the first sequenced plant genome. At 125 million base pairs, it is a small genome for a plant species. Since the sequencing of the genome, much work has been done to assign a function to the 26,000 genes so far found in the genome, many of which have no known function.
The small size and rapid life cycle were also important traits for selecting Arabidopsis as a model organism. From germination to mature seed is approximately six weeks. Its small size is convenient for cultivation in a small space and it produces a large amount of seed.
Finally, plant transformation in Arabidopsis is easy utilizing Agrobacterium tumefaciens to transfer DNA to the plant genome.
History of Arabidopsis as a model organism
The first mutant in Arabidopsis was documented by Alexander Braun in 1873, describing a mutant plant now known as AGAMOUS, that was cloned in 1990. Yet the potential of Arabidopsis as a model organism was not documented until 1943. Friedrich Laibach had first published the chromosome number for Arabidopsis in 1907 and came to realise its potential as a model organism that he first proposed in 1943. His student Erna Reinholz published her thesis on Arabidopsis in 1945 that described the first collection of Arabidopsis mutants that they generated using x-ray mutagenesis. Laibach continued his important contributions to Arabidopsis research by collecting a large number of ecotypes. With the help of Albert Kranz, these were organised into the current ecotype collection that contains over 750 natural accessions of Arabidopsis thaliana from around the world.
In the 1950’s and 1960’s John Langridge and George Rédei played an important role in establishing Arabidopsis as a useful organism for biological experiments in the laboratory setting. Rédei's wrote several scholarly reviews on Arabidopsis that were instrumental in introducing the model to the scientific community.
The start of the Arabidopsis research community dates to a newsletter called Arabidopsis Information Service that was established in 1964. The following year the first International Arabidopsis Conference was held in Göttingen, Germany in 1965.
In the 1980’s Arabidopsis started to become widely used in plant research laboratories around the world. It was one plant of several candidates that included maize, petunia and tobacco. The latter two were attractive since they were easily transformable, while maize was already a well established genetic model for plant biology. The breakthrough year for Arabidopsis as the preferred model plant came in 1986 when T-DNA mediated transformation was first published and this coincided with the first gene to be cloned and published.
Research
Non-mendelian inheritance
Breaking research (2005) from scientists at Purdue University studying Arabidopsis discovered what one termed a "parallel path of inheritance", an alternative to previously known mechanisms of DNA repair. This phenomena was observed in mutations of a gene named HOTHEAD. Plants mutant in this gene exhibit organ fusion and pollen can germinate on all plant surfaces, not just the stigma. After spending over a year eliminating simpler explanations, studies indicated that the plants "cached" versions of their ancestors genetic code going back at least four generations. Arabidopsis was able to use the earlier records as templates to correct the HOTHEAD mutation and other SNP's in the genome. Early hypotheses propose that the record may be RNA-based. [1]
Light sensing
The five photoreceptors phytochrome A, B, C, D and E mediate red light based phototropic response. Understanding the function of these receptors has helped plant biologists understanding the signalling cascades that regulate photoperiodism, germination, de-etiolation and shade avoidance in plants.
Arabidopsis has been used extensively in the study of the genetic basis of phototropism, chloroplast alignment, and stomatal aperture and other blue light-influenced processes. These traits respond to the blue light in the environment and this light is percieved by the phototropin light receptors. Another blue light receptor known as cryptochrome is also know to function in Arabidopsis and is especially important for light entrainment to control the plants circadian rhythms.
Light response have even been found in roots that were not thought to respond to light. While gravitropic response of Arabidopsis root organs is the predominant tropic effect in these organs, specimens treated with mutagens and then selected for the absence of gravitropic action have shown both negative phototropic response to blue or white light, and positive phototropic response to red light.
See also
External links
- The Arabidopsis Information Resource (TAIR)
- Nature Gateway on Arabidopsis
- The Arabidopsis Book - comprehensive electronic book
- Arabidopsis thaliana: another "model organism"
- Salk Institute Genomic Analysis Laboratory
- Danish biotech firm Aresa Biotection uses a genetically modified Thale Cress to detect compounds like explosives (land mines)
