Thale cress, native to temperate regions of the Old World northern hemisphere, is now established in suitable, disturbed habitats globally. It is no use as either human food or medicine but has become a model for all aspects of experimental botanical research ranging from population and evolutionary biology through physiology and biochemistry to cell and developmental biology.
German botanists have investigated thale cress for more than 400 years. In 1588, an obscure account of the Harz forest flora, by the Thuringian physician Johannes Thal, was published posthumously. Tucked away among the woodcuts is the first illustration of a diminutive plant Thal called 'Pilosella siliquata'. In 1753, Carolus Linnaeus used Thal's illustration when he described Arabis thaliana, which, about one century later, was transferred to the genus Arabidopsis.
However, documenting diversity is not enough. People want to understand how plants live, therefore experimentation must augment descriptive plant science. By the early twentieth century, when Friedrich Laibach was searching for a plant cytological model, the experimental approach was firmly established. For some reason, Laibach chose thale cress but abandoned it when he discovered it had tiny chromosomes. However, in Nazi Germany, Laibach and his students started to use thale cress to investigate the mutagenic effects of radiation and build a collection of mutants. After the war, Laibach continued to build his collection so that it encompassed thale cress ecotypes from across the globe. By the mid-1960s, the case for thale cress as a model plant was strong. By the late-1980s, with the backing of national and international funding agencies, the global scientific community embraced the advantages of cooperation and the thale cress model.
Thale cress is an excellent model since it has one of the smallest plant nuclear genomes (c. 157 million base pairs divided across five chromosomes) known, the genome has been fully sequenced and functions assigned to tens of thousands of the encoded genes and proteins. For genetic research, the plant's small physical size makes it convenient for growing plants in vast numbers, whilst the short life cycle (c. six weeks) means many generations can be produced in a single year. Thale cress regularly sets large quantities of selfed seed but it may be readily crossed. Furthermore, it can be routinely transformed to create genetically modified, experimental plants. Importantly, data and genetic information are shared among research groups, whilst seed and DNA stocks are readily available through international resource centres.
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