How is DNA found in animal cells
The genome of a plant has been deciphered for the first time
Michael Seifert University communication
Eberhard Karls University of Tübingen
Publication in 'Nature' with the participation of Tübingen researchers
The inconspicuous plant Arabidopsis thaliana - in English thale cress - is a kind of model plant for geneticists all over the world, whose genes and their function are examined in detail. Now the genome of the thale cress and thus of the first plant has been completely deciphered. Several research institutions have been involved in gene sequencing since 1996 in the Arabidopsis Genome Initiative (AGI). The research results are published in today's issue of the journal Nature (908, December 14, 2000) in a joint effort by numerous scientists. Researchers from Tübingen under the direction of Prof. Gerd Jürgens from the Center for Molecular Biology of Plants (ZMBP) also worked on the analysis of the genetic data.
The decoding of the thale cress genes, which are collectively referred to as the genome, was preceded by the genome sequencing of some bacteria and, with the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster, two animal creatures. The sequences of most human genes are also known from the HUGO project. The genetic material or genome of animals and plants is distributed on chromosomes. The genes are arranged on the chromosomes. They store some kind of instructions for making proteins. The numerous different proteins fulfill specific functions, for example in the structure of the cell, in energy metabolism and in the defense against pathogens.
The nuclei of the cells of the Arabidopsis plants each contain five chromosomes. In total, the researchers found around 25,000 genes during sequencing. The decoding of the genome resulted in a long sequence of letters that symbolized the various building blocks of the genes. The sequence of letters alone does not offer researchers much insight if the function of the proteins they represent is not known. The analysis of the data, as it was done by the Tübingen working group when deciphering the Arabidopsis genome, therefore forms an important part of the research. A comparison with known genes of other living beings provides important information about the function of unknown genes. Structural similarities between the new gene sequences and those already known and stored in databases can be determined using special computer programs. Often the meaning or function of the unexplored genes can then be predicted.
In evolution, the unicellular precursors of animals and plants separated from one another at an early stage. Only the unicellular organisms have incorporated a bacterium that drives photosynthesis. This gave rise to the chloroplast, which today enables plants to use sunlight as an energy source. Most of the bacterial genome later migrated from the chloroplast into the cell nucleus. This finding is confirmed by the genome analysis: A considerable part of the plant genetic material shows similarities to the genome of photosynthetically active bacteria. Plant cells also differ in their organization from animal cells, e.g. by a cell wall that prevents their mobility. To what extent such differences are reflected in the genetic equipment, Prof. Jürgens has examined together with former employees who are now working at the Bioinformatics Institute MIPS in Munich. What all real cells have in common is a cell structure and machinery with which proteins and other molecules are sorted and transported to their destinations in the cell. Arabidopsis also has the necessary genetic information. However, the connection of the cell structure to the surface of the cell differs, and Arabidopsis apparently lacks the information to produce the connection molecules known from animals. Cell division is also completely different. In animals, the cell constricts from the outside in, thus separating the daughter cells from one another. Plant cells, on the other hand, form the separating membrane between the daughter cells by fusing membrane vesicles on a special cell structure from the inside out. The genome analysis now shows that Arabidopsis lacks the information for the constriction. Conversely, Arabidopsis has special genetic information for the fusion of the membrane vesicles.
But the genome analysis of thale cress also offered the scientists a few surprises. The genome of Arabidopsis seemed to have doubled in part over the course of the plant's development. However, the two copies do not contain exactly the same genes. How the plant organizes the use of the parallel instructions is questionable. In addition to the genes similar to animals and bacteria, a high proportion of the plant's own genes were found. The geneticists hope that their research will yield findings that can also be used to improve the genetic engineering of cereal plants, for example.
Prof. Gerd Juergens
Center for Molecular Biology of Plants
On the morning spot 1
72076 Tuebingen, Germany
Tel. 0 70 71/2 9788 87
Fax 0 70 71/29 57 97
Features of this press release:
Biology, information technology, animal / land / forest
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