Arabidopsis only occurs in the northern hemisphere. The researchers in Cologne together with their colleagues in other countries have found samples of semi-dwarf Arabidopsis in 23 locations throughout Europe, Asia, and Japan. Using genetic crossbreeding experiments, they have shown that this characteristic can be traced back to a change in the GA20ox1 gene in most of the plant specimens gathered. This gene is especially interesting in Arabidopsis, as mutations only cause the semi-dwarfism and have no further negative effects on the performance of the plants, even though gibberellin is an important plant growth factor. "The reason for this", according to Koornneef, "is that Arabidopsis possesses other additional genes for gibberellin biosynthesis. These genes jump in if GA20ox1 does not function. They apparently can compensate for all of the effects of the loss, except for the semi-dwarfism."
What changes cause Arabidopsis to switch the GA20ox1 gene off in the wild? Koornneef and his colleagues have identified six different genetic causes for the semi-dwarfism. These include mutations that the prevent the growth factor from being formed with the correct size, mutations that replace especially important amino acids with useless ones, as well as mutations that prevent the proper splicing of messenger RNA prior to the protein biosynthesis. In addition, the scientists have also found mutations that alter the reading frame of the GA20ox1 gene by removing part of the gene, then lengthening the gene sequence through insertion of foreign DNA, a so-called transposon.
Moreover, Koornneef and his colleagues were able to show that Arabidopsis only rarely displays semi-dwarfism in the wild. They describe the frequency of this trait as between one and five per cent. "If the freq
|Contact: Dr. Maarten Koornneef|