Agrobacterium-Mediated Transformation of Non-Plant Organisms

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During the last decade it became clear that the ability of Agrobacterium to transform host organisms is not restricted to plants, but that numerous other organisms are transformable by Agrobacterium under laboratory conditions. It has been shown that Agrobacterium-mediated transformation is possible for at least 80 different non-plant species. Most of these organisms are fungi including yeasts, but also mammalian cells and algae can be transformed. Agrobacterium-mediated transformation is not restricted to eukaryotes as Agrobacterium is also able to act on the gram positive bacterium Streptomyces lividans. In general, the procedures for the transformation of different organisms are similar, but each organism has its own conditions for optimal transformation efficiency. Nowadays Agrobacterium-mediated transformation is the method of choice for the transformation of various fungi as transformation efficiencies are much higher than with other methods and the transformation protocols are relatively facile. Agrobacterium can transfer not only DNA but also proteins to the host organisms through its type four secretion system. This protein transfer has been shown for both plants and the yeast Saccharomyces cerevisiae. A major issue in the transformation of eukaryotic cells is the integration of the foreign DNA at random positions in the genome rather than at specific locations. The ability of Agrobacterium to transform the yeast S. cerevisae offers the possibility to use the many experimental tools available for this organism to fully unravel the mechanisms involved in the Agrobacterium-mediated transformation process. This is especially relevant as in contrast to most other organisms S. cerevisiae has a very efficient system for targeted integration of DNA fragments via homologous recombination. Knowledge of this system has already led to an increased frequency of targeted integration in the yeast Kluyveromyes lactis, in the filamentous fungus Neurospora crassa and the plant Arabidopsis thaliana. The ability of Agrobacterium to transfer T-DNA to a wide variety of eukaryotic and some prokaryotic organisms may have important implications for evolution. Future research has to show whether Agrobacterium-mediated transformation contributed to horizontal gene transfer between microorganisms in the rhizosphere.