| ||||||||||||||||||||
Assault on the sensors
A fascinating aspect of cellular behaviour, whether the cells are part of a multicellular organism or exist as a single-celled species, is cell-to-cell signalling. For example, many bacterial species can monitor the density of the cell population by sensing the concentration of signalling molecules. This is particularly important for those activities that are not undertaken until a particular cell density (or quorum) is reached. Amongst the range of sensing molecules, N-acylhomoserine lactones (AHLs) are the most widespread. An example of an activity requiring a quorum is the infection of plants by pathogenic bacteria; furthermore, some potential hosts secrete as a defence mechanism chemicals that modify quorum sensing. Thus, R. G. Fray (University of Nottingham, pp. 245-253) has suggested that it may possible to engineer plants so that they interfere with quorum sensing in potential pathogens, thus conferring resistance. He then presents his own work and reviews the work of others in support of this hypothesis. Tobacco plants transformed with the yen1 gene from Yersinia enterocolitica produce AHLs and restore pathogenicity to an avirulent strain of the potato rot bacterium Erwinia carotovora. Furthermore, potatoes transformed with the same gene become susceptible to E. carotovora infection at inoculum levels much lower than those normally needed to mount an effective infection. Finally, transgenic tobacco and potato plants expressing a Bacillus gene encoding an AHL-degrading enzyme are resistant to E. carotovora even at very high inoculum potentials. This is clearly an interesting and potentially very exciting approach to engineering plant-pathogen resistance. However, it is not without its problems. Many non-pathogenic bacteria, important residents of the rhizosphere, also use AHLs for signalling. It is important that crops engineered to produce AHL-degrading enzymes are targeted specifically at those AHLs produced by pathogens. Nevertheless, this is an important line of research and we look forward to further developments.
Professor J.A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||