295 Defence signalling pathways in cereals Pietro Piffanelli, Alessandra Devoto and Paul Schulze-Lefert* The combination of mutational and molecular studies has shed hosts. One would expect non-pathogenic strains either to light on the role of reactive oxygen intermediates and exhibit perturbations in these developmental programs or programmed cell death in cereal disease resistance to affect more specialised steps, for example those which mechanisms. Rice Rac1 and barley Rar1 represent conserved establish a communication with the host metabolism. In disease resistance signalling genes, which may have related the past three years, the use of insertional mutagenesis, in functions in animals. The analysis of non-pathogenic particular restriction enzyme mediated integration Magnaporthe grisea mutants may provide novel tools to study (REMI) mutagenesis, has successfully identified compo- host defence pathways. nents controlling pathogenicity of the cereal pathogen Magnaporthe grisea [12,13]. Perhaps unexpectedly, some of Addresses these pathogenicity mutants have also shed light on host The Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich defence mechanisms and signalling. NR4 7UH, UK *e-mail:
[email protected] M. grisea is a hemibiotrophic filamentous ascomycete that Current Opinion in Plant Biology 1999, 2:295–300 parasitises many grasses, including cereal crops such as rice, wheat, barley, and millet [14,15]. Appressorium for- http://biomednet.com/elecref/1369526600200295 mation is a key step during pathogenesis not only for © Elsevier Science Ltd ISSN 1369-5266 Magnaporthe, but also for other ascomycete and basid- Abbreviations iomycete plant pathogens. Appressoria are essential for 7TM seven transmembrane host cell wall penetration, as they prepare for the transition CHORD cysteine- and histidine-rich domain from extracellular to invasive life style.