The water mould Phytophthora infestans, responsible for devastating the potato crop of Western Europe in the mid-nineteenth century, has recently been in the spotlight (see Nature 7 June). As Eric Holub discusses on page 516, this terrible agricultural disaster had one positive outcome — it triggered considerable interest in plant pathology. Empowered by the availability of the Arabidopsis thaliana genome sequence, this field is now providing new insights into the resistance of plants to disease. In particular, the highly polymorphic R genes, which mediate pathogen-specific resistance, have allowed plants to keep up an arms race with pathogens that are also diversifying to overcome the resistance of their hosts. Research into the origin and evolution of R genes has depended on a well-annotated A. thaliana genome sequence, and on page 495, Lincoln Stein reviews several approaches to genome annotation. He also discusses the implications of genome annotation for the communication and publication of scientific data.

Research into plant pathogen-resistance proteins has also provided information on their vertebrate homologues, which function in innate immunity — the rapid response pathway to pathogen invasion. Indeed, as discussed in Highlights, one such receptor-encoding gene, NOD2, has been found to underlie susceptibility to Crohn disease — the first identification, by linkage mapping, of a gene involved in a common, human disease. It was partly its homology to previously identified plant R genes that helped to confirm its role in the disorder. Of course, there might be important environmental components to Crohn disease as well, but hopefully it will not take as long to overcome them as it has to combat the effects of P. infestans, which remains an agricultural menace to this day.