Pathogenesis‐related proteins of plants

Abstract Infection of plants with pathogens like viruses or fungi often leads to a response of the host ranging from very mild to very severe. A very mild response usually does not result in considerable changes in the patterns of gene expression of the plant. However, a hypersensitive reaction, e.g., in the case of infection of Samsun NN tobacco with tobacco mosaic virus, is accompanied by a massive increase in the amounts of a large number of different proteins. Among these induced proteins are members of a group of so‐called pathogenesis‐related (PR) proteins. Frequently, the hypersensitively reacting host becomes resistant to subsequent pathogenic attack. The correlation of this phenomenon of acquired resistance and the induced protein synthesis suggests a direct involvement of these proteins in the observed replication deficiency of the pathogen. This has initiated studies by several research groups toward a better understanding of the role of these PR‐proteins in the hypersensitively reacting plant. This review deals with the progress that has been made with the analysis of the host response and the function of the PR proteins in the acquired resistance.