Pathogenesis-related Proteins: Research Progress in the Last 15 Years

An overview of the evolution of knowledge on the nomenclature, classification, induction, occurrence, functions, and role of pathogenesis-related proteins (PRs) is presented, covering generally the last fifteen years. The recommendations for naming and defining PRs are introduced, and the criteria required for the inclusion of new families into PRs are considered. The revision of the previous view on PRs as inducible proteins is argumented, given their constitutive expression in various plant organs and in seeds. Newly-discovered members of PRs families are described, and recent information about functionality of PRs, substantiating their antimicrobial action, is discussed. The biochemical and structural properties, as well as the organ-, tissue-, and cell-localisation, the induction and regulation of PRs are briefly outlined. Recent data about the relevance of PRs to plant development and disease resistance are examined, and the plausible application of engineering of PRs genes for crop improvement is critically commented. The finding that PRs, considered before as plant-specific proteins, are also expressed in other organisms, suggests that these proteins share an evolutionary origin and possess activity essential to the functioning and survival of living organisms.