Significance of Inducible Defense-related Proteins in Infected Plants

Significance of Inducible Defense-related Proteins in Infected Plants

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Significance of Inducible Defense-related Proteins in Infected Plants L.C. van Loon, 1 M. Rep, 2 and C.M.J. Pieterse 1 1 Phytopathology, Institute of Environmental Biology, Science Faculty, Utrecht University, 3508 TB Utrecht, The Netherlands; email: [email protected], [email protected] 2 Plant Pathology, Swammerdam Institute for Life Sciences, Faculty of Science, University of Amsterdam, 1090 GB Amsterdam, The Netherlands; email: [email protected] Annu. Rev. Phytopathol. 2006. 44:135–62 First published online as a Review in Advance on March 3, 2006 The Annual Review of Phytopathology is online at phyto.annualreviews.org doi: 10.1146/ annurev.phyto.44.070505.143425 Copyright c 2006 by Annual Reviews. All rights reserved 0066-4286/06/0908- 0135$20.00 Key Words antimicrobial activity, defense signaling, developmental regulation, pathogenesis-related proteins, resistance, stress alleviation Abstract Inducible defense-related proteins have been described in many plant species upon infection with oomycetes, fungi, bacteria, or viruses, or insect attack. Several types of proteins are common and have been classified into 17 families of pathogenesis-related pro- teins (PRs). Others have so far been found to occur more specifically in some plant species. Most PRs and related proteins are induced through the action of the signaling compounds salicylic acid, jas- monic acid, or ethylene, and possess antimicrobial activities in vitro through hydrolytic activities on cell walls, contact toxicity, and per- haps an involvement in defense signaling. However, when expressed in transgenic plants, they reduce only a limited number of diseases, depending on the nature of the protein, plant species, and pathogen involved. As exemplified by the PR-1 proteins in Arabidopsis and rice, many homologous proteins belonging to the same family are regu- lated developmentally and may serve different functions in specific organs or tissues. Several defense-related proteins are induced dur- ing senescence, wounding or cold stress, and some possess antifreeze activity. Many defense-related proteins are present constitutively in floral tissues and a substantial number of PR-like proteins in pollen, fruits, and vegetables can provoke allergy in humans. The evolution- ary conservation of similar defense-related proteins in monocots and dicots, but also their divergent occurrence in other conditions, sug- gest that these proteins serve essential functions in plant life, whether in defense or not. 135 Annu. Rev. Phytopathol. 2006.44:135-162. Downloaded from arjournals.annualreviews.org by Utrecht University on 08/14/06. For personal use only.
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SA: salicylic acid JA: jasmonic acid ET: ethylene R : resistance gene PR: pathogenesis-related SAR: systemic acquired resistance INTRODUCTION Plants possess both preformed and in- ducible mechanisms to resist pathogen invasion. Extant morphological barriers, secondary metabolites (phytoanticipins), and antimicrobial proteins must be avoided or overcome for pathogens to be able to invade a plant. Once contact has been established, elicitors produced and released
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