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Microbe-associated molecular pattern (MAMP) signatures, synergy, size and charge: influences on perception or mobility and host defence responses |
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| Authors: | SHAZIA N. ASLAM GITTE ERBS KATE L. MORRISSEY MARI-ANNE NEWMAN DELPHINE CHINCHILLA THOMAS BOLLER ANTONIO MOLINARO ROBERT W. JACKSON RICHARD M. COOPER |
| Affiliation: | Department of Biology and Biochemistry, University of Bath, BA2 7AY, UK; Faculty of Life Sciences, Department of Plant Biology and Biotechnology, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg, Denmark; Zurich-Basel Plant Science Centre, Botanical Institute, University of Basel, Hebelstrasse1, 4056 Basel, Switzerland; Dipartimento di Chimica Organica e Biochimica, Universitàdi Napoli, Complesso Universitario Monte SantAngelo, Via Cintia 4, 80126 Napoli, Italy; School of Biological Sciences, University of Reading, Whiteknights, Reading, Berkshire RG6 6AJ, UK |
| Abstract: | Triggering of defences by microbes has mainly been investigated using single elicitors or microbe-associated molecular patterns (MAMPs), but MAMPs are released in planta as complex mixtures together with endogenous oligogalacturonan (OGA) elicitor. We investigated the early responses in Arabidopsis of calcium influx and oxidative burst induced by non-saturating concentrations of bacterial MAMPs, used singly and in combination: flagellin peptide (flg22), elongation factor peptide (elf18), peptidoglycan (PGN) and component muropeptides, lipo-oligosaccharide (LOS) and core oligosaccharides. This revealed that some MAMPs have additive (e.g. flg22 with elf18) and even synergistic (flg22 and LOS) effects, whereas others mutually interfere (flg22 with OGA). OGA suppression of flg22-induced defences was not a result of the interference with the binding of flg22 to its receptor flagellin-sensitive 2 (FLS2). MAMPs induce different calcium influx signatures, but these are concentration dependent and unlikely to explain the differential induction of defence genes [pathogenesis-related gene 1 ( PR1 ), plant defensin gene 1.2 ( PDF1.2 ) and phenylalanine ammonia lyase gene 1 ( PAL1 )] by flg22, elf18 and OGA. The peptide MAMPs are potent elicitors at subnanomolar levels, whereas PGN and LOS at high concentrations induce low and late host responses. This difference might be a result of the restricted access by plant cell walls of MAMPs to their putative cellular receptors. flg22 is restricted by ionic effects, yet rapidly permeates a cell wall matrix, whereas LOS, which forms supramolecular aggregates, is severely constrained, presumably by molecular sieving. Thus, MAMPs can interact with each other, whether directly or indirectly, and with the host wall matrix. These phenomena, which have not been considered in detail previously, are likely to influence the speed, magnitude, versatility and composition of plant defences. |
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