Chemical Communication in a Post-Genomic World (2003) / Chapter Skim
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12 Non-self recognition, transcriptional reprogramming, and secondary metabolite accumulation during plant/pathogen interactions
12 Non-self recognition, transcriptional reprogramming, and secondary metabolite accumulation during plant/pathogen interactions
Pages 57-64
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From page 57... ...
First, the exogenously applied, pathogen-derived signal molecule is a chemically defimed, small, and highly specific peptide elicitor that enables detailed structural aIId functional analyses based on specially desi~ed synthetic modifications. Second, protoplasts denved from these cells retain full elicitor responsiveness and hence are a particularly valuable tool for analyzing gene promoter elements and their transcriptional regulators by using a simple and highly reproducible transfection and transient expression assay.
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From page 58... ...
. As far as applicable to the largely undifferentiated, cultured cells or protoplasts, and as far as individual components have been analyzed, the response to elicitor was essentially the same as that observed with infected, whole-plant tissue, except for the additional occurrence of hypersensitive cell death at true infection sites.
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From page 59... ...
Although gene repression is mechanistically as well as metabolically as interesting a phenomenon as is gene activation, our investigations have been focused mainly on the latter, largely because most of the genes analyzed so far in relation to aromatic secondary metabolism are strongly activated by elicitor. Three major outcomes of these studies are particularly noteworthy: the identification of several distinct classes of elicitor-responsive, cis-acting gene promoter elements; the discovery of two new families of regulatory proteins, the trp/arg/lys/tyr (WRKY)
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From page 60... ...
thaliana) and apart from the recognition of a close structural similarity of boxes P and L both to one another and to the independently defined myeloblastosis recognition element, two more basic discoveries resulting from these studies were the WRKY and CMPG protein families.
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From page 61... ...
cr~spum cells or protoplasts, or at infection sites proper, are several structurally related furanocoumarins and various likewise closely related butylidene phthalide aglycones and glycosides (23~. Both classes of compounds are biosynthetically derived from phenylalanine by combinations of the three common steps of general phenylpropanoid metabolism with two of the many subsequently diverging branch pathways.
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From page 62... ...
Importantly, however, nearly all of these elements are bound more or less efficiently by this particular family member. Considering the large size of the WRKY family of W box-binding proteins and the large number of potential W box-containing sequences and sequence arrangements, this result indicates a vast regulatory potential founded in an almost 14574 1 www.pnas.org/cgi/doi/10.1073/pnas.0831246100 Hierarchical structure of pathogen defense in plants Triggered by non-self recognition, executed by interconnected signalling cascades and superimposed by highly dynamic intracellular rearrangements Universal strategy Step-wise progression from highly localized to systemic defense Multiple functional components Papilla formation; hypersensitive cell death, phytoalexin accumulation; 'systemic acquired resistance' Regulatory motifs/Metabolic pathways Cis-acting elements; regulatory proteins; defense related pathways Genes/mRNAs/Proteins/Metabolites Species-specific structural and functional elements and pathway characteristics Fig.
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From page 63... ...
es seem equally plausible: either there is greater evolutionary pressure on the conservation of the cell wall-bound compounds or this branch of phenylpropanoid metabolism, whether it has a common evolutionary origin in all plants or has converged from multiple origins, has limited degrees of chemical freedom, in contrast to the various pathways generating phytoalexins that have evolved a greater chemical diversity. Although phytoalexin production and cell-wall reinforcement with phenylpropanoid derivatives can be regarded as two independent functional modules occupying parallel hierarchical positions within the overall defense strategy, their speciesspecific patterns of diversity could not differ more.
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From page 64... ...
Conclusions The combination of a universal strategy with an almost infinite number of species-specific variations of the pathogen defense response in plants ideally illustrates the interplay of conceptual richness, metabolic options, physiological constraints and ecological demands within which evolution takes place. Hierarchical subdivision of the overall response into multiple functional modules is executed by interconnected, partly universal, partly species-specific signaling pathways that together mediate an extensive, rapid transcriptional reprogramming of exclusively species-specific genes.
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