Omanische Heilpflanze im Fokus der Phytochemie IPB-Wissenschaftler und Partner aus Dhofar haben jüngst die omanische Heilpflanze Terminalia dhofarica unter die phytochemische Lupe genommen. Die Pflanze ist reich an…
Geschmack ist vorhersagbar: Mit FlavorMiner. FlavorMiner heißt das Tool, das IPB-Chemiker und Partner aus Kolumbien jüngst entwickelt haben. Das Programm kann, basierend auf maschinellem Lernen (KI), anhand der…
Nonhost resistance of Arabidopsis thaliana against Phytophthora infestans, a filamentous eukaryotic microbe and the causal agent of potato late blight, is based on a multilayered defense system. Arabidopsis thaliana controls pathogen entry through the penetration-resistance genes PEN2 and PEN3, encoding an atypical myrosinase and an ABC transporter, respectively, required for synthesis and export of unknown indole compounds. To identify pathogen-elicited leaf surface metabolites and further unravel nonhost resistance in Arabidopsis, we performed untargeted metabolite profiling by incubating a P. infestans zoospore suspension on leaves of WT or pen3 mutant Arabidopsis plants. Among the plant-secreted metabolites, 4-methoxyindol-3-yl-methanol and S-(4-methoxy-indol-3-yl-methyl) cysteine were detected in spore suspensions recollected from WT plants, but at reduced levels from the pen3 mutant plants. In both whole-cell and microsome-based assays, 4-methoxyindol-3-yl-methanol was transported in a PEN3-dependent manner, suggesting that this compound is a PEN3 substrate. The syntheses of both compounds were dependent on functional PEN2 and phytochelatin synthase 1. None of these compounds inhibited mycelial growth of P. infestans in vitro. Of note, exogenous application of 4-methoxyindol-3-yl methanol slightly elevated cytosolic Ca2+ levels and enhanced callose deposition in hydathodes of seedlings treated with a bacterial pathogen-associated molecular pattern (PAMP), flagellin (flg22). Loss of flg22-induced callose deposition in leaves of pen3 seedlings was partially reverted by the addition of 4-methoxyindol-3-yl methanol. In conclusion, we have identified a specific indole compound that is a substrate for PEN3 and contributes to the plant defense response against microbial pathogens.
Publikation
Bartsch, M.; Bednarek, P.; Vivancos, P. D.; Schneider, B.; von Roepenack-Lahaye, E.; Foyer, C. H.; Kombrink, E.; Scheel, D.; Parker, J. E.;Accumulation of Isochorismate-derived 2,3-Dihydroxybenzoic 3-O-β-D-Xyloside in Arabidopsis Resistance to Pathogens and Ageing of LeavesJ. Biol. Chem.28525654-25665(2010)DOI: 10.1074/jbc.M109.092569
An intricate network of hormone signals regulates plant development and responses to biotic and abiotic stress. Salicylic acid (SA), derived from the shikimate/isochorismate pathway, is a key hormone in resistance to biotrophic pathogens. Several SA derivatives and associated modifying enzymes have been identified and implicated in the storage and channeling of benzoic acid intermediates or as bioactive molecules. However, the range and modes of action of SA-related metabolites remain elusive. In Arabidopsis, Enhanced Disease Susceptibility 1 (EDS1) promotes SA-dependent and SA-independent responses in resistance against pathogens. Here, we used metabolite profiling of Arabidopsis wild type and eds1 mutant leaf extracts to identify molecules, other than SA, whose accumulation requires EDS1 signaling. Nuclear magnetic resonance and mass spectrometry of isolated and purified compounds revealed 2,3-dihydroxybenzoic acid (2,3-DHBA) as an isochorismate-derived secondary metabolite whose accumulation depends on EDS1 in resistance responses and during ageing of plants. 2,3-DHBA exists predominantly as a xylose-conjugated form (2-hydroxy-3-β-O-d-xylopyranosyloxy benzoic acid) that is structurally distinct from known SA-glucose conjugates. Analysis of DHBA accumulation profiles in various Arabidopsis mutants suggests an enzymatic route to 2,3-DHBA synthesis that is under the control of EDS1. We propose that components of the EDS1 pathway direct the generation or stabilization of 2,3-DHBA, which as a potentially bioactive molecule is sequestered as a xylose conjugate.
Publikation
Lee, J.; Rudd, J. J.; Macioszek, V. K.; Scheel, D.;Dynamic Changes in the Localization of MAPK Cascade Components Controlling Pathogenesis-related (PR) Gene Expression during Innate Immunity in ParsleyJ. Biol. Chem.27922440-22448(2004)DOI: 10.1074/jbc.M401099200
The activation of mitogen-activated protein kinase (MAPK) cascades is an important mechanism for stress adaptation through the control of gene expression in mammals, yeast, and plants. MAPK activation has emerged as a common mechanism by which plants trigger pathogen defense responses following innate immune recognition of potential microbial pathogens. We are studying the non-host plant defense response of parsley to attempted infection by Phytophthora species using an experimental system of cultured parsley cells and the Phytophthora-derived Pep-13 peptide elicitor. Following receptor-mediated recognition of this peptide, parsley cells trigger a multifaceted innate immune response, involving the activation of three MAPKs that have been shown to function in the oxidative burst-independent activation of defense gene expression. Using this same experimental model we now report the identification of a MAPK kinase (MAPKK) that functions upstream in this pathway. This kinase, referred to as PcMKK5 based on sequence similarity to Arabidopsis thaliana AtMKK5, is activated in parsley cells following Pep-13 treatment and functions as an in vivo activator of all three MAPKs previously shown to be involved in this response. Gain- and loss-of-function mutant versions of PcMKK5, when used in protoplast co-transfection assays, demonstrated that kinase activity of PcMKK5 is required for PR gene promoter activation following Pep-13 treatment. Furthermore, using specific antibodies and immunofluorescent labeling, we demonstrate that activation of MAPKs in parsley cells correlates with an increase in their nuclear localization, which is not detectable for activated PcMKK5. These results suggest that activation of gene expression through MAPK cascades during innate immune responses in plants involves dynamic changes in the localization of the proteins involved, which may reflect the distribution of key protein substrates for the activated MAPKs.
Publikation
Kroj, T.; Rudd, J. J.; Nürnberger, T.; Gäbler, Y.; Lee, J.; Scheel, D.;Mitogen-activated Protein Kinases Play an Essential Role in Oxidative Burst-independent Expression of Pathogenesis-related Genes in ParsleyJ. Biol. Chem.2782256-2264(2003)DOI: 10.1074/jbc.M208200200
Plants are continuously exposed to attack by potential phytopathogens. Disease prevention requires pathogen recognition and the induction of a multifaceted defense response. We are studying the non-host disease resistance response of parsley to the oomycete, Phytophthora sojae using a cell culture-based system. Receptor-mediated recognition of P. sojae may be achieved through a thirteen amino acid peptide sequence (Pep-13) present within an abundant cell wall transglutaminase. Following recognition of this elicitor molecule, parsley cells mount a defense response, which includes the generation of reactive oxygen species (ROS) and transcriptional activation of genes encoding pathogenesis-related (PR) proteins or enzymes involved in the synthesis of antimicrobial phytoalexins. Treatment of parsley cells with the NADPH oxidase inhibitor, diphenylene iodonium (DPI), blocked both Pep-13-induced phytoalexin production and the accumulation of transcripts encoding enzymes involved in their synthesis. In contrast, DPI treatment had no effect upon Pep-13-induced PRgene expression, suggesting the existence of an oxidative burst-independent mechanism for the transcriptional activation ofPR genes. The use of specific antibodies enabled the identification of three parsley mitogen-activated protein kinases (MAPKs) that are activated within the signal transduction pathway(s) triggered following recognition of Pep-13. Other environmental challenges failed to activate these kinases in parsley cells, suggesting that their activation plays a key role in defense signal transduction. Moreover, by making use of a protoplast co-transfection system overexpressing wild-type and loss-of-function MAPK mutants, we show an essential role for post-translational phosphorylation and activation of MAPKs for oxidative burst-independentPR promoter activation.