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Publications - Stress and Develop Biology

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Publications

Schön, M.; Töller, A.; Diezel, C.; Roth, C.; Westphal, L.; Wiermer, M.; Somssich, I. E. Analyses of wrky18 wrky40 Plants Reveal Critical Roles of SA/EDS1 Signaling and Indole-Glucosinolate Biosynthesis for Golovinomyces orontii Resistance and a Loss-of Resistance Towards Pseudomonas syringae pv. tomato AvrRPS4 Mol Plant Microbe Interact 26, 758-767, (2013) DOI: 10.1094/MPMI-11-12-0265-R

Simultaneous mutation of two WRKY-type transcription factors, WRKY18 and WRKY40, renders otherwise susceptible wild-type Arabidopsis plants resistant towards the biotrophic powdery mildew fungus Golovinomyces orontii. Resistance in wrky18 wrky40 double mutant plants is accompanied by massive transcriptional reprogramming, imbalance in salicylic acid (SA) and jasmonic acid (JA) signaling, altered ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) expression, and accumulation of the phytoalexin camalexin. Genetic analyses identified SA biosynthesis and EDS1 signaling as well as biosynthesis of the indole-glucosinolate 4MI3G as essential components required for loss-of-WRKY18 WRKY40–mediated resistance towards G. orontii. The analysis of wrky18 wrky40 pad3 mutant plants impaired in camalexin biosynthesis revealed an uncoupling of pre- from postinvasive resistance against G. orontii. Comprehensive infection studies demonstrated the specificity of wrky18 wrky40–mediated G. orontii resistance. Interestingly, WRKY18 and WRKY40 act as positive regulators in effector-triggered immunity, as the wrky18 wrky40 double mutant was found to be strongly susceptible towards the bacterial pathogen Pseudomonas syringae DC3000 expressing the effector AvrRPS4 but not against other tested Pseudomonas strains. We hypothesize that G. orontii depends on the function of WRKY18 and WRKY40 to successfully infect Arabidopsis wild-type plants while, in the interaction with P. syringae AvrRPS4, they are required to mediate effector-triggered immunity.
Publications

Bethke, G.; Pecher, P.; Eschen-Lippold, L.; Tsuda, K.; Katagiri, F.; Glazebrook, J.; Scheel, D.; Lee, J. Activation of the Arabidopsis thaliana mitogen-activated protein kinase MPK11 by the flagellin-derived elicitor peptide, flg22 Mol Plant Microbe Interact 25, 471-480, (2012) DOI: 10.1094/MPMI-11-11-0281

Mitogen-activated protein kinases (MAPKs) mediate cellular signal transduction during stress responses, as well as diverse growth and developmental processes in eukaryotes. Pathogen infection or treatments with conserved pathogen-associated molecular patterns (PAMPs) such as the bacterial flagellin-derived flg22 peptide are known to activate three Arabidopsis thaliana MAPKs, MPK3, MPK4 and MPK6. Several stresses, including flg22 treatment, are known to increase MPK11 expression but activation of MPK11 has not been shown. Here, we show that MPK11 activity can indeed be increased through flg22 elicitation. A small-scale microarray for profiling defense-related genes revealed that cinnamyl alcohol dehyrogenase 5 (CAD5) requires MPK11 for full flg22-induced expression. An mpk11 mutant showed increased flg22-mediated growth inhibition but no altered susceptibility to Pseudomonas syringae, Botrytis cinerea or Alternaria brassicicola. In mpk3, mpk6, or mpk4 backgrounds, MPK11 is required for embryo/seed development or general viability. Although this developmental deficiency in double mutants and the lack of or only subtle mpk11 phenotypes suggest functional MAPK redundancies, comparison to the paralogous MPK4 reveals distinct functions. Taken together, future investigations of MAPK roles in stress signalling should include MPK11 as a fourth PAMP-activated MAPK.
Publications

Kirsten, S.; Navarro-Quezada, A.; Penselin, D.; Wenzel, C.; Matern, A.; Leitner, A.; Baum, T.; Seiffert, U.; Knogge, W. Necrosis-Inducing Proteins of Rhynchosporium commune, Effectors in Quantitative Disease Resistance Mol Plant Microbe Interact 25, 1314-1325, (2012) DOI: 10.1094/MPMI-03-12-0065-R

The barley pathogen Rhynchosporium commune secretes necrosis-inducing proteins NIP1, NIP2, and NIP3. Expression analysis revealed that NIP1 transcripts appear to be present in fungal spores already, whereas NIP2 and NIP3 are synthesized after inoculation of host plants. To assess the contribution of the three effector proteins to disease development, deletion mutants were generated. The development of these fungal mutants on four barley cultivars was quantified in comparison with that of the parent wild-type strain and with two fungal strains failing to secrete an “active” NIP1 avirulence protein, using quantitative polymerase chain reaction as well as microscopic imaging after fungal green fluorescent protein tagging. The impact of the three deletions varied quantitatively depending on the host genotype, suggesting that the activities of the fungal effectors add up to produce stronger growth patterns and symptom development. Alternatively, recognition events of differing intensities may be converted into defense gene expression in a quantitative manner.
Publications

Eschen-Lippold, L.; Altmann, S.; Rosahl, S. DL-β-Aminobutyric Acid–Induced Resistance of Potato Against Phytophthora infestans Requires Salicylic Acid but Not Oxylipins Mol Plant Microbe Interact 23, 585-592, (2010) DOI: 10.1094/MPMI-23-5-0585

Inducing systemic resistance responses in crop plants is a promising alternative way of disease management. To understand the underlying signaling events leading to induced resistance, functional analyses of plants defective in defined signaling pathway steps are required. We used potato, one of the economically most-important crop plants worldwide, to examine systemic resistance against the devastating late blight pathogen Phytophthora infestans, induced by treatment with dl-β-aminobutyric acid (BABA). Transgenic plants impaired in either the 9-lipoxygenase pathway, which produces defense-related compounds, or the 13-lipoxygenase pathway, which generates jasmonic acid–derived signals, expressed wild-type levels of BABA-induced resistance. Plants incapable of accumulating salicylic acid (SA), on the other hand, failed to mount this type of induced resistance. Consistently, treatment of these plants with the SA analog 2,6-dichloroisonicotinic acid restored BABA-induced resistance. Together, these results demonstrate the indispensability of a functional SA pathway for systemic resistance in potato induced by BABA.
Publications

Brunner, F.; Rosahl, S.; Lee, J.; Rudd, J.J.; Geiler, C.; Kauppinen, S.; Rasmussen, G.; Scheel, D.; Nürnberger, T. Pep-13, a plant defense-inducing pathogen-associated pattern from <em>Phytophthora transglutaminases</em> EMBO J 21, 6681-6688, (2002)

Innate immunity, an ancient form of defense against microbial infection, is well described for animals and is also suggested to be important for plants. Discrimination from self is achieved through receptors that recognize pathogen-associated molecular patterns (PAMPs) not found in the host. PAMPs are evolutionarily conserved structures which are functionally important and, thus, not subject to frequent mutation. Here we report that the previously described peptide elicitor of defense responses in parsley, Pep-13, constitutes a surface-exposed fragment within a novel calcium-dependent cell wall transglutaminase (TGase) from Phytophthora sojae. TGase transcripts and TGase activity are detectable in all Phytophthora species analyzed, among which are some of the most destructive plant pathogens. Mutational analysis within Pep-13 identified the same amino acids indispensable for both TGase and defense-eliciting activity. Pep-13, conserved among Phytophthora TGases, activates defense in parsley and potato, suggesting its function as a genus-specific recognition determinant for the activation of plant defense in host and non-host plants. In summary, plants may recognize PAMPs with characteristics resembling those known to trigger innate immune responses in animals.
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