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Publications - Stress and Develop Biology

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Mönchgesang, S.; Strehmel, N.; Trutschel, D.; Westphal, L.; Neumann, S.; Scheel, D. Plant-to-plant variability in root metabolite profiles of 19 <i>Arabidopsis thaliana</i> accessions is substance-class-dependent Inter J Mol Sci 17, (2016) DOI: 10.3390/ijms17091565

Natural variation of secondary metabolism between different accessions of Arabidopsis thaliana (A. thaliana) has been studied extensively. In this study, we extended the natural variation approach by including biological variability (plant-to-plant variability) and analysed root metabolic patterns as well as their variability between plants and naturally occurring accessions. To screen 19 accessions of A. thaliana, comprehensive non-targeted metabolite profiling of single plant root extracts was performed using ultra performance liquid chromatography/electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC/ESI-QTOF-MS) and gas chromatography/electron ionization quadrupole mass spectrometry (GC/EI-QMS). Linear mixed models were applied to dissect the total observed variance. All metabolic profiles pointed towards a larger plant-to-plant variability than natural variation between accessions and variance of experimental batches. Ratios of plant-to-plant to total variability were high and distinct for certain secondary metabolites. None of the investigated accessions displayed a specifically high or low biological variability for these substance classes. This study provides recommendations for future natural variation analyses of glucosinolates, flavonoids, and phenylpropanoids and also reference data for additional substance classes.

Avrova, A.; Knogge, W. Rhynchosporium commune: a persistent threat to barley cultivation Mol Plant Pathol 13, 986-997, (2012) DOI: 10.1111/j.1364-3703.2012.00811.x

Rhynchosporium commune is a haploid fungus causing scald or leaf blotch on barley, other Hordeum spp. and Bromus diandrus.TaxonomyRhynchosporium commune is an anamorphic Ascomycete closely related to the teleomorph Helotiales genera Oculimacula and Pyrenopeziza.Disease symptomsRhynchosporium commune causes scald‐like lesions on leaves, leaf sheaths and ears. Early symptoms are generally pale grey oval lesions. With time, the lesions acquire a dark brown margin with the centre of the lesion remaining pale green or pale brown. Lesions often merge to form large areas around which leaf yellowing is common. Infection frequently occurs in the leaf axil, which can lead to chlorosis and eventual death of the leaf.Life cycleRhynchosporium commune is seed borne, but the importance of this phase of the disease is not fully understood. Debris from previous crops and volunteers, infected from the stubble from previous crops, are considered to be the most important sources of the disease. Autumn‐sown crops can become infected very soon after sowing. Secondary spread of disease occurs mainly through splash dispersal of conidia from infected leaves. Rainfall at the stem extension growth stage is the major environmental factor in epidemic development.Detection and quantificationRhynchosporium commune produces unique beak‐shaped, one‐septate spores both on leaves and in culture. The development of a specific polymerase chain reaction (PCR) and, more recently, quantitative PCR (qPCR) has allowed the identification of asymptomatic infection in seeds and during the growing season.Disease controlThe main measure for the control of R. commune is the use of fungicides with different modes of action, in combination with the use of resistant cultivars. However, this is constantly under review because of the ability of the pathogen to adapt to host plant resistance and to develop fungicide resistance.

Haapalainen, M.; Engelhardt, S.; Küfner, I.; Li, C.-M.; Nürnberger, T.; Lee, J.; Romantschuk, M.; Taira, S. Functional mapping of harpin HrpZ of Pseudomonas syringae reveals the sites responsible for protein oligomerization, lipid interactions and plant defence induction Mol Plant Pathol 12, 151-166, (2011) DOI: 10.1111/j.1364-3703.2010.00655.x

Harpin HrpZ is one of the most abundant proteins secreted through the pathogenesis-associated type III secretion system of the plant pathogen Pseudomonas syringae. HrpZ shows membrane-binding and pore-forming activities in vitro, suggesting that it could be targeted to the host cell plasma membrane. We studied the native molecular forms of HrpZ and found that it forms dimers and higher order oligomers. Lipid binding by HrpZ was tested with 15 different membrane lipids, with HrpZ interacting only with phosphatidic acid. Pore formation by HrpZ in artificial lipid vesicles was found to be dependent on the presence of phosphatidic acid. In addition, HrpZ was able to form pores in vesicles prepared from Arabidopsis thaliana plasma membrane, providing evidence for the suggested target of HrpZ in the host. To map the functions associated with HrpZ, we constructed a comprehensive series of deletions in the hrpZ gene derived from P. syringae pv. phaseolicola, and studied the mutant proteins. We found that oligomerization is mainly mediated by a region near the C-terminus of the protein, and that the same region is also essential for membrane pore formation. Phosphatidic acid binding seems to be mediated by two regions separate in the primary structure. Tobacco, a nonhost plant, recognizes, as a defence elicitor, a 24-amino-acid HrpZ fragment which resides in the region indispensable for the oligomerization and pore formation functions of HrpZ.
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