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The interdependent effects of the pathogen Didymella pinodes and the symbionts rhizobia and mycorrhiza on Pisum sativum


Supervisor: Stefanie Wienkoop  

PhD student: Reinhard Turetschek

Group: Division of Molecular Systems Biology, Department of Ecogenomics and Systems Biology

Defended on April 27th 2017


Pisum Sativum has a long history of cultivation and is now one of the most grown grain legumes. The lower needs for chemical fertilisers make the plant well suited for sustainable agricultural systems. During the past decades, yield losses were mainly due to pathogenic infestation, with Ascochyta blight as the most severe disease. In this fungal disease complex Didymella pinodes, as the most aggressive pathogen, has been examined intensively. Despite the great number of varieties, no resistance was yet found and several strategies were developed to avoid infestation. In recent years enhanced resistance to pathogens due to previous infestation by symbiotic microorganisms was discovered in several plants. However, only little attention was drawn on the implications of P. Sativum´s symbionts (Rhizobia, Mycorrhiza) on the disease severity as well as the effects of the pathogen on the symbiotic interactions. Within the FWF-project [P24870B22], and in collaboration with the University of Natural Resources and Life Sciences (BOKU), implications of the pathogenic infestation on the tripartite symbiosis of P. Sativum on a molecular  (proteome, metabolome) and physiological level were investigated. A summary can be found at  https://homepage.univie.ac.at/stefanie.wienkoop/fwf24870_en.html.

In our first experiment, the susceptible pea cultivar Messire was inoculated with different combi-nations of symbionts (mycorrhiza, rhizobia, co-inoculation, no symbionts) to examine in what way symbi-onts influence leaf metabolism and to see whether symbiosis affects the plant defense response against D. pinodes. With our obtained results we could show that mycorrhiza and rhizobia alter leaf RNA metabolism and protein synthesis. Mycorrhiza alone influenced metabolic functions handling metals and disposal of reactive oxygen species. Co-inoculation with rhizobia and mycorrhiza caused accumulation of proteins related to a stress response, however, during infection the defence response was dampened. The general defense response against D. pinodes was characterised by accumulation of proteins modulating hormone levels (jasmonate, ethylene), disposal of reactive oxygen species and activation of secondary metabolism including proteins of the P. sativum typical pisatin pathway (i.g. 6a-hydroxymaackiain 3-O-methyltrans-ferase). The legumes inherent interaction with rhizobia lead to enhanced activation of the citric acid cycle, amino acid metabolism and secondary metabolism including proteins involved in the synthesis of pisatin. The data indicate that this is mediated by the phenomena of induced systemic resistance.

A second experiment showed that symbiont interaction influences a susceptible cultivar´s defense response heavier than a tolerant (Protecta) ones. This implied that the infection with D. pinodes had a stronger impact on the symbiotic interaction in the susceptible cultivar, which was noticed in nodule weight and mycorrhiza colonisation. The more effective defense response of the tolerant cultivar distinguished from the susceptible cultivar through sustainment of photosynthesis, provision of sugars and carbon skele-tons supplying secondary metabolism. In addition, sulphur metabolism, functioning of the glutathione-ascorbate hub and hormonal adjustment to avoid induced cell death seem to promote tolerance. 


Please find a list of publications here.

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