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The impact of steroidal glycoalkaloids on the physiology of Phytophthora infestans, the causative agent of potato late blight
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Steroidal glycoalkaloids (SGAs) are plant secondary metabolites known to be toxic to animals and humans and that exert putative roles in defence against pests. The proposed mechanisms of SGA toxicity are sterol-mediated disruption of membranes and inhibition of cholinesterase activity in neurons. It has been suggested that phytopathogenic microorganisms can overcome SGA toxicity by enzymatic deglycosylation of SGAs. Here we have explored SGA-mediated toxicity towards the invasive oomycete Phytophthora infestans, the causative agent of the late blight disease in potato and tomato, as well as the potential for SGA deglycosylation by this species. Our growth studies indicate that solanidine, the non-glycosylated precursor of the potato SGAs α-chaconine and α-solanine, has a greater physiological impact than its glycosylated forms. All of these compounds were incorporated into the mycelium, but only solanidine could strongly inhibit the growth of P. infestans in liquid culture. Genes encoding several glycoside hydrolases with potential activity on SGAs were identified in the genome of P. infestans and were shown to be expressed. However, we found no indication that deglycosylation of SGAs takes place. We present additional evidence for apparent host-specific adaptation to potato SGAs and assess all results in terms of future pathogen management strategies.

National Category
Biological Sciences
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-136549OAI: oai:DiVA.org:su-136549DiVA: diva2:1055147
Available from: 2016-12-11 Created: 2016-12-11 Last updated: 2016-12-12Bibliographically approved
In thesis
1. Analysis of sterol metabolism in the pathogenic oomycetes Saprolegnia parasitica and Phytophthora infestans
Open this publication in new window or tab >>Analysis of sterol metabolism in the pathogenic oomycetes Saprolegnia parasitica and Phytophthora infestans
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The primary objective of this thesis was to investigate the sterol metabolism of two pathogenic oomycetes, specifically the processes of sterol synthesis and sterol acquisition in the fish pathogen Saprolegnia parasitica (Saprolegniales) and the plant pathogen Phytophthora infestans (Peronosporales). Furthermore, the effects of steroidal glycoalkaloids from Solanaceous plants, on P. infestans, were examined. The improved understanding of these processes should help to identify approaches for the identification of new oomycete inhibitors targeting sterol metabolism in agriculture and aquaculture farming systems, and to guide plant-breeding strategies to defend solanaceous plants against oomycetes.

For these reasons, the molecular basis of the metabolic pathways of sterol synthesis and/or sterol acquisition was investigated. Sterols are derived from isoprenoids and indispensable in various biological processes. Our biochemical investigation of an oxidosqualene cyclase revealed that sterol synthesis in S. parasitica begins with the formation of lanosterol (Paper I), and a reconstruction of the complete sterol synthesis pathway to the final compound, fucosterol, in S. parasitica was performed using bioinformatics (Paper II). Complementary to this work, the extent to which P. infestans, which is incapable of de novo sterol synthesis, is able to modify exogenously provided sterols was investigated by determining the growth impact of various sterol supplements in the growth media (Paper II). 

Building on the sterol investigations, the solanaceous sterol derivatives from the glycoalkaloid family were analysed. These compounds contain both a steroidal and a carbohydrate (glycan) moiety. Data obtained by feeding various deuterium-labeled sterols to potato shoots, supported the theory that steroidal glycoalkaloids in Solanum tuberosum are produced from cholesterol (Paper III).  Since these steroidal glycoalkaloids are thought to play a role in plant defense, their physiological effects on P. infestans were investigated (Paper IV). Unexpectedly we found that non-glycosylated steroidal alkaloids had a greater inhibitory effect than steroidal glycoalkaloids.  Steroidal glycoalkaloids derived from other Solanaceous species exhibited different physiological effects on the growth of P. infestans

This research was conducted on two oomycete species belonging to the Saprolegniales and Peronosporales orders, hence the results presented are likely to be representative of each of these two oomycete orders.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2016. 59 p.
National Category
Biochemistry and Molecular Biology
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-136551 (URN)978-91-7649-652-7 (ISBN)978-91-7649-653-4 (ISBN)
Public defence
2017-01-27, sal P216, Arrheniuslaboratorierna, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.

Available from: 2017-01-02 Created: 2016-12-11 Last updated: 2017-01-27Bibliographically approved

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