Functional characterization of sphingobase metabolism and the role of sphingobases in plant programmed cell death
Plant Breeding and Plant Pathology
Plant Cell and Developmental Biology
Final Report Abstract
Sphingolipids, together with other lipids, are part of cellular membranes of all higher organisms. Sphingolipids are synthesized from a fatty acid and a sphingobase (long chain base, LCB) and can be modified with a head group, e.g. a phosphate group. Beside their function in membranes, free sphingobases can function as signalling molecules. In humans, specific sphingobases are involved in many processes, e.g. during inflammation. In plants, the role of free sphingobases is less understood. It is known, however, that free LCB levels increase during cell death reactions, and that LCBs can trigger cell death in plants. The project aimed at a better understanding of the regulation of the levels of free sphingobases in plants to better understand how cell death reactions are controlled. Cell death reactions play a role during plant defence against sprecific pathogens, e.g. by inducing programmed cell death and thereby reducing pathogen spread in infected tissue. The project experimentally addressed the published hypothesis of an antagonistic role of phosphorylated sphingobases (LCB-Ps) on cell death induction by LCBs in the model plant Arabidopsis thaliana. We analyzed transgenic and mutant plants differing in LCB and LCB- P levels, and utilized high resolution mass spectrometry coupled with high-pressure liquid chromatography (HPLC-MS/MS). Unexpectedly, we found experimental evidence clearly contradicting the ‘antagonism hypothesis’. We could show that the degree of cell death reaction is positively correlated with free levels of the LCBs phytosphingosine and dihydrosphingosine. We discovered that published experimental evidence, which seemed to support the antagonism of LCB-Ps was in fact due to methodological reasons, e.g. reduced LCB uptake when LCBs were combined with LCB-Ps. In further approaches, we analyzed in time course experiments the incorporation and degradation processes of the sphingobase dihydrosphinganine using HPLC-MS/MS. Furthermore, we discovered that the sphingobase phytosphingosine has a direct antimicrobial effect on the bacterial plant pathogen Pseudomonas syringae. Results gained in this project improve our understanding of sphingobase homeostasis and the plant cell death reaction, which is important for plant pathogen resistance. With these results - and, in addition, also due to the discovered antimicrobial activity of LCBs against plant pathogens - new approaches can be developed to enhance pathogen resistance of crop plants.
Publications
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(2019) Elevated Levels of Phosphorylated Sphingobases Do Not Antagonize Sphingobase- or Fumonisin B1-Induced Plant Cell Death. Plant and Cell Physiology 60:1109-1119
Glenz R, Schmalhaus D, Krischke M, Mueller MJ, Waller F
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Die Rolle von Sphingobasen in der pflanzlichen Zelltodreaktion. PhD thesis, Julius-Maximilians-Universität Würzburg, 2019
René Glenz
