Sphingolipids in Physcomitrella patens
by Hanno Christoph Resemann
Date of Examination:2018-12-31
Date of issue:2019-05-10
Advisor:Prof. Dr. Ivo Feußner
Referee:Prof. Dr. Ivo Feußner
Referee:Prof. Dr. Volker Lipka
Persistent Address:
http://dx.doi.org/10.53846/goediss-7416
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Abstract
English
The model organism Physcomitrella patens is a bryophyte in the group of non-vascular plants. Evolutionary, bryophytes evolved shortly after the event when plants developed the ability to grow on land. P. patens can therefore be considered a link between marine plants and vascular plants, which makes it interesting for research into how plants adapted to terrestrial conditions. Nevertheless, 10 years after the P. patens genome was sequenced there is still much research to be done on this organism, especially on the analysis of metabolites like lipids. In recent years, P. patens received more attention in genetic, transcriptomic and proteomic studies. The study of lipids, a class of biological compounds that is crucial for all living cells, has however remained very superficial in P. patens. In order to close the gap in research between this organism and plant model organisms like Arabidopsis thaliana we analyzed for the first time the lipid composition of P. patens in 5 different lipid groups and 19 lipid classes. In the analysis, we discovered more than 700 individual lipid species in P. patens via a liquid-chromatography mass-spectrometry approach. Lipids are important in the plants’ reaction to environmental stresses, like cold. When grown at low temperatures, it was observed in this work that P. patens modifies lipids by adjusting the number of double bonds and the length of fatty acids (FA). Lipid modification hereby occurs differently when comparing phospholipids and glycolipids. One lipid-modifying enzyme in P. patens, the cold-induced putative desaturase PpSFD, was analyzed in this work for its phenotype at normal and cold conditions. Ppsfd knock-out (KO) mutants were incapable of producing mono-unsaturated C24-FAs in ceramides and some phospholipids and appeared drier and less viable compared to wild type moss. It was observed that cold-stressed Ppsfd plants do not adjust their lipid composition regarding FA desaturation and length as the wild type moss does. The cold-sensitive A. thaliana KO-mutant Atads2 has a similar disruption of FA desaturation as the Ppsfd KO-mutant in P. patens. PpSFD and AtADS2 were compared on a functional and evolutionary level to understand the relation between these two enzymes. It was discovered that PpSFD and AtADS2 are not closely related and probably have evolved independently from each other. Expressing PpSFD under an overexpression promoter in Atads2 plants complemented the cold-sensitive phenotype. It was observed that the lipid composition in complemented plants is similar to A. thaliana wild type, but the double bond position of unsaturated C24-FAs differs slightly. Overall, this work shed light on the lipid composition in P. patens and how it is adjusted at cold stress conditions. It was observed that the desaturase PpSFD is involved in this mechanism and evolved independently from the functionally similar desaturase AtADS2 from A. thaliana.
Keywords: Physcomitrella; patens; lipids; sphingolipids; desaturase; bryophytes
