Lipids in plant development and stress responses
by Patricia Scholz
Date of Examination:2022-10-24
Date of issue:2023-08-22
Advisor:PD Dr. Till Ischebeck
Referee:PD Dr. Till Ischebeck
Referee:Prof. Dr. Gerhard H. Braus
Referee:Prof. Dr. Peter Dörmann
Persistent Address:
http://dx.doi.org/10.53846/goediss-10064
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Abstract
English
In plant cells, lipids are important components of cellular membranes. There, they act as structure-forming and/or signal-transmitting elements. As signals, lipids are landmarks and thereby important regulators, for example of secretory processes in pollen tubes. One such signalling lipid is phosphatidic acid that can be formed by diacylglycerol kinases (DGKs), however, the role of DGKs in the secretory processes occurring in pollen tubes is so far underexplored. One study described in this thesis sheds light on the importance of DGKs in tobacco pollen tube growth. Here, it is shown for the first time that certain DGKs are localised at the plasma membrane. The tobacco DGK NtDGK5 in particular associates to an important signalling hub in the plasma membrane shortly behind the pollen tube tip to convert diacylglycerol in phosphatidic acid. Interference with NtDGK5 function in tobacco pollen tubes caused the appearance of unusual wavy growth and misshaped tips in pollen tubes. Further transient expression assays highlighted a possible connection of NtDGK5 to the regulation of pectin secretion by other signalling lipids. In conclusion, the localisation and associated phenotypes of NtDGK5 support a role for this enzyme and its product in the fine-tuning of other signalling networks coordinating pectin secretion in tobacco pollen tube growth. Apart from membrane lipids, more hydrophobic storage lipids can be found for example in the core of cytosolic lipid droplets (LDs). This core is delimited by a phospholipid monolayer into which proteins are embedded. These proteins convey to LDs their cellular function, so a deeper understanding of LDs requires more detailed knowledge on the composition and dynamics of the LD proteome. In a further study, we analysed the lipidome of stressed leaves of Arabidopsis revealing that there are increased levels of the LD core component triacylglycerol in reaction to stress, including heat treatment or infection of the plants with either Botrytis cinerea or Pseudomonas syringae pv. tomato DC3000 ΔavrPto/ΔavrPtoB. Furthermore, bottom-up label-free proteomics studies enabled a thorough investigation of the dynamics of the LD proteome under stress. The results highlight especially CALEOSIN 3 as a universal stress-responsive LD protein and the α-DIOXYGENASE 1 as an LD protein that accumulated specifically in reaction to infection. In addition, proteome measurements of LD-enriched fractions from leaves in comparison to total cellular protein enabled the identification of LD-LOCALISED NTF2 FAMILY PROTEIN and CYTOCHROME B5 ISOFORM E as new LD-associated proteins. Similar studies on LDs isolated from roots resulted in the first detailed description of the LD proteome in Arabidopsis roots. More than 20 LD proteins could be identified, which included several proposed or characterised enzymes. These studies establish leaf and root LDs as active players in cellular metabolism and stress response and open up new avenues for future LD research.
Keywords: Diacylglycerol kinase; Pollen tubes; Nicotiana tabacum; Lipid droplets; Proteomics; Arabidopsis thaliana
