Influence of fatty acid desaturation on thylakoid membrane structure and non-photochemical quenching of chlorophyll a fluorescence

• Applicant: Dr. Monique Matzner
• Subject Area: Plant Physiology ; Plant Biochemistry and Biophysics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544914412

The degree of lipid unsaturation in membranes is important for membrane function because it controls membrane fluidity and the lateral diffusion of membrane-embedded protein complexes. The unsaturation of monogalactosyldiacylglycerol (MGDG), the main constituent of the photosynthetic active thylakoid membranes, is influenced in Arabidopsis thaliana primarily by plastidial fatty acid desaturases, FAD5, FAD6, FAD7 and FAD8. Results from my PhD project indicate that the Arabidopsis fad3 mutant, which is deficient in the formation of polyunsaturated fatty acids in the ER, has increased levels of MGDG in the plastid, possibly as part of a mechanism to mobilize polyunsaturated fatty acids for export from the plastid. Despite the knockout of FAD3 does not impact MGDG unsaturation, the mutant displays altered non-photochemical quenching (NPQ) in the plastid, which is one of the most important photoprotective mechanisms in plants. In contrast, the knockout of plastidial localized FAD6 (fad6 mutants) and the triple knockout of FAD3, FAD7 and FAD8 (fad378 mutants) do not lead to changes of MGDG abundance but reduce MGDG unsaturation. However, while changes of lipid properties in the fad6 mutants also lead to low NPQ values fad378 mutants with defects in plastidial formation of polyunsaturated fatty acids exhibit normal NPQ. Since the NPQ combines the activity of several individual components, initial further investigations of the xanthophyll cycle as one of the NPQ components could establish a connection between low NPQ values in fad3 mutants and inhibited de-epoxidation of the pigments of the xanthophyll cycle. These observations suggest that the functions within thylakoid membranes are influenced by biophysical properties of membrane lipids. Furthermore, since the xanthophyll cycle function was not changed in the fad6 mutants this could imply that the function of individual NPQ components depend on certain membrane conditions. Examinations of further individual NPQ components such as the high state energy quenching, state transition or photoinhibition by using their variation in relaxation times can provide information about their functional contribution to the photoprotection of plants changed in their lipid unsaturation. In addition, a broader analysis of the thylakoid membrane properties in fad-mutants such as the abundances and unsaturation degrees of the other thylakoid lipids, the membrane fluidity and membrane integrity can give explanations why certain NPQ components are disturbed. The Walter Benjamin position at the Leipzig University would give me the opportunity to explore the influence of lipid unsaturation on membrane properties and relate it to plant physiology in various aspects, thus making an important contribution to membrane research.

• DFG Programme: WBP Position