Functional characterisation of stress-related fibrillin proteins in the thylakoid membranes of plant chloroplasts

• Applicant: Dr. Jens Lohscheider
• Subject Area: Plant Physiology ; Plant Biochemistry and Biophysics
• Term: from 2014 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255684873

This project aims to elucidate the biochemical properties and physiological roles of two representatives from the plastoglobule-associated fibrillin (FBN) protein family in stress tolerance of plants. Plastoglobules are thylakoid-associated lipid vesicles in cyanobacteria and plastids and contain large amounts of lipophilic molecules, e.g. tocopherols and pigments, and play a vital role in the cellular response to various stress conditions. Apart from the aforementioned molecules, plastoglobules contain a variety of proteins, of which the FBN are the major representatives. It was shown that FBN are involved in stress protection. However, the biochemical and physiological functions of most representatives of this protein family have not been characterised yet. All FBN mainly consist of the so-called PAP/FBN domain, which shares sequence and most probably also structural similarity with lipocalins. Lipocalins are known from bacteria, plants and animals, where they are responsible for the transport of small hydrophobic molecules through hydrophilic compartments. Therefore, it can be assumed that FBN play a role in innerplastidic transport processes. At least 11 subgroups of this protein family can be distinguished, which differ in expression patterns and subcellular localisation. These differences indicate diverse functions of the individual representatives of this protein family. It was shown that only 7 of the 14 FBN in Arabidopsis are core components of plastoglobules while the residual FBN are associated with the thylakoid membrane or localised in the stroma. In the course of this project, two selected and neither localised nor characterised representatives of the FBN in Arabidopsis will be investigated, FBN9 and FBN11. FBN9 was chosen for its strong sequence conservation within the photosynthetic eukaryotes indicating an important and evolutionary old function. FBN11, however, was chosen because of the presence of a protein kinase domain in combination with the PAP/FBN domain. In this project I will investigate the biochemical properties of the selected FBN and try to elucidate their physiological function in stress protection and adaptation. To achieve this, different transgenic mutant lines (loss-of-function and overexpressors) and wild type plants will be exposed to selected stress conditions and compared on the molecular level with a focus on the analysis of plastid proteomes, the antioxidant content and the production of reactive oxygen species. Furthermore, the protein kinase activity of FBN11 will be tested in vitro by using heterologously expressed protein and in vivo by analysis of the plastid phosphoproteome. This will reveal potential substrates for stress-dependent phosphorylation in the chloroplast by FBN11. Revealing the molecular and physiological functions of FBN will contribute to a general understanding of the plastid defence mechanisms and to development of novel concepts for increased stress tolerance in plants.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. Klaas Jan van Wijk