Functional characterization of two families of lipid droplet-associated proteins

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Lipid droplets (LDs, also referred to as oil bodies or oleosomes) are subcellular structures that consist of proteins attached to or embedded in a phospholipid monolayer surrounding a hydrophobic core of mostly triacylglycerol. In plants, LDs occur not only in seeds and pollen but also in vegetative tissues, where they accumulate under stress. Studies in recent years also underlined important functions of LDs in abiotic and biotic stress responses. Previously only few protein families were known that are associated with lipid droplets but we could increase this number in the last years. Now, we aim to understand the subcellular and physiological function of these proteins including two families of proteins from Arabidopsis:SEED LIPID DROPLET PROTEIN 1 and 2 (SLDP1/2) and their binding partner LIPID DROPLET PLASMA MEMBRANE ANCHOR (LIPA) are proteins of previously unknown function that form a complex needed for the association of LDs with the plasma membrane (PM). We now want to study this complex further to show that SLDP1, SLDP2 and LIPA colocalize at LD and PM subdomains that form contact sites and do so in a co-dependent manner. We also want to study the importance of these contact sites under stress and if they play a role in membrane homeostasis. In addition, we want to identify further proteins associated with this complex. One potential interaction partner of SLDP1 was identified in a yeast-2-hybrid screen. This protein, SYNAPTOTAGMIN1, is associated with the PM and could act as a lipid transfer protein. It is furthermore involved in freezing stress tolerance. We want to find out if this protein is also associated with this complex and contributes to its function.We additionally want to study the LD-associated LIPID DROPLET METHYL TRANSFERASEs 1/2 (LIME1/2) and their function in plant metabolism and stress physiology. These proteins are annotated as N-methyltransferases and to be involved in secondary metabolism, but has so far not been studied in any detail. We detected these proteins not only in seedlings but also drought-stressed leaves. We want to identify the substrate and product of the reaction(s) catalyzed by this putative enzymes and the metabolic pathway they are involved in. Furthermore, we want to study the potential role of these enzymes in abiotic and biotic stress. With this project, we aim to broaden the knowledge on LDs in vegetative tissues.