Krawczyk et al. describe a tethering complex that anchors a subset of lipid droplets to the plasma membrane during post-germinative seedling growth in Arabidopsis. https://doi.org/10.1093/plcell/koac095
By Hannah Elisa Krawczyk, Till Ischebeck
Background: Germinating seeds are not yet able to produce energy from sunlight. Therefore, the energy and carbon required for seedling establishment has to be provided from other sources such as oil. Seeds accumulate oil inside organelles called lipid droplets. Besides oil storage, lipid droplets might have additional functions during seedling establishment especially under unfavorable environmental conditions. Unfortunately, research on lipid droplets is hampered by the fact that only few proteins associated to lipid droplets are described in detail. Recently, we discovered several lipid droplet–localized proteins of unknown functions. One such protein is SEED LIPID DROPLET PROTEIN (SLDP).
Question: We set out to investigate SLDP, to understand its cellular function and its role in seedling establishment.
Findings: We determined that SLDP is important for spatial organization of lipid droplets during seedling establishment in the model plant Arabidopsis thaliana. Normally, lipid droplets line the inner side of the plasma membrane that surrounds cells. Loss of SLDP, however, causes lipid droplets to form clusters within the cells. Furthermore, SLDP interacts with another protein, LIPID DROPLET PLASMA MEMBRANE ANCHOR (LIPA), a protein that is anchored to the plasma membrane. Through their interaction, the proteins form a bridge, called membrane contact site, and thereby anchor lipid droplets to the plasma membrane.
Next steps: Although the effect of a loss of SLDP or LIPA on the cellular level is striking, no effect on the level of the whole plant was observed. Next steps will therefore aim at understanding the relevance of a contact site between the plasma membrane and lipid droplets on the level of the cell and the whole organism, especially under unfavorable environmental conditions.
Hannah Elisa Krawczyk, Siqi Sun, Nathan M. Doner, Qiqi Yan, Magdiel Sheng Satha Lim, Patricia Scholz, Philipp William Niemeyer, Kerstin Schmitt, Oliver Valerius, Roman Pleskot, Stefan Hillmer, Gerhard H. Braus, Marcel Wiermer, Robert T. Mullen, Till Ischebeck. (2022). SEED LIPID DROPLET PROTEIN1, SEED LIPID DROPLET PROTEIN2 and LIPID DROPLET PLASMA MEMBRANE ADAPTOR mediate lipid droplet-plasma membrane tethering. Plant Cell. https://doi.org/10.1093/plcell/koac095