SEIPIN isoforms interact with the membrane-tethering protein VAP27-1 for lipid droplet formation

Authors: GREER, MICHAEL - University Of North Texas; CAI, YINGQI - University Of North Texas; GIDDA, SATINDER - University Of Guelph; ESNAY, NICOLAS - University Of North Texas; KRETZSCHMAR, FRANZISKA - Goettingen University; Seay, Damien; MCLINCHIE, ELIZABETH - University Of North Texas; ISCHEBECK, TILL - Goettingen University; MULLEN, ROBERT - University Of Guelph; Dyer, John; CHAPMAN, KENT - University Of North Texas

Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2020
Publication Date: 9/1/2020
Citation: Greer, M.S., Cai, Y., Gidda, S.K., Esnay, N., Kretzschmar, F.K., Seay, D., Mclinchie, E., Ischebeck, T., Mullen, R.T., Dyer, J.M., Chapman, K.D. 2020. SEIPIN isoforms interact with the membrane-tethering protein VAP27-1 for lipid droplet formation. The Plant Cell. 32(9):2932-2950. https://doi.org/10.1105/tpc.19.00771.
DOI: https://doi.org/10.1105/tpc.19.00771

Interpretive Summary: The seed oils of plants are important commodities used for food, feed, cooking, and industrial purposes. While much is known about the enzymes that synthesize oil in seeds, little is known about the mechanisms by which plants compartmentalize oil into organelles called "lipid droplets", which allows the oil to be stored as an emulsion in the aqueous interior of the cell. Recent studies have identified the SEIPIN protein as being critically important for this process. SEIPIN is located in the endoplasmic reticulum (ER) where it serves as a "vent" that allows newly synthesized oil to flow from the ER into an emerging lipid droplet. How SEIPIN performs this function is presently unknown. Collaborative research between scientists at the ARS lab in Maricopa, Arizona and the Universities of North Texas, Guelph, and Goettingen, has now revealed that the SEIPIN protein physically interacts with a protein called VAP27-1 to help form normal-sized lipid droplets. Loss of VAP27-1 resulted in production of aberrant, significantly enlarged lipid droplets in plant seeds. Studies in yeast confirmed that the VAP proteins were important for lipid droplet formation, particularly under conditions of elevated lipid storage. These studies provide fundamental insight to how eukaryotic organisms store oil in the aqueous environment of the cell, and are especially important to those scientists interested in understanding the factors that regulate the production of oil in plant seeds.

Technical Abstract: SEIPIN proteins are localized to endoplasmic reticulum (ER)-lipid droplet (LD) junctions where they mediate the directional formation of LDs into the cytoplasm in eukaryotic cells. Unlike in animal and yeast cells, which have single SEIPIN genes, plants have three distinct SEIPIN isoforms encoded by separate genes. The mechanism of SEIPIN action remains poorly understood, and here we demonstrate that part of the function of two SEIPIN isoforms in Arabidopsis thaliana, AtSEIPIN2 and AtSEIPIN3, depends on their interaction with the Vesicle-Associated Membrane Protein (VAMP)–Associated Protein family member, AtVAP27-1. VAPs play roles in the formation of membrane contact sites and lipid transfer between ER and other organelles, and we show that AtVAP27-1 physically interacts with the N termini of AtSEIPIN2 and AtSEIPIN3 to support the normal formation of LDs. Our results indicate that the ER membrane tethering machinery in plant cells cooperates with select SEIPIN isoforms in LD biogenesis at the ER.