title: Arabidopsis SEIPIN Proteins Modulate Triacylglycerol Accumulation and Influence Lipid Droplet Proliferation.
abstract: The lipodystrophy protein SEIPIN is important for lipid droplet (LD) biogenesis in human and yeast cells. In contrast with the single SEIPIN genes in humans and yeast, there are three SEIPIN homologs in Arabidopsis thaliana, designated SEIPIN1, SEIPIN2, and SEIPIN3. Essentially nothing is known about the functions of SEIPIN homologs in plants. Here, a yeast (Saccharomyces cerevisiae) SEIPIN deletion mutant strain and a plant (Nicotiana benthamiana) transient expression system were used to test the ability of Arabidopsis SEIPINs to influence LD morphology. In both species, expression of SEIPIN1 promoted accumulation of large-sized lipid droplets, while expression of SEIPIN2 and especially SEIPIN3 promoted small LDs. Arabidopsis SEIPINs increased triacylglycerol levels and altered composition. In tobacco, endoplasmic reticulum (ER)-localized SEIPINs reorganized the normal, reticulated ER structure into discrete ER domains that colocalized with LDs. N-terminal deletions and swapping experiments of SEIPIN1 and 3 revealed that this region of SEIPIN determines LD size. Ectopic overexpression of SEIPIN1 in Arabidopsis resulted in increased numbers of large LDs in leaves, as well as in seeds, and increased seed oil content by up to 10% over wild-type seeds. By contrast, RNAi suppression of SEIPIN1 resulted in smaller seeds and, as a consequence, a reduction in the amount of oil per seed compared with the wild type. Overall, our results indicate that Arabidopsis SEIPINs are part of a conserved LD biogenesis machinery in eukaryotes and that in plants these proteins may have evolved specialized roles in the storage of neutral lipids by differentially modulating the number and sizes of lipid droplets.
authors.affiliation: Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203.
authors.forename: Yingqi
authors.identifier: http://orcid.org/0000-0002-0357-5809
authors.initials: Y
authors.lastname: Cai
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390.
authors.forename: Joel M
authors.identifier: http://orcid.org/0000-0001-5483-202X
authors.initials: JM
authors.lastname: Goodman
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Michal
authors.identifier: http://orcid.org/0000-0001-8702-1661
authors.initials: M
authors.lastname: Pyc
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Robert T
authors.identifier: http://orcid.org/0000-0002-6915-7407
authors.initials: RT
authors.lastname: Mullen
authors.affiliation: U.S. Department of Agriculture-Agricultural Research Service, U.S. Arid-Land Agricultural Research Center, Maricopa, Arizona 85138.
authors.forename: John M
authors.identifier: http://orcid.org/0000-0001-6215-0053
authors.initials: JM
authors.lastname: Dyer
authors.affiliation: Department of Biological Sciences, Center for Plant Lipid Research, University of North Texas, Denton, Texas 76203 chapman@unt.edu.
authors.forename: Kent D
authors.identifier: http://orcid.org/0000-0003-0489-3072
authors.initials: KD
authors.lastname: Chapman
mesh_terms: D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D044388:GTP-Binding Protein gamma Subunits / Q000737:chemistry; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D066292:Lipid Droplets / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D014026:Nicotiana / Q000235:genetics; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C432679:BSCL2 protein, human; C527368:Fld1 protein, S cerevisiae; D044388:GTP-Binding Protein gamma Subunits; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D014280:Triglycerides