Arabidopsis SEIPIN proteins modulate triacylglycerol accumulation and influence lipid droplet proliferation

Authors: CAI, YINGQI - University Of North Texas; GOODMAN, JOEL - University Of Texas Southwestern Medical Center; PYC, MICHAL - University Of Guelph; 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: 8/12/2015
Publication Date: 9/11/2015
Publication URL: http://handle.nal.usda.gov/10113/61767
Citation: Cai, Y., Goodman, J.M., Pyc, M., Mullen, R.T., Dyer, J.M., Chapman, K.D. 2015. Arabidopsis SEIPIN proteins modulate triacylglycerol accumulation and influence lipid droplet proliferation. The Plant Cell. 27:2616-2636.

Interpretive Summary: Vegetable oils are major agricultural commodities that are used for food, cooking, and feedstocks for production of biofuels and renewable chemicals. The oils are produced in the seeds of oilseed crops, and the amount of oil per seed is a critical factor in determining overall crop yields. While much is already known about the general biological processes involved in seed oil production, many of the details regarding the underlying cellular processes remain to be determined. In this study, scientists at the ARS lab in Maricopa, Arizona, in collaboration with scientists at the University of North Texas, University of Guelph, and University of Texas Southwestern Medical Center at Dallas, identified a new family of genes involved in formation of “lipid droplets” in plant cells. Lipid droplets are subcellular compartments in which plant oils are stored, and very little is known about how these compartments are assembled and maintained. This study describes a new gene that plays a critical role in this process. Notably, over-expression of this gene increased the number and size of lipid droplets in plant cells, leading to a 10% increase in seed oil content. Taken together, these studies reveal a new mechanism for increasing the seed oil content in plants, whereby genes involved in production of the oil-storing compartments are up-regulated, thereby creating greater “holding capacity” within the seeds. These findings will be of fundamental importance to all scientists and breeders interested in increasing the seed oil content of oilseed crops.

Technical Abstract: The lipodystrophy protein SEIPIN is important for lipid droplet (LD) biogenesis in human and yeast cells. By contrast to the single SEIPIN genes in humans and yeast, there are three SEIPIN homologues in Arabidopsis thaliana, designated At-SEIPIN1, At-SEIPIN2 and At-SEIPIN3. Here, a yeast (Saccharomyces cerevisiae) SEIPIN-deletion-mutant strain and a tobacco (Nicotiana benthamiana) transient expression system were used to test the ability of Arabidopsis SEIPINs to influence LD morphology. In both species, expression of At-SEIPIN1 promoted accumulation of large-sized lipid droplets, while expression of At-SEIPIN2 and especially At-SEIPIN3 promoted small LDs. Arabidopsis SEIPINs increased triacylglycerol levels and altered composition. In tobacco, ER-localized SEIPINs reorganized the normal, reticulated ER structure into discrete ER domains that co-localized with LDs. Amino-terminal deletions and swapping experiments of At-SEIPIN 1 and 3, revealed that this region of SEIPIN determines LD size. Ectopic over-expression of At-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 At-SEIPIN1 resulted in smaller seeds and, as a consequence, a reduction in the amount of oil per seed compared with wild-type.