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Arabidopsis SEIPIN proteins modulate triacylglycerol accumulation and influence lipid droplet proliferation

Yingqi Cai, Joel M. Goodman, Michal Pyc, Robert T. Mullen, John M. Dyer, Kent D. Chapman
Plant cell 2015 v.27 no.9 pp. 2616-2636
Arabidopsis thaliana, Nicotiana benthamiana, RNA interference, Saccharomyces cerevisiae, droplets, genes, humans, leaves, lipid content, plant proteins, seed oils, seeds, tobacco, triacylglycerols, yeasts
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.