title: Differently localized lysophosphatidic acid acyltransferases crucial for triacylglycerol biosynthesis in the oleaginous alga Nannochloropsis.
abstract: The production of renewable bioenergy will be necessary to meet rising global fossil fuel demands. Members of the marine microalgae genus Nannochloropsis produce large quantities of oils (triacylglycerols; TAGs), and this genus is regarded as one of the most promising for biodiesel production. Recent genome sequencing and transcriptomic studies on Nannochloropsis have provided a foundation for understanding its oleaginous trait, but the mechanism underlying oil accumulation remains to be clarified. Here we report Nannochloropsis knock-out strains of four extraplastidic lysophosphatidic acid acyltransferases (LPAT1-LPAT4) that catalyze a major de novo biosynthetic step of TAGs and membrane lipids. We found that the four LPATs are differently involved in lipid metabolic flow in Nannochloropsis. Double knock-outs among the LPATs revealed the pivotal LPATs for TAG biosynthesis, and localization analysis indicated that the stramenopile-specific LPATs (LPAT3 and LPAT4) associated with TAG synthesis reside at the perimeter of lipid droplets. No homologous region has been found with other lipid droplet-associated proteins, however. Lipid droplets are an organelle found in nearly all organisms, and recently they were shown to play important roles in cellular metabolism and signaling. Our results provide direct evidence for the importance of the perimeter of lipid droplet in TAG synthesis in addition to its known role in maintaining TAG stability, and these findings suggest that the oleaginous trait of Nannochloropsis is enabled by the acquisition of LPATs at the perimeter of lipid droplets.
authors.affiliation: School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan.|CREST, JST, Yokohama, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nobusawa
authors.affiliation: School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan.|CREST, JST, Yokohama, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Hori
authors.affiliation: School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan.|CREST, JST, Yokohama, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Mori
authors.affiliation: CREST, JST, Yokohama, Japan.|Earth-Life Science Institute, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, Japan.|Center for Information Biology, National Institute of Genetics, Yata 1111, Mishima, 411-8540, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Kurokawa
authors.affiliation: School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan.|CREST, JST, Yokohama, Japan.|Earth-Life Science Institute, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000378:metabolism*; D056804:Biofuels; D010944:Plants / Q000235:genetics / Q000378:metabolism; D058009:Stramenopiles / Q000201:enzymology* / Q000378:metabolism*; D014280:Triglycerides / Q000096:biosynthesis*
chemical_list: D056804:Biofuels; D014280:Triglycerides; D000217:Acyltransferases; C018764:2-acylglycerophosphate acyltransferase
keywords: 
  Nannochloropsis
  ; biofuels; lipid droplets; lysophosphatidic acid acyltransferase (LPAT); triacylglycerol (TAG)