title: Nannochloropsis, a rich source of diacylglycerol acyltransferases for engineering of triacylglycerol content in different hosts.
abstract: BACKGROUND
  Photosynthetic microalgae are considered a viable and sustainable resource for biofuel feedstocks, because they can produce higher biomass per land area than plants and can be grown on non-arable land. Among many microalgae considered for biofuel production,Nannochloropsis oceanica(CCMP1779) is particularly promising, because following nutrient deprivation it produces very high amounts of triacylglycerols (TAG). The committed step in TAG synthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT). Remarkably, a total of 13 putative DGAT-encoding genes have been previously identified in CCMP1779 but most have not yet been studied in detail.
  
  
  RESULTS
  Based on their expression profile, six out of 12 type-2 DGAT-encoding genes (NoDGTT1-NoDGTT6) were chosen for their possible role in TAG biosynthesis and the respective cDNAs were expressed in a TAG synthesis-deficient mutant of yeast. Yeast expressingNoDGTT5accumulated TAG to the highest level. Over-expression ofNoDGTT5in CCMP1779 grown in N-replete medium resulted in levels of TAG normally observed only after N deprivation. Reduced growth rates accompaniedNoDGTT5over-expression in CCMP1779. Constitutive expression ofNoDGTT5inArabidopsis thalianawas accompanied by increased TAG content in seeds and leaves. A broad substrate specificity for NoDGTT5 was revealed, with preference for unsaturated acyl groups. Furthermore, NoDGTT5 was able to successfully rescue the Arabidopsistag1-1mutant by restoring the TAG content in seeds.
  
  
  CONCLUSIONS
  Taken together, our results identifiedNoDGTT5as the most promising gene for the engineering of TAG synthesis in multiple hosts among the 13 DGAT-encoding genes ofN. oceanicaCCMP1779. Consequently, this study demonstrates the potential of NoDGTT5 as a tool for enhancing the energy density in biomass by increasing TAG content in transgenic crops used for biofuel production.
authors.affiliation: Michigan State University-US Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA ; Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Krzysztof
authors.identifier: 0000-0002-8525-9569
authors.initials: K
authors.lastname: Zienkiewicz
authors.affiliation: Michigan State University-US Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA ; Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany ; Great Lakes Bioenergy Center, Michigan State University, East Lansing, MI 48824 USA.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Zienkiewicz
authors.affiliation: Cell and Molecular Biology Program, Michigan State University, East Lansing, MI 48824 USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Poliner
authors.affiliation: Michigan State University-US Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA.
authors.forename: Zhi-Yan
authors.initials: ZY
authors.lastname: Du
authors.affiliation: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Vollheyde
authors.affiliation: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Herrfurth
authors.affiliation: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany ; Dept. of Plant Breeding, Swedish University of Agricultural Sciences, Alnarp, Sweden.
authors.forename: Sofia
authors.initials: S
authors.lastname: Marmon
authors.affiliation: Department of Plant Biology, Michigan State University, East Lansing, MI 48824 USA.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Farré
authors.affiliation: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, 37073 Göttingen, Germany ; Department of Plant Biochemistry, Göttingen Center for Molecular Biosciences (GZMB), Georg-August-University, 37073 Göttingen, Germany ; Department of Plant Biochemistry, International Center for Advanced Studies of Energy Conversion (ICASEC), Georg-August-University, 37073 Göttingen, Germany.
authors.forename: Ivo
authors.initials: I
authors.lastname: Feussner
authors.affiliation: Michigan State University-US Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824 USA ; Great Lakes Bioenergy Center, Michigan State University, East Lansing, MI 48824 USA ; Department of Plant Biology, Michigan State University, East Lansing, MI 48824 USA ; Department Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824 USA.
authors.forename: Christoph
authors.initials: C
authors.lastname: Benning
keywords: DGAT; Lipid droplets; Lipid storage; Microalgae; Nannochloropsis oceanica; Triacylglycerol