title: Survey of the total fatty acid and triacylglycerol composition and content of 30 duckweed species and cloning of a Δ6-desaturase responsible for the production of γ-linolenic and stearidonic acids in Lemna gibba.
abstract: BACKGROUND
  Duckweeds, i.e., members of the Lemnoideae family, are amongst the smallest aquatic flowering plants. Their high growth rate, aquatic habit and suitability for bio-remediation make them strong candidates for biomass production. Duckweeds have been studied for their potential as feedstocks for bioethanol production; however, less is known about their ability to accumulate reduced carbon as fatty acids (FA) and oil.
  
  
  RESULTS
  Total FA profiles of thirty duckweed species were analysed to assess the natural diversity within the Lemnoideae. Total FA content varied between 4.6% and 14.2% of dry weight whereas triacylglycerol (TAG) levels varied between 0.02% and 0.15% of dry weight. Three FA, 16:0 (palmitic), 18:2Δ9,12 (Linoleic acid, or LN) and 18:3Δ9,12,15 (α-linolenic acid, or ALA) comprise more than 80% of total duckweed FA. Seven Lemna and two Wolffiela species also accumulate polyunsaturated FA containing Δ6-double bonds, i.e., GLA and SDA. Relative to total FA, TAG is enriched in saturated FA and deficient in polyunsaturated FA, and only five Lemna species accumulate Δ6-FA in their TAG. A putative Δ6-desaturase designated LgDes, with homology to a family of front-end Δ6-FA and Δ8-spingolipid desaturases, was identified in the assembled DNA sequence of Lemna gibba. Expression of a synthetic LgDes gene in Nicotiana benthamiana resulted in the accumulation of GLA and SDA, confirming it specifies a Δ6-desaturase.
  
  
  CONCLUSIONS
  Total accumulation of FA varies three-fold across the 30 species of Lemnoideae surveyed. Nine species contain GLA and SDA which are synthesized by a Δ6 front-end desaturase, but FA composition is otherwise similar. TAG accumulates up to 0.15% of total dry weight, comparable to levels found in the leaves of terrestrial plants. Polyunsaturated FA is underrepresented in TAG, and the Δ6-FA GLA and SDA are found in the TAG of only five of the nine Lemna species that produce them. When present, GLA is enriched and SDA diminished relative to their abundance in the total FA pool.
authors.forename: Yiheng
authors.initials: Y
authors.lastname: Yan
authors.forename: Jason
authors.initials: J
authors.lastname: Candreva
authors.forename: Hai
authors.initials: H
authors.lastname: Shi
authors.forename: Evan
authors.initials: E
authors.lastname: Ernst
authors.forename: Robert
authors.initials: R
authors.lastname: Martienssen
authors.forename: Jorg
authors.initials: J
authors.lastname: Schwender
authors.affiliation: Biosciences Department, BNL 463, 50 Bell Ave, Upton, NY 11973, USA. shanklin@bnl.gov.
authors.forename: John
authors.initials: J
authors.lastname: Shanklin
mesh_terms: D000595:Amino Acid Sequence; D029064:Araceae / Q000201:enzymology* / Q000235:genetics; D018533:Biomass; D003001:Cloning, Molecular; D044943:Fatty Acid Desaturases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D015525:Fatty Acids, Omega-3 / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014026:Nicotiana / Q000235:genetics; D014280:Triglycerides / Q000378:metabolism*; D017965:gamma-Linolenic Acid / Q000096:biosynthesis*
chemical_list: D005227:Fatty Acids; D015525:Fatty Acids, Omega-3; D014280:Triglycerides; D017965:gamma-Linolenic Acid; D044943:Fatty Acid Desaturases; C062895:stearidonic acid