title: Overexpression of 3-ketoacyl-acyl-carrier protein synthase IIIs in plants reduces the rate of lipid synthesis.
abstract: A cDNA coding for 3-ketoacyl-acyl-carrier protein (ACP) synthase III (KAS III) from spinach (Spinacia oleracea; So KAS III) was used to isolate two closely related KAS III clones (Ch KAS III-1 and Ch KAS III-2) from Cuphea hookeriana. Both Ch KAS IIIs are expressed constitutively in all tissues examined. An increase in the levels of 16:0 was observed in tobacco (Nicotiana tabacum, WT-SR) leaves overexpressing So KAS III when under the control of the cauliflower mosaic virus-35S promoter and in Arabidopsis and rapeseed (Brassica napus) seeds overexpressing either of the Ch KAS IIIs driven by napin. These data indicate that this enzyme has a universal role in fatty acid biosynthesis, irrespective of the plant species from which it is derived or the tissue in which it is expressed. The transgenic rapeseed seeds also contained lower levels of oil as compared with the wild-type levels. In addition, the rate of lipid synthesis in transgenic rapeseed seeds was notably slower than that of the wild-type seeds. The results of the measurements of the levels of the acyl-ACP intermediates as well as any changes in levels of other fatty acid synthase enzymes suggest that malonyl-ACP, the carbon donor utilized by all the 3- ketoacyl-ACP synthases, is limiting in the transgenic plants. This further suggests that malonyl-coenzyme A is a potential limiting factor impacting the final oil content as well as further extension of 16:0.
authors.affiliation: Oils Division, Calgene, 1920 Fifth Street, Davis, California 95616, USA.
authors.forename: K
authors.initials: K
authors.lastname: Dehesh
authors.forename: H
authors.initials: H
authors.lastname: Tai
authors.forename: P
authors.initials: P
authors.lastname: Edwards
authors.forename: J
authors.initials: J
authors.lastname: Byrne
authors.forename: J G
authors.initials: JG
authors.lastname: Jaworski
mesh_terms: D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001483:Base Sequence; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D007700:Kinetics; D008055:Lipids / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D010938:Plant Oils / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D030821:Plants, Genetically Modified / Q000201:enzymology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D008055:Lipids; D010938:Plant Oils; D010940:Plant Proteins; C077402:3-ketoacyl-acyl carrier protein synthase III; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase