title: Sterol C-24 methyltransferase type 1 controls the flux of carbon into sterol biosynthesis in tobacco seed.
abstract: The first committed step in the conversion of cycloartenol into Delta(5) C24-alkyl sterols in plants is catalyzed by an S-adenosyl-methionine-dependent sterol-C24-methyltransferase type 1 (SMT1). We report the consequences of overexpressing SMT1 in tobacco (Nicotiana tabacum), under control of either the constitutive carnation etched ring virus promoter or the seed-specific Brassica napus acyl-carrier protein promoter, on sterol biosynthesis in seed tissue. Overexpression of SMT1 with either promoter increased the amount of total sterols in seed tissue by up to 44%. The sterol composition was also perturbed with levels of sitosterol increased by up to 50% and levels of isofucosterol and campesterol increased by up to 80%, whereas levels of cycloartenol and cholesterol were decreased by up to 53% and 34%, respectively. Concomitant with the enhanced SMT1 activity was an increase in endogenous 3-hydroxy-3-methylglutaryl coenzyme A reductase activity, from which one can speculate that reduced levels of cycloartenol feed back to up-regulate 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and thereby control the carbon flux into sterol biosynthesis. This potential regulatory role of SMT1 in seed sterol biosynthesis is discussed.
authors.affiliation: Plant Sciences, Colworth House, Unilever Research and Development Laboratory, Sharnbrook, Bedford MK44 1LQ, United Kingdom. niklas.holmberg@alligatorbioscience.com
authors.forename: Niklas
authors.initials: N
authors.lastname: Holmberg
authors.forename: Mark
authors.initials: M
authors.lastname: Harker
authors.forename: Carl L
authors.initials: CL
authors.lastname: Gibbard
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Wallace
authors.forename: John C
authors.initials: JC
authors.lastname: Clayton
authors.forename: Sally
authors.initials: S
authors.lastname: Rawlins
authors.forename: Amanda
authors.initials: A
authors.lastname: Hellyer
authors.forename: Richard
authors.initials: R
authors.lastname: Safford
mesh_terms: D001692:Biological Transport; D002244:Carbon / Q000378:metabolism*; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000378:metabolism; D003001:Cloning, Molecular; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006903:Hydroxymethylglutaryl CoA Reductases / Q000378:metabolism; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D010840:Phytosterols / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified; D012639:Seeds / Q000378:metabolism; D012855:Sitosterols / Q000378:metabolism; D013265:Stigmasterol / Q000031:analogs & derivatives* / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D014315:Triterpenes
chemical_list: D010840:Phytosterols; D012855:Sitosterols; D014315:Triterpenes; C015896:fucosterol; C021273:campesterol; C025473:gamma-sitosterol; D002244:Carbon; D002784:Cholesterol; D013265:Stigmasterol; D006903:Hydroxymethylglutaryl CoA Reductases; C409822:24-methylene-lophenol-C24-methyltransferase; D008780:Methyltransferases; C019609:S-adenosyl-L-methionine-cycloartenol methyltransferase; C100089:cycloartenol