title: Metabolic engineering of soybean affords improved phytosterol seed traits.
abstract: Different combinations of three rate-limiting enzymes in phytosterol biosynthesis, the Arabidopsis thaliana hydroxyl methylglutaryl CoA1 (HMGR1) catalytic subunit linked to either constitutive or seed-specific β-conglycinin promoter, and the Glycine max sterol methyltransferase1 (SMT1) and sterol methyltransferase2-2 (SMT2-2) genes, under the control of seed-specific Glycinin-1 and Beta-phaseolin promoters, respectively, were engineered in soybean plants. Mature seeds of transgenic plants displayed modest increases in total sterol content, which points towards a tight control of phytosterol biosynthesis. However, in contrast to wild-type seeds that accumulated about 35% of the total sterol in the form of intermediates, in the engineered seeds driven by a seed-specific promoter, metabolic flux was directed to Δ(5) -24-alkyl sterol formation (99% of total sterol). The engineered effect of end-product sterol (sitosterol, campesterol, and stigmasterol) over-production in soybean seeds resulted in an approximately 30% increase in overall sitosterol synthesis, a desirable trait for oilseeds and human health. In contradistinction, increased accumulation of cycloartenol and 24(28)-methylencylartanol (55% of the total sterol) was detected in plants harbouring the constitutive t-HMGR1 gene, consistent with the previous studies. Our results support the possibility that metabolic flux of the phytosterol family pathway is differentially regulated in leaves and seeds.
authors.affiliation: Division of Plant Sciences and National Center for Soybean Biotechnology, University of Missouri, Columbia, MO, USA.
authors.forename: Anjanasree K
authors.initials: AK
authors.lastname: Neelakandan
authors.forename: Swetha
authors.initials: S
authors.lastname: Chamala
authors.forename: Babu
authors.initials: B
authors.lastname: Valliyodan
authors.forename: William David
authors.initials: WD
authors.lastname: Nes
authors.forename: Henry T
authors.initials: HT
authors.lastname: Nguyen
mesh_terms: D015139:Blotting, Southern; D060847:Metabolic Engineering / Q000379:methods*; D010840:Phytosterols / Q000096:biosynthesis / Q000378:metabolism*; D030821:Plants, Genetically Modified; D019655:Quantitative Trait, Heritable; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D013025:Glycine max / Q000235:genetics / Q000378:metabolism*; D019076:Transgenes / Q000235:genetics
chemical_list: D010840:Phytosterols