title: Molecular cloning and differential expression analysis of a squalene synthase gene from Dioscorea zingiberensis, an important pharmaceutical plant.
abstract: Diosgenin is a steroid derived from cholesterol in plants and used as a typical initial intermediate for synthesis of numerous steroidal drugs in the world. Commercially, this compound is extracted mainly from the rhizomes or tubers of some Dioscorea species. Squalene synthase (SQS: EC 2.5.1.21) catalyzes the condensation of two molecules of farnesyl diphosphate to form squalene, the first committed step for biosynthesis of plant sterols including cholesterol, and is thought to play an important role in diosgenin biosynthesis. A full-length cDNA of a putative squalene synthase gene was cloned from D. zingiberensis and designated as DzSQS (Genbank Accession Number KC960673). DzSQS was contained an open reading frame of 1,230 bp encoding a polypeptide of 409 amino acids with a predicted molecular weight of 46 kDa and an isoelectric point of 6.2. The deduced amino acid sequence of DzSQS shared over 70 % sequence identity with those of SQSs from other plants. The truncated DzSQS in which 24 amino acids were deleted from the carboxy terminus was expressed in Escherichia coli, and the resultant bacterial crude extract was incubated with farnesyl diphosphate and NADPH. GC-MS analysis showed that squalene was detected in the in vitro reaction mixture. Quantitative real-time PCR analysis revealed that DzSQS was expressed from highest to lowest order in mature leaves, newly-formed rhizomes, young leaves, young stems, and two-year-old rhizomes of D. zingiberensis.
authors.affiliation: Department of Biotechnology, Faculty of Life Science, Hubei University, Wuhan, 430062, Hubei, People's Republic of China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Ye
authors.forename: Runfa
authors.initials: R
authors.lastname: Wang
authors.forename: Liang
authors.initials: L
authors.lastname: Jin
authors.forename: Junhao
authors.initials: J
authors.lastname: Shen
authors.forename: Xiaotong
authors.initials: X
authors.lastname: Li
authors.forename: Ting
authors.initials: T
authors.lastname: Yang
authors.forename: Mengzhuo
authors.initials: M
authors.lastname: Zhou
authors.forename: Zhifan
authors.initials: Z
authors.lastname: Yang
authors.forename: Yongqin
authors.initials: Y
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D027742:Dioscorea / Q000201:enzymology / Q000235:genetics*; D013186:Farnesyl-Diphosphate Farnesyltransferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D008969:Molecular Sequence Data; D009928:Organ Specificity; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics; D010946:Plants, Medicinal / Q000201:enzymology / Q000235:genetics; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D027343:Rhizome / Q000235:genetics; D012717:Sesquiterpenes / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; C004808:farnesyl pyrophosphate; D013186:Farnesyl-Diphosphate Farnesyltransferase