title: Cloning and characterization of squalene synthase and cycloartenol synthase fromSiraitia grosvenorii.
abstract: Mogrosides and steroid saponins are tetracyclic triterpenoids found inSiraitia grosvenorii. Squalene synthase (SQS) and cycloartenol synthase (CAS) are key enzymes in triterpenoid and steroid biosynthesis. In this study, full-length cDNAs ofSgSQSandSgCASwere cloned by a rapid amplification of cDNA-ends with polymerase chain reaction (RACE-PCR) approach. TheSgSQScDNA has a 1254 bp open reading frame (ORF) encoding 417 amino acids, and theSgCAScDNA contains a 2298 bp ORF encoding 765 amino acids. Bioinformatic analysis showed that the deduced SgSQS protein has two transmembrane regions in the C-terminal. BothSgSQSandSgCAShave significantly higher levels in fruits than in other tissues, suggesting that steroids and mogrosides are competitors for the same precursors in fruits. Combinedin silicoprediction and subcellular localization, experiments in tobacco indicated that SgSQS was probably in the cytoplasm or on the cytoskeleton, and SgCAS was likely located in the nucleus or cytosol. These results will provide a foundation for further study ofSgSQSandSgCASgene functions inS. grosvenorii, and may facilitate improvements in mogroside content in fruit by regulating gene expression.
authors.affiliation: The Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100194, China.
authors.forename: Huan
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Hunan Provincial Key laboratory of Crop Germplasm Innovation and Utilization and National Chinese Medicinal Herbs (Hunan) Technology Center, Hunan Agricultural University, Changsha 410128, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Tang
authors.affiliation: Guangxi Botanical Garden of Medicinal Plant, Nanning 530023, China.
authors.forename: Changming
authors.initials: C
authors.lastname: Mo
authors.affiliation: Guangxi Botanical Garden of Medicinal Plant, Nanning 530023, China.
authors.forename: Longhua
authors.initials: L
authors.lastname: Bai
authors.affiliation: The Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100194, China.
authors.forename: Dongping
authors.initials: D
authors.lastname: Tu
authors.affiliation: The Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100194, China.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Ma
keywords: Cloning; Cycloartenol synthase; Expression; Siraitia grosvenorii; Squalene synthase; Steroids; Subcellular localization; Triterpenoids