title: Plant oxidosqualene metabolism: cycloartenol synthase-dependent sterol biosynthesis in Nicotiana benthamiana.
abstract: The plant sterol pathway exhibits a major biosynthetic difference as compared with that of metazoans. The committed sterol precursor is the pentacyclic cycloartenol (9β,19-cyclolanost-24-en-3β-ol) and not lanosterol (lanosta-8,24-dien-3β-ol), as it was shown in the late sixties. However, plant genome mining over the last years revealed the general presence of lanosterol synthases encoding sequences (LAS1) in the oxidosqualene cyclase repertoire, in addition to cycloartenol synthases (CAS1) and to non-steroidal triterpene synthases that contribute to the metabolic diversity of C30H50O compounds on earth. Furthermore, plant LAS1 proteins have been unambiguously identified by peptidic signatures and by their capacity to complement the yeast lanosterol synthase deficiency. A dual pathway for the synthesis of sterols through lanosterol and cycloartenol was reported in the model Arabidopsis thaliana, though the contribution of a lanosterol pathway to the production of 24-alkyl-Δ(5)-sterols was quite marginal (Ohyama et al. (2009) PNAS 106, 725). To investigate further the physiological relevance of CAS1 and LAS1 genes in plants, we have silenced their expression in Nicotiana benthamiana. We used virus induced gene silencing (VIGS) based on gene specific sequences from a Nicotiana tabacum CAS1 or derived from the solgenomics initiative (http://solgenomics.net/) to challenge the respective roles of CAS1 and LAS1. In this report, we show a CAS1-specific functional sterol pathway in engineered yeast, and a strict dependence on CAS1 of tobacco sterol biosynthesis.
authors.affiliation: Institut de Biologie Moléculaire des Plantes du CNRS & Université de Strasbourg, Institut de Botanique, Strasbourg, France.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Gas-Pascual
authors.affiliation: Institut de Biologie Moléculaire des Plantes du CNRS & Université de Strasbourg, Institut de Botanique, Strasbourg, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Berna
authors.affiliation: Institut de Biologie Moléculaire des Plantes du CNRS & Université de Strasbourg, Institut de Botanique, Strasbourg, France.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Bach
authors.affiliation: Institut de Biologie Moléculaire des Plantes du CNRS & Université de Strasbourg, Institut de Botanique, Strasbourg, France.
authors.forename: Hubert
authors.initials: H
authors.lastname: Schaller
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins; D001483:Base Sequence; D019751:Intramolecular Transferases / Q000235:genetics / Q000378:metabolism*; D007810:Lanosterol / Q000096:biosynthesis*; D018515:Plant Leaves / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013185:Squalene / Q000031:analogs & derivatives* / Q000378:metabolism; D013261:Sterols / Q000096:biosynthesis* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D013261:Sterols; D007810:Lanosterol; C520393:oxidosqualene; D013185:Squalene; D019751:Intramolecular Transferases; C513124:LAS1 protein, Arabidopsis; C021923:cycloartenol synthase