Gas-Pascual Elisabet, Berna Anne, Bach Thomas J, Schaller Hubert
Institut de Biologie Moléculaire des Plantes du CNRS & Université de Strasbourg, Institut de Botanique, Strasbourg, France.
PLoS One. 2014 Oct 24;9(10):e109156. doi: 10.1371/journal.pone.0109156. eCollection 2014.
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.
与后生动物相比，植物甾醇途径表现出主要的生物合成差异。六十年代后期的研究表明，甾醇生物合成的关键前体是五环环阿屯醇（9β,19-环羊毛甾-24-烯-3β-醇），而非羊毛甾醇（羊毛甾-8,24-二烯-3β-醇）。然而，过去几年的植物基因组挖掘显示，除了环阿屯醇合酶（CAS1）和有助于地球上C30H50O化合物代谢多样性的非甾体三萜合酶外，角鲨烯环氧酶库中普遍存在编码羊毛甾醇合酶的序列（LAS1）。此外，通过肽段特征以及其互补酵母羊毛甾醇合酶缺陷的能力，已明确鉴定出植物LAS1蛋白。在模式植物拟南芥中报道了通过羊毛甾醇和环阿屯醇合成甾醇的双重途径，尽管羊毛甾醇途径对24-烷基-Δ(5)-甾醇产生的贡献相当小（Ohyama等人，(2009)《美国国家科学院院刊》106, 725）。为了进一步研究CAS1和LAS1基因在植物中的生理相关性，我们在本氏烟草中沉默了它们的表达。我们使用基于来自烟草CAS1的基因特异性序列或来自solgenomics计划（http://solgenomics.net/）的病毒诱导基因沉默（VIGS）来挑战CAS1和LAS1各自的作用。在本报告中，我们展示了工程酵母中特定于CAS1的功能性甾醇途径，以及烟草甾醇生物合成对CAS1的严格依赖性。
