Biosynthesis of Isoprene Units in Euphorbia lathyris Laticifers vs. Other Tissues: MVA and MEP Pathways, Compartmentation and Putative Endophytic Fungi Contribution.

Gastaldo Gastaldo,Motsch Motsch,Rohmer Rohmer,Schaeffer Schaeffer,Lipko Lipko,Adam Adam

doi:10.3390/molecules24234322

Abstract

Euphorbia species are characterized by a net of laticifers producing large amounts of triterpenes. These hydrocarbon-like metabolites can be converted into fuel by the methods of the oil industry. Euphorbia lathyris is easily grown at an industrial scale. In an attempt to increase its triterpene production, the metabolic pathways leading to isoprenoid were investigated by incorporation of 13C labeled glucose and mevalonate and 2H labeled deoxyxylulose as well as by natural abundance isotope ratio GC-MS. Latex triterpenes are exclusively synthesized via the mevalonate (MVA) pathway: this may orient future search for improving the triterpene production in E. lathyris. Phytosterols and their precursors are mainly derived from MVA pathway with a slight contribution of the methylerythritol phosphate (MEP) pathway, whereas phytol is issued from MEP pathway with a minor contribution of the MVA pathway: this is in accordance with the metabolic cross-talk between cytosolic and plastidial compartments in plants. In addition, hopenol B behaved differently from the other latex triterpenes. Its 13C isotope abundance after incorporation of 13C labeled glucose and its natural abundance δ2H signature clearly differed from those of the other latex triterpenes indicating another metabolic origin and suggesting that it may be synthesized by an endophytic fungus.

Highlights

Among the Euphorbiaceae, the genus Euphorbia includes ca. 2000 species with no taxonomic subdivision the existence of four clades has been proposed [1]
All incorporation experiments of labeled precursors showed that the isoprene units of all latex triterpenes from E. lathyris are solely synthesized via the MVA pathway, with no detectable contribution of the methylerythritol phosphate (MEP) pathway
From the incorporation of (1-13 C)glucose and (1,6-13 C2 )glucose, only carbon atoms derived from C-2, C-4 and C-5 of isopentenyl diphosphate (IPP) are labeled with a slight 13 C enrichment at those deriving from C-1 and C-3 of IPP (Scheme 4, Tables 3–5)

Summary

Introduction

Among the Euphorbiaceae, the genus Euphorbia includes ca. 2000 species with no taxonomic subdivision the existence of four clades has been proposed [1]. 2000 species with no taxonomic subdivision the existence of four clades has been proposed [1]. All species are characterized by a net of non-articulated laticifers These specialized cells represent a closed system devoted to the production and storage of latex, a white, milky liquid [4]. This latex is characterized by a high content of isoprenoids, mainly triterpenes with a rather large structural diversity [5,6], and to a lesser extent of diterpenoids, most of them being irritant toxics, causing intense inflammatory reactions and acting often as procarcinogens [7,8]. The triterpene fingerprint of Euphorbia latex has been used as chemotaxonomic marker and allowed division of Molecules 2019, 24, 4322; doi:10.3390/molecules24234322 www.mdpi.com/journal/molecules

Methods

Results

Conclusion