Co‐expression of three MEP pathway genes and geraniol 10‐hydroxylase in internal phloem parenchyma of Catharanthus roseus implicates multicellular translocation of intermediates during the biosynthesis of monoterpene indole alkaloids and isoprenoid‐derived primary metabolites

Abstract

SummaryIn higher plants, isopentenyl diphosphate (IPP) is synthesised both from the plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP) and from the cytosolic mevalonate (MVA) pathways. Primary metabolites, such as phytol group of chlorophylls, carotenoids and the plant hormones abscisic acid (ABA) and gibberellins (GAs) are derived directly from the MEP pathway. Many secondary metabolites, such as monoterpene indole alkaloids (MIAs) in Catharanthus roseus, are also synthesised from this source of IPP. Using Northern blot and in situ hybridisation experiments, we show that three MEP pathway genes (1-deoxy-D-xylulose 5-phosphate synthase (DXS), 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR ) and 2C-methyl-D-erythritol 2,4-cyclodiphosphate synthase (MECS)) and the gene encoding geraniol 10-hydroxylase (G10H ), a cytochrome P450 monooxygenase involved in the ®rst committed step in the formation of iridoid monoterpenoids display identical cell-speci®c expression patterns. The co-localisation of these four transcripts to internal phloem parenchyma of young aerial organs of C. roseus adds a new level of complexity to the multicellular nature of MIA biosynthesis. We predict the translocation of pathway intermediates from the internal phloem parenchyma to the epidermis and, ultimately, to laticifers and idioblasts during MIA biosynthesis. Similarly, the translocation of intermediates from the phloem parenchyma is probably also required during the biosynthesis of hormones and photosynthetic primary metabolites derived from the MEP pathway.

Cell Type–Specific Localization of Transcripts Encoding Nine Consecutive Enzymes Involved in Protoberberine Alkaloid Biosynthesis

“…However, tropinone reductase I, an intermediate enzyme in tropane alkaloid metabolism, resides in the endodermis and nearby cortical cells (Nakajima and Hashimoto, 1999); thus, tropane alkaloid pathway intermediates must be transported between cell types. Intercellular translocation of monoterpenoid indole alkaloid pathway intermediates has also been suggested to occur between internal phloem, epidermis, laticifers, and idioblasts in the leaves of C. roseus (St-Pierre et al, 1999;Irmler et al, 2000;Burlat et al, 2004). Moreover, tropane alkaloids and nicotine are transported from roots to shoots for storage (Facchini, 2001).…”

“…A complex and diversified relationship between cellular differentiation and alkaloid metabolism has emerged. Gene transcripts and enzymes involved in the biosynthesis of monoterpenoid indole alkaloids show differential localization to the internal phloem (Burlat et al, 2004), epidermis, laticifers, and idioblasts (St-Pierre et al, 1999;Irmler et al, 2000) in leaves of Catharanthus roseus. In C. roseus roots, monoterpenoid indole alkaloid biosynthetic gene transcripts and enzymes were localized to the protoderm and cortical cells near the apical meristem.…”

The Plastidial 2-C-Methyl-d-Erythritol 4-Phosphate Pathway Provides the Isoprenyl Moiety for Protein Geranylgeranylation in Tobacco BY-2 Cells

“…However, exogenous sucrose reverses this effect and restores the MEP pathway, GGPP synthesis, and GFP-CaM53 geranylgeranylation. Indeed, evidence abounds for transport of MEP pathway intermediates between cells and tissues (Burlat et al, 2004;Gutié rrez-Nava et al, 2004;Oudin et al, 2007).…”

Cell-specific localization of alkaloids in Catharanthus roseus stem tissue measured with Imaging MS and Single-cell MS

“…Further synthesis involving secologanin and tryptamine occurs in the ECs. Finally, a TIA intermediate, desacetoxyvindoline, moves to the ICs and LCs, and TIAs are accumulated in the vacuole of those cells (10,12,14). In the stem, a similar localization of enzymes of TIA metabolism (TDC, tryptophan decarboxylase; STR, strictosidine synthase; D4H, desacetoxyvindoline 4-hydroxylase; and DAT, deacetylvindoline 4-Oacetyltransferase in Fig.…”