Epidermis is a pivotal site of at least four secondary metabolic pathways in Catharanthus roseus aerial organs

Abstract

Catharanthus roseus produces a wide range of secondary metabolites, some of which present high therapeutic values such as antitumoral monoterpenoid indole alkaloids (MIAs), vinblastine and vincristine, and the hypotensive MIA, ajmalicine. We have recently shown that a complex multicellular organisation of the MIA biosynthetic pathway occurred in C. roseus aerial organs. In particular, the final steps of both the secoiridoid-monoterpene and indole pathways specifically occurred in the epidermis of leaves and petals. Chorismate is the common precursor of indole and phenylpropanoid pathways. In an attempt to better map the spatio-temporal organisation of diverse secondary metabolisms in Catharanthus roseus aerial organs, we studied the expression pattern of genes encoding enzymes of the phenylpropanoid pathway (phenylalanine ammonia-lyase [PAL, E.C. 4.3.1.5], cinnamate 4-hydroxylase [C4H, E.C. 1.14.13.11] and chalcone synthase [CHS, E.C. 2.3.1.74]). In situ hybridisation experiments revealed that CrPAL and CrC4H were specifically localised to lignifying xylem, whereas CrPAL, CrC4H and CrCHS were specifically expressed in the flavonoid-rich upper epidermis. Interestingly, these three genes were co-expressed in the epidermis (at least the upper, adaxial one) together with three MIA-related genes, indicating that single epidermis cells were capable of concomitantly producing a wide range of diverse secondary metabolites (e.g. flavonoïds, indoles, secoiridoid-monoterpenes and MIAs). These results, and data showing co-accumulation of flavonoids and alkaloids in single cells of C. roseus cell lines, indicated the spatio-temporal feasibility of putative common regulation mechanisms for the expression of these genes involved in at least four distinct secondary metabolisms.

Secretory structures in Cochlospermum regium (Schrank) Pilg. (Bixaceae): Distribution and histochemistry

“…Categorically, idioblasts are individual cells with a different chemical composition from that of the surrounding cells; they vary in shape and are classified according to the substances that they synthesize (Castro and Demarco, 2008) and part of the bioactive compound precursor synthesis and storage may exist within the idioblast vacuoles (Mahroug et al, 2006). Several classes of phenolic compounds are synthesized and stored in a large central vacuole or multiple cells of varying sizes present in the idioblastic cytoplasm.…”

The Leaf Epidermome ofCatharanthus roseusReveals Its Biochemical Specialization

“…In most plant species, the epidermis also plays specialized roles in the biosynthesis and accumulation of a wide range of secondary metabolites, including flavonoids, terpenes, and alkaloids, as illustrated in recent localization studies (Dudareva et al, 2005;Kutchan, 2005;Murata and De Luca, 2005;Mahroug et al, 2006). In the case of Catharanthus roseus (Madagascar periwinkle), leaf epidermal cells appear to be specialized for monoterpenoid indole alkaloid (MIA) biosynthesis (St-Pierre et al, 1999;Murata and De Luca, 2005;Mahroug et al, 2006).…”

“…In the case of Catharanthus roseus (Madagascar periwinkle), leaf epidermal cells appear to be specialized for monoterpenoid indole alkaloid (MIA) biosynthesis (St-Pierre et al, 1999;Murata and De Luca, 2005;Mahroug et al, 2006). This medicinal plant is the only commercial source of the valuable dimeric MIAs with anticancer activities vinblastine and vincristine, which are derived from combining vindoline and catharanthine monomers.…”

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

“…TIA metabolism in C. roseus involves more than 20 enzymatic steps and occurs in various cell types, starting from internal phloem-associated parenchyma cells (IPAP cells) through epidermal cells (ECs) to both idioblast cells (ICs) and laticifer cells (LCs) where vindoline and other TIAs are believed to be accumulated (10)(11)(12). Cell type-specific localization of TIA metabolic pathways has been primarily inferred indirectly from the results of in situ RNA hybridization and immunocytochemical localization of the pathway enzymes (13).…”