ATP-binding cassette transporter controls leaf surface secretion of anticancer drug components in Catharanthus roseus

Abstract

The Madagascar periwinkle (Catharanthus roseus) is highly specialized for the biosynthesis of many different monoterpenoid indole alkaloids (MIAs), many of which have powerful biological activities. Such MIAs include the commercially important chemotherapy drugs vinblastine, vincristine, and other synthetic derivatives that are derived from the coupling of catharanthine and vindoline. However, previous studies have shown that biosynthesis of these MIAs involves extensive movement of metabolites between specialized internal leaf cells and the leaf epidermis that require the involvement of unknown secretory processes for mobilizing catharanthine to the leaf surface and vindoline to internal leaf cells. Spatial separation of vindoline and catharanthine provides a clear explanation for the low levels of dimers that accumulate in intact plants. The present work describes the molecular cloning and functional identification of a unique catharanthine transporter (CrTPT2) that is expressed predominantly in the epidermis of young leaves. CrTPT2 gene expression is activated by treatment with catharanthine, and its in planta silencing redistributes catharanthine to increase the levels of catharanthinevindoline drug dimers in the leaves. Phylogenetic analysis shows that CrTPT2 is closely related to a key transporter involved in cuticle assembly in plants and that may be unique to MIA-producing plant species, where it mediates secretion of alkaloids to the plant surface.plasma membrane ABC-PDR-alkaloid transporter | secretion to plant surfaces | gene duplication | metabolic diversification

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

“…2 and 5). These data contrast with previously published reports that showed most catharanthine localized in the wax layer of the leaf tissue (31,32). The reasons for these differences are unclear but may reflect differences between cultivars or differences between leaf and stem tissue.…”

“…A catharanthine transporter responsible for efflux from EC to the wax layer in C. roseus leaf tissue has been already reported (32). It is also possible that symplasmic transport via plasmodesmata may drive movements of TIA intermediates between adjacent cells (Fig.…”

Arabidopsis ABCG34 contributes to defense against necrotrophic pathogens by mediating the secretion of camalexin

“…Absence of PhPDR2 increases insect herbivory in Petunia hybrida leaves and decreases concentrations of the insecticidal steroid petuniasterone (7). CrTPT2, expressed at the plasma membrane of Catharanthus roseus, secretes catharanthine to the leaf surface (8). Lr34, an ABCG transporter in Triticum aestivum (wheat), is one of the few durable resistance genes that protect the plant from multiple pathogens, namely Puccinia triticina and Puccinia striiformis, which cause leaf rust, and Blumeria graminis, which causes powdery mildew (9).…”

Alkaloid transporters in plants

“…Identification of the full-size ABCG transporter CrTPT2 provided insight into how catharanthine formed in leaf epidermal cells is exported to its surface (Yu and De Luca 2013). CrTPT2 belongs to the G subfamily of ABC proteins, which include various members involved in disease resistance, cuticle formation, and hormone transport (Kang et al 2011;Ko et al 2014;Shoji 2014;Zhang et al 2014).…”

“…As shown for CjABCB1, CrTPT2 and NtNUP1, altering the expression of alkaloid transporters influences the accumulation, and sometimes also the production, of relevant alkaloids (Hildreth et al 2011;Pomahacova et al 2009;Shitan et al 2005;Yu and De Luca 2013). However, the mechanistic details underlying these phenomena remain unclear.…”