Alkaloid transporters in plants

Plants produce a multitude of secondary metabolites, including alkaloids with biological activities, and many alkaloids have been used for medicinal purposes. The biosynthetic enzymes and genes involved in alkaloid metabolic pathways exhibit divergent localizations, implying that alkaloid metabolites, including pathway products and intermediates, travel from organelle to organelle, cell to cell, and organ to organ. Biochemical studies have indicated that specific transporters move these metabolites. Indeed, molecular and cellular approaches have identified alkaloid transporters of the ATP-binding cassette (ABC) protein, multidrug and toxic compound extrusion (MATE), and purine permease (PUP) families. Interestingly, some of these transporters were found to be required for the efficient biosynthesis of alkaloids in plants. Here, we provide an updated inventory of alkaloid transporters and discuss the possibility of genetically manipulating the expression of these transporters to increase the accumulation of valuable alkaloid compounds.