Genetic approach to alkaloids

Purine alkaloids Caffeine synthase Camellia sinensis, Coffea arabica 

Pyrrolizidine alkaloids Homospermidine synthase Senecio vemalis, Senecio vulgaris 

Indole alkaloids Tryptophane decarboxylase Catharanthus roseus Camptotheca acuminata 

Isoquinoline Tyrosine/DOPA decarboxylase Papaver somniferum 

Tropane alkaloids Hyoscyamine 6/3-hydroxylase Hyoscyamus niger Atropa belladonna 

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Since 1988, the methods that we use to isolate cDNAs of alkaloid biosynthesis have become ever more facile and sensitive, allowing for more efficient cDNA identification. We do not, however, yet understand enough about the cellular localization of alkaloid formation or about the nature of the catalysts to move completely away from enzymology and biochemistry and to use only molecular genetic techniques to dissect these biosynthetic pathways. Even our most recently successful cDNA isolations and identifications involved classical protein purification. We are beginning now to use proteomics and EST sequencing to identify natural product biosynthetic cDNAs, but these approaches are more feasible when a specialized cell/tissue type in which secondary metabolite biosynthetic pathways are active, can be isolated and used as a protein or RNA source. 

Another approach could be to use genetic engineering to introduce a further step in a biosynthetic pathway, leading to (for the plant) new compounds. This approach has, for example, been used to introduce new flower colors (IS). It could also be of interest in improving the resistance of plants against microorganisms or predators. However, more insight into the role of alkaloids in plant survival in native ecosystems is needed for this. 

Another alkaloid whose production has been successfully improved by genetic engineering in plant cell culture and whole plants is benzylisoquinohne. This was done in poppy plants and cell cultures by RNAi inhibition of the berberme bridge enzyme, which resulted in the production of reticuline [61]. The same enzyme was also targeted in an approach to transfer the benzylisoquinohne alkaloid production from tyrosine in the Papaveraceae, Berberidaceae, Ranunculaceae, Magidiaceae, and other plant famUies into microorganisms [62]. Its transfer in yeast resulted in the... 

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