|Content of Engineering Plant Alkaloid Biosynthetic Pathways
With the successful application of molecular genetic methods to the plant
alkaloid field, we now have sophisticated tools at our disposal to study
regulation of enzymatic biosynthesis, as well as determining the cellular and
subcellular localization of these enzymes. The availability of ever-increasing
numbers of recombinant enzymes has enabled thorough analyses of selected
alkaloid biosynthetic enzymes at the biochemical and structural levels.
Weare just beginning to use this knowledge to metabolically engineer alkaloid
metabolism in plants and in in vitro cultures. Multicellular compartmentation
of alkaloid pathways must be considered if meaningful metabolic engineering
experiments are to be designed; for example, we will need to use promoters
that drive transgene expression in the correct cell types. Regulation of these
pathways at the gene and enzyme level is complex and there is still much to
be learned about metabolite levels, multienzyme complexes, and pathway
interconnections, as we systematically overexpress and suppress gene transcription.
Today, pathway engineering in plants remains highly variable. When
we perturb cellular physiology, metabolite homeostasis and intra- and intercellular
partitioning can be affected in unpredictable ways. Predictive metabolic
engineering to generate plants with tailored alkaloid profiles for basic
research and for commercial production is clearly a challenge for the future.
Key Words: Tryptophan decarboxylase, Strictosidine synthase, Geraniol
10-hydroxylase, Secologanin synthase, Strictosidine glucosidase, Tabersonine
16-hydroxylase, Desacetoxyvindoline 4-hydroxlyase, Deacetylvindoline
4-O-acetyltransferase, Polyneuridine aldehyde esterase, Vinorine synthase,
Tyrosine/dopa decarboxylase, (R,S)-Norcoclaurine 6-O-methyltransferase,
(R,S)-Coclaurine, N-Methyltransferase, (S)-N-Methylcoclaurine 3'-hydroxylase,
(R,S)-3'-Hydroxy-N-methylcoclaurine 4'-O-methyltransferase, (R,S)-Reticuline
7-O-methyltransferase, Salutaridinol 7-O-acetyltransferase, Codeinone
reductase, Berberine bridge enzyme, (S)-Scoulerine 9-O-methyltransferase,
(S)-Canadine synthase, Major latex protein, Putrescine N-methyltransferase,
Tropinone reductase I, Tropinone reductase II, Hyoscyamine 6β-hydroxylase,
Vindoline, Ajmaline, Morphine, Sanguinarine, Laudanine, Hyoscyamine,
Scopolamine, Calistegin, Cocaine, Berberine, Dopamine, Strictosidine.