Expression of strictosidine synthase in selected subcellular compartments of tobacco plant

Strictosidine synthase (STR) is a key enzyme involved in the biosynthesis of terpenoid indole alkaloids (TIA) by condensing tryptamine and secologanin into strictosidine. The transgenic tobacco plants targeting STR to subcellular Compartments were established to express STR in chloroplast, vacuole and endoplasmic reticulum (ER) by the,tobacco stable transformation. It was shown that STR was effectively expressed in the above subcellular Compartments by Western blot analysis and STR enzymatic assay. In vitro, STR enzymatic assay was measured indirectly by fluorimetrically detecting depletion of tryptamine feeding on secologanin in the reaction mixture. The tryptamine were completely depleted by STR in the crude extract of leaves of transgenic tobacco plants targeting and expressing STR in the chloroplast, vacuole and ER, which ascertained the STR functionally targeted to the three subcellular Compartments. To confirm STR correct targeting and expressing in chloroplast, the. chloroplasts were isolated and the fractions of purified chloroplasts were analyzed by Western blot. The hypothesis of STR correct targeting to the chloroplast was tested. The results have implications on our understanding of the complex intracellular trafficking in metabolic intermediates of TIA biosynthesis.