[Molecular genetics and biotechnology in medicinal plants: studies by transgenic plants]

The advances in molecular genetics and biotechnology in the field of medicinal plant research are discussed with focusing on the works using transgenic plants. Differentiated organ cultures and transgenic teratomas, incited by the infection with mutants of Agrobacterium Ti and Ri plasmids, were established in quinolizidine-alkaloid producing plants and Solanaceae plants. These cultured cells were used for the production and bioconversion of specific alkaloids produced in these plants. The methods of integration of foreign genes into medicinal plants were developed using an Ri binary vector. The mode of gene expression driven by TR1'-2' promoters was elucidated in transgenic medicinal plants, e.g., Nicotiana tabacum, Glycyrrhiza uralensis, Digitalis purpurea and Atropa belladonna. The genes for herbicide resistance, mammalian cytochrome P450 and bacterial beta-hydroxydecanoylthioester dehydrase were transferred and expressed in plants either to confer herbicide-resistant trait or to change the pattern of metabolites. The cDNA clones encoding cysteine synthase responsible for sulfur assimilation and biosynthesis of non-protein amino acids were isolated and characterized from Spinacea oleracea and Citrullus vulgaris. The functional lysine residue was identified by site-directed mutagenesis experiments. An over-expression system in Escherichia coli was constructed for the bacterial production of the plant specific non-protein amino acids. We made transgenic N. tabacum integrated with sense- and antisense-constructs of cysteine synthase cDNA driven by cauliflower mosaic virus 35S promoter for the purpose of genetic manipulation of biosynthetic flow of cysteine in plants. The future prospects of medicinal plant research are also discussed in the context of modern plant molecular biology.