Summary

Many secondary metabolites that have been isolated from higher plants are used as important natural resources for pharmaceuticals. Since plant cells have high totipotency, empirical trials to produce these secondary metabolites in In vitro cell and/or tissue culture have been carried out. Over the past 30 years, studies of these cell culture systems have provided a basis for understanding the basic mechanism of biosynthesis, whereas practical applications are still limited due to relatively low productivity. Recent advances in molecular biology in plant sciences, for example, the comprehensive analysis of expressed genes in biosynthesis-specialized cells and integrated analyses of expression profiles, as well as the development of metabolic profiling analysis, have also considerably stimulated the development of metabolic engineering in plants, even in secondary metabolism. The identification of many biosynthetic genes and the characterization of the spatial and developmental regulation of their expression have clarified their importance in the biosynthesis of secondary metabolites and revealed bottlenecks for their production in cell culture. The molecular engineering of secondary metabolites may lead to a new era for the production of medicinal compounds in cell/ tissue cultures as well as in transgenic plants to improve the production and quality of metabolites. The forthcoming decades should be an exciting time for basic and applied sciences regarding secondary metabolite production in plant cells.