Shikonin Biosynthesis in Lithospermum erythrorhizon

Light-induced Negative Regulation of Secondary Metabolism

Abstract

Cell suspension cultures of Lithospermum erythrorhizon, a medicinal plant, produce red naphthoquinone pigments, which are derivatives of shikonin, when cultured in the production medium M9 in darkness, whereas light as well as ammonium ion which is a major component of Linsmaier and Skoog's medium, completely inhibit shikonin production. In the non-pigmented cells, a large amount of shikonin precursor p-hydroxybenzoic acid is accumulated as its O-glucoside instead of shikonin. An overview of the regulation of shikonin biosynthesis and the localization of important intermediates is presented in this review. We also discuss the effect of light in more detail, and characterize the dark-inducible genes (LEDI) which have been isolated from shikonin-producing cells, as well as the establishment of stable transformation of this plant. Furthermore, the latest results of functional analyses of LEDI genes in hairy root cultures are also reported.