Effect of light on gene expression and shikonin formation in cultured Onosma paniculatum cells

The cell culture in a production medium in the dark is capable of producing a large quantity of shikonin and its derivatives, which were completely inhibited when the cell cultures were irradiated with continuous white light and blue light and partially repressed under continuous red light. The expressions of PAL1, 4CL1, and CYP98A6 were induced under continuous red, blue and white light. Transcript levels of HMGR and LDI2 gradually were decreased in the dark and under continuous red light, while no transcriptional product of LDI2 was detected under blue and white light. C4H2 and LePGT1 genes were constantly expressed irrespective of different light conditions. Among the genes studied, the expression of LDI2 was critical for light-regulated shikonin formation. The inducible expression of PAL1, 4CL1, and CYP98A6 as well as the inhibitory transcription of LDI2 mediated by continuous red light irradiation were likely accounted for the reduced accumulation of shikonin.