REGULATORY ROLE OF MICROSOMAL 3-HYDROXY-3-METHYLGLUTARYL-COENZYME-A REDUCTASE FOR SHIKONIN BIOSYNTHESIS IN LITHOSPERMUM-ERYTHRORHIZON CELL-SUSPENSION CULTURES

The carbon skeleton of the naphthoquinone pigment shikonin, which is p roduced in Lithospermum erythrorhizon Sieb. et Zucc. cell-suspension c ultures, is partly derived from the isoprenoid biosynthetic pathway. T he requirement of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG R, EC 1.1.1.34), a key enzyme of the mevalonate route to isoprenoids, for shikonin synthesis was investigated. Conserved regions of sequence s from plant HMGR genes were used to design polymerase chain reaction (PCR) primers for the cloning of a cDNA fragment from L. erythrorhizon . The resulting 443-bp clone was used as a probe for Northern analyses and hybridized to an mRNA of approx. 2.5 kb. Under shikonin-producing conditions, microsomal HMGR enzyme activity as well as mRNA level clo sely correlated with the accumulation of shikonin derivatives. White l ight, which inhibits shikonin formation, was shown to strongly suppres s HMGR gene expression. The results presented here indicate that HMGR plays a significant role in the regulation of shikonin biosynthesis an d that the control appears to act at the transcriptional level.