Abstract
Lithospermum erythrorhizon produces shikonin derivatives, naphthoquinone-type secondary metabolites, in the roots. Shikonin is formed by the coupling of two key intermediates, geranyl diphosphate (GPP) derived from mevalonate pathway and p-hydroxybenzonate via shikimate pathway. It is proved that GPP is provided from mevalonate pathway and the GPP synthase is localized in cytosol as a sole exception in higher plants characterized thus far. From EST information we cloned a homolog of FPP synthase (LeFPPS) as a candidate of GPP synthase of cytosolic localization. Recombinant LeFPPS purified via His-tag demonstrated FPPS activity from GPP and IPP as substrates but not GPPS and FPPS activity from DMAPP and IPP. However, the correlated expression of LeFPPS with shikonin accumulation suggested that the in vivo function of LeFPPS is GPPS. Indeed, the addition of cell-free-extract of L.erythrorhizon converted the FPPS activity to strong GPPS activity, suggesting LeFPPS functions as a catalytic subunit of GPPS in vivo.
