Salvia miltiorrhiza is a medicinal plant widely used in the treatment of cardiovascular
and cerebrovascular diseases. Hydrophilic phenolic acids, including rosmarinic acid
(RA) and lithospermic acid B (LAB), are its primary medicinal ingredients. However,
the biosynthetic pathway of RA and LAB in S. miltiorrhiza is still poorly understood.
In the present study, we accomplished the isolation and characterization of a novel
S. miltiorrhiza Hydroxyphenylpyruvate reductase (HPPR) gene, SmHPPR , which plays
an important role in the biosynthesis of RA. SmHPPR contained a putative catalytic
domain and a NAD(P)H-binding motif. The recombinant SmHPPR enzyme exhibited high
HPPR activity, converting 4-hydroxyphenylpyruvic acid (pHPP) to 4-hydroxyphenyllactic
acid (pHPL), and exhibited the highest affinity for substrate 4-hydroxyphenylpyruvate.
SmHPPR expression could be induced by various treatments, including SA, GA3, MeJA
and Ag + , and the changes in SmHPPR activity were correlated well with hydrophilic
phenolic acid accumulation. SmHPPR was localized in cytoplasm, most likely close
to the cytosolic NADPH-dependent hydroxypyruvate reductase active in photorespiration.
In addition, the transgenic S. miltiorrhiza hairy roots overexpressing SmHPPR
exhibited up to 10-fold increases in the products of hydrophilic phenolic acid pathway.
In conclusion, our findings provide a new insight into the synthesis of active pharmaceutical
compounds at molecular level.