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.